Cyclic nucleotide phosphodiesterases and their role in endocrine cell signaling

Advances in targeting Phosphodiesterase 1: From mechanisms to potential therapeutics

Phosphodiesterase 1 (PDE1) is an enzyme entrusted with the hydrolysis of the second messengers cAMP and cGMP, thereby governing a plethora of metabolic processes, encompassing ion channel modulation and cellular apoptosis. Recent advancements in the realm of small molecule structural variations have greatly facilitated the exploration of innovative applications for PDE1. Remarkably, a recent series of PDE1 inhibitors (PDE1i) have been meticulously formulated and devised, showcasing enhanced selectivity and potency. Among them, ITI-214 has entered Phase II clinical trials, holding promise for the treatment of Parkinson's disease and heart failure. Nevertheless, the majority of current PDE1 inhibitors have encountered substantial side effects in clinical trials attributable to their limited selectivity, this predicament presents a formidable obstacle in the development of specific small molecule inhibitors targeting PDE1. This Perspective endeavors to illuminate the potential design approaches, structure-activity relationships, and biological activities of current PDE1i, aiming to offer support and insights for clinical practice and the development of novel PDE1i.

A two-dimensional finite element model of intercellular cAMP signaling through gap junction channels

While cyclic adenosine monophosphate (cAMP) is typically considered an intracellular signal, it has been shown to spread between adjacent cells through connexin-based gap junction channels, promoting gap junctional intercellular communication (GJIC). Gap junction-mediated signaling is critical for the coordinated function of many tissues, and have been linked with cardiovascular disease, neurogenerative disease, and cancers. In particular, it plays a complex role in tumor suppression or promotion. This work introduces a two-dimensional finite element model that can describe intercellular cAMP signaling in the presence of gap junctions on membrane interfaces. The model was utilized to simulate cAMP transfer through one and two gap junction channels on the interface of a cluster of two pulmonary microvascular endothelial cells. The simulation results were found to generally agree with what has been observed in the literature in terms of GJIC. The research outcomes suggest that the proposed model can be employed to evaluate the permeability properties of a gap junction channel if its cAMP volumetric flow rate can be experimentally measured.

Downregulated INHBB in endometrial tissue of recurrent implantation failure patients impeded decidualization through the ADCY1/cAMP signalling pathway

PURPOSE

This study aims to identify the mechanism of Inhibin Subunit Beta B (INHBB), a member of the transforming growth factor-β (TGF-β) family involved in the regulation of human endometrial stromal cells (HESCs) decidualization in recurrent implantation failure (RIF).

METHODS

RNA-seq was conducted to identify the differentially expressed genes in the endometria from control and RIF patients. RT-qPCR, WB, and immunohistochemistry were performed to analyse the expression levels of INHBB in endometrium and decidualised HESCs. RT-qPCR and immunofluorescence were used to detect changes in the decidual marker genes and cytoskeleton after knockdown INHBB. Then, RNA-seq was used to dig out the mechanism of INHBB regulating decidualization. The cAMP analogue (forskolin) and si-INHBB were used to investigate the involvement of INHBB in the cAMP signalling pathway. The correlation of INHBB and ADCY expression was analysed by Pearson's correlation analysis.

RESULTS

Our results showed significantly reduced expression of INHBB in endometrial stromal cells of women with RIF. In addition, INHBB was increased in the endometrium of the secretory phase and significantly induced in in-vitro decidualization of HESCs. Notably, with RNA-seq and siRNA-mediated knockdown approaches, we demonstrated that the INHBB-ADCY1-mediated cAMP signalling pathway regulates the reduction of decidualization. We found a positive association between the expression of INHBB and ADCY1 in endometria with RIF (R2 = 0.3785, P = 0.0005).

CONCLUSIONS

The decline of INHBB in HESCs suppressed ADCY1-induced cAMP production and cAMP-mediated signalling, which attenuated decidualization in RIF patients, indicating that INHBB is an essential component in the decidualization process.

Pharmacological modulation of phosphodiesterase-7 as a novel strategy for neurodegenerative disorders

Neurodegenerative illness develops as a result of genetic defects that cause changes at numerous levels, including genomic products and biological processes. It entails the degradation of cyclic nucleotides, cyclic adenosine monophosphate (cAMP), and cyclic guanosine monophosphate (cGMP). PDE7 modulates intracellular cAMP signalling, which is involved in numerous essential physiological and pathological processes. For the therapy of neurodegenerative illnesses, the normalization of cyclic nucleotide signalling through PDE inhibition remains intriguing. In this article, we shall examine the role of PDEs in neurodegenerative diseases. Alzheimer's disease, Multiple sclerosis, Huntington's disease, Parkinson's disease, Stroke, and Epilepsy are related to alterations in PDE7 expression in the brain. Earlier, animal models of neurological illnesses including Alzheimer's disease, Parkinson's disease, and multiple sclerosis have had significant results to PDE7 inhibitors, i.e., VP3.15; VP1.14. In addition, modulation of CAMP/CREB/GSK/PKA signalling pathways involving PDE7 in neurodegenerative diseases has been addressed. To understand the etiology, treatment options of these disorders mediated by PDE7 and its subtypes can be the focus of future research.

Functional characteristics and research trends of PDE11A in human diseases (Review)

cAMP and cGMP are important secondary messengers involved in cell regulation and metabolism driven by the G protein-coupled receptor. cAMP is converted via adenylyl cyclase (AC) and activates protein kinase A to phosphorylate intracellular proteins that mediate specific responses. cAMP signaling serves a role at multiple steps in tumorigenesis. The level of cAMP is increased in association with cancer cell formation through activation of AC-stimulatory G protein by mutation. Phosphodiesterases (PDEs) hydrolyze cAMP and cGMP to AMP and GMP. PDEs are composed of 11 families, and each can hydrolyze cAMP and cGMP or both cAMP and cGMP. PDEs perform various roles depending on their location and expression site, and are involved in several diseases, including male erectile dysfunction, pulmonary hypertension, Alzheimer's disease and schizophrenia. PDE11A is the 11th member of the PDE family and is characterized by four splice variants with varying tissue expression and N-terminal regulatory regions. Among tissues, the expression of PDE11A was highest in the prostate, and it was also expressed in hepatic skeletal muscle, pituitary, pancreas and kidney. PDE11A is the first PDE associated with an adrenocortical tumor associated genetic condition. In several studies, three PDE11A mutations have been reported in patients with Cushing syndrome with primary pigmented nodular adrenocortical disease or isolated micronodular adrenocortical disease without other genetic defects. It has been reported that an increase in PDE11A expression affects the proliferation of glioblastoma and worsens patient prognosis. The present mini-review summarizes the location of PDE11A expression, the impact of structural differences and disease relevance.

State-of-the-art review of snake venom phosphodiesterases (svPDEs)

Phosphodiesterases (PDEs) constitute an enzyme group able to hydrolyze nucleic acids as well as some second messengers. Due to this ability and their expression in several human tissues and organs, PDEs can control a gamut of physiological processes. They are also involved in some pathological conditions, such as Alzheimer's disease and erectile dysfunction. PDEs are also expressed in snake venom glands, being called snake venoms phosphodiesterases, or simply svPDEs. The occurrence of these enzymes has already been reported in crotalid, elapid and viperid venoms, such as Crotalus, Naja and Trimeresurus, respectively, but not all of them have been characterized concerning their structure, activity and function. In this review, we are addressing general characteristics of svPDEs, in addition to their structural, biochemical and functional characteristics, and we also report some potential applications of svPDEs.

Targeting Metalloenzymes by Boron-Containing Metal-Binding Pharmacophores

Metalloenzymes have critical roles in a wide range of biological processes and are directly involved in many human diseases; hence, they are considered as important targets for therapeutic intervention. The specific characteristics of metal ion(s)-containing active sites make exploitation of metal-binding pharmacophores (MBPs) critical to inhibitor development targeting metalloenzymes. This Perspective focuses on boron-containing MBPs, which display unique binding modes with metalloenzyme active sites, particularly via mimicking native substrates or tetrahedral transition states. The design concepts regarding boron-containing MBPs are highlighted through the case analyses on five distinct classes of clinically relevant nucleophilic metalloenzymes from medicinal chemistry perspectives. The challenges (e.g., selectivity) faced by some boron-containing MBPs and possible strategies (e.g., bioisosteres) for metalloenzyme inhibitor transformation are also discussed.

A review of synthetic bioactive tetrahydro-β-carbolines: A medicinal chemistry perspective

1, 2, 3, 4-Tetrahydro-β-carboline (THβC) scaffold is widespread in many natural products (NPs) and synthetic compounds which show a variety of pharmacological activities. In this article, we reviewed the design, structures and biological characteristics of reported synthetic THβC compounds, and structure and activity relationship (SAR) of them were also discussed. This work might provide a reference for subsequent drug development based on THβC.

Piclamilast mitigates 1,2-dimethylhydrazine induced colon cancer in rats through modulation of Ras/PI3K/Akt/mTOR and NF-κβ signaling

Colorectal cancer (CRC) is the third leading type of adult cancer in both genders with high morbidity and mortality worldwide. Even though the discovery of many antineoplastic drugs for CRC, the current therapy is not adequately efficient.This study was designed to investigate the effect and mechanism of Piclamilast (PIC), a selective PDE4 inhibitor, on a DMH-induced colorectal cancer (CRC) rat model. The rats were grouped (n = 10) into group 1 (control), group 2 (PIC 3 mg/kg, p.o.), groups 3-5 received DMH (20 mg/kg/week, S.C.), and groups 4 and 5 received PIC (1 and 3 mg/kg/day, p.o.) for 15 weeks. The DMH treatment increased aberrant crypt foci (ACF), Proliferating cell nuclear antigen (PCNA), and TBARS levels, along with decreased antioxidant defenses (GSH, GSH-Px, and catalase). Increased NF-κβ expression and inflammatory cytokines were also evident. PIC dose-dependently reduced ACF and restored oxidative stress and inflammatory markers favorably. Moreover, PIC in its large, tested dose only significantly increased the intracellular level of cAMP and suppressed the activation of Ras and PI3K and its downstream Akt/mTOR signaling. Furthermore, PIC promoted CRC apoptosis, and increased the gene expression of the apoptotic factors, caspase-3 and Bax, and decreased the anti-apoptotic factor Bcl-2. The results of this study show that PIC may be a promising therapeutic agent for the treatment of CRC. PIC might inhibit the proliferation of CRC cells and induce apoptosis via multiple mechanisms that involve its antioxidant effect and inhibition of NF-κβ and Ras/PI3K/Akt/mTOR signaling.

Ameliorative role of rolipram, PDE-4 inhibitor, against sodium arsenite-induced vascular dementia in rats

Arsenic exposure to the population leads to serious health problems like neurotoxicity, nephrotoxicity, and cardiovascular abnormality. In the present study, the work has been commenced to discover the prospect of rolipram a phosphodiestrase-4 (PDE-4) inhibitor against sodium arsenite (SA)-induced vascular endothelial dysfunction (EnDF) leading to dementia in rats. Wistar rats were treated with SA (5 mg/kg body weight/day orally) for 44 days for induction of vascular EnDF and dementia. Learning and memory were evaluated using Morris water maze (MWM) test. Vascular EnDF was evaluated using aortic ring preparation. Various biochemical parameters were also evaluated like brain oxidative stress (viz. reduced glutathione and thiobarbituric acid reactive substances level), serum nitrite/nitrate activity, acetylcholinesterase activity, and inflammatory markers (viz. neutrophil infiltration in brain and myeloperoxidase). SA-treated rats showed poor performance in water maze trials indicating attenuated memory and ability to learn with significant rise (p < 0.05) in brain acetylcholinesterase activity, brain oxidative stress, neutrophil count, and significant decrease (p < 0.05) in serum nitrite/nitrate levels and vascular endothelial functions. Rolipram (PDE-4 inhibitor) treatment (0.03 mg/kg and 0.06 mg/kg body weight, intraperitoneally daily for 14 days) significantly improved memory and learning abilities, and restored various biochemical parameters and EnDF. It is concluded that PDE-4 modulator may be considered the prospective target for the treatment of SA-induced vascular EnDF and related dementia.

FSH mediated cAMP signalling upregulates the expression of Gα subunits in pubertal rat Sertoli cells

Follicle Stimulating Hormone (FSH) acts via FSH-Receptor (FSH-R) by employing cAMP as the dominant secondary messenger in testicular Sertoli cells (Sc) to support spermatogenesis. Binding of FSH to FSH-R, results the recruitment of the intracellular GTP binding proteins, either stimulatory Gαs or inhibitory Gαi that in turn regulate cAMP production in Sc. The cytosolic concentration of cAMP being generated by FSH-R thereafter critically determines the downstream fate of the FSH signalling. The pleiotropic action of FSH due to differential cAMP output during functional maturation of Sc has been well studied. However, the developmental and cellular regulation of the Gα proteins associated with FSH-R is poorly understood in Sc. In the present study, we report the differential transcriptional modulation of the Gα subunit genes by FSH mediated cAMP signalling in neonatal and pubertal rat Sc. Our data suggested that unlike in neonatal Sc, both the basal and FSH/forskolin induced expression of Gαs, Gαi-1, Gαi-2 and Gαi-3 transcripts was significantly (p < 0.05) up-regulated in pubertal Sc. Further investigations involving treatment of Sc with selective Gαi inhibitor pertussis toxin, confirmed the elevated expression of Gi subunits in pubertal Sc. Collectively our results indicated that the high level of Gαi subunits serves as a negative regulator to optimize cAMP production in pubertal Sc.

Natural Molecules as Talented Inhibitors of Nucleotide Pyrophosphatases/Phosphodiesterases (PDEs)

BACKGROUND

Phosphodiesterases (PDEs) are a wide group of enzymes with multiple therapeutic actions, including vasorelaxation, cardiotonic, antidepressant, anti-inflammatory, antithrombotic, anti-spasmolytic, memory-enhancing, and anti-asthmatic. PDEs with eleven subtypes from PDE-1 to PDE-11 typically catalyze the cleavage of the phosphodiester bond and, hence, degrades either cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP).

OBJECTIVE

Several selective or non-selective inhibitors of the PDE subtypes are used clinically, i.e. sildenafil, rolipram, cysteine, etc. Recently, interest in plant-based pharmacologically bioactive compounds having potent PDEs inhibitory potential has increased. Purposely, extensive research has been carried out on natural products to explore new inhibitors of various PDEs. Therefore, this review summarizes the published data on natural PDEs inhibitors and their potential therapeutic applications.

METHODS

For this purpose, natural compounds with PDE inhibitory potential have been surveyed through several databases, including PubMed, Web of Sciences (WoS), Scopus, and Google Scholar.

RESULTS

According to a detailed literature survey, the most promising class of herbal compounds with PDE-inhibiting property has been found to belong to phenolics, including flavonoids (luteolin, kaempferol, icariin, etc.). Many other encouraging inhibitors from plants have also been identified, such as coumarins (23, 24) (licoarylcoumarin and glycocoumarin,), saponins ( agapanthussaponins), lignans (31, 33) [(±)-schizandrin and kobusin], terpenes (28, 29, 31) (perianradulcin A, quinovic acid, and ursolic acid), anthraquinones (18, 19) (emodin and chrysophanol), and alkaloids (Sanjoinine-D) (36).

CONCLUSION

In this review, studies have revealed the PDE-inhibitory potential of natural plant extracts and their bioactive constituents in treating various diseases; however, further clinical studies comprising synergistic use of different therapies (synthetic & natural) to acquire multi-targeted results might also be a promising option.

Regulation of α-cell glucagon secretion: The role of second messengers

Glucagon is a potent glucose‐elevating hormone that is secreted by pancreatic α‐cells. While well‐controlled glucagon secretion plays an important role in maintaining systemic glucose homeostasis and preventing hypoglycaemia, it is increasingly apparent that defects in the regulation of glucagon secretion contribute to impaired counter‐regulation and hyperglycaemia in diabetes. It has therefore been proposed that pharmacological interventions targeting glucagon secretion/signalling can have great potential in improving glycaemic control of patients with diabetes. However, despite decades of research, a consensus on the precise mechanisms of glucose regulation of glucagon secretion is yet to be reached. Second messengers are a group of small intracellular molecules that relay extracellular signals to the intracellular signalling cascade, modulating cellular functions. There is a growing body of evidence that second messengers, such as cAMP and Ca²⁺, play critical roles in α‐cell glucose‐sensing and glucagon secretion. In this review, we discuss the impact of second messengers on α‐cell electrical activity, intracellular Ca²⁺ dynamics and cell exocytosis. We highlight the possibility that the interaction between different second messengers may play a key role in the glucose‐regulation of glucagon secretion.

From Celecoxib to a Novel Class of Phosphodiesterase 5 Inhibitors: Trisubstituted Pyrazolines as Novel Phosphodiesterase 5 Inhibitors with Extremely High Potency and Phosphodiesterase Isozyme Selectivity

A ligand-based approach involving systematic modifications of a trisubstituted pyrazoline scaffold derived from the COX2 inhibitor, celecoxib, was used to develop novel PDE5 inhibitors. Novel pyrazolines were identified with potent PDE5 inhibitory activity lacking COX2 inhibitory activity. Compound d12 was the most potent with an IC₅₀ of 1 nM, which was three times more potent than sildenafil and more selective with a selectivity index of >10,000-fold against all other PDE isozymes. Sildenafil inhibited the full-length and catalytic fragment of PDE5, while compound d12 only inhibited the full-length enzyme, suggesting a mechanism of enzyme inhibition distinct from sildenafil. The PDE5 inhibitory activity of compound d12 was confirmed in cells using a cGMP biosensor assay. Oral administration of compound d12 achieved plasma levels >1000-fold higher than IC₅₀ values and showed no discernable toxicity after repeated dosing. These results reveal a novel strategy to inhibit PDE5 with unprecedented potency and isozyme selectivity.

Phosphodiesterase (1, 3 & 5) inhibitors attenuate diclofenac-induced acute kidney toxicity in rats

Diclofenac, one of the most commonly used non-steroidal anti-inflammatory drugs, leads to severe adverse effects on the kidneys. The aim of the present study was to investigate the potential pretreatment effect of phosphodiesterase (1, 3 & 5) inhibitors on diclofenac-induced acute renal failure in rats. Rats orally received pentoxifylline (100 mg/kg), vinpocetine (20 mg/kg), cilostazol (50 mg/kg), or sildenafil (5 mg/kg) once per day for 6 consecutive days. Diclofenac (15 mg/kg) was injected on day-4, -5 and -6 in all groups except normal control group. The used phosphodiesterase inhibitors significantly reduced the diclofenac-induced elevation in the serum levels of blood urea nitrogen, creatinine and cystatin C. Moreover, the renal tissue contents of tumor necrosis factor (TNF)-α, nuclear factor (NF)-κB as well as the protein expression of toll-like receptor (TLR) 4 and high mobility group box (HMGB) 1 were markedly reduced by the used phosphodiesterase inhibitors, as compared to the diclofenac control. This was reflected on the marked improvement in histopathological changes induced by diclofenac. Sildenafil showed the best protection regarding TNF-α and NF-κB, while cilostazol showed the best results regarding TLR4, HMGB1 and histopathological examination. This study revealed the good protective effect of these phosphodiesterase inhibitors against diclofenac-induced acute renal failure.

Unraveling the structure and function of CdcPDE: A novel phosphodiesterase from Crotalus durissus collilineatus snake venom

This study reports the isolation, structural, biochemical, and functional characterization of a novel phosphodiesterase from Crotalus durissus collilineatus venom (CdcPDE). CdcPDE was successfully isolated from whole venom using three chromatographic steps and represented 0.7% of total protein content. CdcPDE was inhibited by EDTA and reducing agents, demonstrating that metal ions and disulfide bonds are necessary for its enzymatic activity. The highest enzymatic activity was observed at pH 8-8.5 and 37 °C. Kinetic parameters indicated a higher affinity for the substrate bis(p-nitrophenyl) phosphate compared to others snake venom PDEs. Its structural characterization was done by the determination of the protein primary sequence by Edman degradation and mass spectrometry, and completed by the building of molecular and docking-based models. Functional in vitro assays showed that CdcPDE is capable of inhibiting platelet aggregation induced by adenosine diphosphate in a dose-dependent manner and demonstrated that CdcPDE is cytotoxic to human keratinocytes. CdcPDE was recognized by the crotalid antivenom produced by the Instituto Butantan. These findings demonstrate that the study of snake venom toxins can reveal new molecules that may be relevant in cases of snakebite envenoming, and that can be used as molecular tools to study pathophysiological processes due to their specific biological activities.

Phosphodiesterase 5 (PDE5): Structure-function regulation and therapeutic applications of inhibitors

Phosphodiesterase 5 (PDE5) is one of the most well-studied phosphodiesterases (PDEs) that specifically targets cGMP typically generated by nitric oxide (NO)-mediated activation of the soluble guanylyl cyclase. Given the crucial role of cGMP generated through the activation of this cellular signaling pathway in a variety of physiologically processes, pharmacological inhibition of PDE5 has been demonstrated to have several therapeutic applications including erectile dysfunction and pulmonary arterial hypertension. While they are designed to inhibit PDE5, the inhibitors show different affinities and specificities against all PDE subtypes. Additionally, they have been shown to induce allosteric structural changes in the protein. These are mostly attributed to their chemical structure and, therefore, binding interactions with PDE catalytic domains. Therefore, understanding how these inhibitors interact with PDE5 and the structural basis of their selectivity is critically important for the design of novel, highly selective PDE5 inhibitors. Here, we review the structure of PDE5, how its function is regulated, and discuss the clinically available inhibitors that target phosphodiesterase 5, aiming to better understand the structural bases of their affinity and specificity. We also discuss the therapeutic indications of these inhibitors and the potential of repurposing for a wider range of clinical applications.

Phosphodiesterase 2 inhibitor Hcyb1 reverses corticosterone-induced neurotoxicity and depression-like behavior

RATIONALE

Currently available PDE2 inhibitors have poor brain penetration that limits their therapeutic utility in the treatment of depression. Hcyb1 is a novel selective PDE2 inhibitor that was introduced more lipophilic groups with polar functionality to the scaffold pyrazolopyrimidinone to improve the blood-brain barrier (BBB) penetration. Our previous study suggested that Hcyb1 increased the neuronal cell viability and exhibited antidepressant-like effects, which were parallel to the currently available PDE2 inhibitor Bay 60-7550.

OBJECTIVES

The present study investigated whether Hcyb1 protected HT-22 cells against corticosterone-induced neurotoxicity and produced antidepressant-like effects in behavioral tests in stressed mice.

METHODS

The neuroprotective effects of Hcyb1 against corticosterone-induced cell lesion were examined by cell viability (MTS) assay. The enzyme-linked immunosorbent assay (ELISA) and immunoblot analysis were used to determine the levels of cAMP or cGMP and expression of pCREB or BDNF, respectively, in the corticosterone-treated HT-22 cells. The antidepressant-like effects of Hcyb1 were determined in the tail suspension and novelty suppressed feeding tests in stressed mice.

RESULTS

In the cell-based assay, Hcyb1 significantly increased cell viability of HT-22 cells against corticosterone-induced neurotoxicity in a time- and dose-dependent manner. Hcyb1 also rescued corticosterone-induced decreases in both cGMP and cAMP levels, pCREB/CREB and BDNF expression. These protective effects of Hcyb1 were prevented by pretreatment with either the PKA inhibitor H89 or the PKG inhibitor KT5823. Moreover, Hcyb1 reversed acute stress-induced increases in immobility time and the latency to feed in the tail suspension and novelty suppressed feeding tests, respectively, which were prevented by pretreatment with H89 or KT5823.

CONCLUSION

These findings provide evidence that the neuroprotective effects of Hcyb1 are mediated by PDE2-dependent cAMP/cGMP signaling.

Cyclic Nucleotides Signaling and Phosphodiesterase Inhibition: Defying Alzheimer's Disease

Defects in brain functions associated with aging and neurodegenerative diseases benefit insignificantly from existing options, suggesting that there is a lack of understanding of pathological mechanisms. Alzheimer's disease (AD) is such a nearly untreatable, allied to age neurological deterioration for which only the symptomatic cure is available and the agents able to mould progression of the disease, is still far away. The altered expression of phosphodiesterases (PDE) and deregulated cyclic nucleotide signaling in AD has provoked a new thought of targeting cyclic nucleotide signaling in AD. Targeting cyclic nucleotides as an intracellular messenger seems to be a viable approach for certain biological processes in the brain and controlling substantial. Whereas, the synthesis, execution, and/or degradation of cyclic nucleotides has been closely linked to cognitive deficits. In relation to cognition, the cyclic nucleotides (cAMP and cGMP) have an imperative execution in different phases of memory, including gene transcription, neurogenesis, neuronal circuitry, synaptic plasticity and neuronal survival, etc. AD is witnessed by impairments of these basic processes underlying cognition, suggesting a crucial role of cAMP/cGMP signaling in AD populations. Phosphodiesterase inhibitors are the exclusive set of enzymes to facilitate hydrolysis and degradation of cAMP and cGMP thereby, maintains their optimum levels initiating it as an interesting target to explore. The present work reviews a neuroprotective and substantial influence of PDE inhibition on physiological status, pathological progression and neurobiological markers of AD in consonance with the intensities of cAMP and cGMP.

PET Imaging of Phosphodiesterase-4 Identifies Affected Dysplastic Bone in McCune-Albright Syndrome, a Genetic Mosaic Disorder

McCune-Albright syndrome (MAS) is a mosaic disorder arising from gain-of-function mutations in the GNAS gene, which encodes the 3',5'-cyclic adenosine monophosphate (cAMP) pathway-associated G-protein, G_sα. Clinical manifestations of MAS in a given individual, including fibrous dysplasia, are determined by the timing and location of the GNAS mutation during embryogenesis, the tissues involved, and the role of G_sα in the affected tissues. The G_sα mutation results in dysregulation of the cAMP signaling cascade, leading to upregulation of phosphodiesterase type 4 (PDE4), which catalyzes the hydrolysis of cAMP. Increased cAMP levels have been found in vitro in both animal models of fibrous dysplasia and in cultured cells from individuals with MAS but not in humans with fibrous dysplasia. PET imaging of PDE4 with ¹¹C-(R)-rolipram has been used successfully to study the in vivo activity of the cAMP cascade. To date, it remains unknown whether fibrous dysplasia and other symptoms of MAS, including neuropsychiatric impairments, are associated with increased PDE4 activity in humans. Methods: ¹¹C-(R)-rolipram whole-body and brain PET scans were performed on 6 individuals with MAS (3 for brain scans and 6 for whole-body scans) and 9 healthy controls (7 for brain scans and 6 for whole-body scans). Results: ¹¹C-(R)-rolipram binding correlated with known locations of fibrous dysplasia in the periphery of individuals with MAS; no uptake was observed in the bones of healthy controls. In peripheral organs and the brain, no difference in ¹¹C-(R)-rolipram uptake was noted between participants with MAS and healthy controls. Conclusion: This study is the first to find evidence for increased cAMP activity in areas of fibrous dysplasia in vivo. No differences in brain uptake between MAS participants and controls were detected-a finding that could be due to several reasons, including the limited anatomic resolution of PET. Nevertheless, the results confirm the usefulness of PET scans with ¹¹C-(R)-rolipram to indirectly measure increased cAMP pathway activation in human disease.

A two-dimensional finite element model of cyclic adenosine monophosphate (cAMP) intracellular signaling

In this work, we present a two-dimensional finite element analysis (FEA) model that describes fundamental intracellular signals of cyclic adenosine monophosphate (cAMP) in a general fashion. The model was subsequently solved numerically and the results were displayed in forms of time-course plots of cAMP concentration at a cellular location or color-filled contour maps of cAMP signal distribution within the cell at specific time points. Basic intracellular cAMP signaling was described in this model so it can be numerically validated by verifying its numerical results against available analytical solutions and against results obtained from other numerical techniques reported in the literature. This is the first important step before the model can be expanded in future work. Model simulations demonstrate that under certain conditions, sustained cAMP concentrations can be formed within endothelial cells (ECs), similar to those observed in rat pulmonary microvascular ECs. Spatial and temporal cAMP dynamic simulations indicated that the proposed FEA model is an effective tool for the study of the kinetics and spatial spread of second messenger signaling and can be expanded to simulate second messenger signals in the pulmonary vasculature.

Phosphodiesterase inhibitors say NO to Alzheimer's disease

Phosphodiesterases (PDEs) consisted of 11 subtypes (PDE1 to PDE11) and over 40 isoforms that regulate levels of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), the second messengers in cell functions. PDE inhibitors (PDEIs) have been attractive therapeutic targets due to their involvement in diverse medical conditions, e.g. cardiovascular diseases, autoimmune diseases, Alzheimer's disease (AD), etc. Among them; AD with a complex pathology is a progressive neurodegenerative disorder which affect mostly senile people in the world and only symptomatic treatment particularly using cholinesterase inhibitors in clinic is available at the moment for AD. Consequently, novel treatment strategies towards AD are still searched extensively. Since PDEs are broadly expressed in the brain, PDEIs are considered to modulate neurodegenerative conditions through regulating cAMP and cGMP in the brain. In this sense, several synthetic or natural molecules inhibiting various PDE subtypes such as rolipram and roflumilast (PDE4 inhibitors), vinpocetine (PDE1 inhibitor), cilostazol and milrinone (PDE3 inhibitors), sildenafil and tadalafil (PDE5 inhibitors), etc have been reported showing encouraging results for the treatment of AD. In this review, PDE superfamily will be scrutinized from the view point of structural features, isoforms, functions and pharmacology particularly attributed to PDEs as target for AD therapy.

Targeting Metalloenzymes for Therapeutic Intervention

Metalloenzymes are central to a wide range of essential biological activities, including nucleic acid modification, protein degradation, and many others. The role of metalloenzymes in these processes also makes them central for the progression of many diseases and, as such, makes metalloenzymes attractive targets for therapeutic intervention. Increasing awareness of the role metalloenzymes play in disease and their importance as a class of targets has amplified interest in the development of new strategies to develop inhibitors and ultimately useful drugs. In this Review, we provide a broad overview of several drug discovery efforts focused on metalloenzymes and attempt to map out the current landscape of high-value metalloenzyme targets.

Xanthine scaffold: scope and potential in drug development

Medicinal plants have been the basis for discovery of various important marketed drugs. Xanthine is one such lead molecule. Xanthines in various forms (caffeine, theophylline, theobromine, etc) are abode in tea, coffee, cocoa, chocolate etc. giving them popular recognition. These compounds are best known for their diverse pharmaceutical applications as cyclic nucleotide phosphodiesterase inhibition, antagonization of adenosine receptor, anti-inflammatory, anti-microbial, anti-oxidant and anti-tumor activities. These properties incentivize to use xanthine as scaffold to develop new derivatives. Chemical synthesis contributes greater diversity in xanthine based derivatisation. With highlighting the existing challenges in chemical synthesis, the present review focuses the probable solution to fill existing lacuna. The review summarizes the available knowledge of xanthine based drugs development along with exploring new xanthine led chemical synthesis path for bringing diversification in xanthine based research. The main objective of this review is to explore the immense potential of xanthine as scaffold in drug development.

The Phosphodiesterase 9 Inhibitor PF-04449613 Promotes Dendritic Spine Formation and Performance Improvement after Motor Learning

The cyclic nucleotide cGMP is an intracellular second messenger with important roles in neuronal functions and animals' behaviors. The phosphodiesterases (PDEs) are a family of enzymes that hydrolyze the second messengers cGMP and cAMP. Inhibition of phosphodiesterase 9 (PDE9), a main isoform of PDEs hydrolyzing cGMP, has been shown to improve learning and memory as well as cognitive function in rodents. However, the role of PDE9 in regulating neuronal structure and function in vivo remains unclear. Here we used in vivo two-photon microscopy to investigate the effect of a selective PDE9 inhibitor PF-04449613 on the activity and plasticity of dendritic spines of layer V pyramidal neurons in the mouse primary motor cortex. We found that administration of PF-04449613 increased calcium activity of dendrites and dendritic spines of layer V pyramidal neurons in mice under resting and running conditions. Chronic treatment of PF-04449613 over weeks increased dendritic spine formation and elimination under basal conditions. Furthermore, PF-04449613 treatment over 1-7 days increased the formation and survival of new spines as well as performance improvement after rotarod motor training. Taken together, our studies suggest that elevating the level of cGMP with the PDE9 inhibitor PF-04449613 increases synaptic calcium activity and learning-dependent synaptic plasticity, thereby contributing to performance improvement after learning. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 00: 000-000, 2018.

Shedding light on the role of cAMP in mammalian sperm physiology

Mammalian fertilization relies on sperm finding the egg and penetrating the egg vestments. All steps in a sperm's lifetime crucially rely on changes in the second messenger cAMP (cyclic adenosine monophosphate). In recent years, it has become clear that signal transduction in sperm is not a continuum, but rather organized in subcellular domains, e.g. the sperm head and the sperm flagellum, with the latter being further separated into the midpiece, principal piece, and endpiece. To understand the underlying signaling pathways controlling sperm function in more detail, experimental approaches are needed that allow to study sperm signaling with spatial and temporal precision. Here, we will give a comprehensive overview on cAMP signaling in mammalian sperm, describing the molecular players involved in these pathways and the sperm functions that are controlled by cAMP. Furthermore, we will highlight recent advances in analyzing and manipulating sperm signaling with spatio-temporal precision using light.

Structure-Based Design, Synthesis, Biological Evaluation, and Molecular Docking of Novel PDE10 Inhibitors With Antioxidant Activities

Phosphodiesterase 10 is a promising target for the treatment of a series of central nervous system (CNS) diseases. Imbalance between oxidative stress and antioxidant defense systems as a universal condition in neurodegenerative disorders is widely studied as a potential therapy for CNS diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). To discover multifunctional pharmaceuticals as a treatment for neurodegenerative diseases, a series of quinazoline-based derivatives with PDE10 inhibitory activities and antioxidant activities were designed and synthesized. Nine out of 13 designed compounds showed good PDE10 inhibition at the concentration of 1.0 μM. Among these compounds, eight exhibited moderate to excellent antioxidant activity with ORAC (oxygen radical absorbance capacity) value above 1.0. Molecular docking was performed for better understanding of the binding patterns of these compounds with PDE10. Compound 11e, which showed remarkable inhibitory activity against PDE10 and antioxidant activity may serve as a lead for the further modification.

Three-dimensional models of Mycobacterium tuberculosis proteins Rv1555, Rv1554 and their docking analyses with sildenafil, tadalafil, vardenafil drugs, suggest interference with quinol binding likely to affect protein's function

Background

Earlier based on bioinformatics analyses, we had predicted the Mycobacterium tuberculosis (M.tb) proteins; Rv1555 and Rv1554, among the potential new tuberculosis drug targets. According to the ‘TB-drugome’ the Rv1555 protein is ‘druggable’ with sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra) drugs. In the present work, we intended to understand via computer modeling studies, how the above drugs are likely to inhibit the M.tb protein’s function.

Results

The three-dimensional computer models for M.tb proteins; Rv1555 and Rv1554 constructed on the template of equivalent membrane anchor subunits of the homologous E.coli quinol fumarate reductase respiratory protein complex, followed by drug docking analyses, suggested that the binding of above drugs interferes with quinol binding sites. Also, we experimentally observed the in-vitro growth inhibition of E.coli bacteria containing the homologous M.tb protein sequences with sildenafil and tadalafil drugs.

Conclusions

The predicted binding sites of the drugs is likely to affect the above M.tb proteins function as quinol binding is known to be essential for electron transfer function during anaerobic respiration in the homologous E.coli protein complex. Therefore, sildenafil and related drugs currently used in the treatment of male erectile dysfunction targeting the human phosphodiesterase 5 enzyme may be evaluated for their plausible role as repurposed drugs to treat human tuberculosis.

Electronic supplementary material

The online version of this article (10.1186/s12900-018-0085-4) contains supplementary material, which is available to authorized users.

Docking and quantitative structure-activity relationship of bi-cyclic heteroaromatic pyridazinone and pyrazolone derivatives as phosphodiesterase 3A (PDE3A) inhibitors

PDE3s belong to the phosphodiesterases family, where the PDE3A isoform is the major subtype in platelets involved in the cAMP regulation pathway of platelet aggregation. PDE3A inhibitors have been designed as potential antiplatelet agents. In this work, a homology model of PDE3A was developed and used to obtain the binding modes of bicyclic heteroaromatic pyridazinones and pyrazolones. Most of the studied compounds adopted similar orientations within the PDE3A active site, establishing hydrogen bonds with catalytic amino acids. Besides, the structure-activity relationship of the studied inhibitors was described by using a field-based 3D-QSAR method. Different structure alignment strategies were employed, including template-based and docking-based alignments. Adequate correlation models were obtained according to internal and external validations. In general, QSAR models revealed that steric and hydrophobic fields describe the different inhibitory activities of the compounds, where the hydrogen bond donor and acceptor fields have minor contributions. It should be stressed that structural elements of PDE3A inhibitors are reported here, through descriptions of their binding interactions and their differential affinities. In this sense, the present results could be useful in the future design of more specific and potent PDE3A inhibitors that may be used for the treatment of cardiovascular diseases.

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

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

Assessing protein-ligand binding modes with computational tools: the case of PDE4B

In a first step in the discovery of novel potent inhibitor structures for the PDE4B family with limited side effects, we present a protocol to rank newly designed molecules through the estimation of their IC[Formula: see text] values. Our protocol is based on reproducing the linear relationship between the logarithm of experimental IC[Formula: see text] values [[Formula: see text](IC[Formula: see text])] and their calculated binding free energies ([Formula: see text]). From 13 known PDE4B inhibitors, we show here that (1) binding free energies obtained after a docking process by AutoDock are not accurate enough to reproduce this linear relationship; (2) MM-GB/SA post-processing of molecular dynamics (MD) trajectories of the top ranked AutoDock pose improves the linear relationship; (3) by taking into account all representative structures obtained by AutoDock and by averaging MM-GB/SA computations on a series of 40 independent MD trajectories, a linear relationship between [Formula: see text](IC[Formula: see text]) and the lowest [Formula: see text] is achieved with [Formula: see text].

TCF21 is related to testis growth and development in broiler chickens

Background

Large amounts of fat deposition often lead to loss of reproductive efficiency in humans and animals. We used broiler chickens as a model species to conduct a two-directional selection for and against abdominal fat over 19 generations, which resulted in a lean and a fat line. Direct selection for abdominal fat content also indirectly resulted in significant differences (P < 0.05) in testis weight (TeW) and in TeW as a percentage of total body weight (TeP) between the lean and fat lines.

Results

A total of 475 individuals from the generation 11 (G₁₁) were genotyped. Genome-wide association studies revealed two regions on chicken chromosomes 3 and 10 that were associated with TeW and TeP. Forty G₁₆ individuals (20 from each line), were further profiled by focusing on these two chromosomal regions, to identify candidate genes with functions that may be potentially related to testis growth and development. Of the nine candidate genes identified with database mining, a significant association was confirmed for one gene, TCF21, based on mRNA expression analysis. Gene expression analysis of the TCF21 gene was conducted again across 30 G₁₉ individuals (15 individuals from each line) and the results confirmed the findings on the G₁₆ animals.

Conclusions

This study revealed that the TCF21 gene is related to testis growth and development in male broilers. This finding will be useful to guide future studies to understand the genetic mechanisms that underlie reproductive efficiency.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-017-0299-0) contains supplementary material, which is available to authorized users.

Towards selective phosphodiesterase 2A (PDE2A) inhibitors: a patent review (2010 - present)

INTRODUCTION

The cyclic nucleotides cAMP and cGMP are ubiquitous intracellular second messengers regulating a large variety of biological processes. The intracellular concentration of these biologically relevant molecules is modulated by the activity of phosphodiesterases (PDEs), a class of enzymes that is grouped in 11 families. The expression of PDEs is tissue- and cell-specific allowing spatiotemporal integration of multiple signaling cascades. PDE2A is a dual substrate enzyme and is expressed in both the periphery and in the central nervous system, however its expression is highest in the brain, where it is mainly localized in the cortex, hippocampus, and striatum. This suggests that this enzyme may regulate intraneuronal cGMP and cAMP levels in brain areas involved in emotion, perception, concentration, learning and memory.

AREAS COVERED

This review covers the patent applications published between January 2010 and February 2016 on phosphodiesterase 2A inhibitors.

EXPERT OPINION

Recent publications in the literature and in filed patent applications demonstrate the interest of pharmaceutical companies for PDE2A. This has increased the insights of its possible therapeutic role but the few clinical trials were terminated. Based on the ongoing interest in the field it is likely that new clinical trials can be expected and will unravel the therapeutic potential of PDE2A inhibition.

Molecular Mechanisms for cAMP-Mediated Immunoregulation in T cells - Role of Anchored Protein Kinase A Signaling Units

The cyclic AMP/protein kinase A (cAMP/PKA) pathway is one of the most common and versatile signal pathways in eukaryotic cells. A-kinase anchoring proteins (AKAPs) target PKA to specific substrates and distinct subcellular compartments providing spatial and temporal specificity for mediation of biological effects channeled through the cAMP/PKA pathway. In the immune system, cAMP is a potent negative regulator of T cell receptor-mediated activation of effector T cells (Teff) acting through a proximal PKA/Csk/Lck pathway anchored via a scaffold consisting of the AKAP Ezrin holding PKA, the linker protein EBP50, and the anchoring protein phosphoprotein associated with glycosphingolipid-enriched microdomains holding Csk. As PKA activates Csk and Csk inhibits Lck, this pathway in response to cAMP shuts down proximal T cell activation. This immunomodulating pathway in Teff mediates clinically important responses to regulatory T cell (Treg) suppression and inflammatory mediators, such as prostaglandins (PGs), adrenergic stimuli, adenosine, and a number of other ligands. A major inducer of T cell cAMP levels is PG E2 (PGE2) acting through EP2 and EP4 prostanoid receptors. PGE2 plays a crucial role in the normal physiological control of immune homeostasis as well as in inflammation and cancer immune evasion. Peripherally induced Tregs express cyclooxygenase-2, secrete PGE2, and elicit the immunosuppressive cAMP pathway in Teff as one tumor immune evasion mechanism. Moreover, a cAMP increase can also be induced by indirect mechanisms, such as intercellular transfer between T cells. Indeed, Treg, known to have elevated levels of intracellular cAMP, may mediate their suppressive function by transferring cAMP to Teff through gap junctions, which we speculate could also be regulated by PKA/AKAP complexes. In this review, we present an updated overview on the influence of cAMP-mediated immunoregulatory mechanisms acting through localized cAMP signaling and the therapeutical increasing prospects of AKAPs disruptors in T-cell immune function.

The glial cell modulator ibudilast attenuates neuroinflammation and enhances retinal ganglion cell viability in glaucoma through protein kinase A signaling

Glaucoma is a neurodegenerative disease and the leading cause of irreversible blindness worldwide. Vision deficits in glaucoma result from the selective loss of retinal ganglion cells (RGC). Glial cell-mediated neuroinflammation has been proposed to contribute to disease pathophysiology, but whether this response is harmful or beneficial for RGC survival is not well understood. To test this, we characterized the role of ibudilast, a clinically approved cAMP phosphodiesterase (PDE) inhibitor with preferential affinity for PDE type 4 (PDE4). Here, we demonstrate that intraocular administration of ibudilast dampened macroglia and microglia reactivity in the retina and optic nerve hence decreasing production of proinflammatory cytokines in a rat model of ocular hypertension. Importantly, ibudilast promoted robust RGC soma survival, prevented axonal degeneration, and improved anterograde axonal transport in glaucomatous eyes without altering intraocular pressure. Intriguingly, ocular hypertension triggered upregulation of PDE4 subtype A in Müller glia, and ibudilast stimulated cAMP accumulation in these cells. Co-administration of ibudilast with Rp-cAMPS, a cell-permeable and non-hydrolysable cAMP analog that inhibits protein kinase A (PKA), completely blocked ibudilast-induced neuroprotection. Collectively, these data demonstrate that ibudilast, a safe and well-tolerated glial cell modulator, attenuates gliosis, decreases levels of proinflammatory mediators, and enhances neuronal viability in glaucoma through activation of the cAMP/PKA pathway. This study provides insight into PDE4 signaling as a potential target to counter the harmful effects associated with chronic gliosis and neuroinflammation in glaucoma.

A combination of pharmacophore modeling, atom-based 3D-QSAR, molecular docking and molecular dynamics simulation studies on PDE4 enzyme inhibitors

Phosphodiesterases 4 enzyme is an attractive target for the design of anti-inflammatory and bronchodilator agents. In the present study, pharmacophore and atom-based 3D-QSAR studies were carried out for pyrazolopyridine and quinoline derivatives using Schrödinger suite 2014-3. A four-point pharmacophore model was developed using 74 molecules having pIC50 ranging from 10.1 to 4.5. The best four feature model consists of one hydrogen bond acceptor, two aromatic rings, and one hydrophobic group. The pharmacophore hypothesis yielded a statistically significant 3D-QSAR model, with a high correlation coefficient (R(2 )= .9949), cross validation coefficient (Q(2 )= .7291), and Pearson-r (.9107) at six component partial least square factor. The external validation indicated that our QSAR model possessed high predictive power with R(2) value of .88. The generated model was further validated by enrichment studies using the decoy test. Molecular docking, free energy calculation, and molecular dynamics (MD) simulation studies have been performed to explore the putative binding modes of these ligands. A 10-ns MD simulation confirmed the docking results of both stability of the 1XMU-ligand complex and the presumed active conformation. Outcomes of the present study provide insight in designing novel molecules with better PDE4 inhibitory activity.

Computational Analysis of the Mechanism and Thermodynamics of Inhibition of Phosphodiesterase 5A by Synthetic Ligands

Phosphodiesterases are a large class of enzymes mediating a number of physiological processes ranging from immune response to platelet aggregation to cardiac and smooth muscle relaxation. In particular, phosphodiesterase 5 (PDE5) plays an important role in mediating sexual arousal, and it is the central molecular target in treatments of erectile dysfunction. In this study, we look at the mechanism and thermodynamics of the binding of selective inhibitors sildenafil (Viagra) and vardenafil (Levitra) to PDE5 using molecular dynamics simulations. Our simulations of PDE5 with and without sildenafil suggest a binding mechanism in which two loops surrounding the binding pocket of the enzyme (H loop, residues 660-683, and M loop, 787-812) execute sizable conformational changes (∼1 nm), clamping the ligand in the pocket. Also, we note significant changes in the coordination pattern of the divalent ions in the active site of the enzyme, as well as marked changes in the collective motions of the enzyme when the ligand is bound. Using the thermodynamic integration approach we calculate the relative free energies of binding of sildenafil, vardenafil, and demethyl-vardenafil, providing a test of the quality of the force field and the ligand parametrization used. Finally, using the single-step perturbation (SSP) technique, we calculate the relative binding free energies of these three ligands as well. In particular, we focus on critical evaluation of the SSP technique and examine the effects of computational parallelization on the efficiency of the technique. As a technical improvement, we demonstrate that an ensemble of relatively short SSP trajectories (10 × 0.5 ns) markedly outperforms a single trajectory of the same total length (1 × 5 ns) when it comes to sampling efficiency, resulting in significant real-time savings.

Revisiting bacterial cyclic nucleotide phosphodiesterases: cyclic AMP hydrolysis and beyond

Cyclic-3',5'-adenosine monophosphate (cAMP) is a universal second messenger that regulates vital activities in bacteria and eukaryotes. Enzymes that hydrolyze cAMP, called phosphodiesterases (PDEs), negatively regulate the levels of this messenger molecule and are therefore crucial for signal 'termination'. In this minireview, I shall summarize the available literature on bacterial cAMP-PDEs, with particular emphasis on enzymes belonging to the ubiquitously encoded Class III PDE family exemplified by CpdA from Escherichia coli and Rv0805 from Mycobacterium tuberculosis. Using available biochemical, structural and biological information, I shall make a case for re-examining the functions of these enzymes as merely regulators of intrabacterial cAMP levels and suggest that some members of this class may have evolved cAMP-independent functions as well. Finally, I shall highlight the major lacunae in our understanding of these enzymes and present unanswered questions in the area.

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.

Granulocyte-colony stimulating factor activates JAK2/PI3K/PDE3B pathway to inhibit corticosterone synthesis in a neonatal hypoxic-ischemic brain injury rat model

OBJECTIVE

Our previous study demonstrated that granulocyte-colony stimulating factor (G-CSF)-induced neuroprotection is accompanied by an inhibition of corticosterone production in a neonatal hypoxic-ischemic (HI) rat model. The present study investigates how G-CSF inhibits corticosterone production, using adrenal cortical cells and HI rat pups.

METHODS

Cholera toxin was used to induce corticosterone synthesis in a rodent Y1 adrenal cortical cell line by increasing cyclic adenosine monophosphate (cAMP). Both corticosterone and cAMP were quantitatively measured using a commercial enzyme-linked immunosorbent assay (ELISA). The downstream signaling components of the G-CSF receptor, including Janus Kinase 2 (JAK2)/Phosphatidylinositol-3-kinase (PI3K)/Protein kinase B (Akt) and Phosphodiesterase 3B (PDE3B), were detected by western blot. Sprague-Dawley rat pups at the age of 10days (P10) were subjected to unilateral carotid artery ligation followed by hypoxia for 2.5hours. Brain infarction volumes were determined using 2,3,5-triphenyltetrazolium chloride monohydrate (TTC) staining.

RESULTS

G-CSF at 30ng/ml inhibited corticosterone synthesis but lost its inhibitory effect at higher doses. The inhibitory effect of G-CSF was conferred by interfering with cAMP signaling via the activation of the JAK2/PI3K/PDE3B signaling pathway. The degradation of cAMP by G-CSF signaling reduced corticosterone production. This mechanism was further verified in the neonatal HI brain injury rat model, in which inhibition of PDE3B reversed the protective effects of G-CSF.

CONCLUSION

Our data suggest that the neuroprotective G-CSF reduces corticosterone synthesis at the adrenal level by degrading intracellular cAMP via activation of the JAK2/PI3K/PDE3B pathway.

Cyclic decidualization of the human endometrium in reproductive health and failure

Decidualization denotes the transformation of endometrial stromal fibroblasts into specialized secretory decidual cells that provide a nutritive and immunoprivileged matrix essential for embryo implantation and placental development. In contrast to most mammals, decidualization of the human endometrium does not require embryo implantation. Instead, this process is driven by the postovulatory rise in progesterone levels and increasing local cAMP production. In response to falling progesterone levels, spontaneous decidualization causes menstrual shedding and cyclic regeneration of the endometrium. A growing body of evidence indicates that the shift from embryonic to maternal control of the decidual process represents a pivotal evolutionary adaptation to the challenge posed by invasive and chromosomally diverse human embryos. This concept is predicated on the ability of decidualizing stromal cells to respond to individual embryos in a manner that either promotes implantation and further development or facilitates early rejection. Furthermore, menstruation and cyclic regeneration involves stem cell recruitment and renders the endometrium intrinsically capable of adapting its decidual response to maximize reproductive success. Here we review the endocrine, paracrine, and autocrine cues that tightly govern this differentiation process. In response to activation of various signaling pathways and genome-wide chromatin remodeling, evolutionarily conserved transcriptional factors gain access to the decidua-specific regulatory circuitry. Once initiated, the decidual process is poised to transit through distinct phenotypic phases that underpin endometrial receptivity, embryo selection, and, ultimately, resolution of pregnancy. We discuss how disorders that subvert the programming, initiation, or progression of decidualization compromise reproductive health and predispose for pregnancy failure.

Resveratrol and curcumin enhance pancreatic β-cell function by inhibiting phosphodiesterase activity

Resveratrol (RES) and curcumin (CUR) are polyphenols that are found in fruits and turmeric, and possess medicinal properties that are beneficial in various diseases, such as heart disease, cancer, and type 2 diabetes mellitus (T2DM). Results from recent studies have indicated that their therapeutic properties can be attributed to their anti-inflammatory effects. Owing to reports stating that they protect against β-cell dysfunction, we studied their mechanism(s) of action in β-cells. In T2DM, cAMP plays a critical role in glucose- and incretin-stimulated insulin secretion as well as overall pancreatic β-cell health. A potential therapeutic target in the management of T2DM lies in regulating the activity of phosphodiesterases (PDEs), which degrade cAMP. Both RES and CUR have been reported to act as PDE inhibitors in various cell types, but it remains unknown if they do so in pancreatic β-cells. In our current study, we found that both RES (0.1-10 μmol/l) and CUR (1-100 pmol/l)-regulated insulin secretion under glucose-stimulated conditions. Additionally, treating β-cell lines and human islets with these polyphenols led to increased intracellular cAMP levels in a manner similar to 3-isobutyl-1-methylxanthine, a classic PDE inhibitor. When we investigated the effects of RES and CUR on PDEs, we found that treatment significantly downregulated the mRNA expression of most of the 11 PDE isozymes, including PDE3B, PDE8A, and PDE10A, which have been linked previously to regulation of insulin secretion in islets. Furthermore, RES and CUR inhibited PDE activity in a dose-dependent manner in β-cell lines and human islets. Collectively, we demonstrate a novel role for natural-occurring polyphenols as PDE inhibitors that enhance pancreatic β-cell function.

Phosphodiesterases and adrenal Cushing in mice and humans

The majority of benign adrenal cortex lesions leading to Cushing syndrome are associated to one or another abnormality of the cAMP/cGMP-phosphodiesterase signaling pathway. Phosphodiesterases (PDEs) are key regulatory enzymes of intracellular cAMP/cGMP levels. These second messengers play important regulatory roles in controlling steroidogenesis in the adrenal. Disruption of PDEs has been associated with a number of adrenal diseases. Specifically, genetic mutations have been associated with benign adrenal lesions, leading to Cushing syndrome and/or related adrenal hyperplasias. A Genome Wide Association study, in 2006, led to the identification of mutations in 2 PDE genes: PDE8B and PDE11A; mutations in these 2 genes modulate steroidogenesis. Further human studies have identified PDE2 as also directly regulating steroidogenesis. PDE2 decreases aldosterone production. This review focuses on the most recent knowledge we have gained on PDEs and their association with adrenal steroidogenesis and altered function, through analysis of patient cohorts and what we have learned from mouse studies.

Central role of soluble adenylyl cyclase and cAMP in sperm physiology

Cyclic adenosine 3',5'-monophosphate (cAMP), the first second messenger to be described, plays a central role in cell signaling in a wide variety of cell types. Over the last decades, a wide body of literature addressed the different roles of cAMP in cell physiology, mainly in response to neurotransmitters and hormones. cAMP is synthesized by a wide variety of adenylyl cyclases that can generally be grouped in two types: transmembrane adenylyl cyclase and soluble adenylyl cyclases. In particular, several aspects of sperm physiology are regulated by cAMP produced by a single atypical adenylyl cyclase (Adcy10, aka sAC, SACY). The signature that identifies sAC among other ACs, is their direct stimulation by bicarbonate. The essential nature of cAMP in sperm function has been demonstrated using gain of function as well as loss of function approaches. This review unifies state of the art knowledge of the role of cAMP and those enzymes involved in cAMP signaling pathways required for the acquisition of fertilizing capacity of mammalian sperm. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Pharmacophore based virtual screening, molecular docking and biological evaluation to identify novel PDE5 inhibitors with vasodilatory activity

Prompted by the role of PDE5 and its closely associated cAMP and cGMP in hypertension, we have attempted to discover novel PDE5 inhibitors through ligand based virtual screening. Rigorously validated model comprising of one HBA, one HY and one RA was used as a query to search the NCI database leading to retrieval of many compounds which were screened on the basis of estimated activity, fit value and Lipinski's violation. Selected compounds were subjected to docking studies which resulted into visualization of potential interaction capabilities of NCI compounds in line to pharmacophoric features. Finally three compounds were subjected to in vitro evaluation using the isolated rat aortic model. The results showed that all three compounds are potent and novel PDE5 inhibitors with vasodilatory activity range from 10(-2) to 10(-5) M.