Phosphodiesterase inhibitors say NO to Alzheimer's disease

Corydalis ternata Nakai Alleviates Cognitive Decline in Alzheimer's Disease by Reducing β-Amyloid and Neuroinflammation

Recently, natural herbs have gained increasing attention owing to their comparatively low toxicity levels and the abundance of historical medical documentation regarding their use. Nevertheless, owing to a lack of knowledge regarding these herbs and their compounds, attempts to find those that could be beneficial for treating diseases have often been ad hoc; thus, there is now a growing demand for an in silico method to identify beneficial herbs. In this study, we present a computational approach for identifying natural herbs specifically effective in treating cognitive decline in Alzheimer's disease (AD) sufferers, which analyzes the similarities between herbal compounds and known drugs targeting AD-related proteins. Our in silico method suggests that Corydalis ternata can improve cognitive decline in AD sufferers. Behavioral tests with an AD mouse model for the confirmation of the in silico prediction reveals that C. ternata significantly alleviated the cognitive decline (memory and motor functions) caused by neurodegeneration. Further pathology analyses reveal that C. ternata decreases the level of Aβ plaques, reduces neuroinflammation, and promotes autophagy flux, and thus C. ternata can be clinically effective for preventing mild cognitive impairment during the early stages of AD. These findings highlight the potential utility of our in silico method and the potential clinical application of the identified natural herb in treating and preventing AD.

Opportunities and perspectives of small molecular phosphodiesterase inhibitors in neurodegenerative diseases

Phosphodiesterase (PDE) is a superfamily of enzymes that are responsible for the hydrolysis of two second messengers: cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). PDE inhibition promotes the gene transcription by activating cAMP-response element binding protein (CREB), initiating gene transcription of brain-derived neurotrophic factor (BDNF). The procedure exerts neuroprotective profile, and motor and cognitive improving efficacy. From this point of view, PDE inhibition will provide a promising therapeutic strategy for treating neurodegenerative disorders. Herein, we summarized the PDE inhibitors that have entered the clinical trials or been discovered in recent five years. Well-designed clinical or preclinical investigations have confirmed the effectiveness of PDE inhibitors, such as decreasing Aβ oligomerization and tau phosphorylation, alleviating neuro-inflammation and oxidative stress, modulating neuronal plasticity and improving long-term cognitive impairment.

Protective effect of PDE4B subtype-specific inhibition in an App knock-in mouse model for Alzheimer's disease

Meta-analysis of genome-wide association study data has implicated PDE4B in the pathogenesis of Alzheimer's disease (AD), the leading cause of senile dementia. PDE4B encodes one of four subtypes of cyclic adenosine monophosphate (cAMP)-specific phosphodiesterase-4 (PDE4A-D). To interrogate the involvement of PDE4B in the manifestation of AD-related phenotypes, the effects of a hypomorphic mutation (Pde4bY358C) that decreases PDE4B's cAMP hydrolytic activity were evaluated in the AppNL-G-F knock-in mouse model of AD using the Barnes maze test of spatial memory, 14C-2-deoxyglucose autoradiography, thioflavin-S staining of β-amyloid (Aβ) plaques, and inflammatory marker assay and transcriptomic analysis (RNA sequencing) of cerebral cortical tissue. At 12 months of age, AppNL-G-F mice exhibited spatial memory and brain metabolism deficits, which were prevented by the hypomorphic PDE4B in AppNL-G-F/Pde4bY358C mice, without a decrease in Aβ plaque burden. RNA sequencing revealed that, among the 531 transcripts differentially expressed in AppNL-G-F versus wild-type mice, only 13 transcripts from four genes - Ide, Btaf1, Padi2, and C1qb - were differentially expressed in AppNL-G-F/Pde4bY358C versus AppNL-G-F mice, identifying their potential involvement in the protective effect of hypomorphic PDE4B. Our data demonstrate that spatial memory and cerebral glucose metabolism deficits exhibited by 12-month-old AppNL-G-F mice are prevented by targeted inhibition of PDE4B. To our knowledge, this is the first demonstration of a protective effect of PDE4B subtype-specific inhibition in a preclinical model of AD. It thus identifies PDE4B as a key regulator of disease manifestation in the AppNL-G-F model and a promising therapeutic target for AD.

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 case-control study of phosphodiesterase-5 inhibitor use and Alzheimer's disease and related dementias among male and female patients aged 65 years and older supporting the need for a phase III clinical trial

BACKGROUND

Phosphodiesterase-5 inhibitors (PDE5i) have been evaluated as a novel treatment for Alzheimer's disease and related dementias (ADRD), but two recent cohort studies have offered opposing conclusions.

METHODS

We performed an unmatched case-control study using electronic medical records from a large healthcare system to evaluate the association of PDE5i use and ADRD in patients ≥65 years old.

RESULTS

Odds of PDE5i exposure were 64.2%, 55.7%, and 54.0% lower in patients with ADRD than controls among populations with erectile dysfunction, benign prostatic hyperplasia, and pulmonary hypertension, respectively. We observed odds ratios less than unity among males and females and with exposure to the PDE5i sildenafil (Viagra®) and tadalafil (Cialis®). We also evaluated the odds of exposure to two other common treatments for pulmonary hypertension: endothelin receptor antagonists (ERA) and calcium channel blockers (CCB). The odds of ERA exposure were 63.2% lower, but the odds of CCB exposure were 30.7% higher, in patients with ADRD than controls among the population with pulmonary hypertension.

CONCLUSIONS

Our results reconcile the opposing conclusions from the previous observational studies and support further research into using PDE5i for prevention and treatment of ADRD.

The role of Phosphodiesterase-1 and its natural product inhibitors in Alzheimer's disease: A review

Phosphodiesterase-1 (PDE1) is a versatile enzyme that has surprisingly received considerable attention as a possible therapeutic target in Alzheimer's disease (AD) because it maintains the homeostasis of 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in the brain. 3',5'-cyclic adenosine monophosphate and 3',5'-cyclic guanosine monophosphate are the two key second messengers that regulate a broad range of intracellular processes and neurocognitive functions, specifically memory and cognition, associated with Alzheimer's disease. However, the lack of available selective drugs on the market poses challenges to identifying the beneficial effects of natural products. The present review focuses on Phosphodiesterase-1 and its isoforms, splicing variants, location, distribution, and function; the role of Phosphodiesterase-1 inhibitors in Alzheimer's disease; and the use of vinpocetine and natural products as specific Phosphodiesterase-1 inhibitors. Moreover, it aims to provide ongoing updates, identify research gaps, and present future perspectives. This review indicates the potential role of Phosphodiesterase-1 inhibitors in the treatment of neurodegenerative disorders, such as Alzheimer's disease. Certain clinical trials on the alleviation of Alzheimer's disease in patients are still in progress. Among de novo outcomes, the employment of Phosphodiesterase-1 inhibitors to treat Alzheimer's disease is an important advancement given the absence of particular therapies in the pipeline for this highly prevalent disease. To sum up, Phosphodiesterase-1 inhibition has been specifically proposed as a critical therapeutic approach for Alzheimer's disease. This study provides a comprehensive review on the biological and pharmacological aspects of Phosphodiesterase-1, its role on the Alzheimer's diseases and its significance as Alzheimer's disease therapeutic target in drug discovery from natural products. This review will help clinical trials and scientific research exploring new entities for the treatment and prevention of Alzheimer's disease.

Plant based food bioactives: A boon or bane for neurological disorders

Neurological disorders are the foremost occurring diseases across the globe resulting in progressive dysfunction, loss of neuronal structure ultimately cell death. Therefore, attention has been drawn toward the natural resources for the search of neuroprotective agents. Plant-based food bioactives have emerged as potential neuroprotective agents for the treatment of neurodegenerative disorders. This comprehensive review primarily focuses on various plant food bioactive, mechanisms, therapeutic targets, in vitro and in vivo studies in the treatment of neurological disorders to explore whether they are boon or bane for neurological disorders. In addition, the clinical perspective of plant food bioactives in neurological disorders are also highlighted. Scientific evidences point toward the enormous therapeutic efficacy of plant food bioactives in the prevention or treatment of neurological disorders. Nevertheless, identification of food bioactive components accountable for the neuroprotective effects, mechanism, clinical trials, and consolidation of information flow are warranted. Plant food bioactives primarily act by mediating through various pathways including oxidative stress, neuroinflammation, apoptosis, excitotoxicity, specific proteins, mitochondrial dysfunction, and reversing neurodegeneration and can be used for the prevention and therapy of neurodegenerative disorders. In conclusion, the plant based food bioactives are boon for neurological disorders.

Inhibition of phosphodiesterase: A novel therapeutic target for the treatment of mild cognitive impairment and Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and is ranked as the 6th leading cause of death in the US. The prevalence of AD and dementia is steadily increasing and expected cases in USA is 14.8 million by 2050. Neuroinflammation and gradual neurodegeneration occurs in Alzheimer's disease. However, existing medications has limitation to completely abolish, delay, or prevent disease progression. Phosphodiesterases (PDEs) are large family of enzymes to hydrolyze the 3'-phosphodiester links in cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in signal-transduction pathways for generation of 5'-cyclic nucleotides. It plays vital role to orchestrate several pharmacological activities for proper cell functioning and regulating the levels of cAMP and cGMP. Several evidence has suggested that abnormal cAMP signaling is linked to cognitive problems in neurodegenerative disorders like AD. Therefore, the PDE family has become a widely accepted and multipotential therapeutic target for neurodegenerative diseases. Notably, modulation of cAMP/cGMP by phytonutrients has a huge potential for the management of AD. Natural compounds have been known to inhibit phosphodiesterase by targeting key enzymes of cGMP synthesis pathway, however, the mechanism of action and their therapeutic efficacy has not been explored extensively. Currently, few PDE inhibitors such as Vinpocetine and Nicergoline have been used for treatment of central nervous system (CNS) disorders. Considering the role of flavonoids to inhibit PDE, this review discussed the therapeutic potential of natural compounds with PDE inhibitory activity for the treatment of AD and related dementia.

Discovery of novel phosphodiesterase-1 inhibitors for curing vascular dementia: suppression of neuroinflammation by blocking NF-κB transcription regulation and activating cAMP/CREB axis

Vascular dementia (VaD) is the second commonest type of dementia which lacks of efficient treatments currently. Neuroinflammation as a prominent pathological feature of VaD, is highly involved in the development of VaD. In order to verify the therapeutic potential of PDE1 inhibitors against VaD, the anti-neuroinflammation, memory and cognitive improvement were evaluated in vitro and in vivo by a potent and selective PDE1 inhibitor 4a. Also, the mechanism of 4a in ameliorating neuroinflammation and VaD was systematically explored. Furthermore, to optimize the drug-like properties of 4a, especially for metabolic stability, 15 derivatives were designed and synthesized. As a result, candidate 5f, with a potent IC₅₀ value of 4.5 nmol/L against PDE1C, high selectivity over PDEs, and remarkable metabolic stability, efficiently ameliorated neuron degeneration, cognition and memory impairment in VaD mice model by suppressing NF-κB transcription regulation and activating cAMP/CREB axis. These results further identified PDE1 inhibition could serve as a new therapeutic strategy for treatment of VaD.

Patchouli alcohol as a selective estrogen receptor β agonist ameliorates AD-like pathology of APP/PS1 model mice

Clinical evidence shows that postmenpausal women are almost twice as likely to develop Alzheimer's disease (AD) as men of the same age, and estrogen is closely related to the occurrence of AD. Estrogen receptor (ER) α is mainly expressed in the mammary gland and other reproductive organs like uterus while ERβ is largely distributed in the hippocampus and cardiovascular system, suggesting that ERβ selective agonist is a valuable drug against neurodegenerative diseases with low tendency in inducing cancers of breast and other reproductive organs. In this study we identified a natural product patchouli alcohol (PTA) as a selective ERβ agonist which improved the cognitive defects in female APP/PS1 mice, and explore the underlying mechanisms. Six-month-old female APP/PS1 mice were administered PTA (20, 40 mg · kg-1 · d-1, i.g.) for 90 days. We first demonstrated that PTA bound to ERβ with a dissociation constant (KD) of 288.9 ± 35.14 nM in microscale thermophoresis. Then we showed that PTA administration dose-dependently ameliorated cognitive defects evaluated in Morris water maze and Y-maze testes. Furthermore, PTA administration reduced amyloid plaque deposition in the hippocampus by promoting microglial phagocytosis; PTA administration improved synaptic integrity through enhancing BDNF/TrkB/CREB signaling, ameliorated oxidative stress by Catalase level, and regulated Bcl-2 family proteins in the hippocampus. The therapeutic effects of PTA were also observed in vitro: PTA (5, 10, 20 μM) dose-dependently increased phagocytosis of o-FAM-Aβ42 in primary microglia and BV2 cells through enhancing ERβ/TLR4 signaling; PTA treatment ameliorated o-Aβ25-35-induced reduction of synapse-related proteins VAMP2 and PSD95 in primary neurons through enhancing ERβ/BDNF/TrkB/CREB pathways; PTA treatment alleviated o-Aβ25-35-induced oxidative stress in primary neurons through targeting ERβ and increasing Catalase expression. Together, this study has addressed the efficacy of selective ERβ agonist in the amelioration of AD and highlighted the potential of PTA as a drug lead compound against the disease.

Literature-based drug-drug similarity for drug repurposing: impact of Medical Subject Headings term refinement and hierarchical clustering

Background: We describe herein, an improved procedure for drug repurposing based on refined Medical Subject Headings (MeSH) terms and hierarchical clustering method. Materials & methods: In the present study, we have employed MeSH data from MEDLINE (2019), 1669 US FDA approved drugs from Open FDA and a refined set of MeSH terms. Refinement of MeSH terms was performed to include terms related to mechanistic information of drugs and diseases. Results and Conclusions: In-depth analysis of the results obtained, demonstrated greater efficiency of the proposed approach, based on refined MeSH terms and hierarchical clustering, in terms of number of selected drug candidates for repurposing. Further, analysis of misclustering and size of noise clusters suggest that the proposed approach is reliable and can be employed in drug repurposing.

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.

Combined ligand-based and structure-based design of PDE 9A inhibitors against Alzheimer's disease

PDE9 enzyme hydrolyzes cGMP, which is involved in the regulation of synaptic plasticity through the NMDA pathway (a well-known excitotoxic target for AD) via activation of calcium/calmodulin-dependent neuronal NO synthases in the postsynaptic neurons. The inhibition of PDE9 leads to elevated cGMP levels, causing enhanced NMDA signaling and thus contributing to an increase in synaptic plasticity and stabilization. Therefore, it could be considered a pertinent target for AD drug discovery. PF-04447943 and BI-409306 targeting PDE9 are undergoing clinical trials (Phase II). The present study encompasses a pharmacophoric approach to identify potent PDE9 inhibitors using various computational methods. Pharmacophores generated from the PDB 6A3N yielded 37,554 virtual hits, which underwent drug likeliness and PAINS filtering to arrive at a few virtual leads. The leads were further subjected to extra precision docking, ADMET predictions, and molecular dynamics. The final hits, ZINC000001305675 and ZINC000000377099, showed superior docking scores of - 10.90 and - 10.30 kcal/mol and satisfactory predicted ADMET scores. The hits were subjected to molecular dynamics (MD) studies, wherein they formed stable complexes with PDE9 protein and had ligand RMSDs within acceptable limits. The processes involved in the combined ligand and structure-based strategies.

Resurrection of sildenafil: potential for Huntington's Disease, too?

The phosphodiesterase-5 inhibitor sildenafil was postulated to reduce the risk for Alzheimer’s Disease. Since preclinical data revealed beneficial effects in Huntington’s Disease (HD), we now for the first time investigated effects of sildenafil in HD patients using the database ENROLL-HD. We demonstrate beneficial effects on motoric, functional and cognitive capacities in cross-sectional data. Those effects were not explained by underlying fundamental molecular genetic or demographic data. It remains unsolved, if effects are due to behavioral differences or due to direct dose-dependent neurobiological modulations.

The Role of Sildenafil in Treating Brain Injuries in Adults and Neonates

Sildenafil is a recognized treatment for patients suffering from erectile dysfunction and pulmonary hypertension. However, new evidence suggests that it may have a neuroprotective and a neurorestorative role in the central nervous system of both adults and neonates. Phosphodiesterase type 5-the target of sildenafil-is distributed in many cells throughout the body, including neurons and glial cells. This study is a comprehensive review of the demonstrated effects of sildenafil on the brain with respect to its function, extent of injury, neurons, neuroinflammation, myelination, and cerebral vessels.

Potential role of IP3/Ca2+ signaling and phosphodiesterases: Relevance to neurodegeneration in Alzheimer's disease and possible therapeutic strategies

Despite large investments by industry and governments, no disease-modifying medications for the treatment of patients with Alzheimer's disease (AD) have been found. The failures of various clinical trials indicate the need for a more in-depth understanding of the pathophysiology of AD and for innovative therapeutic strategies for its treatment. Here, we review the rational for targeting IP3 signaling, cytosolic calcium dysregulation, phosphodiesterases (PDEs), and secondary messengers like cGMP and cAMP, as well as their correlations with the pathophysiology of AD. Various drugs targeting these signaling cascades are still in pre-clinical and clinical trials which support the ideas presented in this article. Further, we describe different molecular mechanisms and medications currently being used in various pre-clinical and clinical trials involving IP3/Ca⁺² signaling. We also highlight various isoforms, as well as the functions and pharmacology of the PDEs broadly expressed in different parts of the brain and attempt to unravel the potential benefits of PDE inhibitors for use as novel medications to alleviate the pathogenesis of AD.

Pharmacological exploration of triazole based therapeutics for Alzheimer disease: An overview

Abstract:

Alzheimer`s disease (AD) is an irreversible progressive neurodegenerative disorder which may account for approximately 60-70% cases of dementia worldwide. AD is characterized by impaired behavioural and cognitive functions including memory, language, conception, attentiveness, judgment, and reasoning problems. The two important hallmarks of AD are the appearance of plaques and tangles of amyloid beta (Aβ) and tau proteins, respectively, in the brain based on the etiology of the disease including cholinergic impairment, metal dyshomeostasis, oxidative stress, and degradation of neurotransmitters. Currently, the used medication only provides alleviation of symptoms but not effective in curing the disease that is creating by an urge to develop new molecules to treat AD. Heterocyclic compounds have proven their ability to be developed as drugs for the treatment of various diseases. The five-membered heterocyclic compound triazole has received foremost fascination for the discovery of new drugs due to the possibility of structural variation and proved its significance in various drug categories. Therefore, this review summarizes mainly the recent advancements in the development of novel 1,2,3-triazole and 1,2,4-triazole based molecules in the drug discovery process for targeting various AD targets such as phosphodiesterase 1 (PDE1) Inhibitors, Apoptosis signal-regulating kinase 1 (ASK1) inhibitors, Somatostatin receptor subtype-4 (SSTR4) agonist, many other druggable targets, molecular modelling studies as well as various methodology for the synthesis of triazoles containing molecules such as Click reaction, Pellizzari and Einhorn-Brunner Reaction.

Histone deacetylase 6 inhibitors with blood-brain barrier penetration as a potential strategy for CNS-Disorders therapy

Histone deacetylase 6 inhibitors (HDAC6is) have been applied to certain cancer diseases and more recently to central nervous system (CNS) disorders including Rett syndrome, Alzheimer's and Parkinson's diseases, and major depressive disorder. Brain penetrance is the major challenge for the development of HDAC6is as potential therapeutics for CNS disorders due in part to the polarity of hydroxamate ZBG. Hence, only a handful of brain-penetrant HDAC6is have been reported and a few display appropriate in vitro and in vivo activities in models of neurological diseases in last decades. This review summarizes the contemporary research being done on HADC6is with brain penetration both the biological pathways involved and the structural modification attempts.

Baicalein Ameliorates Aβ-Induced Memory Deficits and Neuronal Atrophy via Inhibition of PDE2 and PDE4

Inhibition of phosphodiesterase 2 and 4 (PDE2A and PDE4) increases the intracellular cAMP and/or cGMP levels, which may prevent Amyloid β 42 oligomers (Aβ) related cognitive impairment and dementias. Baicalein, one of natural flavones found in the root of Scutellaria baicalensis Georgi, has a wide range of pharmacological activities including antioxidant and anti-inflammatory effects. However, no studies suggest whether baicalein mediated anti-Alzheimer’s disease (AD) events involve PDEs subtypes-mediated neuroprotective pathways. The present study examined whether memory enhancing effects of baicalein on Aβ- induced cognitive impairment are related to regulating neuroplasticity via PDE2 and PDE4 subtypes dependent cAMP/cGMP neuroprotective pathway. The results suggested that microinjected of Aβ into CA1 of hippocampus induced cognitive and memory impairment in mice, as evidenced by decreased recognition index in the novel object recognition (NOR) task, impaired memory acquisition, retention and retrieval in the Morris water maze (MWM) and shuttle box tests. These effects were reversed by treatment with baicalein for 14 days. Moreover, Aβ-induced neuronal atrophy and decreased expression of two synaptic proteins, synaptophysin and PSD 95, were prevented by baicalein. The increased expression of PDE2A and PDE4 subtypes (PDE4A, PDE4B and PDE4D), and decreased levels of cAMP/cGMP, pCREB/CREB and BDNF induced by Aβ were also blocked by chronic treatment of baicalein for 14 days. These findings suggest that baicalein’s reversal of Aβ-induced memory and cognitive disorder may involve the regulation of neuronal remodeling via regulation of PDE2/PDE4 subtypes related cAMP/cGMP -pCREB-BDNF pathway.

Inhibition of Histone Deacetylase 6 (HDAC6) as a therapeutic strategy for Alzheimer's disease: A review (2010-2020)

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders, which is characterized by the primary risk factor, age. Several attempts have been made to treat AD, while most of them end in failure. However, with the deepening study of pathogenesis of AD, the expression of HDAC6 in the hippocampus, which plays a major role of the memory formation, is becoming worth of notice. Neurofibrillary tangles (NFTs), a remarkable lesion in AD, has been characterized in association with the abnormal accumulation of hyperphosphorylated Tau, which is mainly caused by the high expression of HDAC6. On the other hand, the hypoacetylated tubulin induced by HDAC6 is also fatal for the neuronal transport, which is the key impact of the formation of axons and dendrites. Overall, the significantly increased expression of HDAC6 in brain regions is deleterious to neuron survival in AD patients. Based on the above research, the inhibition of HDAC6 seems to be a potential therapeutic method for the treatment of AD. Up to now, various types of HDAC6 inhibitors have been discovered. This review mainly analyzes the HDAC6 inhibitors reported amid 2010-2020 in terms of their structure, selectivity and pharmacological impact towards AD. And we aim at facilitating the design and development of better HDAC6 inhibitors in the future.

Protect Effects of Seafood-Derived Plasmalogens Against Amyloid-Beta (1-42) Induced Toxicity via Modulating the Transcripts Related to Endocytosis, Autophagy, Apoptosis, Neurotransmitter Release and Synaptic Transmission in SH-SY5Y Cells

To investigate the underlying mechanisms of decreased plasmalogens (Pls) levels in neurodegenerative diseases, here the effects of seafood-derived Pls on undifferentiated and differentiated human SH-SY5Y neuroblastoma cells exposed to amyloid-β_1-42 was analyzed. Transcriptional profiles indicated that a total of 6,581 differentially expressed genes (DEGs) were significantly identified among different experimental groups, and KEGG analysis indicated that these DEGs were related to AD, endocytosis, synaptic vesicle cycle, autophagy and cellular apoptosis. After Pls treatment, the striking expression changes of ADORA2A, ATP6V1C2, CELF6, and SLC18A2 mRNA strongly suggest that Pls exerts a beneficial role in alleviating AD pathology partly by modulating the neurotransmitter release and synaptic transmission at the transcriptional level. Besides these, GPCRs are also broadly involved in Pls-signaling in neuronal cells. These results provide evidence for supporting the potential use of Pls as an effective therapeutic approach for AD.

Treating Erectile Dysfunction with Prescription Medications & Natural Products: A Pharmacist's Guide

Stigma surrounding erectile dysfunction creates a difficult environment for appropriate management. Knowledge of the condition and treatment options presents a unique opportunity for pharmacists to optimize a safe and affordable plan that meets patient needs.

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.

Gastrodin promotes hippocampal neurogenesis via PDE9-cGMP-PKG pathway in mice following cerebral ischemia

Gastrodin, which is extracted from the Chinese herbal medicine Gastrodia elata Blume, can ameliorate neurogenesis after cerebral ischemia. However, it's possible underlying mechanisms remain still elusive. PDE9-cGMP-PKG signaling pathway is involved in the proliferation of neural stem cells (NSCs) after cerebral ischemia. In this study, we investigated whether the beneficial effect of gastrodin on hippocampal neurogenesis after cerebral ischemia is correlated with the PDE9-cGMP-PKG signaling pathway. Bilateral common carotid artery occlusion (BCCAO) in mice and oxygen-glucose deprivation/reoxygenation (OGD/R) in primary cultured hippocampal NSCs were used to mimic brain ischemic injury. The Morris water maze (MWM) test was executed to detect spatial learning and memory. Proliferation, differentiation, and mature neurons were examined using immunofluorescence. The survival and proliferation of NSCs were assessed by CCK-8 assay and BrdU immunofluorescence staining, respectively. ELISA and western blot were used to detect the level of the PDE9-cGMP-PKG signaling pathway. In BCCAO mice, administering gastrodin (50 and 100 mg/kg) for 14 d restored cognitive behaviors; meanwhile, neurogenesis in hippocampus was stimulated, and PDE9 was inhibited and cGMP-PKG was activated by gastrodin. Consistent with the results, administering gastrodin (from 0.01-1 μmol/L) for 48 h dose-dependently ameliorated the cell viability and promoted greatly the proliferation in primary hippocampal NSCs exposed to OGD/R. Gastrodin further decreased PDE9 activity and up-regulated cGMP-PKG level. KT5823, a PKG inhibitor, markedly abrogated the protective effects of gastrodin on OGD/R-injured NSCs, accompanied by the down-regulation of PKG protein expression, but had no effects on PDE9 activity and cGMP level. Gastrodin could accelerate hippocampal neurogenesis after cerebral ischemia, which is mediated, at least partly, by PDE9-cGMP-PKG signaling pathway.

Diabetic Theory in Anti-Alzheimer's Drug Research and Development. Part 2: Therapeutic Potential of cAMP-Specific Phosphodiesterase Inhibitors

Alzheimer's disease (AD) is one of the most prevalent age-related neurodegenerative disease that affects the cognition, behavior, and daily activities of individuals. Studies indicate that this disease is characterized by several pathological mechanisms, including the accumulation of amyloid-beta peptide, hyperphosphorylation of tau protein, impairment of cholinergic neurotransmission, and increase in inflammatory responses within the central nervous system. Chronic neuroinflammation associated with AD is closely related to disturbances in metabolic processes, including insulin release and glucose metabolism. As AD is also called type III diabetes, diverse compounds having antidiabetic effects have been investigated as potential drugs for its symptomatic and disease-modifying treatment. In addition to insulin and oral antidiabetic drugs, scientific attention has been paid to cyclic-3',5'-adenosine monophosphate (cAMP)-specific phosphodiesterase (PDE) inhibitors that can modulate the concentration of glucose and related hormones and exert beneficial effects on memory, mood, and emotional processing. In this review, we present the most recent reports focusing on the involvement of cAMP-specific PDE4, PDE7, and PDE8 in glycemic and inflammatory response controls as well as the potential utility of the PDE inhibitors in the treatment of AD. Besides the results of in vitro and in vivo studies, the review also presents recent reports from clinical trials.

Advances in Cyclic Nucleotide Phosphodiesterase-Targeted PET Imaging and Drug Discovery

Cyclic nucleotide phosphodiesterases (PDEs) control the intracellular concentrations of cAMP and cGMP in virtually all mammalian cells. Accordingly, the PDE family regulates a myriad of physiological functions, including cell proliferation, differentiation and apoptosis, gene expression, central nervous system function, and muscle contraction. Along this line, dysfunction of PDEs has been implicated in neurodegenerative disorders, coronary artery diseases, chronic obstructive pulmonary disease, and cancer development. To date, 11 PDE families have been identified; however, their distinct roles in the various pathologies are largely unexplored and subject to contemporary research efforts. Indeed, there is growing interest for the development of isoform-selective PDE inhibitors as potential therapeutic agents. Similarly, the evolving knowledge on the various PDE isoforms has channeled the identification of new PET probes, allowing isoform-selective imaging. This review highlights recent advances in PDE-targeted PET tracer development, thereby focusing on efforts to assess disease-related PDE pathophysiology and to support isoform-selective drug discovery.

Design, Synthesis, and Evaluation of Dihydropyranopyrazole Derivatives as Novel PDE2 Inhibitors for the Treatment of Alzheimer's Disease

Phosphodiesterase 2 (PDE2) has been regarded as a novel target for the treatment of Alzheimer’s disease (AD). In this study, we obtained (R)-LZ77 as a hit compound with moderate PDE2 inhibitory activity (IC₅₀ = 261.3 nM) using a high-throughput virtual screening method based on molecular dynamics. Then, we designed and synthesized 28 dihydropyranopyrazole derivatives as PDE2 inhibitors. Among them, compound (+)-11h was the most potent PDE2 inhibitor, with an IC₅₀ value of 41.5 nM. The molecular docking of PDE2-(+)-11h reveals that the 4-(trifluoromethyl)benzyl)oxyl side chain of the compound enters the H-pocket and forms strong hydrophobic interactions with L770/L809/F862, which improves inhibitory activity. The above results may provide insight for further structural optimization of highly potent PDE2 inhibitors and may lay the foundation for their use in the treatment of AD.

Sildenafil Alleviates Murine Experimental Autoimmune Encephalomyelitis by Triggering Autophagy in the Spinal Cord

Multiple Sclerosis (MS) is a neuroinflammatory and chronic Central Nervous System (CNS) disease that affects millions of people worldwide. The search for more promising drugs for the treatment of MS has led to studies on Sildenafil, a phosphodiesterase type 5 Inhibitor (PDE5I) that has been shown to possess neuroprotective effects in the Experimental Autoimmune Encephalomyelitis (EAE), an animal model of MS. We have previously shown that Sildenafil improves the clinical score of EAE mice via modulation of apoptotic pathways, but other signaling pathways were not previously covered. Therefore, the aim of the present study was to further investigate the effects of Sildenafil treatment on autophagy and nitrosative stress signaling pathways in EAE. 24 female C57BL/6 mice were divided into the following groups: (A) Control - received only water; (B) EAE - EAE untreated mice; (C) SILD - EAE mice treated with 25mg/kg of Sildenafil s.c. The results showed that EAE mice presented a pro-nitrosative profile characterized by high tissue nitrite levels, lowered levels of p-eNOS and high levels of iNOS. Furthermore, decreased levels of LC3, beclin-1 and ATG5, suggests impaired autophagy, and decreased levels of AMPK in the spinal cord were also detected in EAE mice. Surprisingly, treatment with Sildenafil inhibited nitrosative stress and augmented the levels of LC3, beclin-1, ATG5, p-CREB and BDNF and decreased mTOR levels, as well as augmented p-AMPK. In conclusion, we propose that Sildenafil alleviates EAE by activating autophagy via the eNOS-NO-AMPK-mTOR-LC3-beclin1-ATG5 and eNOS-NO-AMPK-mTOR-CREB-BDNF pathways in the spinal cord.

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

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

Compartmentalized Signaling in Aging and Neurodegeneration

The cyclic AMP (cAMP) signalling cascade is necessary for cell homeostasis and plays important roles in many processes. This is particularly relevant during ageing and age-related diseases, where drastic changes, generally decreases, in cAMP levels have been associated with the progressive decline in overall cell function and, eventually, the loss of cellular integrity. The functional relevance of reduced cAMP is clearly supported by the finding that increases in cAMP levels can reverse some of the effects of ageing. Nevertheless, despite these observations, the molecular mechanisms underlying the dysregulation of cAMP signalling in ageing are not well understood. Compartmentalization is widely accepted as the modality through which cAMP achieves its functional specificity; therefore, it is important to understand whether and how this mechanism is affected during ageing and to define which is its contribution to this process. Several animal models demonstrate the importance of specific cAMP signalling components in ageing, however, how age-related changes in each of these elements affect the compartmentalization of the cAMP pathway is largely unknown. In this review, we explore the connection of single components of the cAMP signalling cascade to ageing and age-related diseases whilst elaborating the literature in the context of cAMP signalling compartmentalization.

Alterations in cyclic nucleotide signaling are implicated in healthy aging and age-related pathologies of the brain

It is not only important to consider how hormones may change with age, but also how downstream signaling pathways that couple to hormone receptors may change. Among these hormone-coupled signaling pathways are the 3',5'-cyclic guanosine monophosphate (cGMP) and 3',5'-cyclic adenosine monophosphate (cAMP) intracellular second messenger cascades. Here, we test the hypothesis that dysfunction of cAMP and/or cGMP synthesis, execution, and/or degradation occurs in the brain during healthy and pathological diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. Although most studies report lower cyclic nucleotide signaling in the aged brain, with further reductions noted in the context of age-related diseases, there are select examples where cAMP signaling may be elevated in select tissues. Thus, therapeutics would need to target cAMP/cGMP in a tissue-specific manner if efficacy for select symptoms is to be achieved without worsening others.

Scope of β-Secretase (BACE1)-Targeted Therapy in Alzheimer's Disease: Emphasizing the Flavonoid Based Natural Scaffold for BACE1 Inhibition

Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most common form of dementia in the world. Studies report the presence of extracellular amyloid plaques consisting of β-amyloid peptide and intracellular tangles consisting of hyperphosphorylated tau proteins as the histopathological indicators of AD. The process of β-amyloid peptide generation by sequential cleavage of amyloid precursor protein by β-secretase (BACE1) and γ-secretase, followed by its aggregation to form amyloid plaques, is the mechanistic basis of the amyloid hypothesis. Other popular hypotheses related to the pathogenesis of AD include the tau hypothesis and the oxidative stress hypothesis. Various targets of the amyloid cascade are now in prime focus to develop drugs for AD. Many BACE1 inhibitors, β-amyloid aggregation inhibitors, and Aβ clearance strategies using monoclonal antibodies are in various stages of clinical trials. This review provides an in-depth evaluation of the role of BACE1 in disease pathogenesis and also highlights the therapeutic approaches developed to find more potent but less toxic inhibitors for BACE1, particularly emphasizing the natural scaffold as a nontoxic lead for BACE1 inhibition. Cellular targets and signaling cascades involving BACE1 have been highlighted to understand the physiological role of BACE1. This knowledge is extremely crucial to understand the toxicity evaluations for BACE1-targeted therapy. We have particularly highlighted the scope of flavonoids as a new generation of nontoxic BACE1 inhibitory scaffolds. The structure-activity relationship of BACE1 inhibition for this group of compounds has been highlighted to provide a guideline to design more selective highly potent inhibitors. The review aims to provide a holistic overview of BACE1-targeted therapy for AD that paves the way for future drug development.

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.

Homogeneous single-label cGMP detection platform for the functional study of nitric oxide-sensitive (soluble) guanylyl cyclases and cGMP-specific phosphodiesterases

Cardiovascular diseases are the number one death worldwide. Nitric oxide (NO)-NO-sensitive (soluble) guanylyl cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway regulates diverse set of important physiological functions, including maintenance of cardiovascular homeostasis. Resting and activated sGC enzyme converts guanosine triphosphate to an important second messenger cGMP. In addition to traditional NO generators, a number of sGC activators and stimulators are currently in clinical trials aiming to support or increase sGC activity in various pathological conditions. cGMP-specific phosphodiesterases (PDEs), which degrade cGMP to guanosine monophosphate, play key role in controlling the cGMP level and the strength or length of the cGMP-dependent cellular signaling. Thus, PDE inhibitors also have clear clinical applications. Here, we introduce a homogeneous quenching resonance energy transfer (QRET) for cGMP to monitor both sGC and PDE activities using high throughput screening adoptable method. We demonstrate that using cGMP-specific antibody, sGC or PDE activity and the effect of small molecules modulating their function can be studied with sub-picomole cGMP sensitivity. The results further indicate that the method is suitable for monitoring enzyme reactions also in complex biological cellular homogenates and mixture.

Pharmacological management of dementia with Lewy bodies with a focus on zonisamide for treating parkinsonism

INTRODUCTION

Dementia with Lewy bodies (DLB) has no approved symptomatic or disease-modifying treatments in the US and Europe, despite being the second most common cause of neurodegenerative dementia.

AREAS COVERED

Herein, the authors briefly review the DLB drug development pipeline, providing a summary of the current pharmacological intervention studies. They then focus on the anticonvulsant zonisamide, a benzisoxazole derivative with a sulfonamide group and look at its value for treating parkinsonism in DLB.

EXPERT OPINION

Several new compounds are being tested in DLB, the most innovative being those aimed at decreasing brain accumulation of α-synuclein. Unfortunately, new drug testing is challenging in terms of consistent diagnostic criteria and lack of reliable biomarkers. Few randomized controlled trials (RCTs) are well-designed, with enough power to detect significant drug effects. Levodopa monotherapy can treat the parkinsonism in DLB, but it can cause agitation or visual hallucination worsening. Two Phase II/III RCTs of DLB patients recently reported a statistically significant improvement in motor function in those receiving zonisamide as an adjunctive treatment to levodopa. New biomarker strategies and validated outcome measures for DLB or prodromal DLB may enhance clinical trial design for the development of specific disease-modifying treatments.

Characterization of Resveratrol, Oxyresveratrol, Piceatannol and Roflumilast as Modulators of Phosphodiesterase Activity. Study of Yeast Lifespan

Our desire to live longer has led to an ever-increasing number of novel antiaging products. However, few molecules have any real effect and new ones need to be studied before they can be used commercially. In this contribution, activation of the caloric restriction (CR) pathway was studied using different three (resveratrol, oxyresveratrol and piceatannol)-a family with demonstrated bioactivity on phosphodiesterase activity. The high-affinity phosphodiesterase type 2 (PDE2) of Saccharomyces cerevisiae was expressed in Escherichia coli, purified and characterized. The activity and the inhibitory activity of each stilbene was studied, and the findings were compared in vitro and in silico with those obtained with roflumilast-a human PDE4 inhibitor widely used in chronic obstructive pulmonary diseases. Finally, an in vivo chronological lifespan assay using WT S. cerevisiae and ΔPDE2 S. cerevisiae strains was carried out. It was demonstrated that stilbenes can modulate yPDE2 activity, increasing the lifespan of the yeast by 18% over a control (in combination with other pathways). In addition, roflumilast increased the lifespan in the WT strain. The findings as a whole would increase the range of lifespan products available and suggest novel uses for approved drugs.

Identification of New Targets and the Virtual Screening of Lignans against Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the progressive disturbance in cognition and affects approximately 36 million people, worldwide. However, the drugs used to treat this disease are only moderately effective and do not alter the course of the neurodegenerative process. This is because the pathogenesis of AD is mainly associated with oxidative stress, and current drugs only target two enzymes involved in neurotransmission. Therefore, the present study sought to identify potential multitarget compounds for enzymes that are directly or indirectly involved in the oxidative pathway, with minimal side effects, for AD treatment. A set of 159 lignans were submitted to studies of QSAR and molecular docking. A combined analysis was performed, based on ligand and structure, followed by the prediction of absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties. The results showed that the combined analysis was able to select 139 potentially active and multitarget lignans targeting two or more enzymes, among them are c-Jun N-terminal kinase 3 (JNK-3), protein tyrosine phosphatase 1B (PTP1B), nicotinamide adenine dinucleotide phosphate oxidase 1 (NOX1), NADPH quinone oxidoreductase 1 (NQO1), phosphodiesterase 5 (PDE5), nuclear factor erythroid 2-related factor 2 (Nrf2), cycloxygenase 2 (COX-2), and inducible nitric oxide synthase (iNOS). The authors conclude that compounds (06) austrobailignan 6, (11) anolignan c, (19) 7-epi-virolin, (64) 6-[(2R,3R,4R,5R)-3,4-dimethyl-5-(3,4,5-trimethoxyphenyl)oxolan-2-yl]-4-methoxy-1,3-benzodioxole, (116) ococymosin, and (135) mappiodoinin b have probabilities that confer neuroprotection and antioxidant activity and represent potential alternative AD treatment drugs or prototypes for the development of new drugs with anti-AD properties.

Glucosamine Enhancement of BDNF Expression and Animal Cognitive Function

Brain-derived neurotrophic factor (BDNF) is an important factor for memory consolidation and cognitive function. Protein kinase A (PKA) signaling interacts significantly with BDNF-provoked downstream signaling. Glucosamine (GLN), a common dietary supplement, has been demonstrated to perform a variety of beneficial physiological functions. In the current study, an in vivo model of 7-week-old C57BL/6 mice receiving daily intraperitoneal injection of GLN (0, 3, 10 and 30 mg/animal) was subjected to the novel object recognition test in order to determine cognitive performance. GLN significantly increased cognitive function. In the hippocampus GLN elevated tissue cAMP concentrations and CREB phosphorylation, and upregulated the expression of BDNF, CREB5 and the BDNF receptor TrkB, but it reduced PDE4B expression. With the in vitro model in the HT22 hippocampal cell line, GLN exposure significantly increased protein and mRNA levels of BDNF and CREB5 and induced cAMP responsive element (CRE) reporter activity; the GLN-mediated BDNF expression and CRE reporter induction were suppressed by PKA inhibitor H89. Our current findings suggest that GLN can exert a cognition-enhancing function and this may act at least in part by upregulating the BDNF levels via a cAMP/PKA/CREB-dependent pathway.

Perspectives for New and More Efficient Multifunctional Ligands for Alzheimer's Disease Therapy

Despite tremendous research efforts at every level, globally, there is still a lack of effective drugs for the treatment of Alzheimer's disease (AD). The biochemical mechanisms of this devastating neurodegenerative disease are not yet clearly understood. This review analyses the relevance of multiple ligands in drug discovery for AD as a versatile toolbox for a polypharmacological approach to AD. Herein, we highlight major targets associated with AD, ranging from acetylcholine esterase (AChE), beta-site amyloid precursor protein cleaving enzyme 1 (BACE-1), glycogen synthase kinase 3 beta (GSK-3β), N-methyl-d-aspartate (NMDA) receptor, monoamine oxidases (MAOs), metal ions in the brain, 5-hydroxytryptamine (5-HT) receptors, the third subtype of histamine receptor (H3 receptor), to phosphodiesterases (PDEs), along with a summary of their respective relationship to the disease network. In addition, a multitarget strategy for AD is presented, based on reported milestones in this area and the recent progress that has been achieved with multitargeted-directed ligands (MTDLs). Finally, the latest publications referencing the enlarged panel of new biological targets for AD related to the microglia are highlighted. However, the question of how to find meaningful combinations of targets for an MTDLs approach remains unanswered.

2-(3,4-Dihydroxyphenyl)-4-(2-(4-nitrophenyl)hydrazono)-4H-chromene-3,5,7-triol

On the basis of the knowledge from traditional herbal and folk medicine, flavonoids are among the most studied chemical classes of natural compounds for their potential activity as phosphodiesterase 5 (PDE5) inhibitors. We here describe the preparation of a semi-synthetic hydrazone derivative of quercetin, 2-(3,4-dihydroxyphenyl)-4-(2-(4-nitrophenyl)hydrazono)-4H-chromene-3,5,7-triol, that was obtained via a single-step modification of the natural compound. The product was characterized by NMR, mass spectrometry and HPLC. Preliminary molecular modeling studies suggest that this compound could efficiently interact with PDE5.

Therapeutic Potential of Phosphodiesterase Inhibitors against Neurodegeneration: The Perspective of the Medicinal Chemist

Increasing human life expectancy prompts the development of novel remedies for cognitive decline: 44 million people worldwide are affected by dementia, and this number is predicted to triple by 2050. Acetylcholinesterase and N-methyl-d-aspartate receptors represent the targets of currently available drugs for Alzheimer’s disease, which are characterized by limited efficacy. Thus, the search for therapeutic agents with alternative or combined mechanisms of action is wide open. Since variations in 3′,5′-cyclic adenosine monophosphate, 3′,5′-cyclic guanosine monophosphate, and/or nitric oxide levels interfere with downstream pathways involved in memory processes, evidence supporting the potential of phosphodiesterase (PDE) inhibitors in contrasting neurodegeneration should be critically considered. For the preparation of this Review, more than 140 scientific papers were retrieved by searching PubMed and Scopus databases. A systematic approach was adopted when overviewing the different PDE isoforms, taking into account details on brain localization, downstream molecular mechanisms, and inhibitors currently under study, according to available in vitro and in vivo data. In the context of drug repurposing, a section focusing on PDE5 was introduced. Original computational studies were performed to rationalize the emerging evidence that suggests the role of PDE5 inhibitors as multi-target agents against neurodegeneration. Moreover, since such compounds must cross the blood–brain barrier and reach inhibitory concentrations in the central nervous system to exert their therapeutic activity, physicochemical parameters were analyzed and discussed. Taken together, literature and computational data suggest that some PDE5 inhibitors, such as tadalafil, represent promising candidates.

Insight into GEBR-32a: Chiral Resolution, Absolute Configuration and Enantiopreference in PDE4D Inhibition

Alzheimer's disease is the most common type of dementia, affecting millions of people worldwide. One of its main consequences is memory loss, which is related to downstream effectors of cyclic adenosine monophosphate (cAMP). A well-established strategy to avoid cAMP degradation is the inhibition of phosphodiesterase (PDE). In recent years, GEBR-32a has been shown to possess selective inhibitory properties against PDE type 4 family members, resulting in an improvement in spatial memory processes without the typical side effects that are usually correlated with this mechanism of action. In this work, we performed the HPLC chiral resolution and absolute configuration assignment of GEBR-32a. We developed an efficient analytical and semipreparative chromatographic method exploiting an amylose-based stationary phase, we studied the chiroptical properties of both enantiomers and we assigned their absolute configuration by 1H-NMR (nuclear magnetic resonance). Lastly, we measured the IC50 values of both enantiomers against both the PDE4D catalytic domain and the long PDE4D3 isoform. Results strongly support the notion that GEBR-32a inhibits the PDE4D enzyme by interacting with both the catalytic pocket and the regulatory domains.

Preconditioning with PDE1 Inhibitors and Moderate-Intensity Training Positively Affect Systemic Redox State of Rats

Taken into consideration that oxidative stress response after preconditioning with phosphodiesterase inhibitors (PDEIs) and moderate physical activity has still not been clarified, the aim of this study was to assess the effects of PDEIs alone or in combination with physical activity, on systemic redox status. The study was carried out on 96 male Wistar albino rats classified into two groups. The first group included animals exposed only to pharmacological preconditioning (PreC) maneuver (sedentary control (CTRL, 1 ml/day saline, n = 12), nicardipine (6 mg/kg/day of NIC, n = 12), vinpocetine (10 mg/kg/day of VIN, n = 12), and nimodipine (NIM 10 mg/kg/day of, n = 12). The second included animals exposed to preconditioning with moderate-intensity training (MIT) on treadmill for 8 weeks. After 5 weeks from the start of training, the animals were divided into four subgroups depending on the medication to be used for pharmacological PreC: moderate-intensity training (MIT+ 1 ml/day saline, n = 12), nicardipine (MIT+ 6 mg/kg/day of NIC, n = 12), vinpocetine (MIT+ 10 mg/kg/day of VIN, n = 12), and nimodipine (MIT+ 10 mg/kg/day of NIM, n = 12). After three weeks of pharmacological preconditioning, the animals were sacrificed. The following oxidative stress parameters were measured spectrophotometrically: nitrites (NO₂⁻), superoxide anion radical (O₂⁻), hydrogen peroxide (H₂O₂), index of lipid peroxidation (TBARS), superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH). Our results showed that PDE1 and MIT preconditioning decreased the release of prooxidants and improved the activity of antioxidant enzymes thus preventing systemic oxidative stress.

Phenolic compounds profile, neuroprotective effect and antioxidant potential of a commercial Turkish coffee

ABSTRACT Objective The purpose of this study is to determine the phenolic and flavonoid contents, and antioxidant activities and neuroprotective effects of powdered coffee sample of a commercial coffee brand originated from Sivas, Turkey. Methods Total phenolic, flavonoid and antioxidant contents, enzymatic and non-enzymatic antioxidative activities based on 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity, metal chelating potential, reducing power, superoxide dismutase and catalase activity tests and lipid peroxidation inhibition potentials of the ethanolic and aqueous extracts of the coffee sample were assayed using the commonly preferred spectrophotometric methods. Furthermore the extracts’ cholinesterase and tyrosinase inhibition potentials were evaluated. Phenolic profiles of the coffee sample were investigated using high performance liquid chromatography. Results Catechin was the most frequently detected phenolic acid. In addition, it was demonstrated that the water extract has a significant impact when compared with standard antioxidants. While the SC50 (sufficient concentration to obtain 50% of a maximum scavenging capacity) value for the scavenging activity of 2,2-diphenyl-1-picrylhydrazyl free radical was calculated as being 0.08mg/mL for water extract, the amount of chelating agents with half Fe2+ ions in the medium was found to be 0.271mg/mL. Additionally, it was shown that 0.1mg/mL concentration of both extracts prevents lipid peroxidation by 8%. Compared with standard drugs, inhibition potentials of cholinesterase and tyrosinase enzymes were considered as moderately acceptable in these samples. Conclusion Besides the extracts’ enzymatic antioxidant activity, their inhibition potential on cholinesterase and tyrosinase enzymes – which are important clinical enzymes – reveal that this natural source can be used as a valuable resource in different fields, especially in medicine.