Effects of two selective phosphodiesterase type 5 inhibitors, sildenafil and vardenafil, on object recognition memory and hippocampal cyclic GMP levels in the rat

Individual contribution of PDE4B and PDE4D subfamilies to the prevention of object location memory impairments induced by sleep deprivation

Insufficient sleep compromises the cAMP signaling pathway in the hippocampus, negatively impacting hippocampus-dependent memory. In the current study, we explored whether selective PDE4B or selective PDE4D inhibition can improve hippocampus-dependent spatial memory in the object location test (OLT) in mice after sleep deprivation (SD). The results demonstrated that SD impaired the OLT performance, and both A-33 and zatolmilast protected against the negative consequences of SD when administered at the start and middle of the SD period. These findings suggest that both PDE4B and PDE4D subfamilies contribute to the beneficial effect of PDE4 inhibition against SD-induced memory consolidation impairment.

Time-dependent fear memory generalization triggered by phosphodiesterase 5 inhibition during reconsolidation

Fear generalization, a lack of discrimination between safe and unsafe cues, is a hallmark of posttraumatic stress disorder. The phosphodiesterase 5 (PDE5) regulates the cyclic guanosine monophosphate (cGMP) pathway, which has been proposed to be involved in fear memory generalization. However, whether PDE5 activity underlies fear memory generalization remains unexplored. Considering the importance of retrieval-induced reconsolidation in memory maintenance, we aimed to investigate whether PDE5 inhibition during reconsolidation of recent fear memory affects generalization over time in adult male Wistar rats submitted to contextual fear conditioning. The PDE5 inhibition with vardenafil (VAR) 1 mg/kg i.p. during reconsolidation triggered a time-dependent fear generalization without affecting fear memory in the paired context. Fear generalization and impaired pattern separation appear to be interlinked. Likewise, an impairment of object pattern separation was observed in the VAR-treated group at the remote time point. These effects depended on memory retrieval and were restricted to the reconsolidation time window. A chemogenetic inhibition of the anterior cingulate cortex (ACC), a region involved in allocating remote memories and generalization, prevented the effects of VAR. Moreover, VAR infusion into the ACC (6 μg/0.2 μL) after retrieval also promoted fear generalization and impaired OPS in remote time point, suggesting that ACC underlies the behavioral outcomes of the treatment with VAR. In conclusion, our results suggest that inhibiting PDE5 during the reconsolidation of a recent fear memory recruits the activity of the ACC, triggering fear memory generalization and impairing object pattern separation over time.

Preventive effect of propolis on cognitive decline in Alzheimer's disease model mice

Brazilian green propolis (propolis) is a chemically complex resinous substance that is a potentially viable therapeutic agent for Alzheimer's disease. Herein, propolis induced a transient increase in intracellular Ca2+ concentration ([Ca2+]i) in Neuro-2A cells; moreover, propolis-induced [Ca2+]i elevations were suppressed prior to 24-h pretreatment with amyloid-β. To reveal the effect of [Ca2+]i elevation on impaired cognition, we performed memory-related behavioral tasks in APP-KI mice relative to WT mice at 4 and 12 months of age. Propolis, at 300-1000 mg/kg/d for 8 wk, significantly ameliorated cognitive deficits in APP-KI mice at 4 months, but not at 12 months of age. Consistent with behavioral observations, injured hippocampal long-term potentiation was markedly ameliorated in APP-KI mice at 4 months of age following repeated propolis administration. In addition, repeated administration of propolis significantly activated intracellular calcium signaling pathway in the CA1 region of APP-KI mice. These results suggest a preventive effect of propolis on cognitive decline through the activation of intracellular calcium signaling pathways in CA1 region of AD mice model.

Molecular mechanisms of morphine tolerance and dependence; novel insights and future perspectives

Drug addiction is a devastating condition that poses a serious burden on the society. The use of some drugs like morphine for their tremendous analgesic properties is also accompanied with developing tolerance, dependence and the withdrawal symptoms. These symptoms are frequently severe enough to reinforce the person in recovery to start over the use of drug again and hinder the clinical use of drugs like morphine for chronic pain. Research into opioid receptors and related molecular pathways has seen resurgence in the wake of the growing opioid epidemic. The current study provides a comprehensive scientific exploration of the molecular mechanisms and underlying signalling in morphine tolerance and dependence. It also critically evaluates current therapeutic approaches, shedding light on their efficacy and limitations, and future prospects.

Sildenafil prevents chronic psychosocial stress-induced working memory impairment: Role of brain-derived neurotrophic factor

Background

Psychosocial stress, a common feature in modern societies, impairs cognitive functions. It is suggested that stress hormones and elevated excitatory amino acids during stress are responsible for stress-induced cognitive deficits. Reduced brain-derived neurotrophic factor (BDNF) levels, increased oxidative stress, and alteration of synaptic plasticity biomarkers are also possible contributors to the negative impact of stress on learning and memory. Sildenafil citrate is a selective phosphodiesterase type 5 (PDE5) inhibitor and the first oral therapy for the treatment of erectile dysfunction. It has been shown that sildenafil improves learning and memory and possesses antioxidant properties. We hypothesized that administering sildenafil to stressed rats prevents the cognitive deficit induced by chronic psychosocial stress.

Methods

Psychosocial stress was generated using the intruder model. Sildenafil 3 mg/kg/day was administered intraperitoneally to animals. Behavioral studies were conducted to test spatial learning and memory using the radial arm water maze. Then, the hippocampal BDNF level and several antioxidant markers were assessed.

Results

This study revealed that chronic psychosocial stress impaired short-term but not long-term memory. The administration of sildenafil prevented this short-term memory impairment. Chronic psychosocial stress markedly reduced the level of hippocampal BDNF (P˂0.05), and this reduction in BDNF was normalized by sildenafil treatment. In addition, neither chronic psychosocial stress nor sildenafil significantly altered the activity of measured oxidative parameters (P > 0.05).

Conclusion

Chronic psychosocial stress induces short-term memory impairment. The administration of sildenafil citrate prevented this impairment, possibly by normalizing the level of BDNF.

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.

PDE5 inhibitor drugs for use in dementia

Alzheimer's disease and related dementias (ADRD) remain a major health-care challenge with few licensed medications. Repurposing existing drugs may afford prevention and treatment. Phosphodiesterase-5 (PDE5) is widely expressed in vascular myocytes, neurons, and glia. Potent, selective, Food and Drug Administration-approved PDE5 inhibitors are already in clinical use (sildenafil, vardenafil, tadalafil) as vasodilators in erectile dysfunction and pulmonary arterial hypertension. Animal data indicate cognitive benefits of PDE5 inhibitors. In humans, real-world patient data suggest that sildenafil and vardenafil are associated with reduced dementia risk. While a recent clinical trial of acute tadalafil on cerebral blood flow was neutral, there may be chronic actions of PDE5 inhibition on cerebrovascular or synaptic function. We provide a perspective on the potential utility of PDE5 inhibitors for ADRD. We conclude that further prospective clinical trials with PDE5 inhibitors are warranted. The choice of drug will depend on brain penetration, tolerability in older people, half-life, and off-target effects.

HIGHLIGHTS

Potent phosphodiesterase-5 (PDE5) inhibitors are in clinical use as vasodilators.In animals PDE5 inhibitors enhance synaptic function and cognitive ability.In humans the PDE5 inhibitor sildenafil is associated with reduced risk of Alzheimer's disease.Licensed PDE5 inhibitors have potential for repurposing in dementia.Prospective clinical trials of PDE5 inhibitors are warranted.

Pyrazolopyrimidinone Based Selective Inhibitors of PDE5 for the Treatment of Erectile Dysfunction

Continuing research with our earlier finding of sildenafil based analogs in the search of new inhibitors of PDE5 for erectile dysfunction suggested that there is a scope of modifications at N-methylpiperazine ring with hydrophobic region followed by hydrogen bond donor or acceptor region. However, the leads identified earlier had some limitations like poor pharmacokinetic (PK) profile, low aqueous solubility and poor bioavailability. In this direction, a new series of sildenafil based analogs were designed, synthesized and screened for their PDE5 inhibitory activity. In this series compound 18 was found to have excellent in vitro activity with selectivity towards PDE5 isozyme, also the in vivo activity and pharmacokinetic profile was excellent. The cyp inhibition and CaCO2 permeability was also excellent for compound 18.

Improvement of cognitive dysfunction by a novel phosphodiesterase type 5 inhibitor, Tadalafil

There is substantial evidence for the modulatory role of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterases (PDEs) in memory and synaptic plasticity, and an increase in intracellular cGMP facilitates these processes. The present study was aimed at the neuropharmacological investigations of tadalafil (TAD 5, 10, and 20 mg/kg, p.o.) and further involvement of nitric oxide (NO)-cGMP in its effects. The effects of tadalafil and its combination with N^G -nitro-L-arginine methyl ester (L-NAME) were investigated in scopolamine- and diabetes-induced cognitive dysfunction using elevated plus maze (EPM) and object recognition (ORT) tests. The results of EPM revealed that the scopolamine- and diabetes-induced learning and memory deficit was dose dependently attenuated after administration of TAD (TAD 10 and 20 mg/kg, p.o.) in both paradigms studied. Administration of L-NAME (20 mg/kg) aggravated scopolamine- and diabetes-induced learning and memory deficit. Co-administration of L-NAME (20 mg/kg) after TAD (20 mg/kg) produced significant increase in cognitive performance as compared to scopolamine- and diabetic- control group. This showed that L-NAME (20 mg/kg) aggravated scopolamine- and diabetes-induced learning and memory deficit was significantly reversed by TAD (20 mg/kg). The results of the present study revealed that tadalafil by inhibiting PDE5 possibly elevated the cGMP level that through a diversity of its substrates produced neuropharmacological effects in cognitive dysfunction.

No association between initiation of phosphodiesterase-5 inhibitors and risk of incident Alzheimer's disease and related dementia: results from the Drug Repurposing for Effective Alzheimer's Medicines study

We evaluated the hypothesis that phosphodiesterase-5 inhibitors, including sildenafil and tadalafil, may be associated with reduced incidence of Alzheimer's disease and related dementia using a patient-level cohort study of Medicare claims and cell culture-based phenotypic assays. We compared incidence of Alzheimer's disease and related dementia after phosphodiesterase-5 inhibitor initiation versus endothelin receptor antagonist initiation among patients with pulmonary hypertension after controlling for 76 confounding variables through propensity score matching. Across four separate analytic approaches designed to address specific types of biases including informative censoring, reverse causality, and outcome misclassification, we observed no evidence for a reduced risk of Alzheimer's disease and related dementia with phosphodiesterase-5 inhibitors;hazard ratio (95% confidence interval): 0.99 (0.69-1.43), 1.00 (0.71-1.42), 0.67 (0.43-1.06), and 1.15 (0.57-2.34). We also did not observe evidence that sildenafil ameliorated molecular abnormalities relevant to Alzheimer's disease in most cell culture-based phenotypic assays. These results do not provide support to the hypothesis that phosphodiesterase-5 inhibitors are promising repurposing candidates for Alzheimer's disease and related dementia.

Roflumilast, a Phosphodiesterase-4 Inhibitor, Ameliorates Sleep Deprivation-Induced Cognitive Dysfunction in C57BL/6J Mice

Sleep deprivation (SD) interferes with long-term memory and cognitive functions by overactivation of phosphodiesterase (PDEs) enzymes. PDE4, a nonredundant regulator of the cyclic nucleotides (cAMP), is densely expressed in the hippocampus and is involved in learning and memory processes. In the present study, we investigated the effects of Roflumilast (ROF), a PDE4B inhibitor, on sleep deprivation-induced cognitive dysfunction in a mouse model. Memory assessment was performed using a novel object recognition task, and the hippocampal cAMP level was estimated by the ELISA method. The alterations in the expressions of PDE4B, amyloid-β (Aβ), CREB, BDNF, and synaptic proteins (Synapsin I, SAP 97, PSD 95) were assessed to gain insights into the possible mechanisms of action of ROF using the Western blot technique. Results show that ROF reversed SD-induced cognitive decline in mice. ROF downregulated PDE4B and Aβ expressions in the brain. Additionally, ROF improved the cAMP level and the protein expressions of synapsin I, SAP 97, and PSD 95 in the hippocampal region of SD mice. Taken together, these results suggest that ROF can suppress the deleterious effects of SD-induced cognitive dysfunction via the PDE4B-mediated cAMP/CREB/BDNF signaling cascade.

Propolis Promotes Memantine-Dependent Rescue of Cognitive Deficits in APP-KI Mice

Propolis is a complex resinous substance that is relevant as a therapeutic target for Alzheimer's disease (AD) and other neurodegenerative diseases. In this study, we confirmed that propolis (Brazilian green propolis) further enhances the rescue of cognitive deficits by the novel AD drug memantine in APP-KI mice. In memory-related behavior tasks, administration of a single dose of propolis at 1-100 mg/kg p.o. significantly enhanced the rescue of cognitive deficits by memantine at 1 mg/kg p.o. in APP-KI mice. In in vitro studies, propolis significantly increased intracellular Ca²⁺ concentration and calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation in Kir6.2-overexpressed N2A cells treated with memantine. Propolis also significantly increased adenosine 5'-triphosphate (ATP) contents and CaMKII autophosphorylation, which was impaired in Aβ-treated Kir6.2-overexpressed N2A cells. Similarly, repeated administration of propolis at 100 mg/kg p.o. for 8 weeks further enhanced the rescue of cognitive deficits by memantine in APP-KI mice. Consistent with the rescued cognitive deficits in APP-KI mice, repeated administration of propolis markedly ameliorated memantine-dependent rescue of injured long-term potentiation (LTP) in APP-KI mice, concomitant with increased CaMKII autophosphorylation and calcium/calmodulin-dependent protein kinase IV (CaMKIV) phosphorylation in the hippocampal CA1 region. Furthermore, repeated administration of both memantine and propolis significantly restored the decreased ATP contents in the CA1 region of APP-KI mice. Finally, we confirmed that repeated administration of memantine at 1 mg/kg p.o. and propolis at 100 mg/kg p.o. for 8 weeks failed to restore the cognitive deficits in Kir6.2-/- mice. Our study demonstrates that propolis increases ATP contents and promotes the amelioration of cognitive deficits rescued by memantine via Kir6.2 channel inhibition in the CA1 region.

Demonstration of Ameliorating Effect of Vardenafil Through Its Anti-Inflammatory and Neuroprotective Properties in Autism Spectrum Disorder Induced by Propionic Acid on Rat Model

Introduction: Autism spectrum disorder (ASD) is a neurodevelopmental disorder with complex etiology. In this study, we aimed to determine the ameliorating effects of vardenafil in the ASD rat model induced by propionic acid (PPA) in terms of neurobehavioral changes and also support these effects with histopathological changes, brain biochemical analysis and magnetic resonance spectroscopy (MRS) findings.Materials and Methods: Twenty-one male rats were randomly assigned into 3 groups. Group 1 (control, 7 rats) did not receive treatment. Rats in groups 2 and 3 were given PPA at the dose of 250 mg/kg/day intraperitoneally for 5 days. After PPA administration, animals in group 2 (PPAS, 7 rats) were given saline and animals in group 3 (PPAV, 7 rats) were given vardenafil. Behavioral tests were performed between the 20th and 24th days of the study. The rats were taken for MRS on the 25^th day. At the end of the study, brain levels of interleukin-2 (IL-2), IL-17, tumor necrosis factor-α, nerve growth factor, cGMP and lactate levels were measured. In the cerebellum and the CA1 and CA3 regions of the hippocampus, counts of neurons and Purkinje cells and glial fibrillary acidic protein (associated with gliosis) were evaluated histologically.Results: Three chamber sociability and passive avoiding test, histopathological results, lactate levels derived from MRS, and biochemical biomarkers revealed significant differences among the PPAV and PPAS groups.Conclusion: We concluded that vardenafil improves memory and social behaviors and prevent loss of neuronal and Purkinje cell through its anti-inflammatory and neuroprotective effect.

How do phosphodiesterase-5 inhibitors affect cancer? A focus on glioblastoma multiforme

Since the discovery of phosphodiesterase-5 (PDE5) enzyme overexpression in the central nervous system (CNS) malignancies, investigations have explored the potential capacity of current PDE5 inhibitor drugs for repositioning in the treatment of brain tumors, notably glioblastoma multiforme (GBM). It has now been recognized that these drugs increase brain tumors permeability and enhance standard chemotherapeutics effectiveness. More importantly, studies have highlighted the promising antitumor functions of PDE5 inhibitors, e.g., triggering apoptosis, suppressing tumor cell growth and invasion, and reversing tumor microenvironment (TME) immunosuppression in the brain. However, contradictory reports have suggested a pro-oncogenic role for neuronal cyclic guanosine monophosphate (cGMP), indicating the beneficial function of PDE5 in the brain of GBM patients. Unfortunately, due to the inconsistent preclinical findings, only a few clinical trials are evaluating the therapeutic value of PDE5 inhibitors in GBM treatment. Accordingly, additional studies should be conducted to shed light on the precise effect of PDE5 inhibitors in GBM biology regarding the existing molecular heterogeneities among individuals. Here, we highlighted and discussed the previously investigated mechanisms underlying the impacts of PDE5 inhibitors in cancers, focusing on GBM to provide an overview of current knowledge necessary for future studies.

A review of behavioral methods for the evaluation of cognitive performance in animal models: Current techniques and links to human cognition

INTRODUCTION

Memory is defined as the ability to store, maintain and retrieve information. Learning is the acquisition of information that changes behavior and memory. Stress, dementia, head trauma, amnesia, Alzheimer's, Huntington, Parkinson's, Wernicke-Korsakoff syndrome (WKS) may be mentioned among the diseases in which memory and learning are affected. The task of understanding deficits in memory and learning in humans is daunting due to the complexity of neural and cognitive mechanisms in the nervous system. This job is made more difficult for clinicians and researchers by the fact that many techniques used to research memory are not ethically acceptable or technically feasible for use in humans. Thus, animal models have been necessary alternative for studying normal and disordered learning and memory. This review attempts to bridge these domains to allow biomedical researchers to have a firm grasp of "memory" and "learning" as constructs in humans whereby they may then select the proper animal cognitive test.

RESULTS AND CONCLUSION

Various tests (open field habituation test, Y-maze test, passive avoidance test, step-down inhibitory avoidance test, active avoidance test, 8-arms radial maze test, Morris water maze test, radial arm water maze, novel object recognition test and gait function test) have been designed to evaluate different kinds of memory. Each of these tests has their strengths and limits. Abnormal results obtained using these tasks in non-human animals indicate malfunctions in memory which may be due to several physiological and psychological diseases of nervous system. Further studies by using the discussed tests can be very beneficial for achieving a therapeutic answer to these diseases.

Memantine improves cognitive deficits via KATP channel inhibition in olfactory bulbectomized mice

Patients with Alzheimer's disease (AD) demonstrate severely impaired olfactory systems, which occur in the early stages of the disease. Olfactory bulbectomy (OBX) in mice elicits cognitive deficits, and reduces cholinergic activity in the hippocampus. Here, we confirmed that the novel AD drug memantine rescues cognitive deficits via ATP-sensitive potassium (K_ATP) channel inhibition in OBX mice. Repeated memantine administration at 1-3 mg/kg p.o. for 14 days starting at 10 days after OBX surgery significantly rescued cognitive deficits in OBX mice, as assessed using Y-maze, novel object recognition, and passive avoidance tasks. Consistent with the rescued cognitive deficits in OBX mice, long-term potentiation (LTP) in the hippocampal cornu ammonis (CA) 1 region was markedly restored with memantine administration. As demonstrated by immunoblotting, the reductions of calcium/calmodulin-dependent protein kinase II (CaMKII) α (Thr-286) autophosphorylation and calcium/calmodulin-dependent protein kinase IV (CaMKIV; Thr-196) phosphorylation in the CA1 region of OBX mice were significantly restored with memantine. Conversely, pre-treatment with pinacidil, a K_ATP channel opener, failed to reinstate hippocampal LTP and CaMKII/CaMKIV activities in the CA1 region. Finally, improvement of cognitive deficits by memantine treatments was observed in OBX-operated Kir6.1 heterozygous (+/-) mice but not in OBX-operated Kir6.2 heterozygous (+/-) mice. Overall, our study demonstrates that memantine rescues OBX-induced cognitive deficits via Kir6.2 channel inhibition in the CA1 region.

Cyclic GMP in Liver Cirrhosis-Role in Pathophysiology of Portal Hypertension and Therapeutic Implications

The NO-cGMP signal transduction pathway plays a crucial role in tone regulation in hepatic sinusoids and peripheral blood vessels. In a cirrhotic liver, the key enzymes endothelial NO synthase (eNOS), soluble guanylate cyclase (sGC), and phosphodiesterase-5 (PDE-5) are overexpressed, leading to decreased cyclic guanosine-monophosphate (cGMP). This results in constriction of hepatic sinusoids, contributing about 30% of portal pressure. In contrast, in peripheral arteries, dilation prevails with excess cGMP due to low PDE-5. Both effects eventually lead to circulatory dysfunction in progressed liver cirrhosis. The conventional view of portal hypertension (PH) pathophysiology has been described using the "NO-paradox", referring to reduced NO availability inside the liver and elevated NO production in the peripheral systemic circulation. However, recent data suggest that an altered availability of cGMP could better elucidate the contrasting findings of intrahepatic vasoconstriction and peripheral systemic vasodilation than mere focus on NO availability. Preclinical and clinical data have demonstrated that targeting the NO-cGMP pathway in liver cirrhosis using PDE-5 inhibitors or sGC stimulators/activators decreases intrahepatic resistance through dilation of sinusoids, lowering portal pressure, and increasing portal venous blood flow. These results suggest further clinical applications in liver cirrhosis. Targeting the NO-cGMP system plays a role in possible reversal of liver fibrosis or cirrhosis. PDE-5 inhibitors may have therapeutic potential for hepatic encephalopathy. Serum/plasma levels of cGMP can be used as a non-invasive marker of clinically significant portal hypertension. This manuscript reviews new data about the role of the NO-cGMP signal transduction system in pathophysiology of cirrhotic portal hypertension and provides perspective for further studies.

Soluble Guanylate Cyclase Stimulator Vericiguat Enhances Long-Term Memory in Rats without Altering Cerebral Blood Volume

Vascular cognitive impairment (VCI) is characterized by impairments in cerebral blood flow (CBF), endothelial function and blood-brain barrier (BBB) integrity. These processes are all physiologically regulated by the nitric oxide (NO)-soluble guanylate cyclase (sGC)-cGMP signaling pathway. Additionally, cGMP signaling plays an important role in long-term potentiation (LTP) underlying memory formation. Therefore, targeting the NO-sGC-cGMP pathway may be a therapeutic strategy for treating VCI. Hence, in this study we investigated whether sGC stimulator vericiguat has potential as a cognitive enhancer. The effects of vericiguat on long-term memory were measured in rats using an object location task. Due to the low brain-penetrance of vericiguat found in this study, it was investigated whether in the absence of BBB limitations, vericiguat enhanced hippocampal plasticity using an ex vivo memory acquisition-like chemical LTP model. Finally, peripheral effects were measured by means of blood pressure and cerebral blood volume. Vericiguat successfully enhanced long-term memory and increased hippocampal plasticity via enhanced translocation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors to the cell membrane, while blood pressure and cerebral blood volume were unaltered. Although the memory enhancing effects in this study are likely due to peripheral effects on the cerebral microvasculature, sGC stimulation may provide a new therapeutic strategy for treating VCI, especially when BBB integrity is reduced.

Targeting Alzheimer's disease with multimodal polypeptide-based nanoconjugates

Alzheimer's disease (AD), the most prevalent form of dementia, remains incurable mainly due to our failings in the search for effective pharmacological strategies. Here, we describe the development of targeted multimodal polypeptide-based nanoconjugates as potential AD treatments. Treatment with polypeptide nanoconjugates bearing propargylamine moieties and bisdemethoxycurcumin or genistein afforded neuroprotection and displayed neurotrophic effects, as evidenced by an increase in dendritic density of pyramidal neurons in organotypic hippocampal culture. The additional conjugation of the Angiopep-2 targeting moiety enhanced nanoconjugate passage through the blood-brain barrier and modulated brain distribution with nanoconjugate accumulation in neurogenic areas, including the olfactory bulb. Nanoconjugate treatment effectively reduced neurotoxic β amyloid aggregate levels and rescued impairments to olfactory memory and object recognition in APP/PS1 transgenic AD model mice. Overall, this study provides a description of a targeted multimodal polyglutamate-based nanoconjugate with neuroprotective and neurotrophic potential for AD treatment.

Inhibition of PDE2 and PDE4 synergistically improves memory consolidation processes

Phosphodiesterases (PDE) are the only enzymes that degrade cAMP and cGMP which are second messengers crucial to memory consolidation. Different PDE inhibitors have been developed and tested for their memory-enhancing potential, but the occurrence of side effects has hampered clinical progression. As separate inhibition of the PDE2 and PDE4 enzyme family has been shown to enhance memory, we investigated whether concurrent treatment with a PDE2 and PDE4 inhibitor can have synergistic effects on memory consolidation processes. We found that combined administration of PF-999 (PDE2 inhibitor) and roflumilast (PDE4 inhibitor) increases the phosphorylation of the AMPA receptor subunit GluR1 and induces CRE-mediated gene expression. Moreover, when combined sub-effective and effective doses of PF-999 and roflumilast were administered after learning, time-dependent forgetting was abolished in an object location memory task. Pharmacokinetic assessment indicated that combined treatment does not alter exposure of the individual compounds. Taken together, these findings suggest that combined PDE2 and PDE4 inhibition has synergistic effects on memory consolidation processes at sub-effective doses, which could therefore provide a therapeutic strategy with an improved safety profile.

Role of phosphodiesterases in the pathophysiology of neurodevelopmental disorders

Phosphodiesterases (PDEs) are enzymes involved in the homeostasis of both cAMP and cGMP. They are members of a family of proteins that includes 11 subfamilies with different substrate specificities. Their main function is to catalyze the hydrolysis of cAMP, cGMP, or both. cAMP and cGMP are two key second messengers that modulate a wide array of intracellular processes and neurobehavioral functions, including memory and cognition. Even if these enzymes are present in all tissues, we focused on those PDEs that are expressed in the brain. We took into consideration genetic variants in patients affected by neurodevelopmental disorders, phenotypes of animal models, and pharmacological effects of PDE inhibitors, a class of drugs in rapid evolution and increasing application to brain disorders. Collectively, these data indicate the potential of PDE modulators to treat neurodevelopmental diseases characterized by learning and memory impairment, alteration of behaviors associated with depression, and deficits in social interaction. Indeed, clinical trials are in progress to treat patients with Alzheimer's disease, schizophrenia, depression, and autism spectrum disorders. Among the most recent results, the application of some PDE inhibitors (PDE2A, PDE3, PDE4/4D, and PDE10A) to treat neurodevelopmental diseases, including autism spectrum disorders and intellectual disability, is a significant advance, since no specific therapies are available for these disorders that have a large prevalence. In addition, to highlight the role of several PDEs in normal and pathological neurodevelopment, we focused here on the deregulation of cAMP and/or cGMP in Down Syndrome, Fragile X Syndrome, Rett Syndrome, and intellectual disability associated with the CC2D1A gene.

Moderate treadmill exercise improves spatial learning and memory deficits possibly via changing PDE-5, IL-1 β and pCREB expression

Alzheimer's is a progressive disorder of the nervous system. Prior studies suggested that physical activity contributes to the improvement of cognitive impairment and slows down pathogenesis of AD; however, the exact mechanisms for this have not been fully understood. Therefore, in this study, we examined the effect of aerobic training before and after induction of Alzheimer's on spatial learning and memory, expression of interleukin-1 beta (IL-1β), cAMP-responsive element-binding protein (pCREB), and Phosphodiesterase-5 (PDE-5) in the hippocampus of male rats Wistar. Aβ was microinjected into the CA1 area of the hippocampus animals. The moderate treadmill exercise protocols for pre and post induction of Alzheimer's were the same (5 days/week, for 4 weeks with a customized regime). The Morris Water Maze (MWM) method has been to assess spatial learning and memory. The real time-PCR method was used to measure gene expression. Our results showed that intra-hippocampal injection of Aβ1-42 impaired spatial learning and memory which was accompanied by reduced pCREB activity and elevated IL-1β and PDE-5 in the hippocampus of rats. In contrast, moderate treadmill exercise ameliorated the Aβ1-42-induced spatial learning and memory deficit, which was accompanied by restored pCREB activity and decreasing IL-1β and PDE-5 levels. In conclusion, our finding suggests that exercise before and after Alzheimer's induction leads to an increase in pCREB and an alleviation of inflammation which likely involved in ameliorating spatial learning and memory deficits in an animal model of AD.

Phosphodiesterase-5 inhibitors: Shedding new light on the darkness of depression?

BACKGROUND

Phosphodiesterase-5 inhibitors (PDE5Is) are used to treat erectile dysfunction (ED). Recently, the antidepressant-like effect of PDE5Is was demonstrated in animal models of depression. In clinical settings, PDE5Is were studied only for ED associated depression. Hence, there are no studies evaluating the effects of PDE5Is for the treatment of major depressive disorder (MDD) without ED. In this review article, we aimed to discuss the use of PDE5Is in the context of MDD, highlighting the roles of PDE genes in the development of MDD, the potential mechanisms by which PDE5Is can be beneficial for MDD and the potentials and limitations of PDE5Is repurposing to treat MDD.

METHODS

We used PubMed (MEDLINE) database to collect the studies cited in this review. Papers written in English language regardless the year of publication were selected.

RESULTS

A few preclinical studies support the antidepressant-like activity of PDE5Is. Clinical studies in men with ED and depression suggest that PDE5Is improve depressive symptoms. No clinical studies were conducted in subjects suffering from depression without ED. Antidepressant effect of PDE5Is may be explained by multiple mechanisms including inhibition of brain inflammation and modulation of neuroplasticity.

LIMITATIONS

The low number of preclinical and absence of clinical studies to support the antidepressant effect of PDE5Is.

CONCLUSIONS

No clinical trial was conducted to date evaluating PDE5Is in depressed patients without ED. PDE5Is' anti-inflammatory and neuroplasticity mechanisms may justify the potential antidepressant effect of these drugs. Despite this, clinical trials evaluating their efficacy in depressed patients need to be conducted.

Role of cyclic nucleotides and their downstream signaling cascades in memory function: Being at the right time at the right spot

A plethora of studies indicate the important role of cAMP and cGMP cascades in neuronal plasticity and memory function. As a result, altered cyclic nucleotide signaling has been implicated in the pathophysiology of mnemonic dysfunction encountered in several diseases. In the present review we provide a wide overview of studies regarding the involvement of cyclic nucleotides, as well as their upstream and downstream molecules, in physiological and pathological mnemonic processes. Next, we discuss the regulation of the intracellular concentration of cyclic nucleotides via phosphodiesterases, the enzymes that degrade cAMP and/or cGMP, and via A-kinase-anchoring proteins that refine signal compartmentalization of cAMP signaling. We also provide an overview of the available data pointing to the existence of specific time windows in cyclic nucleotide signaling during neuroplasticity and memory formation and the significance to target these specific time phases for improving memory formation. Finally, we highlight the importance of emerging imaging tools like Förster resonance energy transfer imaging and optogenetics in detecting, measuring and manipulating the action of cyclic nucleotide signaling cascades.

Concurrent Effects of Exercise and Curcumin on Spatial Learning and Memory in Sensitized Male Mice Following Morphine Administration

BACKGROUND

Exercise and Curcumin have positive effects on spatial memory and cognition independently. The present study aims to investigate whether the combination of ineffectual dosage of these factors can affect cognition and as a solvent if DMSO is involved in Curcumin effects.

MATERIALS AND METHODS

Male NMRI mice (1-month-old) swam (1 week) for 60 minutes (5days/week) and injected with morphine (2.5 mg/ml/kg, intraperitoneal) for five days. Spatial learning and memory were assessed by Moris Water Maze test on the 10th day after stopping morphine injection.

RESULTS

The findings revealed that exercise, dimethyl sulfoxide (DMSO), and Curcumin increased memory formation induced by 2.5 mg/ml/kg morphine. DMSO+exercise decreased memory formation induced by morphine, but curcumin +exercise could return the effect of DMSO on the cognition.

CONCLUSION

As a solvent, DMSO had independent effects on memory, which lead to memory impairment in combination with exercise. Therefore, considering its unpredictable effects on cognitive performance, it should be replaced with another solvent or might be used carefully in behavioral experiments.

Differential Impact of Ad Libitum or Intermittent High-Fat Diets on Bingeing Ethanol-Mediated Behaviors

Background: Dietary factors have significant effects on the brain, modulating mood, anxiety, motivation and cognition. To date, no attention has been paid to the consequences that the combination of ethanol (EtOH) and a high-fat diet (HFD) have on learning and mood disorders during adolescence. The aim of the present work was to evaluate the biochemical and behavioral consequences of ethanol binge drinking and an HFD consumption in adolescent mice. Methods: Animals received either a standard diet or an HFD (ad libitum vs. binge pattern) in combination with ethanol binge drinking and were evaluated in anxiety and memory. The metabolic profile and gene expression of leptin receptors and clock genes were also evaluated. Results: Excessive white adipose tissue and an increase in plasma insulin and leptin levels were mainly observed in ad libitum HFD + EtOH mice. An upregulation of the Lepr gene expression in the prefrontal cortex and the hippocampus was also observed in ad libitum HFD groups. EtOH-induced impairment on spatial memory retrieval was absent in mice exposed to an HFD, although the aversive memory deficits persisted. Mice bingeing on an HFD only showed an anxiolytic profile, without other alterations. We also observed a mismatch between Clock and Bmal1 expression in ad libitum HFD animals, which were mostly independent of EtOH bingeing. Conclusions: Our results confirm the bidirectional influence that occurs between the composition and intake pattern of a HFD and ethanol consumption during adolescence, even when the metabolic, behavioral and chronobiological effects of this interaction are dissociated.

Eucommia ulmoides Oliv. Leaf Extract Improves Erectile Dysfunction in Streptozotocin-Induced Diabetic Rats by Protecting Endothelial Function and Ameliorating Hypothalamic-Pituitary-Gonadal Axis Function

Erectile dysfunction (ED) is a major complication of diabetes mellitus. Eucommia ulmoides Oliv. is used as a traditional medicine for male impotence, but no systematic study has examined its effect on diabetes-associated ED. In this study, we investigated the effects of Eucommia ulmoides Oliv. leaf extract (EULE) on restoring erectile function in streptozotocin (STZ)-induced diabetic rats model. After 16 weeks of treatment, EULE administration had significantly increased intracavernosal pressure, nitric oxide (NO) levels, and cyclic guanosine monophosphate (cGMP) concentrations. Serum superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) levels were markedly higher and serum malondialdehyde (MDA) levels were lower in the EULE-treated groups than in the diabetic model group. EULE restored NO biosynthesis by significantly increasing protein kinase B (Akt) and endothelial NO synthase (eNOS) activation. Furthermore, EULE is likely to benefit the hypothalamic-pituitary-gonadal (HPG) axis, as it increased gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone (T) concentrations as well as hormone receptors Gnrhr, Fshr, and Lhr expression levels. Hence, EULE attenuates oxidative stress, increases NO production, and activates the Akt-eNOS pathway to restore endothelial function; moreover, EULE enhances the HPG axis to improve erectile function. These results suggest that EULE may represent a new therapeutic avenue for diabetes-associated ED.

From molecules to patients: exploring the therapeutic role of soluble guanylate cyclase stimulators

Nitric oxide (NO) signaling represents one of the major regulatory pathways for cardiovascular function. After the discovery of NO, awarded with the Nobel Prize in 1998, this signaling cascade was stepwise clarified. We now have a good understanding of NO production and NO downstream targets such as the soluble guanylyl cyclases (sGCs) which catalyze cGMP production. Based on the important role of NO-signaling in the cardiovascular system, intense research and development efforts are currently ongoing to fully exploit the therapeutic potential of cGMP increase. Recently, NO-independent stimulators of sGC (sGC stimulators) were discovered and characterized. This new compound class has a unique mode of action, directly binding to sGC and triggering cGMP production. The first sGC stimulator made available to patients is riociguat, which was approved in 2013 for the treatment of different forms of pulmonary hypertension (PH). Besides riociguat, other sGC stimulators are in clinical development, with vericiguat in phase 3 clinical development for the treatment of chronic heart failure (HF). Based on the broad impact of NO/cGMP signaling, sGC stimulators could have an even broader therapeutic potential beyond PH and HF. Within this review, the NO/sGC/cGMP/PKG/PDE-signaling cascade and the major pharmacological intervention sites are described. In addition, the discovery and mode of action of sGC stimulators and the clinical development in PH and HF is covered. Finally, the preclinical and clinical evidence and treatment approaches for sGC stimulators beyond these indications and the cardiovascular disease space, like in fibrotic diseases as in systemic sclerosis (SSc), are reviewed.

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.

Sildenafil Improves Vascular and Metabolic Function in Patients with Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the leading cause of degenerative dementia in the aging population. Patients with AD have alterations in cerebral hemodynamic function including reduced cerebral blood flow (CBF) and cerebral metabolic rate. Therefore, improved cerebrovascular function may be an attractive goal for pharmaceutical intervention in AD.

OBJECTIVE

We wished to observe the acute effects of sildenafil on cerebrovascular function and brain metabolism in patients with AD.

METHODS

We used several novel non-invasive MRI techniques to investigate the alterations of CBF, cerebral metabolic rate of oxygen (CMRO2), and cerebrovascular reactivity (CVR) after a single dose of sildenafil administration in order to assess its physiological effects in patients with AD. CBF, CMRO2, and CVR measurements using MRI were performed before and one hour after the oral administration of 50 mg sildenafil. Baseline Montreal Cognitive Assessment score was also obtained.

RESULTS

Complete CBF and CMRO2 data were obtained in twelve patients. Complete CVR data were obtained in eight patients. Global CBF and CMRO2 significantly increased (p = 0.03, p = 0.05, respectively) following sildenafil administration. Voxel-wise analyses of CBF maps showed that increased CBF was most pronounced in the bilateral medial temporal lobes. CVR significantly decreased after administration of sildenafil.

CONCLUSION

Our data suggest that a single dose of sildenafil improves cerebral hemodynamic function and increases cerebral oxygen metabolism in patients with AD.

The phosphodiesterase 5 inhibitor, KJH-1002, reverses a mouse model of amnesia by activating a cGMP/cAMP response element binding protein pathway and decreasing oxidative damage

BACKGROUND AND PURPOSE

Inhibition of PDE5 improves synaptic plasticity and memory via enhancing cGMP expression, thus activating the cGMP/cAMP response element binding protein (CREB) signalling pathway. This study investigated the effects of a PDE5 inhibitor on scopolamine-induced cognitive dysfunction, using memory-related behavioural tests and biochemical assays.

EXPERIMENTAL APPROACH

In mice were pretreated with PDE5 inhibitor, amnesia was induced by scopolamine. The learning and memory abilities of mice were tested using the Morris water maze test, the Y-maze test, the passive avoidance test and the novel object recognition test in sequence. Expression of memory-related bio-molecules and oxidative stress parameters in brain tissue were measured using Western blot and spectrophotometry respectively.

KEY RESULTS

KJH-1002, a novel and potent inhibitor of PDE5 (IC₅₀ 0.059 ± 0.04 nmol·L^-1 ), was synthesized. In the behavioural tests, it markedly improved the memory performance impaired by scopolamine, indicating a restoration of cognitive function in the mice. Moreover, KJH-1002 increased cGMP levels in the cortex and the scopolamine-reduced expression of phosphorylated CREB, Levels of ERK 1/2, Akt and brain-derived neurotrophic factor in the cortex and hippocampus were restored by KJH-1002 treatment. In addition, KJH-1002 administration increased the activities of SOD, glutathione peroxidase and glutathione reductase, and decreased the level of malondialdehyde.

CONCLUSION AND IMPLICATIONS

KJH-1002 restored cognitive function in scopolamine-induced amnesia mice by activating the cGMP/CREB signalling pathway and attenuating oxidative stress. The beneficial effects of KJH-1002 on cognition indicate its potential as a therapeutic candidate for Alzheimer's disease.

Sildenafil protects neuronal cells from mitochondrial toxicity induced by β-amyloid peptide via ATP-sensitive K+ channels

To understand the molecular mechanisms underlying the beneficial effects of sildenafil in animal models of neurological disorders, we investigated the effects of sildenafil on the mitochondrial toxicity induced by β-amyloid (Aβ) peptide. Treatment of HT-22 hippocampal neuronal cells with Aβ_25∼35 results in increased mitochondrial Ca²⁺ load, which is subsequently suppressed by sildenafil as well as by diazoxide, a selective opener of the ATP-sensitive K⁺ channels (K_ATP). However, the suppressive effects of sildenafil and diazoxide are significantly attenuated by 5-hydroxydecanoic acid (5-HD), a K_ATP inhibitor. The increased mitochondrial Ca²⁺ overload is accompanied by decrease in the intracellular ATP concentration, increase in intracellular ROS generation, occurrence of mitochondrial permeability transition, and activation of caspase-9 and cell death. Exposure to sildenafil inhibited the mitochondria-associated changes and cell death induced by Aβ. However, the inhibitory effects of sildenafil are abolished or weakened in the presence of 5-HD, suggesting that opening of the mitochondrial K_ATP is required for sildenafil to exert these effects. Taken together, these results indicate that at the mitochondrial levels, sildenafil plays a protective role towards neuronal cell in an environment rich in Aβ, and exerts its effects via the mitochondrial K_ATP channels-dependent mechanisms.

Inhibition of phosphodiesterases as a strategy to achieve neuroprotection in Huntington's disease

Huntington's disease (HD) is a fatal neurodegenerative condition, due to a mutation in the IT15 gene encoding for huntingtin. Currently, disease-modifying therapy is not available for HD, and only symptomatic drugs are administered for the management of symptoms. In the last few years, preclinical and clinical studies have indicated that pharmacological strategies aimed at inhibiting cyclic nucleotide phosphodiesterase (PDEs) may develop into a novel therapeutic approach in neurodegenerative disorders. PDEs are a family of enzymes that hydrolyze cyclic nucleotides into monophosphate isoforms. Cyclic nucleotides are second messengers that transduce the signal of hormones and neurotransmitters in many physiological processes, such as protein kinase cascades and synaptic transmission. An alteration in their balance results in the dysregulation of different biological mechanisms (transcriptional dysregulation, immune cell activation, inflammatory mechanisms, and regeneration) that are involved in neurological diseases. In this review, we discuss the action of phosphodiesterase inhibitors and their role as therapeutic agents in HD.

Increased motor neuron resilience by small molecule compounds that regulate IGF-II expression

The selective vulnerability of motor neurons in amyotrophic lateral sclerosis (ALS) is evident by sparing of a few subpopulations during this fast progressing and debilitating degenerative disease. By studying the gene expression profile of resilient vs. vulnerable motor neuron populations we can gain insight in what biomolecules and pathways may contribute to the resilience and vulnerability. Several genes have been found to be differentially expressed in the vulnerable motor neurons of the cervical spinal cord as compared to the spared motor neurons in CNIII/IV. One gene that is differentially expressed and present at higher levels in less vulnerable motor neurons is insulin-like growth factor II (IGF-II). The motor neuron protective effect of IGF-II has been demonstrated both in vitro and in SOD1 transgenic mice. Here, we have screened a library of small molecule compounds and identified inducers of IGF-II mRNA and protein expression. Several identified compounds significantly protected motor neurons from glutamate excitotoxicity in vitro. One of the compounds, vardenafil, resulted in a complete motor neuron protection, an effect that was reversed by blocking receptors of IGF-II. When administered to naïve rats vardenafil was present in the cerebrospinal fluid and increased IGF-II mRNA expression in the spinal cord. When administered to SOD1 transgenic mice, there was a significant delay in motor symptom onset and prolonged survival. Vardenafil also increased IGF-II mRNA and protein levels in motor neurons derived from healthy subject and ALS patient iPSCs, activated a human IGF-II promoter and improved survival of ALS-patient derived motor neurons in culture. Our findings suggest that modulation of genes differentially expressed in vulnerable and resilient motor neurons may be a useful therapeutic approach for motor neuron disease.

Type 5 phosphodiesterase regulates glioblastoma multiforme aggressiveness and clinical outcome

Expression of type 5 phosphodiesterase (PDE5), a cGMP-specific hydrolytic enzyme, is frequently altered in human cancer, but its specific role in tumorigenesis remains controversial. Herein, by analyzing a cohort of 69 patients affected by glioblastoma multiforme (GBM) who underwent chemo- and radiotherapy after surgical resection of the tumor, we found that PDE5 was strongly expressed in cancer cells in about 50% of the patients. Retrospective analysis indicated that high PDE5 expression in GBM cells significantly correlated with longer overall survival of patients. Furthermore, silencing of endogenous PDE5 by short hairpin lentiviral transduction (sh-PDE5) in the T98G GBM cell line induced activation of an invasive phenotype. Similarly, pharmacological inhibition of PDE5 activity strongly enhanced cell motility and invasiveness in T98G cells. This invasive phenotype was accompanied by increased secretion of metallo-proteinase 2 (MMP-2) and activation of protein kinase G (PKG). Moreover, PDE5 silencing markedly enhanced DNA damage repair and cell survival following irradiation. The enhanced radio-resistance of sh-PDE5 GBM cells was mediated by an increase of poly(ADP-ribosyl)ation (PARylation) of cellular proteins and could be counteracted by poly(ADP-ribose) polymerase (PARP) inhibitors. Conversely, PDE5 overexpression in PDE5-negative U87G cells significantly reduced MMP-2 secretion, inhibited their invasive potential and interfered with DNA damage repair and cell survival following irradiation. These studies identify PDE5 as a favorable prognostic marker for GBM, which negatively affects cell invasiveness and survival to ionizing radiation. Moreover, our work highlights the therapeutic potential of targeting PKG and/or PARP activity in this currently incurable subset of brain cancers.

Flavonoid glycosides isolated from Epimedium brevicornum and their estrogen biosynthesis-promoting effects

Epimedium brevicornum Maxim has a long history of use in the treatment of estrogen deficiency-related diseases. However, the chemical constituents and mechanism of action of this medicinal plant are not fully understood. In the present study, we isolated four new isoprenylated flavonoid glycosides, as well as 16 known flavonoids (13 isoprenylated flavonoids), from this plant. The chemical structures of the new flavonoid glycosides were elucidated by extensive spectroscopic analysis. The new compounds 1–4 were potent promoters of estrogen biosynthesis in human ovarian granulosa-like KGN cells. ZW1, an isoprenylated flavonoid analogue and a specific inhibitor of phosphodiesterase 5 (PDE5), was synthesized and used to explore the mechanism of the isoprenylated analogues on estrogen biosynthesis. ZW1 treatment increased estrogen production by upregulation of aromatase mRNA and protein expression. ZW1 increased the phosphorylation of cAMP response element-binding protein (CREB). Further study showed that the inhibition of PDE5 by ZW1 increased estrogen biosynthesis partly through suppression of phosphodiesterase 3 (PDE3). Our results suggested that the isoprenylated flavonoids from E. brevicornum may produce beneficial health effects through the promotion of estrogen biosynthesis. PDE5 warrants further investigation as a new therapeutic target for estrogen biosynthesis in the prevention and treatment of estrogen-deficiency related diseases.

Amyloid-β Peptide Is Needed for cGMP-Induced Long-Term Potentiation and Memory

High levels of amyloid-β peptide (Aβ) have been related to Alzheimer's disease pathogenesis. However, in the healthy brain, low physiologically relevant concentrations of Aβ are necessary for long-term potentiation (LTP) and memory. Because cGMP plays a key role in these processes, here we investigated whether the cyclic nucleotide cGMP influences Aβ levels and function during LTP and memory. We demonstrate that the increase of cGMP levels by the phosphodiesterase-5 inhibitors sildenafil and vardenafil induces a parallel release of Aβ due to a change in the approximation of amyloid precursor protein (APP) and the β-site APP cleaving enzyme 1. Moreover, electrophysiological and behavioral studies performed on animals of both sexes showed that blocking Aβ function, by using anti-murine Aβ antibodies or APP knock-out mice, prevents the cGMP-dependent enhancement of LTP and memory. Our data suggest that cGMP positively regulates Aβ levels in the healthy brain which, in turn, boosts synaptic plasticity and memory.SIGNIFICANCE STATEMENT Amyloid-β (Aβ) is a key pathogenetic factor in Alzheimer's disease. However, low concentrations of endogenous Aβ, mimicking levels of the peptide in the healthy brain, enhance hippocampal long-term potentiation (LTP) and memory. Because the second messenger cGMP exerts a central role in LTP mechanisms, here we studied whether cGMP affects Aβ levels and function during LTP. We show that cGMP enhances Aβ production by increasing the APP/BACE-1 convergence in endolysosomal compartments. Moreover, the cGMP-induced enhancement of LTP and memory was disrupted by blockade of Aβ, suggesting that the physiological effect of the cyclic nucleotide on LTP and memory is dependent upon Aβ.

Combined l-citrulline and glutathione administration prevents neuronal cell death following transient brain ischemia

We previously reported that oral l-citrulline (l-Cit) administration antagonizes neuronal cell death in hippocampus following transient brain ischemia and that oral glutathione (GSH) administration prevents neuronal death through antioxidant activity. Here, we tested potential synergy of combined l-Cit and GSH administration in protection against neuronal death following cerebral ischemia. One day after a 20-min bilateral common carotid artery occlusion (BCCAO), mice were orally administered l-Cit or GSH alone (at 40 or 100mg/kgp.o.) or both (at 40mg/kgp.o. each) daily for 10days. The combination, but not l-Cit or GSH alone at 40mg/kgp.o., significantly prevented neuronal death in the hippocampal CA1 region in BCCAO mice. Consistently, combined l-Cit and GSH administration improved memory-related behavioral deficits observed in BCCAO mice. Combination treatment also significantly rescued reduced endothelial nitric oxide synthase (eNOS) protein levels and antagonized eNOS S-glutathionylation seen following BCCAO ischemia. Recovery of eNOS activity was confirmed by in vivo NO production in hippocampus of BCCAO mice. Taken together, combined administration of l-Cit with GSH rescues eNOS function, thereby inhibiting delayed neuronal death in hippocampus.

Clearing Amyloid-β through PPARγ/ApoE Activation by Genistein is a Treatment of Experimental Alzheimer's Disease

Amyloid-β (Aβ) clearance from brain, which is decreased in Alzheimer's disease, is facilitated by apolipoprotein E (ApoE). ApoE is upregulated by activation of the retinoid X receptor moiety of the RXR/PPARγ dimeric receptor. Genistein, a non-toxic, well-tested, and inexpensive drug activates the other moiety of the receptor PPARγ. Treatment of an Alzheimer's disease mouse model with genistein results in a remarkable and rapid improvement in various parameters of cognition, such as hippocampal learning, recognition memory, implicit memory, and odor discrimination. This is associated with a lowering of Aβ levels in brain, in the number and the area of amyloid plaques (confirmed in vivo by positron emission tomography) as well as in microglial reactivity. Finally, incubation of primary astrocytes with genistein results in a PPARγ-mediated increased release of ApoE. Our results strongly suggest that controlled clinical trials should be performed to test the effect of genistein as treatment of human Alzheimer's disease.

Pharmacological Rescue of Long-Term Potentiation in Alzheimer Diseased Synapses

Long-term potentiation (LTP) is an activity-dependent and persistent increase in synaptic transmission. Currently available techniques to measure LTP are time-intensive and require highly specialized expertise and equipment, and thus are not well suited for screening of multiple candidate treatments, even in animal models. To expand and facilitate the analysis of LTP, here we use a flow cytometry-based method to track chemically induced LTP by detecting surface AMPA receptors in isolated synaptosomes: fluorescence analysis of single-synapse long-term potentiation (FASS-LTP). First, we demonstrate that FASS-LTP is simple, sensitive, and models electrically induced LTP recorded in intact circuitries. Second, we conducted FASS-LTP analysis in two well-characterized Alzheimer's disease (AD) mouse models (3xTg and Tg2576) and, importantly, in cryopreserved human AD brain samples. By profiling hundreds of synaptosomes, our data provide the first direct evidence to support the idea that synapses from AD brain are intrinsically defective in LTP. Third, we used FASS-LTP for drug evaluation in human synaptosomes. Testing a panel of modulators of cAMP and cGMP signaling pathways, FASS-LTP identified vardenafil and Bay-73-6691 (phosphodiesterase-5 and -9 inhibitors, respectively) as potent enhancers of LTP in synaptosomes from AD cases. These results indicate that our approach could provide the basis for protocols to study LTP in both healthy and diseased human brains, a previously unattainable goal.

SIGNIFICANCE STATEMENT

Learning and memory depend on the ability of synapses to strengthen in response to activity. Long-term potentiation (LTP) is a rapid and persistent increase in synaptic transmission that is thought to be affected in Alzheimer's disease (AD). However, direct evidence of LTP deficits in human AD brain has been elusive, primarily due to methodological limitations. Here, we analyze LTP in isolated synapses from AD brain using a novel approach that allows testing LTP in cryopreserved brain. Our analysis of hundreds of synapses supports the idea that AD-diseased synapses are intrinsically defective in LTP. Further, we identified pharmacological agents that rescue LTP in AD, thus opening up a new avenue for drug screening and evaluation of strategies for alleviating memory impairments.

Neuroprotective effects of sildenafil against oxidative stress and memory dysfunction in mice exposed to noise stress

Noise exposure has been well characterized as an environmental stressor, and is known to have auditory and non-auditory effects. Phosphodiesterase 5 (PDE5) inhibitors affect memory and hippocampus plasticity through various signaling cascades which are regulated by cGMP. In this study, we investigated the effects of sildenafil on memory deficiency, neuroprotection and oxidative stress in mice caused by chronic noise exposure. Mice were exposed to noise for 4h every day up to 14days at 110dB SPL of noise level. Sildenafil (15mg/kg) was orally administered 30min before noise exposure for 14days. Behavioral assessments were performed using novel object recognition (NOR) test and radial arm maze (RAM) test. Higher levels of memory dysfunction and oxidative stress were observed in noise alone-induced mice compared to control group. Interestingly, sildenafil administration increased memory performance, decreased oxidative stress, and increased neuroprotection in the hippocampus region of noise alone-induced mice likely through affecting memory related pathways such as cGMP/PKG/CREB and p25/CDK5, and induction of free radical scavengers such as SOD1, SOD2, SOD3, Prdx5, and catalase in the brain of stressed mice.

Possible overlapping time frames of acquisition and consolidation phases in object memory processes: a pharmacological approach

In previous studies, we have shown that acetylcholinesterase inhibitors and phosphodiesterase inhibitors (PDE-Is) are able to improve object memory by enhancing acquisition processes. On the other hand, only PDE-Is improve consolidation processes. Here we show that the cholinesterase inhibitor donepezil also improves memory performance when administered within 2 min after the acquisition trial. Likewise, both PDE5-I and PDE4-I reversed the scopolamine deficit model when administered within 2 min after the learning trial. PDE5-I was effective up to 45 min after the acquisition trial and PDE4-I was effective when administered between 3 and 5.5 h after the acquisition trial. Taken together, our study suggests that acetylcholine, cGMP, and cAMP are all involved in acquisition processes and that cGMP and cAMP are also involved in early and late consolidation processes, respectively. Most important, these pharmacological studies suggest that acquisition processes continue for some time after the learning trial where they share a short common time frame with early consolidation processes. Additional brain concentration measurements of the drugs suggest that these acquisition processes can continue up to 4-6 min after learning.

Renal Integrin-Linked Kinase Depletion Induces Kidney cGMP-Axis Upregulation: Consequences on Basal and Acutely Damaged Renal Function

Soluble guanylyl cyclase (sGC) is activated by nitric oxide (NO) and produces cGMP, which activates cGMP-dependent protein kinases (PKG) and is hydrolyzed by specific phosphodiesterases (PDE). The vasodilatory and cytoprotective capacity of cGMP-axis activation results in a therapeutic strategy for several pathologies. Integrin-linked kinase (ILK), a major scaffold protein between the extracellular matrix and intracellular signaling pathways, may modulate the expression and functionality of the cGMP-axis-related proteins. We introduce ILK as a novel modulator in renal homeostasis as well as a potential target for cisplatin (CIS)-induced acute kidney injury (AKI) improvement. We used an adult mice model of depletion of ILK (cKD-ILK), which showed basal increase of sGC and PKG expressions and activities in renal cortex when compared with wildtype (WT) littermates. Twenty-four h activation of sGC activation with NO enhanced the filtration rate in cKD-ILK. During AKI, cKD-ILK maintained the cGMP-axis upregulation with consequent filtration rates enhancement and ameliorated CIS-dependent tubular epithelial-to-mesenchymal transition and inflammation and markers. To emphasize the role of cGMP-axis upregulation due to ILK depletion, we modulated the cGMP axis under AKI in vivo and in renal cultured cells. A suboptimal dose of the PDE inhibitor ZAP enhanced the beneficial effects of the ILK depletion in AKI mice. On the other hand, CIS increased contractility-related events in cultured glomerular mesangial cells and necrosis rates in cultured tubular cells; ILK depletion protected the cells while sGC blockade with ODQ fully recovered the damage.

From bedside to bench--meeting report of the 7th International Conference on cGMP "cGMP: generators, effectors and therapeutic implications" in Trier, Germany, from June 19th to 21st 2015

During the past decade, our knowledge on the physiology, pathophysiology, basic pharmacology, and clinical pharmacology of the second messenger (cGMP) has increased tremendously. It is now well-established that cGMP, generated by soluble and particulate guanylate cyclases, is highly compartmentalized in cells and regulates numerous body functions. New cGMP-regulated physiological functions include meiosis and temperature perception. cGMP is involved in the genesis of numerous pathologies including cardiovascular, pulmonary, endocrine, metabolic, neuropsychiatric, eye, and tumor diseases. Several new clinical uses of stimulators and activators of soluble guanylate cyclase and of phosphodiesterase inhibitors such as heart failure, kidney failure, cognitive disorders, obesity bronchial asthma, and osteoporosis are emerging. The combination of neprilysin inhibitors-enhancing stimulation of the particulate guanylate cyclase pathway by preventing natriuretic peptide degradation-with angiotensin AT1 receptor antagonists constitutes a novel promising strategy for heart failure treatment. The role of oxidative stress in cGMP signaling, application of cGMP sensors, and gene therapy for degenerative eye diseases are emerging topics. It is anticipated that cGMP research will further prosper over the next years and reach out into more and more basic and clinical disciplines.

Dehydroepiandrosterone administration improves memory deficits following transient brain ischemia through sigma-1 receptor stimulation

Dehydroepiandrosterone (DHEA) is the most abundant neurosteroid synthesized de novo in the central nervous system. Oral DHEA administration elicits neuroprotection and cognitive improvement, but mechanisms underlying these functions in cerebral ischemia have remained unclear. Since DHEA is the endogenous ligand for the sigma-1 receptor (σ1R), we determined whether oral DHEA administration prevents neuronal cell death and improves cognition via σ1R stimulation in brain ischemia using a 20-min bilateral common carotid artery occlusion (BCCAO) mouse model. Twenty-four hours after BCCAO ischemia, mice were administered DHEA (15 or 30mg/kg p.o.) daily for 11 consecutive days. Memory deficits following brain ischemia were improved by DHEA administration dose-dependently. Accordingly, DHEA administration significantly prevented neuronal cell death in the hippocampal CA1 region in BCCAO mice. Interestingly, DHEA administration rescued decreases in Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and phosphorylation of extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) in the CA1 region. Moreover, DHEA administration significantly ameliorated decreases in adenosine 5'-triphosphate (ATP) levels and decreased σ1R expression levels in CA1 following BCCAO ischemia. Finally, co-treatment of mice with the σ1R antagonist NE-100 (1mg/kg, p.o.) blocked DHEA effects on memory improvement and neuroprotection in ischemic mice. Taken together, DHEA prevents neuronal cell death and activates CaMKII via σ1R stimulation, thereby improving cognitive deficits following brain ischemia.

Phosphodiesterase-4 inhibitors ameliorates cognitive deficits in deoxycorticosterone acetate induced hypertensive rats via cAMP/CREB signaling system

Phosphodiesterase-4 (PDE-4) inhibitors promote memory by blocking the degradation of cAMP. Existing evidence also shows that neuronal survival and plasticity are dependent on the phosphorylation of cAMP-response element-binding protein. In this regard, PDE-4 inhibitors have also been shown to reverse pharmacologically and genetically induced memory impairment in animal models. In the present study, the authors examined the effect of both rolipram and roflumilast (PDE-4 inhibitors) on the impairment of learning and memory observed in hypertensive rats. Deoxycorticosterone acetate (DOCA) salt hypertensive model was used to induce learning and memory deficits. The mRNA expression of different PDE-4 subtypes along with the protein levels of pCREB and BDNF in the hippocampus was quantified. Systolic blood pressure was significantly increased in DOCA salt hypertensive rats when compared to sham operated rats. This effect was reversed by clonidine, an α2 receptor agonist, while PDE-4 inhibitors did not. PDE-4 inhibitors significantly improved the time-induced memory deficits in object recognition task (ORT). In DOCA salt hypertensive rats, the gene expression of PDE-4B and PDE-4D was significantly increased. Furthermore, both pCREB and BDNF showed decreased levels of expression in hypertensive rats in comparison to sham operated rats. Repeated administration of PDE-4 inhibitors significantly decreased both PDE-4B and PDE-4D with an increase in the expression of pCREB and BDNF in hypersensitive rats. Also, rolipram, roflumilast and roflumilast N-oxide showed a linear increase in the plasma and brain concentrations after ORT. Our present findings suggested that PDE-4 inhibitors ameliorate hypertension-induced learning impairment via cAMP/CREB signaling that regulates BDNF expression downstream in the rat hippocampus.

Herbs to curb cyclic nucleotide phosphodiesterase and their potential role in Alzheimer's disease

Cyclic nucleotides viz., cAMP/cGMP has been well known to play important role in cellular function and deficiency in their levels has been implicated in the pathogenesis of various neurodegenerative disorders including Alzheimer's disease (AD). Phosphodiesterases (PDE) are the enzymes involved in the metabolism of cyclic nucleotides and the inhibition of phosphodiesterases is considered to be viable strategy to restore the level of cyclic nucleotides and their functions in the brain. Various synthetic PDE inhibitors had been used clinically for various disorders and also suggested to be useful candidates for treating neurological disorders. However, side effects of these synthetic PDE inhibitors have limited their use in clinical practice. Natural plant extracts or their bio-active compounds are considered to be safe and are widely acceptable. During the last decade, many plant extracts or their bio-active compounds were tested pre-clinically for PDE inhibitory activity and are reported to be equally potent in inhibiting PDE's, as that of synthetic compounds. The present review is aimed to discuss the potential plant extract/compounds with PDE inhibitory activity and critically discuss their potential role in Alzheimer's disease.