cyclic-gmp and Alzheimer-Disease

Alzheimer's disease (AD), one of the greatest threats to human health, is characterized by declined cognition and changed behavior. Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) that play an important role in learning and memory are hydrolyzed by phosphodiesterases (PDEs). Most PDE isoforms are highly expressed in the brain, and the inhibition of PDEs is beneficial to counteract AD. Thus, targeting PDEs represents a therapeutic potential for this disease. So far, a variety of PDE inhibitors have been discovered with significant cognitive enhancement effects in animal models and more than ten agents have entered into clinical trials. In this review, we summarize PDE mediated cyclic nucleotide signaling pathways, PDE family members involved in AD and recent advance of PDE inhibitors in preclinical and clinical studies, trying to provide an outlook of PDE inhibitors for the treatment of AD in future.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Alzheimer Disease; Animals; Cognition; Cyclic GMP; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases

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

Topics: Alzheimer Disease; Calcium Signaling; Cyclic GMP; Humans; Inositol 1,4,5-Trisphosphate Receptors; Molecular Targeted Therapy; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Signal Transduction

Cyclic guanosine monophosphate (cGMP) is a ubiquitous second messenger and a key molecule in many important signaling cascades in the body and brain, including phototransduction, olfaction, vasodilation, and functional hyperemia. Additionally, cGMP is involved in long-term potentiation (LTP), a cellular correlate of learning and memory, and recent studies have identified the cGMP-increasing drug Sildenafil as a potential risk modifier in Alzheimer's disease (AD). AD development is accompanied by a net increase in the expression of nitric oxide (NO) synthases but a decreased activity of soluble guanylate cyclases, so the exact sign and extent of AD-mediated imbalance remain unclear. Moreover, human patients and mouse models of the disease present with entangled deregulation of both cGMP and Ca

Topics: Alzheimer Disease; Animals; Calcium; Calcium Signaling; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Long-Term Potentiation; Mice; Nitric Oxide; Nitric Oxide Synthase

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

Topics: Alzheimer Disease; Animals; Cyclic AMP; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 7; Multiple Sclerosis; Neurodegenerative Diseases; Parkinson Disease

The nitric oxide (NO)/cGMP pathway has been extensively studied for its pivotal role in synaptic plasticity and memory processes, resulting in an increase of cAMP response element-binding (CREB) phosphorylation, and consequent synthesis of plasticity-related proteins. The NO/cGMP/CREB signaling is downregulated during aging and neurodegenerative disorders and is affected by Amyloid-β peptide (Aβ) and tau protein, whose increase and deposition is considered the key pathogenic event of Alzheimer's disease (AD). On the other hand, in physiological conditions, the crosstalk between the NO/cGMP/PKG/CREB pathway and Aβ ensures long-term potentiation and memory formation. This review summarizes the current knowledge on the interaction between the NO/cGMP/PKG/CREB pathway and Aβ in the healthy and diseased brain, offering a new perspective to shed light on AD pathophysiology. We will focus on the synaptic mechanisms underlying Aβ physiological interplay with cGMP pathway and how this balance is corrupted in AD, as high levels of Aβ interfere with NO production and cGMP molecular signaling leading to cognitive impairment. Finally, we will discuss results from preclinical and clinical studies proposing the increase of cGMP signaling as a therapeutic strategy in the treatment of AD.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Cyclic GMP; Humans; Nitric Oxide; Signal Transduction

Nitric oxide (NO) is a gaseous molecule that plays a multifactorial role in several cellular processes. In the central nervous system, the NO dual nature in neuroprotection and neurotoxicity has been explored to unveil its involvement in Alzheimer's disease (AD). A growing body of research shows that the activation of the NO signaling pathway leading to the phosphorylation of the transcription factor cyclic adenine monophosphate responsive element binding protein (CREB) (so-called NO/cGMP/PKG/CREB signaling pathway) ameliorates altered neuroplasticity and memory deficits in AD animal models. In addition to NO donors, several other pharmacological agents, such as phosphodiesterase 5 (PDE5) inhibitors have been used to activate the pathway and rescue memory disorders. PDE5 inhibitors, including sildenafil, tadalafil and vardenafil, are marketed for the treatment of erectile dysfunction and arterial pulmonary hypertension due to their vasodilatory properties. The ability of PDE5 inhibitors to interfere with the NO/cGMP/PKG/CREB signaling pathway by increasing the levels of cGMP has prompted the hypothesis that PDE5 inhibition might be used as an effective therapeutic strategy for the treatment of AD. To this end, newly designed PDE5 inhibitors belonging to different chemical classes with improved pharmacologic profile (e.g. higher potency, improved selectivity, and blood-brain barrier penetration) have been synthesized and evaluated in several animal models of AD. In addition, recent medicinal chemistry effort has led to the development of agents concurrently acting on the PDE5 enzyme and a second target involved in AD. Both marketed and investigational PDE5 inhibitors have shown to reverse cognitive defects in young and aged wild type mice as well as transgenic mouse models of AD and tauopathy using a variety of behavioral tasks. These studies confirmed the therapeutic potential of PDE5 inhibitors as cognitive enhancers. However, clinical studies assessing cognitive functions using marketed PDE5 inhibitors have not been conclusive. Drug discovery efforts by our group and others are currently directed towards the development of novel PDE5 inhibitors tailored to AD with improved pharmacodynamic and pharmacokinetic properties. In summary, the present perspective reports an overview of the correlation between the NO signaling and AD, as well as an outline of the PDE5 inhibitors used as an alternative approach in altering the NO pathway leading to an improvement

Topics: Alzheimer Disease; Animals; Cyclic AMP Response Element-Binding Protein; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Disease Models, Animal; Humans; Nitric Oxide; Phosphodiesterase 5 Inhibitors; Signal Transduction

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.

Topics: Alzheimer Disease; Animals; Cyclic AMP; Cyclic GMP; Humans; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Signal Transduction

Alzheimer's disease (AD), characterized by a progressive impairment of memory and cognition, is a major health problem in both developing and developed countries. Currently, no drugs can reverse the progression of AD. Phosphodiesterase 5 (PDE5) is a critical component of the cyclic guanosine monophosphate/protein kinase G (cGMP/PKG) signaling pathway in neurons, the inhibition of which has produced neuroprotective effects, and PDE5 inhibitors have recently been thought to be potential therapeutic agents for AD. In this paper, we summarized the outstanding progress that has been made in PDE5 inhibitors as anti-AD agents with encouraging results in animal studies, clinical trials and the investigations on the underlying mechanisms. The novel PDE5 inhibitors reported recently in the treatment of AD were also reviewed and discussed.

Topics: Alzheimer Disease; Animals; Cognition; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Cyclic Nucleotide Phosphodiesterases, Type 5; Flavonoids; Humans; Neurons; Neuroprotective Agents; Phosphodiesterase 5 Inhibitors; Purinones; Pyrimidines; Signal Transduction; Sildenafil Citrate; Sulfonamides; Tadalafil; Vardenafil Dihydrochloride

cAMP and cGMP are well established second messengers required for long-term potentiation (LTP) and memory formation/consolidation. By contrast, amyloid β (Aβ), mostly known as one of the main culprits for Alzheimer's disease (AD), has received relatively little attention in the context of plasticity and memory. Of note, however, low physiological concentrations of Aβ seem necessary for LTP induction and for memory formation. This should come as no surprise, since hormesis emerged as a central dogma in biology. Additionally, recent evidence indicates that Aβ is one of the downstream effectors for cAMP and cGMP to trigger synaptic plasticity and memory. We argue that these emerging findings depict a new scenario that should change the general view on the amyloidogenic pathway, and that could have significant implications for the understanding of AD and its pharmacological treatment in the future.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Cyclic AMP; Cyclic GMP; Humans; Memory

Phosphodiesterase (PDE) inhibitors improve signaling pathways in brain circuits by increasing intracellular cyclic adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP). In the last decade, the first clinical studies investigating selective PDE inhibitors in Alzheimer's disease (AD) have been initiated, based on their positive effects on cognitive processes and neuroprotection in numerous animal studies. Areas covered: This article reviews the clinical studies investigating the pro-cognitive/neuroprotective effects of PDE inhibitors in patients with AD, as well as in age-associated memory impaired elderly and patients with mild cognitive impairment (MCI), the prodromal stage of AD. PDE inhibitors will also be discussed with respect to adverse effects including safety and tolerability. Expert opinion: The limited available data of clinical studies with PDE inhibitors tested in different populations of AD patients do not allow the drawing of any concrete conclusion yet. Currently, studies with a PDE3 (cilostazol) or PDE9 inhibitor (BI 409,306) are still ongoing in patients with MCI or AD, respectively. Studies with PDE4 inhibitors (HT-0712, roflumilast and BPN14770) in healthy elderly and elderly with age-associated memory impairments indicate that the optimum dose and/or inhibiting the most relevant PDE isoform hold great promise when tested in the appropriate population of patients with MCI or AD eventually.

Topics: Aged; Alzheimer Disease; Animals; Clinical Trials, Phase I as Topic; Clinical Trials, Phase II as Topic; Cognitive Dysfunction; Cyclic AMP; Cyclic GMP; Drug Design; Drugs, Investigational; Humans; Phosphodiesterase Inhibitors; Signal Transduction

Cyclic nucleotide PDEs are a super-family of enzymes responsible for regulating intracellular levels of the second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Through their catalysis, PDEs are able to exert tight regulation over these important intracellular signaling cascades. Previously, PDEs have been implicated in learning and memory, as well as in mood disorders, such as anxiety and depression. PDE2 is of special interest due to its high level of expression in the forebrain, specifically in the isocortex, entorhinal cortex, striatum, hippocampus, amygdala, and medial habenula. Many of these brain regions are considered participants of the limbic system, which is known as the emotional regulatory center of the brain, and is important for modulating emotion and long-term memory. Therefore, PDE2s coincidental expression in these areas suggests an important role for PDE2 in these behaviors, and researchers are continuing to uncover the complex connections. It was shown that PDE2 inhibitors have pro-cognitive effects in tests of memory, including the object recognition test. PDE2 inhibitors are also protective against cognitive deficits in various models of cognitive impairment. Additionally, PDE2 inhibitors are protective against many different forms of stress-induced anxiety-like and depression-like behaviors. Currently, there is a great need for novel therapeutics for the treatment of mood and cognitive disorders, especially anxiety and depression, and other neurodegenerative diseases, such as Alzheimer's disease, and PDE2 is emerging as a viable target for future drug development for many of these diseases.

Topics: Alzheimer Disease; Anxiety Disorders; Brain; Cyclic AMP; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 2; Depressive Disorder; Humans; Mental Disorders; Neurodegenerative Diseases; Phosphodiesterase Inhibitors; Stress, Psychological

In the central nervous system endothelial nitric oxide (NO) is an essential molecule responsible for the preservation of the functional integrity of the neurovascular unit. NO causes vasodilatation and is an important inhibitor of platelet aggregation, smooth muscle cell proliferation, and white blood cell adhesion. In addition, endothelium-derived NO exerts anti-inflammatory and pro-angiogenic effects. More recently, it has been recognized that endothelial NO modulates the expression and processing of amyloid precursor protein in cerebrovascular endothelium and neuronal tissue. Studies in endothelial NO synthase (eNOS) knockout mice indicate that endothelial NO functions as a neurovascular protective molecule during aging. Indeed, genetic inactivation of eNOS exacerbates the detrimental effects of aging on cerebrovascular, microglial, and neuronal functions as well as on cognition. These findings suggest that the preservation of healthy endothelium and normal function of eNOS might be important therapeutic targets. Because the beneficial effects of NO are mostly mediated by the activation of guanylate cyclase/cyclic GMP signaling, inhibitors of phosphodiesterase isoforms, or activation of this signaling with exercise, may offer therapeutic opportunities in the prevention and treatment of aging-induced cognitive decline and Alzheimer's disease. Most recent advances in understanding the molecular mechanisms linking loss of endothelial NO with cognitive decline will be discussed in this review. (Circ J 2016; 80: 1499-1503).

Topics: Alzheimer Disease; Animals; Cognition; Cyclic GMP; Endothelium, Vascular; Humans; Mice; Mice, Knockout; Microglia; Neurons; Nitric Oxide; Nitric Oxide Synthase Type III; Second Messenger Systems

cAMP-response element-binding protein (CREB) plays a central role in various aspects of central nervous system (CNS) function, ranging from the developmental stages to neuronal plasticity and survival in adult brain. Activation of CREB plays a crucial role in learning and memory and is at the convergence of multiple intracellular signaling cascades including CAMKII and MAPK. This review focuses on the important functions of nitric oxide (NO) in activating CREB via the NO receptor, soluble guanylyl cyclase (sGC), and production of the second messenger, cGMP. The involvement of the NO/cGMP signaling pathway in synaptic plasticity suggests several avenues for therapeutic intervention, and targeting early synaptic degeneration could be an attractive approach for the development of novel disease-modifying approaches to treat cognition and memory dysfunction in neurodegenerative diseases.

Topics: Alzheimer Disease; Central Nervous System; CREB-Binding Protein; Cyclic GMP; Humans; Neurodegenerative Diseases; Neuronal Plasticity; Nitric Oxide; Phosphoric Diester Hydrolases; Signal Transduction; Soluble Guanylyl Cyclase; Synapses

Neuronal inflammation is a systematically organized physiological step often triggered to counteract an invading pathogen or to rid the body of damaged and/or dead cellular debris. At the crux of this inflammatory response is the deployment of nonneuronal cells: microglia, astrocytes, and blood-derived macrophages. Glial cells secrete a host of bioactive molecules, which include proinflammatory factors and nitric oxide (NO). From immunomodulation to neuromodulation, NO is a renowned modulator of vast physiological systems. It essentially mediates these physiological effects by interacting with cyclic GMP (cGMP) leading to the regulation of intracellular calcium ions. NO regulates the release of proinflammatory molecules, interacts with ROS leading to the formation of reactive nitrogen species (RNS), and targets vital organelles such as mitochondria, ultimately causing cellular death, a hallmark of many neurodegenerative diseases. AD is an enervating neurodegenerative disorder with an obscure etiology. Because of accumulating experimental data continually highlighting the role of NO in neuroinflammation and AD progression, we explore the most recent data to highlight in detail newly investigated molecular mechanisms in which NO becomes relevant in neuronal inflammation and oxidative stress-associated neurodegeneration in the CNS as well as lay down up-to-date knowledge regarding therapeutic approaches targeting NO.

Topics: Alzheimer Disease; Animals; Cyclic GMP; Humans; Inflammation; Nitric Oxide; Nitric Oxide Synthase; Oxidative Stress; Signal Transduction

Nitric oxide (NO)/solube GC (sGC)/cGMP signaling is important for modulating synaptic transmission and plasticity in the hippocampus and cerebral cortex, which are critical for learning and memory. Physiological concentrations of NO also elicit anti-apoptotic/prosurvival effects against various neurotoxic challenges and brain insults through multiple mechanisms. Depression of the NO/sGC pathway is a feature of Alzheimer's disease (AD), attributed to amyloid-β neuropathology, and altered expression and activity of NOS, sGC and PDE enzymes. Different classes of NO-releasing hybrid drugs, including nomethiazoles, NO-NSAIDs and NO-acetylcholinesterase inhibitors were designed to deliver low concentrations of exogenous NO to the CNS while targeting other underlying disease mechanisms, such as excitotoxicity, neuro-inflammation and acetylcholine deficiency, respectively. Incorporating a NO-donating moiety may also reduce gastrointestinal and liver toxicity of the parent drugs. Progress has also been made in targeting downstream sGC and PDE enzymes. The PDE9 inhibitor PF-04447943 has completed Phase II clinical trials for AD. The search for effective NO-donating hybrid drugs, CNS-targeting sGC stimulators/activators and selective PDE inhibitors is an important goal for pharmacotherapy that manipulates NO biochemical pathways involved in cognitive function and neuroprotection. Rigorous preclinical validation of target engagement, and optimization of pharmacokinetic and toxicity profiles are likely to advance more drug candidates into clinical trials for mild cognitive impairment and early stage AD.

Topics: Alzheimer Disease; Central Nervous System; Cyclic GMP; Enzyme Inhibitors; Guanylate Cyclase; Humans; Nitric Oxide; Nitric Oxide Synthase; Phosphoric Diester Hydrolases; Receptors, Cytoplasmic and Nuclear; Signal Transduction; Soluble Guanylyl Cyclase

Sphingolipids represent a major class of lipids in which selected family members act as bioactive molecules that control diverse cellular processes, such as proliferation, differentiation, growth, senescence, migration and apoptosis. Emerging evidence reveals that sphingomyelinase/ceramide pathway plays a pivotal role in neurodegenerative diseases that involve mitochondrial dysfunction, oxidative stress and apoptosis. Minocycline, a semi-synthetic second-generation tetracycline derivative in clinical use for infection control, is also considered an effective protective agent in various neurodegenerative diseases in pre-clinical studies. Acting via multiple mechanisms, including anti-inflammatory, anti-oxidative and anti-apoptotic effects, minocycline is a desirable candidate for clinical trials in both acute brain injury as well as chronic neurodegenerative disorders. This review is focused on the anti-apoptotic and anti-oxidative mechanisms of minocycline against neurotoxicity induced by sphingomyelinase/ceramide in relation to neurodegeneration, particularly Alzheimer's disease and cerebral ischemia.

Topics: Alzheimer Disease; Antioxidants; Apoptosis; Brain Ischemia; Ceramides; Cyclic GMP; Humans; Minocycline; Mitochondria; Nitric Oxide; Oxidative Stress; Proto-Oncogene Proteins c-bcl-2; Signal Transduction; Sphingomyelin Phosphodiesterase; Thioredoxins

Cyclic guanosine monophosphate (cGMP) is an important secondary messenger synthesized by the guanylyl cyclases which are found in the soluble (sGC) and particular isoforms. In the central nervous system, the nitric oxide (NO)-sensitive sGC isoform is the major enzyme responsible for cGMP synthesis. Phosphodiesterases (PDEs) are enzymes for hydrolysis of cGMP in the brain, and they are mainly isoforms 2, 5, and 9. The NO/cGMP signaling pathway has been shown to play an important role in the process underlying learning and memory. Aging is associated with an increase in PDE expression and activity and a decrease in cGMP concentration. In addition, aging is also associated with an enhancement of neuronal NO synthase, a lowering of endothelial, and no alteration in inducible activity. The observed changes in NMDA receptor density along with the Ca(2+)/NO/cGMP pathway underscore the lower synaptic plasticity and cognitive performance during aging. This notion is in agreement with last data indicating that inhibitors of PDE2 and PDE9 improve learning and memory in older rats. In this review, we focus on recent studies supporting the role of Ca(2+)/NO/cGMP pathway in aging and Alzheimer's disease.

Topics: Aging; Alzheimer Disease; Animals; Cognition; Cyclic GMP; Guanylate Cyclase; Humans; Nitric Oxide Synthase; Phosphoric Diester Hydrolases; Protein Isoforms; Signal Transduction

Amyloid-beta (Abeta), a peptide thought to play a crucial role in Alzheimer's disease (AD), has attracted scientific interest with the aim of characterizing the mechanisms by which it is involved in AD pathogenesis. Abeta has been found to markedly impair hippocampal long-term potentiation (LTP), a widely studied cellular model of synaptic plasticity that is thought to underlie learning and memory. The overall purpose of this review is to define the role of the nitric oxide (NO)/cGMP/cAMP-regulatory element binding (CREB) pathway in beta-amyloid-induced changes of basal neurotransmission and synaptic plasticity in the hippocampus, a structure within the temporal lobe of the brain critical for memory storage.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Cyclic AMP Response Element-Binding Protein; Cyclic GMP; Hippocampus; Humans; Long-Term Potentiation; Neuronal Plasticity; Nitric Oxide; Synapses

A pathological glia activation, stimulated by inflammatory proteins, beta-amyloid, or brain ischemia, is discussed as a common pathogenic factor for progressive nerve cell damage in vascular and Alzheimer dementia. A critical point seems to be reached, if the cytokine-controlled microglial upregulation causes a secondary activation of astrocytes which loose the negative feedback control, are forced to give up their physiological buffering function, and may add to neuronal damage by the release of nitric oxide (NO) and by promoting toxic beta-amyloid formation. A strengthening of the cyclic adenosine-5',3'-monophosphate (cAMP) signaling exerted a differential inhibition of the stimulatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) released from cultured rat microglia, but maintained the negative feedback signal IL-6; cAMP inhibited also the release of free oxygen radicals (OR) but not of NO. Reinforcement of the NO-induced cyclic guanosine monophosphate (cGMP) increase by blockade of the phosphodiesterase (PDE) subtype-5 with propentofylline counterbalanced the toxic NO action that causes with OR neuronal damage by peroxynitrate formation. In rat cultured astrocytes, a prolonged cAMP elevation favored cell differentiation, the expression of a mature ion channel patter, and an improvement of the extracellular glutamate uptake. Cyclic AMP signaling could be strengthened by PDE blockade and by raising extracellular adenosine, which stimulates A2 receptor-mediated cAMP synthesis. Via an A1 receptor-mediated effect, elevated adenosine was found to overcome a deficient intracellular calcium mobilization resulting from an impaired muscarinic signaling at pathologically decreased acetylcholine concentrations. We suggest that pharmaca, which elevate extracellular adenosine and/or block the degradation of cyclic nucleotides, may be used to counteract glia-related neuronal damage in dementing processes.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Astrocytes; Cyclic AMP; Cyclic GMP; Dementia, Vascular; Humans; Inflammation; Microglia; Models, Neurological; Neuroglia; Rats; Signal Transduction

Our previous study suggested that inhibition of Phosphodiesterase 2 ameliorates memory loss upon exposure to oxidative stress. While whether memory enhancing effects of PDE2 inhibition on Alzheimer's disease mouse model are involved in antioxidant defense and neuronal remodeling, are largely unexplored. The present study addressed whether and how PDE2 inhibitor Bay 60-7550 rescued Aβ oligomers (Aβo)-induced neuronal damage and memory impairment. The results suggested that exposure of primary cortical neurons to Aβo induced neuronal cells damage and increased PDE2 expression, which were paralleled to an increase in the oxidative parameter malondialdehyde (MDA) level and cellular apoptosis. However, this Aβo-induced oxidative damage was blocked by pre-treatment with protein kinase A or G (PKA or PKG) inhibitor, suggesting the involvement of cAMP/cGMP signaling. Moreover, microinjection of Aβo into the prefrontal cortex of mice increased the MDA level; while Bay 60-7550 reversed this effect and increased antioxidant and anti-apoptotic factors, i.e. increased trolox-equivalent-antioxidant capacity and Bcl-2/Bax ratio. Bay 60-7550 also rescued Aβo-induced synaptic atrophy and memory deficits, as evidenced by the increased synaptic proteins' levels and spine density in the prefrontal cortex, and improved cognitive behaviors by decreased working memory errors in the eight-arm maze and increased discrimination index in the novel object recognition test. These findings suggest that inhibition of PDE2 contributes to antioxidant defense and neuronal remodeling by regulation of cAMP/cGMP signaling, which provide a theoretical basis for the future use of PDE2 inhibitors as the anti-AD drugs.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Antioxidants; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 2; Hippocampus; Memory Disorders; Mice; Mice, Inbred ICR; Neurons; Peptide Fragments; Phosphodiesterase Inhibitors

Alzheimer's disease (AD) pathology is associated with complex interactions among multiple factors, involving an intertwined network of various signaling pathways. The polypharmacological approach is an emerging therapeutic strategy that has been proposed to overcome the multifactorial nature of AD by targeting multiple pathophysiological factors including amyloid-β (Aβ) and phosphorylated tau. We evaluated a blood-brain barrier penetrating phosphodiesterase 5 (PDE5) inhibitor, mirodenafil (5-ethyl-2-7-n-propyl-3,5-dihydrro-4H-pyrrolo[3,2-d]pyrimidin-4-one), for its therapeutic effects on AD with polypharmacological properties.. To evaluate the potential of mirodenafil as a disease-modifying AD agent, mirodenafil was administered to test its effects on the cognitive behaviors of the APP-C105 AD mouse model using the Morris water maze and passive avoidance tests. To investigate the mechanisms of action that underlie the beneficial disease-modifying effects of mirodenafil, human neuroblastoma SH-SY5Y cells and mouse hippocampal HT-22 cells were used to show mirodenafil-induced alterations associated with the cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase (PKG)/cAMP-responsive element-binding protein (CREB) pathway, apoptotic cell death, tau phosphorylation, amyloidogenesis, the autophagy-lysosome pathway, glucocorticoid receptor (GR) transcriptional activity, and the Wnt/β-catenin signaling.. Here, mirodenafil is demonstrated to improve cognitive behavior in the APP-C105 mouse model. Mirodenafil not only reduced the Aβ and phosphorylated tau burdens in vivo, but also ameliorated AD pathology induced by Aβ through the modulation of the cGMP/PKG/CREB signaling pathway, glycogen synthase kinase 3β (GSK-3β) activity, GR transcriptional activity, and the Wnt/β-catenin signaling in neuronal cells. Interestingly, homodimerization and nuclear localization of GR were inhibited by mirodenafil, but not by other PDE5 inhibitors. In addition, only mirodenafil reduced the expression levels of the Wnt antagonist Dickkopf-1 (Dkk-1), thus activating the Wnt/β-catenin signaling.. These findings strongly suggest that the PDE5 inhibitor mirodenafil shows promise as a potential polypharmacological drug candidate for AD treatment, acting on multiple key signaling pathways involved in amyloid deposition, phosphorylated tau burden, the cGMP/PKG/CREB pathway, GSK-3β kinase activity, GR signaling, and the Wnt/β-catenin signaling. Mirodenafil administration to the APP-C105 AD mouse model also improved cognitive behavior, demonstrating the potential of mirodenafil as a polypharmacological AD therapeutic agent.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; beta Catenin; Cyclic GMP; Disease Models, Animal; Glycogen Synthase Kinase 3 beta; Humans; Mice; Neuroblastoma; Phosphodiesterase 5 Inhibitors; Phosphorylation; Pyrimidinones; Sulfonamides; tau Proteins

Alzheimer disease (AD) is a chronic neurodegenerative disease with multi-pathways pathogenesis. Sildenafil is a selective phosphodiesterase-5 inhibitor with a potential benefit in the treatment of AD. This study investigated the possible mechanisms underlying the effect of sildenafil in AD with emphasis on vascular endothelial growth factor (VEGF), and vascular cell adhesion molecule-1 (VCAM-1). Twenty-four adult male rats were classified into four groups; control group: received vehicles, sildenafil-control: received sildenafil (15 mg/kg/day, p.o.), AD group received Aluminum (25 mg/kg/day, p.o.), AD-treated group: received sildenafil (15 mg/kg/day, p.o.) for 6 weeks. AD was assessed by memory performance test and confirmed by histopathological examination and immunostaining of, neurogenesis marker nestin and α-synuclein. The levels of VEGF-A, VCAM-1, oxidative stress markers and TNF-α in brain tissue were evaluated. AD rats showed histopathological evidences of AD; along with increased latency time in the memory test. There was a decrease in VEGF-A, and an increase in VCAM-1, TNF-α, and oxidative stress markers. Immunohistochemical study showed a significant increase in α-synuclein and a significant decrease in nestin expressions in brain tissues. Sildenafil administration ameliorated the histopathological changes and decreased latency time. Such effect was associated with a decrease in VCAM-1, TNF-α and oxidative stress as well as an increase in VEGF-A. Sildenafil caused a significant increase in nestin and a decrease in α-synuclein immunostaining. These findings suggested a protective effect of sildenafil via modulation of VEGF-A, and VCAM-1.

Topics: alpha-Synuclein; Aluminum Chloride; Alzheimer Disease; Animals; Brain; Cyclic GMP; Glutathione; Male; Malondialdehyde; Memory; Nestin; Neuroprotective Agents; Nitric Oxide; Oxidative Stress; Rats; Sildenafil Citrate; Superoxide Dismutase; Tumor Necrosis Factor-alpha; Vascular Cell Adhesion Molecule-1; Vascular Endothelial Growth Factor A

Alzheimer's disease (AD) is the most prevalent age-dependent neurodegenerative disease characterized by progressive impairment of memory and cognitive functions. Cyclic nucleotides like cAMP and cGMP are well-known to play an important role in learning and memory functions. Enhancement of cAMP and cGMP levels in the hippocampus by phosphodiesterase (PDE) inhibitors might be a novel therapeutic approach for AD. Thus, the present study was planned to explore the therapeutic potential of roflumilast (RFM) and tadalafil (TDF) phosphodiesterase inhibitors in intracerebroventricular (ICV) Aβ1-42 induced AD in rats.. ICV Aβ1-42 was administered in rats followed by treatment with RFM (0.05 mg/kg) and TDF (0.51 mg/kg) for 15 days. Novel object recognition (NOR), and Morris water maze (MWM) test were performed during the drug treatment schedule. On the day, 22 rats were sacrificed, and hippocampus was separated for biochemical, neuroinflammation, and histopathological analysis.. Aβ1-42 infused rats were induce behavioral impairment and increased AChE, BACE-1, Aβ1-42, GSK-3β, phosphorylated tau (p-Tau), pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) levels, oxidative stress (increased MDA, Nitrite and decreased GSH), histopathological changes, and reduced cAMP, cGMP, and BDNF levels. RFM and TDF significantly attenuated Aβ1-42 induced memory deficits and neuropathological alterations in the hippocampus.. The outcomes of the current study indicate that RFM and TDF lead to memory enhancement through upregulation of cAMP/cGMP/BDNF pathway, thus they may have a therapeutic potential in cognitive deficits associated with AD.

Topics: Alzheimer Disease; Aminopyridines; Amyloid beta-Peptides; Animals; Benzamides; Brain-Derived Neurotrophic Factor; Cyclic AMP; Cyclic GMP; Cyclopropanes; Cytokines; Gene Expression Regulation; Hippocampus; Male; Memory Disorders; Morris Water Maze Test; Oxidative Stress; Peptide Fragments; Random Allocation; Rats; Rats, Wistar; Tadalafil; Vasodilator Agents

We previously demonstrated that cyclic guanosine monophosphate (cGMP) stimulates amyloid precursor protein (APP) and beta-secretase (BACE1) approximation in neuronal endo-lysosomal compartments, thus boosting the production of amyloid-β (Aβ) peptides and enhancing synaptic plasticity and memory. Here, we further investigated the mechanism by which cGMP regulates the subcellular localization of APP and BACE1, finding that the cyclic nucleotide inhibits the activity of Rab5, a small GTPase associated with the plasma membrane and early endosomes. Accordingly, we also found that expression of a dominant-negative Rab5 mutant increases both APP-BACE1 approximation and Aβ extracellular levels, therefore mimicking the effects induced by cGMP. These results reveal a functional correlation between the cGMP/Aβ pathway and the activity of Rab5 that may contribute to the understanding of Alzheimer's disease pathophysiology.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Amyloid Precursor Protein Secretases; Animals; Aspartic Acid Endopeptidases; Cell Line; Cell Membrane; Cyclic GMP; Endosomes; Mice; rab5 GTP-Binding Proteins; Second Messenger Systems

Icariside II (ICS II) is an active component from Epimedium brevicornum, a Chinese medicine extensively used in China. Our previous study has proved that ICS II protects against learning and memory impairments and neuronal apoptosis in the hippocampus induced by beta-amyloid25-35 (Aβ25-35) in rats. However, its in-depth underlying mechanisms remain still unclear. Hence this study was designed to explore the potential underlying mechanisms of ICS II by experiments with an in vivo model of Aβ25-35-induced cognitive deficits in rats combined with a neuronal-like PC12 cells injury in vitro model.. The cognitive deficits was measured using Morris water maze test, and apoptosis, intracellular reactive oxygen species (ROS) and mitochondrial ROS levels were detected by TUNEL, DCFH-DA and Mito-SOX staining, respectively. Expression of Bcl-2, Bax, brain derived neurotrophic factor (BDNF), tyrosine receptor kinase B (TrkB), and cAMP response element binding (p-CREB) and active-Caspase 3 levels were evaluated by Western blot.. It was found that ICS II, a phosphodiesterase-5 inhibitor, significantly attenuated cognitive deficits caused by Aβ25-35 injection in rats, and ICS II not only significantly enhanced the expression of BDNF and TrkB, but also activated CREB. Furthermore, ICS II also significantly abrogated Aβ25-35-induced PC12 cell injury, and inhibited Aβ25-35-induced intracellular reactive oxygen species (ROS) overproduction, as well as mitochondrial ROS levels. In addition, ICS II up-regulated the expressions of BDNF and TrkB consistent with the findings in vivo. ANA-12, a TrkB inhibitor, blocked the neuroprotective effect of ICS II on Aβ25-35-induced neuronal injury.. ICS II mitigates Aβ25-35-induced cognitive deficits and neuronal cell injury by upregulating the BDNF/TrkB/CREB signaling, suggesting that ICS II can be used as a potential therapeutic agent for dementia, such as Alzheimer's disease.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Apoptosis; Brain-Derived Neurotrophic Factor; Caspase 3; Cyclic AMP Response Element-Binding Protein; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 5; Flavonoids; Hippocampus; Male; Maze Learning; PC12 Cells; Peptide Fragments; Proto-Oncogene Proteins c-bcl-2; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Receptor, trkB; Signal Transduction

Phosphodiesterase 5 (PDE5) hydrolyzes cyclic guanosine monophosphate (cGMP) leading to increased levels of the cAMP response element binding protein (CREB), a transcriptional factor involved with learning and memory processes. We previously reported potent quinoline-based PDE5 inhibitors (PDE5Is) for the treatment of Alzheimer's disease (AD). However, the low aqueous solubility rendered them undesirable drug candidates. Here we report a series of novel PDE5Is with two new scaffolds, 1,2,3,4-tetrahydrobenzo[b][1,6]naphthyridine and 2,3-dihydro-1H-pyrrolo[3,4-b]quinolin-1-one. Among them, compound 6c, 2-acetyl-10-((3-chloro-4-methoxybenzyl)amino)-1,2,3,4-tetrahydrobenzo[b][1,6]naphthyridine-8-carbonitrile, the most potent compound, has an excellent in vitro IC

Topics: Alzheimer Disease; Animals; Binding Sites; Cyclic AMP Response Element-Binding Protein; Cyclic GMP; Humans; Mice; Molecular Docking Simulation; Naphthyridines; Phosphodiesterase 5 Inhibitors; Quinolines; Solubility; Structure-Activity Relationship

A recent controlled trial has established that high-dose biotin supplementation - 100 mg, three times daily - has a stabilizing effect on progression of multiple sclerosis (MS). Although this effect has been attributed to an optimization of biotin's essential cofactor role in the brain, a case can be made that direct stimulation of soluble guanylate cyclase (sGC) by pharmacological concentrations of biotin plays a key role in this regard. The utility of high-dose biotin in MS might reflect an anti-inflammatory effect of cGMP on the cerebral microvasculature, as well on oligodendrocyte differentiation and on Schwann cell production of neurotrophic factors thought to have potential for managing MS. But biotin's ability to boost cGMP synthesis in the brain may have broader neuroprotective potential. In many types of neurons and neural cells, cGMP exerts neurotrophic-mimetic effects - entailing activation of the PI3K-Akt and Ras-ERK pathways - that promote neuron survival and plasticity. Hippocampal long term potentiation requires nitric oxide synthesis, which in turn promotes an activating phosphorylation of CREB via a pathway involving cGMP and protein kinase G (PKG). In Alzheimer's disease (AD), amyloid beta suppresses this mechanism by inhibiting sGC activity; agents which exert a countervailing effect by boosting cGMP levels tend to restore effective long-term potentiation in rodent models of AD. Moreover, NO/cGMP suppresses amyloid beta production within the brain by inhibiting expression of amyloid precursor protein and BACE1. In conjunction with cGMP's ability to oppose neuron apoptosis, these effects suggest that high-dose biotin might have potential for the prevention and management of AD. cGMP also promotes neurogenesis, and may lessen stroke risk by impeding atherogenesis and hypertrophic remodeling in the cerebral vasculature. The neuroprotective potential of high-dose biotin likely could be boosted by concurrent administration of brain-permeable phosphodiesterase-5 inhibitors.

Topics: Aging; Alzheimer Disease; Amyloid beta-Peptides; Biotin; Brain; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Cyclic Nucleotide Phosphodiesterases, Type 5; Extracellular Signal-Regulated MAP Kinases; Humans; Long-Term Potentiation; Microcirculation; Multiple Sclerosis; Neurogenesis; Neuroprotective Agents; Phosphatidylinositol 3-Kinases; Phosphodiesterase Inhibitors; Randomized Controlled Trials as Topic; Signal Transduction

In Alzheimer's disease (AD), cerebral arteries, in contrast to cerebral microvessels, show both cerebral amyloid angiopathy (CAA) -dependent and -independent vessel wall pathology. However, it remains unclear whether CAA-independent vessel wall pathology affects arterial function, thereby chronically reducing cerebral perfusion, and, if so, which mechanisms mediate this effect. To this end, we assessed the ex vivo vascular function of the basilar artery and a similar-sized peripheral artery (femoral artery) in the Swedish-Arctic (SweArc) transgenic AD mouse model at different disease stages. Furthermore, we used quantitative immunohistochemistry to analyze CAA, endothelial morphology, and molecular pathways pertinent to vascular relaxation. We found that endothelium-dependent, but not smooth muscle-dependent, vasorelaxation was significantly impaired in basilar and femoral arteries of 15-mo-old SweArc mice compared with that of age-matched wild-type and 6-mo-old SweArc mice. This impairment was accompanied by significantly reduced levels of cyclic GMP, indicating a reduced nitric oxide (NO) bioavailability. However, no age- and genotype-related differences in oxidative stress as measured by lipid peroxidation were observed. Although parenchymal capillaries, arterioles, and arteries showed abundant CAA in the 15-mo-old SweArc mice, no CAA or changes in endothelial morphology were detected histologically in the basilar and femoral artery. Thus our results suggest that, in this AD mouse model, dysfunction of large intracranial, extracerebral arteries important for brain perfusion is mediated by reduced NO bioavailability rather than by CAA. This finding supports the growing body of evidence highlighting the therapeutic importance of targeting the cerebrovasculature in AD.. We show that vasorelaxation of the basilar artery, a large intracranial, extracerebral artery important for cerebral perfusion, is impaired independent of cerebral amyloid angiopathy in a transgenic mouse model of Alzheimer's disease. Interestingly, this dysfunction is specifically endothelium related and is mediated by impaired nitric oxide-cyclic GMP bioavailability.

Topics: Aging; Alzheimer Disease; Amyloid beta-Peptides; Animals; Basilar Artery; Biological Availability; Cerebral Amyloid Angiopathy; Cerebral Arteries; Cerebrovascular Circulation; Cyclic GMP; Disease Models, Animal; Endothelium, Vascular; Femoral Artery; Immunohistochemistry; Male; Mice; Mice, Transgenic; Nitric Oxide; Vasodilation

A novel systems therapeutics approach, involving simultaneous inhibition of phosphodiesterase 5 (PDE5) and histone deacetylase (HDAC), has been validated as a potentially novel therapeutic strategy for the treatment of Alzheimer's disease (AD). First-in-class dual inhibitors bearing a sildenafil core have been very recently reported, and the lead molecule 7 has proven this strategy in AD animal models. Because scaffolds may play a critical role in primary activities and ADME-Tox profiling as well as on intellectual property, we have explored alternative scaffolds (vardenafil- and tadalafil-based cores) and evaluated their impact on critical parameters such as primary activities, permeability, toxicity, and in vivo (pharmacokinetics and functional response in hippocampus) to identify a potential alternative lead molecule bearing a different chemotype for in vivo testing.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Adenosine Triphosphate; Alzheimer Disease; Animals; Cell Line, Transformed; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 5; Histone Deacetylase Inhibitors; Humans; Leukocytes, Mononuclear; Mice; Microsomes, Liver; Models, Molecular; Neuroglia; Neurons; Phosphodiesterase 5 Inhibitors

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.. 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.

Topics: Alzheimer Disease; Animals; Cyclic AMP; Cyclic GMP; Electric Stimulation; Flow Cytometry; Humans; Long-Term Potentiation; Male; Mice; Mice, Inbred C57BL; Phosphodiesterase Inhibitors; Rats, Sprague-Dawley; Receptors, AMPA; Signal Transduction; Synapses; Synaptosomes

Alzheimer's disease (AD) is a neurodegenerative disorder, primarily affecting memory. That disorder is thought to be a consequence of neuronal network disturbances and synapse loss. Decline in cognitive function is associated with a high burden of neuropsychiatric symptoms (NPSs) such as depression. The cyclic nucleotides cyclic adenosine-3',5'-monophosphate (cAMP) and cyclic guanosine-3',5'-monophosphate (cGMP) are essential second messengers that play a crucial role in memory processing as well as synaptic plasticity and are potential therapeutic targets. Biomarkers that are able to monitor potential treatment effects and that reflect the underlying pathology are of crucial interest.. In this study, we measured cGMP and cAMP in cerebrospinal fluid (CSF) in a cohort of 133 subjects including 68 AD patients and 65 control subjects. To address the association with disease progression we correlated cognitive status with cyclic nucleotide levels. Because a high burden of NPSs is associated with decrease in cognitive function, we performed an exhaustive evaluation of AD-relevant marker combinations in a depressive subgroup.. We show that cGMP, but not cAMP, levels in the CSF of AD patients are significantly reduced compared with the control group. Reduced cGMP levels in AD patients correlate with memory impairment based on Mini-Mental State Examination score (r = 0.17, p = 0.048) and tau as a marker of neurodegeneration (r = -0.28, p = 0.001). Moreover, we were able to show that AD patients suffering from current depression show reduced cGMP levels (p = 0.07) and exhibit a higher degree of cognitive impairment than non-depressed AD patients.. These results provide further evidence for an involvement of cGMP in AD pathogenesis and accompanying co-morbidities, and may contribute to elucidating synaptic plasticity alterations during disease progression.

Topics: Aged; Alzheimer Disease; Amyloid beta-Peptides; Biomarkers; Cognition; Cohort Studies; Cyclic AMP; Cyclic GMP; Depression; Disease Progression; Female; Humans; Male; Mental Status Schedule; Middle Aged; Peptide Fragments; tau Proteins

Neurofibrillar tangles caused by intracellular hyperphosphorylated tau inclusion and extracellular amyloid β peptide deposition are hallmarks of Alzheimer's disease. Tau contains one or two cysteine residues in three or four repeats of the microtubule binding region following alternative splicing of exon 10, and formation of intermolecular cysteine disulfide bonds accelerates tau aggregation. 8-Nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) acts as a novel second messenger of nitric oxide (NO) by covalently binding cGMP to cysteine residues by electrophilic properties, a process termed protein S-guanylation. Here we studied S-guanylation of tau and its effects on tau aggregation. 8-Nitro-cGMP exposure induced S-guanylation of tau both in vitro and in tau-overexpressed HEK293T cells. S-guanylated tau inhibited heparin-induced tau aggregation in a thioflavin T assay. Atomic force microscopy observations indicated that S-guanylated tau could not form tau granules and fibrils. Further biochemical analyses showed that S-guanylated tau was inhibited at the step of tau oligomer formation. In P301L tau-expressing Neuro2A cells, 8-nitro-cGMP treatment significantly reduced the amount of sarcosyl-insoluble tau. NO-linked chemical modification on cysteine residues of tau could block tau aggregation, and therefore, increasing 8-nitro-cGMP levels in the brain could become a potential therapeutic strategy for Alzheimer's disease.

Topics: Alzheimer Disease; Cyclic GMP; HEK293 Cells; Humans; Nitric Oxide; Protein Aggregates; Protein Processing, Post-Translational; tau Proteins

Levels of the cyclic nucleotides guanosine 3', 5'-monophosphate (cGMP) or adenosine 3', 5'-monophosphate (cAMP) that play important roles in memory processes are not characterized in Alzheimer's disease (AD). The aim of this study was to analyse the levels of these nucleotides in cerebrospinal fluid (CSF) samples from patients diagnosed with clinical and prodromal stages of AD and study the expression level of the enzymes that hydrolyzed them [phosphodiesterases (PDEs)] in the brain of AD patients vs.. For cGMP and cAMP CSF analysis, the cohort (n = 79) included cognitively normal participants (subjective cognitive impairment), individuals with stable mild cognitive impairment or AD converters (sMCI and cMCI), and mild AD patients. A high throughput liquid chromatography-tandem mass spectrometry method was used. Interactions between CSF cGMP or cAMP with mini-mental state examination (MMSE) score, CSF Aβ(1-42) and CSF p-tau were analysed. For PDE4, 5, 9 and 10 expression analysis, brains of AD patients vs. controls (n = 7 and n = 8) were used.. cGMP, and not cAMP levels, were significantly lower in the CSF of patients diagnosed with mild AD when compared with nondemented controls. CSF levels of cGMP showed a significant association with MMSE-diagnosed clinical dementia and with CSF biomarker Aβ42 in AD patients. Significant increase in PDE5 expression was detected in temporal cortex of AD patients compared with that of age-matched healthy control subjects. No changes in the expression of others PDEs were detected.. These results support the potential involvement of cGMP in the pathological and clinical development of AD. The cGMP reduction in early stages of AD might participate in the aggravation of amyloid pathology and cognitive decline.

Topics: Aged; Alzheimer Disease; Brain; Cognitive Dysfunction; Cyclic AMP; Cyclic GMP; Female; Humans; Male; Middle Aged; Neuropsychological Tests; Phosphoric Diester Hydrolases

Synaptic dysfunction is a key event in pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD) where synapse loss pathologically correlates with cognitive decline and dementia. Although evidence suggests that aberrant protein production and aggregation are the causative factors in familial subsets of such diseases, drugs singularly targeting these hallmark proteins, such as amyloid-β, have failed in late stage clinical trials. Therefore, to provide a successful disease-modifying compound and address synaptic dysfunction and memory loss in AD and mixed pathology dementia, we repurposed a clinically proven drug, CMZ, with neuroprotective and anti-inflammatory properties via addition of nitric oxide (NO) and cGMP signaling property.. The novel compound, NMZ, was shown to retain the GABAA potentiating actions of CMZ in vitro and sedative activity in vivo. Importantly, NMZ restored LTP in hippocampal slices from AD transgenic mice, whereas CMZ was without effect. NMZ reversed amnestic blockade of acetylcholine receptors by scopolamine as well as NMDA receptor blockade by a benzodiazepine and a NO synthase inhibitor in the step-through passive avoidance (STPA) test of learning and working memory. A PK/PD relationship was developed based on STPA analysis coupled with pharmacokinetic measures of drug levels in the brain: at 1 nM concentration in brain and plasma, NMZ was able to restore memory consolidation in mice.. Our findings show that NMZ embodies a promising pharmacological approach targeting synaptic dysfunction and opens new avenues for neuroprotective intervention strategies in mixed pathology AD, neurodegeneration, and dementia.

Topics: Alzheimer Disease; Animals; Chlormethiazole; CREB-Binding Protein; Cyclic GMP; Disease Models, Animal; Drug Repositioning; GABA-A Receptor Agonists; Hippocampus; Long-Term Potentiation; Male; Mice; Mice, Transgenic; Neuroprotective Agents; Nitric Oxide; Nootropic Agents; Signal Transduction; Synapses; Xenopus laevis

Phosphodiesterase-5 (PDE5) inhibitors are predominantly used in the treatment of erectile dysfunction, and have been recently shown to have a potential therapeutic effect for the treatment of Alzheimer's disease (AD) through stimulation of nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signalling by elevating cGMP, which is a secondary messenger involved in processes of neuroplasticity. In the present study, the effects of a PDE5 inhibitor, icarrin (ICA), on learning and memory as well as the pathological features in APP/PS1 transgenic AD mice were investigated. Ten-month-old APP/PS1 transgenic mice overexpressing human amyloid precursor protein (APP695swe) and presenilin 1 (PS1-dE9) were given ICA (30 and 60 mg/kg) or sildenafil (SIL) (2 mg/kg), age-matched wild-type (WT) mice were given ICA (60 mg/kg), and APP/PS1 and WT control groups were given an isovolumic vehicle orally twice a day for four months. Results demonstrated that ICA treatments significantly improved learning and memory of APP/PS1 transgenic mice in Y-maze tasks. The amyloid precursor protein (APP), amyloid-beta (Aβ1-40/42) and PDE5 mRNA and/or protein levels were increased in the hippocampus and cortex of APP/PS1 mice, and ICA treatments decreased these physiopathological changes. Furthermore, ICA-treated mice showed an increased expression of three nitric oxide synthase (NOS) isoforms at both mRNA and protein levels, together with increased NO and cGMP levels in the hippocampus and cortex of mice. These findings demonstrate that ICA improves learning and memory functions in APP/PS1 transgenic mice possibly through the stimulation of NO/cGMP signalling and co-ordinated induction of NOS isoforms.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Animals; Cerebral Cortex; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 5; Disease Models, Animal; Dose-Response Relationship, Drug; Flavonoids; Hippocampus; Humans; Male; Maze Learning; Mice, Transgenic; Nitric Oxide; Nitric Oxide Synthase; Nootropic Agents; Peptide Fragments; Phosphodiesterase 5 Inhibitors; Presenilin-1; Random Allocation

The cyclic nucleotide cGMP is an important intracellular messenger for synaptic plasticity and memory function in rodents. Therefore, inhibition of cGMP degrading phosphodiesterases, like PDE9A, has gained interest as potential target for treatment of cognition deficits in indications like Alzheimer's disease (AD). In fact, PDE9A inhibition results in increased hippocampal long-term potentiation and exhibits procognitive effects in rodents. To date, however, no evidence has been published linking PDE9A inhibition to the pathologic hallmarks of AD such as amyloid beta (Aβ) deposition. Therefore, we investigated the role of PDE9A inhibition in an AD relevant context by testing its effects on Aβ-related deficits in synaptic plasticity and cognition. The PDE9A inhibitor BAY 73-6691 was found to restore long-term potentiation impaired by Aβ42 oligomers. Furthermore, we demonstrated that BAY 73-6691 enhanced cGMP levels in the hippocampus of APP transgenic tg2576 mice and improved memory performance of these mice. Altogether, our results support the hypothesis that inhibition of PDE9A could be a beneficial approach for the treatment of memory impairment in AD patients.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Alzheimer Disease; Amyloid beta-Peptides; Animals; Cognition; Cyclic GMP; Hippocampus; Long-Term Potentiation; Male; Memory; Mice; Mice, Transgenic; Molecular Targeted Therapy; Neuronal Plasticity; Peptide Fragments; Pyrazoles; Pyrimidines; Rats, Wistar

Memory deficit is a marker of Alzheimer's disease (AD) that has been highly associated with the dysfunction of cyclic GMP (cGMP) signaling and an ongoing inflammatory process. Phosphodiesterase-5 (PDE5) inhibitors prevent the breakdown of cGMP and are currently studied as a possible target for cognitive enhancement. However, it is still unknown whether inhibition of PDE5 reversed β-amyloid peptide (Aβ)-induced neuroinflammation in APP/PS1 transgenic (Tg APP/PS1) mice. The present study evaluated the cognitive behaviors, inflammatory mediators, and cGMP/PKG/pCREB signaling in 15-month-old Tg APP/PS1 mice and age-matched wild-type (WT) mice that were treated with PDE5 inhibitor sildenafil and the inhibitor of cGMP-dependent protein kinase Rp-8-Br-PET-cGMPS. In comparison with WT mice, Tg APP/PS1 mice were characterized by impaired cognitive ability, neuroinflammatory response, and down-regulated cGMP signaling. Sildenafil reversed these memory deficits and cGMP/PKG/pCREB signaling dysfunction; it also reduced both the soluble Aβ1-40 and Aβ1-42 levels in the hippocampus. These effects of sildenafil were prevented by intra-hippocampal infusion of the Rp-8-Br-PET-cGMPS. These results suggest that sildenafil could restore cognitive deficits in Tg APP/PS1 mice by the regulation of PKG/pCREB signaling, anti-inflammatory response and reduction of Aβ levels.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Analysis of Variance; Animals; Cognition Disorders; Cyclic GMP; Cytokines; Disease Models, Animal; Dose-Response Relationship, Drug; Encephalitis; Exploratory Behavior; Humans; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Phosphodiesterase 5 Inhibitors; Piperazines; Presenilin-1; Purines; Recognition, Psychology; RNA, Messenger; Sildenafil Citrate; Sulfones; Thionucleotides

Exotoxin Y (ExoY) is a type III secretion system effector found in ~ 90% of the Pseudomonas aeruginosa isolates. Although it is known that ExoY causes inter-endothelial gaps and vascular leak, the mechanisms by which this occurs are poorly understood. Using both a bacteria-delivered and a codon-optimized conditionally expressed ExoY, we report that this toxin is a dual soluble adenylyl and guanylyl cyclase that results in intracellular cAMP and cGMP accumulation. The enzymatic activity of ExoY caused phosphorylation of endothelial Tau serine 214, accumulation of insoluble Tau, inter-endothelial cell gap formation, and increased macromolecular permeability. To discern whether the cAMP or cGMP signal was responsible for Tau phosphorylation and barrier disruption, pulmonary microvascular endothelial cells were engineered for the conditional expression of either wild-type guanylyl cyclase, which synthesizes cGMP, or a mutated guanylyl cyclase, which synthesizes cAMP. Sodium nitroprusside stimulation of the cGMP-generating cyclase resulted in transient Tau serine 214 phosphorylation and gap formation, whereas stimulation of the cAMP-generating cyclase induced a robust increase in Tau serine 214 phosphorylation, gap formation, and macromolecular permeability. These results indicate that the cAMP signal is the dominant stimulus for Tau phosphorylation. Hence, ExoY is a promiscuous cyclase and edema factor that uses cAMP and, to some extent, cGMP to induce the hyperphosphorylation and insolubility of endothelial Tau. Because hyperphosphorylated and insoluble Tau are hallmarks in neurodegenerative tauopathies such as Alzheimer disease, acute Pseudomonas infections cause a pathophysiological sequela in endothelium previously recognized only in chronic neurodegenerative diseases.

Topics: Adenylyl Cyclases; Alzheimer Disease; Bacterial Toxins; Cell Line; Cell Membrane Permeability; Cyclic AMP; Cyclic GMP; Endothelial Cells; Exotoxins; Guanylate Cyclase; Humans; Phosphorylation; Pseudomonas aeruginosa; Pseudomonas Infections; Second Messenger Systems; Substrate Specificity; tau Proteins

Transgenic (Tg) mice overexpressing human amyloid precursor protein (APP) mutants reproduce features of early Alzheimer's disease (AD) including memory deficit, presence of β-amyloid (Aβ) oligomers, and age-associated formation of amyloid deposits. In this study we used hippocampal microdialysis to characterize the signaling of N-methyl-d-aspartic acid receptors (NMDA-Rs) in awake and behaving AD Tg mice. The NMDA-R signaling is central to hippocampal synaptic plasticity underlying memory formation and several lines of evidence implicate the role of Aβ oligomers in effecting NMDA-R dysfunction. CA1 NMDA-Rs were stimulated by NMDA infused through reverse microdialysis while changes in the cyclic guanosine monophosphate (cGMP) concentration in the brain interstitial fluid (ISF) were used to determine NMDA-Rs responsiveness. While 4 months old wild type C57BL/6 mice mounted robust cGMP response to the NMDA challenge, the same stimulus failed to significantly change the cGMP level in 4 and 15 months old APP(SW) and 4 months old APP(SW)/PS1(L166P) Tg mice, which were all on C57BL/6 background. Lack of response to NMDA in AD Tg mice occurred in the absence of changes in expression levels of several synaptic proteins including synaptophysin, NR1 NMDA-R subunit and postsynaptic density protein 95, which indicates lack of profound synaptic degeneration. Aβ oligomers were detected in all three AD Tg mice groups and their concentration in the hippocampus ranged from 40.5±3.6ng/g in 4 months old APP(SW) mice to 60.8±15.9ng/g in 4 months old APP(SW)/PS1(L166P) mice. Four months old APP(SW) mice had no Aβ amyloid plaques, while the other two AD Tg mice groups showed evidence of incipient Aβ amyloid plaque formation. Our studies describes a novel approach useful to study the function of NMDA-Rs in awake and behaving AD Tg mice and demonstrate impairment of NMDA-R response in the presence of endogenously formed Aβ oligomers but predating onset of Aβ amyloidosis.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Cyclic GMP; Hippocampus; Mice; Mice, Inbred C57BL; Microdialysis; Receptors, N-Methyl-D-Aspartate; Signal Transduction; Synaptophysin

Caffeine and melatonin have been shown to protect the Swedish mutant amyloid precursor protein (APP(sw)) transgenic mouse model of Alzheimer's disease from cognitive dysfunction. But their mechanisms of action remain incompletely understood. These Alzheimer's mice have extensive mitochondrial dysfunction, which likely contributes to their cognitive decline. To further explore the mechanism through which caffeine and melatonin protect cognitive function in these mice, we monitored the function of isolated mitochondria from APP(sw) mice treated with caffeine, melatonin, or both in their drinking water for one month. Melatonin treatment yielded a near complete restoration of mitochondrial function in assays of respiratory rate, membrane potential, reactive oxygen species production, and ATP levels. Caffeine treatment by itself yielded a small increase in mitochondrial function. However, caffeine largely blocked the large enhancement of mitochondrial function provided by melatonin. Studies with N2a neuroblastoma cells stably expressing APP(sw) showed that specific inhibition of cAMP-dependent phosphodiesterase (PDE) 4 or cGMP-dependent PDE5 also blocked melatonin protection of mitochondrial function, but A(2a) and A₁ adenosine receptor antagonists were without effect. Melatonin or caffeine at the concentrations used to modulate mitochondrial function in the cells had no effect on cAMP-dependent PDE activity or cellular cAMP or cGMP levels. Therefore, caffeine and increased cyclic nucleotide levels likely block melatonin signaling to mitochondria by independent mechanisms that do not involve adenosine receptor antagonism. The results of this study indicate that melatonin restores mitochondrial function much more potently than caffeine in APP(sw) transgenic mouse and cell models of Alzheimer's disease.

Topics: Adenosine Triphosphate; Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Antioxidants; Caffeine; Cells, Cultured; Central Nervous System Stimulants; Cyclic AMP; Cyclic GMP; Enzyme-Linked Immunosorbent Assay; In Vitro Techniques; Melatonin; Membrane Potential, Mitochondrial; Mice; Mice, Transgenic; Mitochondria; Mitochondrial Diseases; Neurons; Oxygen Consumption; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Reactive Oxygen Species; Signal Transduction; Transfection

the exact etiology of sporadic Alzheimer disease (AD) is unclear, but it is interesting that several cardiovascular risk factors are associated with higher incidence of AD. The link between these risk factors and AD has yet to be identified; however, a common feature is endothelial dysfunction, specifically, decreased bioavailability of nitric oxide (NO).. to determine the relationship between endothelial derived NO and the expression and processing of amyloid precursor protein (APP).. we used human brain microvascular endothelial cells to examine the role of NO in modulating APP expression and processing in vitro. Inhibition of endothelial nitric oxide synthase (eNOS) with the specific NOS inhibitor L-NAME (N(G)-nitro-l-arginine methyl ester) led to increased APP and BACE1 (β-site APP-cleaving enzyme1) protein levels, as well as increased secretion of the amyloidogenic peptide amyloid β (Aβ) (control 10.93 ± 0.70 pg/mL; L-NAME 168.21 ± 27.38 pg/mL; P<0.001). To examine the role of NO in modulation of APP expression and processing in vivo, we used brain and cerebral microvessels from eNOS-deficient (eNOS(-/-)) mice. Brain tissue from eNOS(-/-) mice had statistically higher APP and BACE1 protein levels, as well as increased BACE1 enzyme activity and Aβ (Aβ(1)(-)(42) wild-type control, 0.737 pg/mg; eNOS(-/-), 1.475 pg/mg; P<0.05), compared with wild-type controls (n=6 to 8 animals per background). Brain microvessels from eNOS(-/-) mice also showed statistically higher BACE1 protein levels as compared with wild-type control.. our data suggest that endothelial NO plays an important role in modulating APP expression and processing within the brain and cerebrovasculature. The NO/cGMP pathway may be an important therapeutic target in preventing and treating mild cognitive impairment, as well as AD.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Amyloid Precursor Protein Secretases; Animals; Aspartic Acid Endopeptidases; Brain; Brain Chemistry; Cerebrovascular Circulation; Cyclic GMP; Endothelial Cells; Endothelium, Vascular; Humans; Mice; Microcirculation; Nitric Oxide; Nitric Oxide Synthase Type III

Memory loss, synaptic dysfunction, and accumulation of amyloid beta-peptides (A beta) are major hallmarks of Alzheimer's disease (AD). Downregulation of the nitric oxide/cGMP/cGMP-dependent protein kinase/c-AMP responsive element-binding protein (CREB) cascade has been linked to the synaptic deficits after A beta elevation. Here, we report that the phosphodiesterase 5 inhibitor (PDE5) sildenafil (Viagra), a molecule that enhances phosphorylation of CREB, a molecule involved in memory, through elevation of cGMP levels, is beneficial against the AD phenotype in a mouse model of amyloid deposition. We demonstrate that the inhibitor produces an immediate and long-lasting amelioration of synaptic function, CREB phosphorylation, and memory. This effect is also associated with a long-lasting reduction of A beta levels. Given that side effects of PDE5 inhibitors are widely known and do not preclude their administration to a senile population, these drugs have potential for the treatment of AD and other diseases associated with elevated A beta levels.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Analysis of Variance; Animals; Conditioning, Classical; Cyclic AMP Response Element-Binding Protein; Cyclic GMP; Disease Models, Animal; Immunohistochemistry; Injections, Intraperitoneal; Memory; Mice; Mice, Transgenic; Mutation; Neuropsychological Tests; Phosphodiesterase 5 Inhibitors; Phosphodiesterase Inhibitors; Phosphorylation; Piperazines; Polymerase Chain Reaction; Psychomotor Performance; Purines; Sildenafil Citrate; Spatial Behavior; Sulfones; Synaptic Transmission; Time Factors; Treatment Outcome

We studied the mRNA expression of cGMP-hydrolysing phosphodiesterases (PDEs) in selected brain areas of normal elderly people and patients with Alzheimer's disease. Using radioactive in-situ hybridization histochemistry we found a widespread distribution of the mRNA for PDE2 and PDE9, whereas no specific hybridization signal was observed for PDE5. We observed PDE2 and PDE9 mRNA in all cortical areas studied (insular cortex, entorhinal cortex and visual cortex), although to a different extent. PDE2 mRNA was high in the claustrum, whereas PDE9 mRNA was moderate. PDE2 and PDE9 mRNAs was present in the putamen. No cGMP-hydrolysing PDE expression was observed in the globus pallidus. PDE2 and PDE9 mRNA was observed in all subareas of the hippocampus; however, there were significant differences in the amount of expression. In the Purkinje and cerebellar granule cells only PDE9 expression was observed. PDE2 and PDE9 mRNA expression was not significantly different in Alzheimer's disease brains.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Aged; Aged, 80 and over; Alzheimer Disease; Brain; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 2; Female; Gene Expression; Humans; In Situ Hybridization; Male; Middle Aged; Phosphoric Diester Hydrolases; Statistics, Nonparametric

Amyloid-beta (Abeta), a peptide thought to play a crucial role in Alzheimer's disease (AD), has many targets that, in turn, activate different second-messenger cascades. Interestingly, Abeta has been found to markedly impair hippocampal long-term potentiation (LTP). To identify a new pathway that might be responsible for such impairment, we analyzed the role of the nitric oxide (NO)/soluble guanylyl cyclase (sGC)/cGMP/cGMP-dependent protein kinase (cGK)/cAMP-responsive element-binding protein (CREB) cascade because of its involvement in LTP. The use of the NO donor 2-(N,N-dethylamino)-diazenolate-2-oxide diethylammonium salt (DEA/NO), the sGC stimulator 3-(4-amino-5-cyclopropylpyrimidine-2-yl)-1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridine, or the cGMP-analogs 8-bromo-cGMP and 8-(4-chlorophenylthio)-cGMP reversed the Abeta-induced impairment of CA1-LTP through cGK activation. Furthermore, these compounds reestablished the enhancement of CREB phosphorylation occurring during LTP in slices exposed to Abeta. We also found that Abeta blocks the increase in cGMP immunoreactivity occurring immediately after LTP and that DEA/NO counteracts the effect of Abeta. These results strongly suggest that, when modulating hippocampal synaptic plasticity, Abeta downregulates the NO/cGMP/cGK/CREB pathway; thus, enhancement of the NO/cGMP signaling may provide a novel approach to the treatment of AD and other neurodegenerative diseases with elevated production of Abeta.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Cyclic AMP Response Element-Binding Protein; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Fluorescent Antibody Technique; Guanylate Cyclase; Hippocampus; Hydrazines; Long-Term Potentiation; Male; Mice; Mice, Inbred C57BL; Neuronal Plasticity; Nitric Oxide; Nitric Oxide Donors; Nitrogen Oxides; Organ Culture Techniques; Peptide Fragments; Phosphorylation; Up-Regulation

An 8-amino-acid peptide, NAPVSIPQ (NAP), was identified as the smallest active element of activity-dependent neuroprotective protein that exhibits potent neuroprotective action. Potential signal transduction pathways include cGMP production and interference with inflammatory mechanisms, tumor necrosis factor-alpha, and MAC1-related changes. Because of its intrinsic structure, NAP might interact with extracellular proteins and also transverse membranes. NAP-associated protection against oxidative stress, glucose deprivation, and apoptotic mechanisms suggests interference with fundamental processes. This paper identifies p53, a key regulator of cellular apoptosis, as an intracellular target for NAP's activity.

Topics: Alzheimer Disease; Animals; Apoptosis; Brain; Brain Ischemia; Cyclic GMP; Down-Regulation; Encephalitis; Macrophage-1 Antigen; Neuroprotective Agents; Oligopeptides; Oxidative Stress; PC12 Cells; Rats; Tumor Necrosis Factor-alpha; Tumor Suppressor Protein p53

beta-amyloid (Abeta) peptides are the major protein components of senile plaques in Alzheimer's disease (AD) brains. Vascular damage and reactive gliosis are found colocalized with amyloid deposits in AD brains, suggesting that the vasculature may be a clinically significant site of AD pathology. Our results show that freshly solubilized Abeta1-40 enhances the vasoconstriction induced by endothelin-1 (ET-1) and increases resistance to relaxation triggered by nitric oxide (NO), suggesting that Abeta may oppose the NO/cGMP pathway. Using specific inhibitors and activators of the NO/cGMP pathway, we show that Abeta vasoactivity is not due to a modulation of nitric oxide synthase (NOS) or soluble guanylyl cyclase (sGC). However, we find that a selective cGMP phosphodiesterase (cGMP-PDE) inhibitor (dipyridamole) is able to interactively block the enhanced vasoconstriction as well as the opposition to relaxation induced by Abeta, suggesting that Abeta could effect the activity of this enzyme. Cyclic GMP levels, but not cAMP concentrations, are reduced after Abeta treatment of rat aortic rings, further substantiating this hypothesis. Moreover, in examination of this pathway in another cell type pertinent to AD, we find that Abeta induces a proinflammatory response in microglia as evidenced by increased leukotriene B4 release. We show that both dipyridamole and compounds which increase cGMP levels prevent Abeta-induced microglial inflammation. Our results suggest that therapeutic intervention aimed at reduction of microglial-mediated inflammation via inhibition of cGMP-PDE or elevation of cGMP may be beneficial in the treatment of AD.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Aorta; Cells, Cultured; Cyclic AMP; Cyclic GMP; Guanylate Cyclase; In Vitro Techniques; Inflammation Mediators; Male; Microglia; Nitric Oxide; Nitric Oxide Donors; Nitroprusside; Phosphodiesterase Inhibitors; Rats; Rats, Sprague-Dawley; Vasomotor System

Synaptic dysfunction and degeneration are believed to underlie the cognitive deficits that characterize Alzheimer's disease, and overactivation of glutamate receptors under conditions of increased oxidative stress and metabolic compromise may contribute to the neurodegenerative process in many different disorders. The secreted form of amyloid precursor protein (sAPPalpha), which is released from neurons in an activity-dependent manner, can modulate neurite outgrowth, synaptic plasticity, and neuron survival. We now report that sAPPalpha can enhance glucose and glutamate transport in synaptic compartments. Treatment of cortical synaptosomes with nanomolar concentrations of sAPPalpha resulted in an attenuation of impairment of glutamate and glucose transport induced by exposure to amyloid beta-peptide and Fe2+. The protective effect of sAPPalpha was mimicked by treatment with 8-bromo-cyclic GMP and blocked by a cyclic GMP-dependent protein kinase inhibitor, suggesting that protective action of sAPPalpha is mediated by cyclic GMP. Our data suggest that glucose and glutamate transport can be regulated locally at the level of the synapse and further suggest important roles for sAPPalpha and cyclic GMP in modulating synaptic physiology under normal and pathophysiological conditions.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Alkaloids; Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Animals; Apoptosis; Biological Transport; Carbazoles; Cerebral Cortex; Cyclic GMP; Enzyme Inhibitors; Female; Ferrous Compounds; Glucose; Glutamic Acid; Indoles; Lipid Peroxidation; Neurons; Neurotoxins; Oxidative Stress; Rats; Rats, Sprague-Dawley; Synapses; Synaptosomes; Tritium

Since increasing evidence suggests that upregulation of the cAMP-second messenger system may be implicated in Alzheimer's disease neurodegeneration, we have compared the cAMP and cGMP levels in cerebrospinal fluid (CSF) from patients with dementia of the Alzheimer type (DAT, n=10) with those from nondemented age-matched controls (n=10). Our results show that cAMP levels, but not cGMP, are significantly (p<0.01) elevated in CSF from patients with DAT compared to those from nondemented controls. Moreover, a linear regression analysis demonstrated a significant correlation (r=0.62; p<0.01) between cAMP and tau protein levels in CSF when controls and patients with DAT were studied together. These results suggest that upregulation of cAMP-signaling pathway is implicated in Alzheimer's disease physiopathology.

Topics: Aged; Alzheimer Disease; Cyclic AMP; Cyclic GMP; Female; Humans; Linear Models; Male; Middle Aged; Signal Transduction; tau Proteins

We previously demonstrated that secreted forms of the Alzheimer's beta-amyloid precursor protein (sAPP) elevate cyclic GMP (cGMP) in primary neuronal cultures and that this effect is responsible for the modulation of neuronal calcium homoeostasis by sAPP. We have investigated further the mechanism by which sAPP elevates cGMP. Inhibition of the formation of nitric oxide or carbon monoxide did not affect the ability of sAPP to lower rapidly intraneuronal calcium levels or elevate cGMP, suggesting that sAPP does not activate a soluble (cytosolic) guanylate cyclase. A dose-dependent stimulation of cGMP formation by sAPP was observed in brain membrane preparations. The stimulation was also dependent on the presence of ATP. These data suggest that sAPP activates a membrane-associated guanylate cyclase, perhaps similar to those present in the receptors for the natriuretic peptides and sperm motility factors.

Topics: Adenosine Triphosphate; Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Calcium; Cell Membrane; Cells, Cultured; Cyclic GMP; Embryo, Mammalian; Enzyme Activation; Guanylate Cyclase; Hippocampus; Neurons; Rats; Rats, Sprague-Dawley

Particulate and soluble guanylyl cyclase activities were studied in postmortem temporal cortex from a series of Alzheimer's disease patients and matched control subjects. Particulate guanylyl cyclase activity was not significantly different between groups. In contrast, the Vmax values for basal and sodium nitroprusside-stimulated soluble guanylyl cyclase activities were approximately 50% lower in the Alzheimer's disease cases, compared to controls. This difference between groups was statistically significant for sodium nitroprusside-stimulated, but not for the basal, enzyme activities. These results provide the first evidence for a loss of nitric oxide responsive guanylyl cyclase activity in Alzheimer's disease brain.

Topics: Aged; Alzheimer Disease; Autopsy; Cyclic GMP; Dose-Response Relationship, Drug; Guanylate Cyclase; Humans; Kinetics; Magnesium; Nitric Oxide; Temporal Lobe

The Alzheimer's disease (AD) beta-amyloid precursor proteins (beta APPs) are large membrane-spanning proteins that give rise to the beta A4 peptide deposited in AD amyloid plaques. beta APPs can also yield soluble forms (APPss) that are potently neuroprotective against glucose deprivation and glutamate toxicity, perhaps through their ability to lower the intraneuronal calcium concentration ([Ca2+]i). We have investigated the mechanism through which APPss exert these effects on cultured hippocampal neurons. The ability of APPss to lower rapidly [Ca2+]i was mimicked by membrane-permeable analogues of cyclic AMP (cAMP) and cyclic GMP (cGMP), as well as agents that elevate endogenous levels of these cyclic nucleotides. However, only cGMP content was increased by APPs treatment, and specific inhibition of cGMP-dependent protein kinase (but not cAMP-dependent kinase) blocked the activity of APPss. A membrane-permeable analogue of cGMP (8-bromo-cGMP) also mimicked the ability of APPss to attenuate the elevation of [Ca2+]i by glutamate, apparently through inhibition of NMDA receptor activity. In addition, 8-bromo-cGMP afforded protection against glucose deprivation and glutamate toxicity, and the protection by APPss against glucose deprivation was blocked by an inhibitor of cGMP-dependent kinase. Together, these data suggest that APPss mediate their [Ca2+]i-lowering and excitoprotective effects on target neurons through increases in cGMP levels.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Calcium; Cells, Cultured; Colforsin; Cyclic AMP; Cyclic GMP; Glutamic Acid; Hippocampus; Neurons; Rats

Topics: Adenosine Diphosphate; Alzheimer Disease; Brain Chemistry; Cell Communication; Cyclic GMP; Humans; Huntington Disease; Neurotransmitter Agents; Nitric Oxide

The cyclic nucleotide changes were studied under 10(-6) M isoproterenol (IP), 10(-6) M carbachol and 10(-8) M Met-enkephalin (Met-enk) stimulations in polymorphonuclear granulocytes (PMNLs) of middle-aged (aged 35-52 years) and elderly (aged 61-97 years) healthy subjects, as well as of patients with Alzheimer's disease (AD) (aged 58-65 years). From our results we can conclude that in the case of middle-aged healthy subjects only the IP caused a marked cAMP elevation while in elderly and AD all the applied substances stimulated the cAMP at different degrees. Concerning the cGMP levels in PMNLs, we observed a marked increase under carbachol and Met-enk stimulation, in middle-aged subjects, while in the elderly a weak change was obtained by carbachol. In AD practically no change of cGMP levels could be obtained. Thus, the main features of AD are a cAarP response to Met-enk and an abolition of a GarP response to carbachol. We can conclude that in PMNLs of elderly and patients with AD we assist to an altered post-receptorial signal transduction mechanism, which seems to be even more marked in the case of AD comparing to normal aging.

Topics: Aged; Aged, 80 and over; Aging; Alzheimer Disease; Carbachol; Cyclic AMP; Cyclic GMP; Enkephalin, Methionine; Humans; Male; Middle Aged; Neutrophils; Signal Transduction

Three, 4-dihydroxyphenylacetic acid (DOPAC); 3-methoxy, 4-hydroxyphenylacetic acid (HVA); 3-methoxy; 4-hydroxyphenylglycol (MHPG); adenosine 3', 5'-cyclic monophosphate (cyclic AMP); and guanosine 3', 5'-cyclic monophosphate (cyclic GMP) were measured in cerebrospinal fluid (CSF) of patients with dementia of Alzheimer type (DAT) and controls. DOPAC levels were lower and HVA levels were higher in DAT patients than in controls. In the most rostral fractions of CSF from DAT patients there was a negative correlation between DOPAC and cyclic AMP levels. In addition, patients with onset of DAT symptoms before the age of 65 had lower DOPAC levels, a higher HVA/DOPAC ratio, and higher cyclic nucleotide levels than patients with late onset of DAT. By combining DOPAC and cyclic AMP levels, we could clearly distinguish these two groups.

Topics: 3,4-Dihydroxyphenylacetic Acid; Aged; Alzheimer Disease; Catecholamines; Cyclic AMP; Cyclic GMP; Homovanillic Acid; Humans; Methoxyhydroxyphenylglycol; Middle Aged; Nucleotides, Cyclic

Topics: Adult; Aged; Aging; Alzheimer Disease; Cyclic AMP; Cyclic GMP; Dementia; DNA Repair; Down Syndrome; Energy Metabolism; Histocompatibility Testing; Humans; Immunologic Capping; Isoantigens; Lymphocyte Activation; T-Lymphocytes

Cyclic guanosine monophosphate (cGMP) levels have been measured in the cerebrospinal fluid of patients with various neurological diseases. The subjects with epilepsy or cerebrovascular diseases do not show any difference from the controls. Moreover, in the CSF of patients having cerebral tumors the levels of cGMP are markedly increased. This change is in line with previous in vitro studies on the increase of cGMP during cell growth and cell proliferation showing that the role of the nucleotide is important for the control of the life cycle of the cell.

Topics: Adolescent; Adult; Aged; Alzheimer Disease; Brain Neoplasms; Cerebrovascular Disorders; Cyclic GMP; Epilepsy; Female; Humans; Hydrocephalus, Normal Pressure; Male; Middle Aged; Multiple Sclerosis