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The editorial discusses the role of cyclic nucleotide phosphodiesterases (PDEs) in regulating cAMP and cGMP levels in the endocrine system. PDEs are enzymes that control the breakdown of these second messengers, influencing various cellular functions and signaling pathways. The article highlights the potential therapeutic applications of PDE inhibitors (PDEi) in treating endocrine disorders, cancer, cardiovascular diseases, and other conditions. Additionally, it explores the complex interactions of cAMP and cGMP signaling in hormone release, cancer progression, and the renin-angiotensin-aldosterone system. [Extracted from the article]

Background: Cardiac fibrosis, a key contributor to heart failure, is driven by the activation of cardiac fibroblasts (CFs), often induced by angiotensin II (Ang II). Relaxin, a peptide hormone, has been reported to counteract fibrotic processes. This study aims to investigate the anti-fibrotic effects of relaxin on Ang II-induced CF activation, with a focus on the involvement of the nitric oxide/cyclic guanosine monophosphate (NO/cGMP) signaling pathway. Methods: Primary CFs were isolated and treated with Ang II to induce fibrotic activation. Relaxin was used to assess its antifibrotic effects. Inhibitors of the NO/cGMP pathway, NG-nitro-L-arginine methyl ester (L-NAME) (a nitric oxide synthase inhibitor) and 1H-(1,2,4)-Oxadiazolo-(4,3-a) quinoxalin-1-one (ODQ) (a guanylyl cyclase inhibitor), were co-administered to examine their effects on relaxin-mediated inhibition. Proliferation and migration were assessed using 5-Ethynyl-2'-deoxyuridine incorporation and Transwell assays. Western blot analysis was conducted to measure the expression of alpha-smooth muscle actin (α-SMA), collagen I, and collagen III, key markers of fibroblast activation. Nitric oxide, cGMP, total nitric oxide synthase (TNOS), and inducible nitric oxide synthase (iNOS) levels were measured in the culture media. Results: Ang II significantly increased CF proliferation, migration, and the expression of fibrosis markers α-SMA, collagen I, and collagen III. Relaxin treatment markedly reduced these effects. Inhibition of the NO/cGMP pathway by L-NAME or ODQ partially reversed relaxin’s suppressive effects on CF proliferation and migration. Relaxin restored Ang II-induced reductions in NO, cGMP, and TNOS levels, while iNOS levels remained largely unchanged, except for a reduction in the L-NAME group. Conclusion: Relaxin attenuates Ang II-induced cardiac fibroblast activation and fibrosis primarily through the NO/cGMP signaling pathway. [ABSTRACT FROM AUTHOR]

A major intracellular messenger implicated in synaptic plasticity and cognitive functions both in health and disease is cyclic GMP (cGMP). Utilizing a photoactivatable guanylyl cyclase (BlgC) actuator to increase cGMP in dentate granule neurons of the hippocampus by light, we studied the effects of spatiotemporal cGMP elevations in synaptic and cognitive functions. At medial perforant path to dentate gyrus (MPP-DG) synapses, we found enhanced long-term potentiation (LTP) of synaptic responses when postsynaptic cGMP was elevated during the induction period. Basal synaptic transmission and the paired-pulse ratio were unaffected, suggesting the cGMP effect on LTP was postsynaptic in origin. In behaving mice implanted with a fiber optic and wireless LED device, their performance following DG photoactivation (5–10 min) was studied in a variety of behavioral tasks. There were enhancements in reference memory and social behavior within tens of minutes following DG BlgC photoactivation, and with time (hours), an anxiogenic effect developed. Thus, postsynaptic cGMP elevations, specifically in the DG and specifically during conditions that evoke synaptic plasticity or during experience, are able to rapidly modify synaptic strength and behavioral responses, respectively. The optogenetics technology and new roles for cGMP in the DG may have applications in brain disorders that are impacted by dysregulated cGMP signaling, such as Alzheimer's disease. [ABSTRACT FROM AUTHOR]

This review summarizes recent advances in understanding the role of the nitric oxide (NO) and cyclic GMP (cGMP) pathway in stem cells. The levels of expression of various components of the pathway are changed during the differentiation of pluripotent embryonic stem cells. In undifferentiated stem cells, NO regulates self-renewal and survival predominantly through cGMP-independent mechanisms. Natriuretic peptides influence the growth of undifferentiated stem cells by activating particulate isoforms of guanylyl cyclases in a cGMP-mediated manner. The differentiation, recruitment, survival, migration, and homing of partially differentiated precursor cells of various types are sensitive to regulation by endogenous levels of NO and natriuretic peptides produced by stem cells, within surrounding tissues, and by the application of various pharmacological agents known to influence the cGMP pathway. Numerous drugs and formulations target various components of the cGMP pathway to influence the therapeutic efficacy of stem cell-based therapies. Thus, pharmacological manipulation of the cGMP pathway in stem cells can be potentially used to develop novel strategies in regenerative medicine. [ABSTRACT FROM AUTHOR]

Phosphodiesterase type 5 (PDE5) is an enzyme primarily found in the smooth muscle of the corpus cavernosum and also highly expressed in the substantia nigra, cerebellum, caudate, hippocampal regions and cerebellar purkinje cells, responsible for selectively breaking down cyclic guanosine monophosphate (cGMP) into 5′‐GMP and regulate intracellular cGMP levels. As a second messenger, cyclic GMP enhances signals at postsynaptic receptors and triggers downstream effector molecules, leading to changes in gene expression and neuronal responses. Additionally, cGMP signaling transduction cascade, present in the brain, is also essential for learning and memory processes. Mechanistically, PDE5 inhibitors share structural similarities with cGMP, competitively binding to PDE5 and inhibiting cGMP hydrolysis. This action enhances the effects of nitric oxide, resulting in anti‐inflammatory and neuroprotective effects. Neurodegenerative disorders entail the progressive loss of neuron structure, culminating in neuronal cell death, with currently available drugs providing only limited symptomatic relief, rendering neurodegeneration considered incurable. PDE5 inhibitors have recently emerged as a potential therapeutic approach for neurodegeneration, neuroinflammation, and diseases involving cognitive impairment. This review elucidates the principal roles of 3′,5′‐cyclic adenosine monophosphate (cAMP) and cGMP signaling pathways in neuronal functions, believed to play pivotal roles in the pathogenesis of various neurodegenerative disorders. It provides an updated assessment of PDE5 inhibitors as disease‐modifying agents for conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, cerebral ischemia, Huntington's disease, and neuroinflammation. The paper aims to review the current understanding of PDE5 inhibitors, which concurrently regulate both cAMP and cGMP signaling pathways, positing that they may exert complementary and synergistic effects in modifying neurodegeneration, thus presenting a novel direction in therapeutic discovery. Moreover, the review provides critical about biological functions, therapeutic potentials, limitations, challenges, and emerging applications of selective PDE5 inhibitors. This comprehensive overview aims to guide future academic and industrial endeavors in this field. [ABSTRACT FROM AUTHOR]

Growing evidence suggests that neuroinflammation is not just a consequence of neurodegeneration in pathologies such as Alzheimer's disease, Parkinson's disease, Huntington's disease or Amyotrophic lateral sclerosis, but it is rather a determinant factor, which plays a pivotal role in the onset and progression of these disorders. Neuroinflammation can affect cells and processes in the central nervous system (CNS) as well as immune cells, and might precede protein aggregation, which is a hallmark of the neurodegenerative process. Standard treatment methods are far from being able to counteract inflammation and delay neurodegeneration. Remarkably, phosphodiesterase 5 inhibitors (PDE5is), which represent potent vasoactive drugs used as a first-line treatment for erectile dysfunction (ED), display important anti-inflammatory effects through cyclic guanosine monophosphate (cGMP) level stabilization. Since PDE5 hydrolyzes cGMP, several studies positioned PDE5 as a therapeutic target, and more specifically, PDE5is as potential alternative strategies for the treatment of a variety of neurological disorders. Indeed, PDE5is can limit neuroinflammation and enhance synaptic plasticity, with beneficial effects on cognitive function and memory. The aim of this review is to provide an overview of some of the main processes underlying neuroinflammation and neurodegeneration which may be potential targets for PDE5is, focusing on sildenafil, the most extensively studied. Current strategies using PDEis for the treatment of neurodegenerative diseases will be summarized. [ABSTRACT FROM AUTHOR]

Increasing cyclic GMP activates 26S proteasomes via phosphorylation by Protein Kinase G and stimulates the intracellular degradation of misfolded proteins. Therefore, agents that raise cGMP may be useful therapeutics against neurodegenerative diseases and other diseases in which protein degradation is reduced and misfolded proteins accumulate, including Charcot Marie Tooth 1A and 1B peripheral neuropathies, for which there are no treatments. Here we increased cGMP in the S63del mouse model of CMT1B by treating for three weeks with either the phosphodiesterase 5 inhibitor tadalafil, or the brain-penetrant soluble guanylyl cyclase stimulator CYR119. Both molecules activated proteasomes in the affected peripheral nerves, reduced polyubiquitinated proteins, and improved myelin thickness and nerve conduction. CYR119 increased cGMP more than tadalafil in the peripheral nerves of S63del mice and elicited greater biochemical and functional improvements. To determine whether raising cGMP could be beneficial in other neuropathies, we first showed that polyubiquitinated proteins and the disease-causing protein accumulate in the sciatic nerves of the C3 mouse model of CMT1A. Treatment of these mice with CYR119 reduced the levels of polyubiquitinated proteins and the disease-causing protein, presumably by increasing their degradation, and improved myelination, nerve conduction, and motor coordination. Thus, pharmacological agents that increase cGMP are promising treatments for CMT1 neuropathies and may be useful against other proteotoxic and neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

The phosphodiesterases type 5 (PDE5) are catalytic enzymes converting the second messenger cyclic guanosine monophosphate (cGMP) to 5’ GMP. While intracellular cGMP reduction is associated with several detrimental effects, cGMP stabilization associates with numerous benefits. The PDE5 specific inhibitors, PDE5i, found their explosive fortune as first-line treatment for erectile dysfunction (ED), due to their powerful vasoactive properties. The favorable effect for ED emerged as side-effect when PDE5i were originally proposed for coronary artery disease (CAD). From that point on, the use of PDE5i captured the attention of researchers, clinicians, and companies. Indeed, PDE5-induced intracellular cGMP stabilization offers a range of therapeutic opportunities associated not only with vasoactive effects, but also with immune regulatory/ anti-inflammatory actions. Chronic inflammation is acknowledged as the common link underlying most non-communicable diseases, including metabolic and cardiac diseases, autoimmune and neurodegenerative disorders, cancer. In this scenario, the clinical exploitation of PDE5i is undeniably beyond ED, representing a potential therapeutic tool in several human diseases. This review aims to overview the biological actions exerted by PDE5i, focusing on their ability as modulators of inflammation-related human diseases, with particular attention to inflammatory-related disorders, like cardiac diseases and cancer. [ABSTRACT FROM AUTHOR]

The coordination of assimilation pathways for all the elements that make up cellular components is a vital task for every organism. Integrating the assimilation and use of carbon (C) and nitrogen (N) is of particular importance because of the high cellular abundance of these elements. Starch is one of the most important storage polymers of photosynthetic organisms, and a complex regulatory network ensures that biosynthesis and degradation of starch are coordinated with photosynthetic activity and growth. Here, we analyzed three starch metabolism enzymes of Chlamydomonas reinhardtii that we captured by a cyclic guanosine monophosphate (cGMP) affinity chromatography approach, namely, soluble starch synthase STA3, starch‐branching enzyme SBE1, and α‐amylase AMA2. While none of the recombinant enzymes was directly affected by the presence of cGMP or other nucleotides, suggesting an indirect binding to cGMP, AMA2 activity was stimulated in the presence of L‐glutamine (Gln). This activating effect required the enzyme's N‐terminal aspartate kinase–chorismate mutase–tyrA domain. Gln is the first N assimilation product and not only a central compound for the biosynthesis of N‐containing molecules but also a recognized signaling molecule for the N status. Our observation suggests that AMA2 might be a means to coordinate N and C metabolism at the enzymatic level, increasing the liberation of C skeletons from starch when high Gln levels signal an abundance of assimilated N. [ABSTRACT FROM AUTHOR]

Priapism, defined as a prolonged and often painful penile erection occurring without sexual stimulation or desire, is a common complication in sickle cell disease (SCD), affecting up to 48% of male patients. This condition presents significant clinical challenges and can lead to erectile dysfunction if not properly managed. Current pharmacological treatments for SCD-related priapism are primarily reactive rather than preventative, highlighting a gap in effective medical intervention strategies. A critical factor in developing priapism is the reduced basal bioavailability of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in erectile tissues. New prevention strategies should ideally target the underlying pathophysiology of the disease. Compounds that stimulate and activate soluble guanylate cyclase (sGC) emerge as potential therapeutic candidates since these compounds have the property of inducing cGMP production by sGC. This review explores the potential of sGC stimulators and activators in treating priapism associated with SCD. We discuss the advantages of these agents in the face of the challenging pathophysiology of SCD. Additionally, the review underscores the impact of intravascular hemolysis and oxidative stress on priapism pathophysiology in SCD, areas in which sGC stimulators and activators may also have beneficial therapeutic effects. [ABSTRACT FROM AUTHOR]

Simple Summary: Alcohol-associated liver disease (ALD) is a global health problem with high morbidity and mortality. ALD is a multifactorial disease which manifests as lipid accumulation in the liver, hepatic inflammation, fibrosis, and cirrhosis. Due to the complexity of this disease, and despite extensive research to find a cure, there is no FDA-approved therapy to date. Cyclic nucleotides are important second messengers regulating numerous processes in the cells of the body. Their levels and signaling are tightly controlled by sophisticated molecular networks. We have found that cyclic nucleotide levels change in the livers of patients with ALD as well as in mice chronically fed alcohol. These changes are associated with significant alterations in the expression of genes involved in the regulation of cyclic nucleotide signaling and inflammatory/fibrotic processes. Our findings could lead to the development of novel targeted therapies for ALD. Background: Cyclic nucleotides are second messengers, which play significant roles in numerous biological processes. Previous work has shown that cAMP and cGMP signaling regulates various pathways in liver cells, including Kupffer cells, hepatocytes, hepatic stellate cells, and cellular components of hepatic sinusoids. Importantly, it has been shown that cAMP levels and enzymes involved in cAMP homeostasis are affected by alcohol. Although the role of cyclic nucleotide signaling is strongly implicated in several pathological pathways in liver diseases, studies describing the changes in genes regulating cyclic nucleotide metabolism in ALD are lacking. Methods: Male C57B/6 mice were used in an intragastric model of alcohol-associated steatohepatitis (ASH). Liver injury, inflammation, and fibrogenesis were evaluated by measuring plasma levels of injury markers, liver tissue cytokines, and gene expression analyses. Liver transcriptome analysis was performed to examine the effects of alcohol on regulators of cyclic AMP and GMP levels and signaling. cAMP and cGMP levels were measured in mouse livers as well as in livers from healthy human donors and patients with alcohol-associated hepatitis (AH). Results: Our results show significant changes in several phosphodiesterases (PDEs) with specificity to degrade cAMP (Pde4a, Pde4d, and Pde8a) and cGMP (Pde5a, Pde6d, and Pde9a), as well as dual-specificity PDEs (Pde1a and Pde10a) in ASH mouse livers. Adenylyl cyclases (ACs) 7 and 9, which are responsible for cAMP generation, were also affected by alcohol. Importantly, adenosine receptor 1, which has been implicated in the pathogenesis of liver diseases, was significantly increased by alcohol. Adrenoceptors 1 and 3 (Adrb), which couple with stimulatory G protein to regulate cAMP and cGMP signaling, were significantly decreased. Additionally, beta arrestin 2, which interacts with cAMP-specific PDE4D to desensitize G-protein-coupled receptor to generate cAMP, was significantly increased by alcohol. Notably, we observed that cAMP levels are much higher than cGMP levels in the livers of humans and mice; however, alcohol affected them differently. Specifically, cGMP levels were higher in patients with AH and ASH mice livers compared with controls. As expected, these changes in liver cyclic nucleotide signaling were associated with increased inflammation, steatosis, apoptosis, and fibrogenesis. Conclusions: These data strongly implicate dysregulated cAMP and cGMP signaling in the pathogenesis of ASH. Future studies to identify changes in these regulators in a cell-specific manner could lead to the development of novel targeted therapies for ASH. [ABSTRACT FROM AUTHOR]

Pancreatic ductal adenocarcinoma (PDAC) is a type of cancer with a high mortality rate. Current treatments for PDACs often have side effects, and drug resistance in cancer stem cells (CSCs) would be also a problem. Cyclic guanosine monophosphate (cGMP) suppresses the mitochondrial function of PDACs and inhibits their CSC properties. Metabolic regulation plays a crucial role in the maintenance of CSC phenotype, and we hypothesized that cGMP induction suppresses cancer stem cell properties in the cancer cell through energy-related signaling pathways. We demonstrated that induction of cGMP upregulated the PPARα/PDK4 pathway and suppressed CSC properties in PDAC, and patients with pancreatic cancer with high PDK4 gene expression had a better prognosis than those with low gene expression. Therefore, these mechanisms may provide new therapeutic targets for the eradication of pancreatic CSCs. • cGMP production promoted the gene expression of PPAR and PDK4 in Panc-1 cells. • PDK4 mediated suppression of cancer stemness by cGMP production. • Patients with pancreatic cancer with high PDK4 gene expression had better prognosis. [ABSTRACT FROM AUTHOR]

Background: Phosphodiesterases (PDEs) have been associated with psychiatric disorders in observational studies; however, the causality of associations remains unestablished. Methods: Specifically, cyclic nucleotide PDEs were collected from genome-wide association studies (GWASs), including PDEs obtained by hydrolyzing both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) (PDE1A, PDE2A, and PDE3A), specific to cGMP (PDE5A, PDE6D, and PDE9A) and cAMP (PDE4D and PDE7A). We performed a bidirectional two-sample Mendelian randomization (MR) analysis to investigate the relationship between PDEs and nine psychiatric disorders. The inverse-variance-weighted (IVW) method, MR-Egger, and weighted median were used to estimate causal effects. The Cochran's Q test, MR-Egger intercept test, MR Steiger test, leave-one-out analyses, funnel plot, and MR pleiotropy residual sum and outlier (MR-PRESSO) were used for sensitivity analyses. Results: The PDEs specific to cAMP were associated with higher-odds psychiatric disorders. For example, PDE4D and schizophrenia (SCZ) (odds ratios (OR) = 1.0531, PIVW = 0.0414), as well as major depressive disorder (MDD) (OR = 1.0329, PIVW = 0.0011). Similarly, PDE7A was associated with higher odds of attention-deficit/hyperactivity disorder (ADHD) (OR = 1.0861, PIVW = 0.0038). Exploring specific PDE subtypes and increase intracellular cAMP levels can inform the development of targeted interventions. We also observed PDEs (which hydrolyzes both cAMP and cGMP) was associated with psychiatric disorders [OR of PDE1A was 1.0836 for autism spectrum disorder; OR of PDE2A was 0.8968 for Tourette syndrome (TS) and 0.9449 for SCZ; and OR of PDE3A was 0.9796 for MDD; P < 0.05]. Furthermore, psychiatric disorders also had some causal effects on PDEs [obsessive–compulsive disorder on increased PDE6D and decreased PDE2A and PDE4D; anorexia nervosa on decreased PDE9A]. The results of MR were found to be robust using multiple sensitivity analysis. Conclusions: In this study, potential causal relationships between plasma PDE proteins and psychiatric disorders were established. Exploring other PDE subtypes not included in this study could provide a more comprehensive understanding of the role of PDEs in psychiatric disorders. The development of specific medications targeting PDE subtypes may be a promising therapeutic approach for treating psychiatric disorders. [ABSTRACT FROM AUTHOR]

Key message: Endogenous cGMP operates downstream of CH4 control of adventitious rooting, following by the regulation in the expression of cell cycle regulatory and auxin signaling-related genes. Methane (CH4) is a natural product from plants and microorganisms. Although exogenously applied CH4 and cyclic guanosine monophosphate (cGMP) are separately confirmed to be involved in the control of adventitious root (AR) formation, the possible interaction still remains elusive. Here, we observed that exogenous CH4 not only rapidly promoted cGMP synthesis through increasing the activity of guanosine cyclase (GC), but also induced cucumber AR development. These responses were obviously impaired by the removal of endogenous cGMP with two GC inhibitors. Anatomical evidence showed that the emerged stage (V) among AR primordia development might be the main target of CH4–cGMP module. Genetic evidence revealed that the transgenic Arabidopsis that overexpressed the methyl-coenzyme M reductase gene (MtMCR) from Methanobacterium thermoautotrophicum not only increased-cGMP production, but also resulted in a pronounced AR development compared to wild-type (WT), especially with the addition of CH4 or the cell-permeable cGMP derivative 8-Br-cGMP. qPCR analysis confirmed that some marker genes associated with cell cycle regulatory and auxin signaling were closely related to the brand-new CH4–cGMP module in AR development. Overall, our results clearly revealed an important function of cGMP in CH4 governing AR formation by modulating auxin-dependent pathway and cell cycle regulation. [ABSTRACT FROM AUTHOR]

This current study examined the role of calcium (Ca) and Cyclic GMP (cGMP) in mitigating the adverse effect of salt stress through magnetopriming of soybean cultivar JS-335 seeds with a static magnetic field (SMF, 200 mT for 1 h). The salt stress (50 mMNaCl) extensively reduced the early seedling growth (64%), vigour Index-I (71%), vigour Index-II (39%), total amylase (59%), protease (63%), and nitrate reductase (NR, 19%) activities in un-primed soybean seedlings. However, magnetopriming and Ca treatment enhanced all of these measured parameters along with remarkable increase in reactive oxygen species (ROS) and nitric oxide (NO) content. The exogenous application of Ca2+, cGMP and ROS regulators such as nifedipine (Ca2+ channel blocker), EGTA, ethylene glycol-β-amino ethyl ether tetra acetic acid (Ca2+chelators), genistein (cGMP blocker), and dimethyl thiourea (DMTU, H2O2 inhibitor) negatively affects the SMF-induced seedling length, seedling vigour, ROS, NO, and enzyme activities such as protease, total amylase, and NR in soybean seedlings. Results presented by using specific various biochemical inhibitors of Ca, cGMP, or ROS signalling in vivo indicated that Ca and cGMP are also involved with ROS and NO in the signal transduction of magnetic field enthused soybean seed germination and seedling growth under salt stress. [ABSTRACT FROM AUTHOR]

Soluble guanylate cyclase (sGC) stands as a pivotal regulatory element in intracellular signalling pathways, mediating the formation of cyclic guanosine monophosphate (cGMP) and impacting diverse physiological processes across tissues. Increased formation of reactive oxygen species (ROS) is widely recognized to modulate cGMP signalling. Indeed, oxidatively damaged, and therefore inactive sGC, contributes to poor vascular reactivity and more severe neurological damage upon stroke. However, the specific involvement of cGMP in redox signalling remains elusive. Here, we demonstrate a significant cGMP-dependent reduction of reactive oxygen and nitrogen species upon sGC activation under hypoxic conditions, independent of any potential scavenger effects. Importantly, this reduction is directly mediated by downregulating NADPH oxidase (NOX) 4 and 5 during reperfusion. Using an in silico simulation approach, we propose a mechanistic link between increased cGMP signalling and reduced ROS formation, pinpointing NF-κB1 and RELA/p65 as key transcription factors regulating NOX4/5 expression. In vitro studies revealed that p65 translocation to the nucleus was reduced in hypoxic human microvascular endothelial cells following sGC activation. Altogether, these findings unveil the intricate regulation and functional implications of sGC, providing valuable insights into its biological significance and ultimately therapeutic potential. [Display omitted] • Activation of sGC post-hypoxia lowers ROS without relying on scavenger effects. • In silico predictions links increased cGMP to reduced ROS via NF-κB1 and RELA/p65. • p65 nuclear translocation decreases with sGC activation by downregulating NOX4/5. • Insights into sGC regulation highlight its potential for improving stroke therapies. [ABSTRACT FROM AUTHOR]

Background: Intracellular levels of cyclic nucleotides can also be controlled by the action of multidrug resistance protein types 4 (MRP4) and 5 (MRP5). To date, no studies evaluated the role of their inhibition in an animal model of erectile dysfunction (ED). Objectives: To evaluate the effect of a 2‐week treatment with MK571, an inhibitor of the efflux of cyclic nucleotides in the ED of obese mice. Materials and methods: Mice were divided in three groups: (i) lean, (ii) obese, and (iii) obese + MK571. The corpus cavernosum (CC) were isolated, and concentration–response curves to acetylcholine (ACh), sodium nitroprusside (SNP), and tadalafil in addition to electrical field stimulation (EFS) were carried out in phenylephrine pre‐contracted tissues. Expression of ABCC4 and ABCC5, intracellular levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), the protein levels for pVASPSer157 and pVASPSer239, and the intracavernous pressure (ICP) were also determined. The intracellular and extracellular (supernatant) ratios in CC from obese and lean stimulated with a cGMP‐increasing substance (BAY 58‐2667) in the absence and presence of MK571 (20 μM, 30 min) were also assessed. Results: The treatment with MK571 completely reversed the lower relaxing responses induced by EFS, ACh, SNP, and tadalafil observed in obese mice CC in comparison with untreated obese mice. Cyclic GMP and p‐VASPSer239 expression were significantly reduced in CC from obese groups. MK571 promoted a sixfold increase in cGMP without interfering in the protein expression of p‐VASPSer239. Neither the cAMP levels nor p‐VASPSer157 were altered in MK571‐treated animals. The ICP was ∼50% lower in obese than in the lean mice; however, the treatment with MK571 fully reversed this response. Expressions of ABCC4 and ABCC5 were not different between groups. The intra/extracellular ratio of cGMP was similar in CC from obese and lean mice stimulated with BAY 58‐2667. Conclusions: The MRPs inhibition by MK571 favored the accumulation of cGMP in the smooth muscle cells, thus improving the smooth muscle relaxation and the erectile function in obese mice. [ABSTRACT FROM AUTHOR]

The visual process begins with the absorption of photons by photopigments of cone and rod photoreceptors in the retina. In this process, the signal is first amplified by a cyclic guanosine monophosphate (cGMP)-based signaling cascade and then converted into an electrical signal by cyclic nucleotide-gated (CNG) channels. CNG channels are purely ligand-gated channels whose activity can be controlled by cGMP, which induces a depolarizing Na+/Ca2+ current upon binding to the channel. Structurally, CNG channels belong to the superfamily of pore-loop cation channels and share structural similarities with hyperpolarization-activated cyclic nucleotide (HCN) and voltage-gated potassium (KCN) channels. Cone and rod photoreceptors express distinct CNG channels encoded by homologous genes. Mutations in the genes encoding the rod CNG channel (CNGA1 and CNGB1) result in retinitis-pigmentosa-type blindness. Mutations in the genes encoding the cone CNG channel (CNGA3 and CNGB3) lead to achromatopsia. Here, we review the molecular properties of CNG channels and describe their physiological and pathophysiological roles in the retina. Moreover, we summarize recent activities in the field of gene therapy aimed at developing the first gene therapies for CNG channelopathies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Vardenafil (VDF) is a relatively new phosphodiesterase-5 inhibitor that has limited oral bioavailability (≈15%). The objective of this study was to develop bilosome-based mucoadhesive buccal sponge for augmenting the oral bioavailability of VDF. VDF-loaded bilosomes were fabricated and optimized using a Box-Behnken design. The optimized VDF-loaded bilosomal formulation was assessed for surface morphology, particle size, thermal characteristics, and in vitro release. Afterwards, the optimized bilosomal formulation was incorporated into a cellulose-based matrix to obtain buccal sponge, which was evaluated for ex vivo permeation studies, in vivo oral bioavailability, and in vivo serum concentration of cyclic guanosine monophosphate (cGMP). The mean particle size and entrapment efficiency (%) of optimized bilosome formulation were 282.6 ± 9.5 nm and 82.95 ± 3.5%, respectively. In vitro release studies at pH 6.8 emphasized the potential of optimized bilosomal formulation to sustain VDF release for 12 h. Ex vivo permeation study using sheep buccal mucosa indicated significant enhancement in penetration of VDF from bilosomal buccal sponge compared to plain VDF gel. Pharmacokinetic study in Albino rats showed ~5 fold increase in relative bioavailability with bilosomal buccal sponge, compared to VDF suspension. In addition, VDF-loaded bilosomal buccal sponge triggered higher serum levels of cGMP, a biomarker of VDF in vivo efficacy, compared to oral VDF suspension. To sum up, bilosomes might represent a potential nanocarrier for buccal delivery of VDF, enhancing its oral bioavailability and therapeutic efficacy. [ABSTRACT FROM AUTHOR]

The disease retinitis pigmentosa (RP) leads to photoreceptor degeneration by a yet undefined mechanism(s). In several RP mouse models (i.e., rd mice), a high cyclic GMP (cGMP) level within photoreceptors is detected, suggesting that cGMP plays a role in degeneration. The rap guanine exchange factor 4 (EPAC2) is activated by cyclic AMP (cAMP) and is an accepted cGMP-interacting protein. It is unclear whether and how cGMP interacts with EPAC2 in degenerating photoreceptors; we therefore investigated EPAC2 expression and interactions with cGMP and cAMP in retinas of the rd1 and rd10 models for retinal degeneration. EPAC2 expression in the photoreceptor layer increased significantly during rd1 and rd10 degeneration, and an increase in EPAC2 interactions with cGMP but not cAMP in the rd1 was also seen via a proximity ligation assay on histological sections. Retinal explant cultures revealed that pharmacological inhibition of the EPAC2 activity reduced the photoreceptor layer thickness in the rd10 retina, suggesting that EPAC2 inhibition promotes degeneration. Taken together, our results support the hypothesis that high degeneration-related cGMP leads to increased EPAC2 and cGMP interactions, inhibiting EPAC2. By inference, EPAC2 could have neuroprotective capacities that may be exploited in the future. [ABSTRACT FROM AUTHOR]

Cyclic guanosine monophosphate (cGMP), produced by guanylate cyclase (GC), activates protein kinase G (PKG) and regulates cardiac remodeling. cGMP/PKG signal is activated by two intrinsic pathways: nitric oxide (NO)-soluble GC and natriuretic peptide (NP)-particulate GC (pGC) pathways. Activation of these pathways has emerged as a potent therapeutic strategy to treat patients with heart failure, given cGMP-PKG signaling is impaired in heart failure with reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF). Large scale clinical trials in patients with HFrEF have shown positive results with agents that activate cGMP-PKG pathways. In patients with HFpEF, however, benefits were observed only in a subgroup of patients. Further investigation for cGMP-PKG pathway is needed to develop better targeting strategies for HFpEF. This review outlines cGMP-PKG pathway and its modulation in heart failure. [ABSTRACT FROM AUTHOR]

In vitro fertilization (IVF) is currently one of the most effective methods of infertility treatment. An alternative to commonly used ovarian hyperstimulation can become extracorporeal maturation of oocytes (in vitro maturation; IVM). Fertilization and normal development of the embryo depends on the cytoplasmic, nuclear and genomic maturity of the oocyte. The microenvironment of the ovarian follicle and maternal signals, which mediate bidirectional communication between granulosa, cumulus and oocyte cells, influence the growth, maturation and acquisition of oocyte development capability. During oogenesis in mammals, the meiosis is inhibited in the oocyte at the prophase I of the meiotic division due to the high cAMP level. This level is maintained by the activity of C-type natriuretic peptide (CNP, NPPC) produced by granulosa cells. The CNP binds to the NPR2 receptor in cumulus cells and is responsible for the production of cyclic guanosine monophosphate (cGMP). The cGMP penetrating into the oocyte through gap junctions inhibits phosphodiesterase 3A (PDE3A), preventing cAMP hydrolysis responsible for low MPF activity. The LH surge during the reproductive cycle reduces the activity of the CNP/NPR2 complex, which results in a decrease in cGMP levels in cumulus cells and consequently in the oocyte. Reduced cGMP concentration unblocks the hydrolytic activity of PDE3A, which decreases cAMP level inside the oocyte. This leads to the activation of MPF and resumption of meiosis. The latest IVM methods called SPOM, NFSOM or CAPA IVM consist of two steps: prematuration and maturation itself. Taking into account the role of cAMP in inhibiting and then unblocking the maturation of oocytes, they have led to a significant progress in terms of the percentage of mature oocytes in vitro and the proportion of properly developed embryos in both animals and humans. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) signaling in biology relies on its activating cyclic guanosine monophosphate (cGMP) production by the NO receptor soluble guanylyl cyclase (sGC). sGC must obtain heme and form a heterodimer to become functional, but paradoxically often exists as an immature heme-free form in cells and tissues. Based on our previous finding that NO can drive sGC maturation, we investigated its basis by utilizing a fluorescent sGC construct whose heme level can be monitored in living cells. We found that NO generated at physiologic levels quickly triggered cells to mobilize heme to immature sGC. This occurred when NO was generated within cells or by neighboring cells, began within seconds of NO exposure, and led cells to construct sGC heterodimers and thus increase their active sGC level by several-fold. The NO-triggered heme deployment involved cellular glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-heme complexes and required the chaperone hsp90, and the newly formed sGC heterodimers remained functional long after NO generation had ceased. We conclude that NO at physiologic levels triggers assembly of its own receptor by causing a rapid deployment of cellular heme. Redirecting cellular heme in response to NO is a way for cells and tissues to modulate their cGMP signaling and to more generally tune their hemeprotein activities wherever NO biosynthesis takes place. [ABSTRACT FROM AUTHOR]

Soluble guanylyl cyclase (sGC, also called GC1) is the main receptor for nitric oxide (NO) that catalyzes the production of the second messenger molecule, 3′5′ cyclic guanosine monophosphate (cGMP) leading to vasorelaxation, and inhibition of leukocyte recruitment and platelet aggregation. Enhancing cGMP levels, through sGC agonism or inhibition of cGMP breakdown via phosphodiesterase inhibition, has yielded FDA approval for several cGMP modifier therapies for treatment of cardiovascular and pulmonary diseases. While basic research continues to improve our understanding of cGMP signaling and as new therapies evolve to elevate cGMP levels, we provide a short methodological primer for measuring cGMP and cGMP-mediated vascular relaxation for investigators. • Nitric oxide (•NO) stimulates soluble guanylyl cyclase (sGC) to catalyze the production of cyclic guanosine 3′, 5′-monophosphate (cGMP) • We provide general guidelines for assessing sGC-cGMP signaling pathway in cells and tissue as well as measuring ex vivo •NO-sGC-cGMP mediated vascular relaxation • By combining cell and tissue-based measurements of cGMP and myography, one can rigorously assess the impact of new physiological factors and pharmacological modulators that influence •NO -cGMP signaling [ABSTRACT FROM AUTHOR]

Chronic kidney diseaQueryse (CKD) is associated with oxidative stress which can interrupt the nitric oxide (NO)/soluble guanylyl cyclase (sGC) signaling and decrease cyclic guanosine monophosphate (cGMP) production. Low cGMP concentrations can cause kidney damage and progression of CKD. The novel sGC activator runcaciguat targets the oxidized and heme-free form of sGC, restoring cGMP production under oxidative stress. The purpose of this study is to investigate if runcaciguat could provide an effective treatment for CKD. Runcaciguat was used for the treatment not only in rat CKD models with different etiologies and comorbidities, namely of hypertensive rats, the renin transgenic (RenTG) rat, and angiotensin-supplemented (ANG-SD) rat, but also in rats with diabetic and metabolic CKD, the Zucker diabetic fatty (ZDF) rat. The treatment duration was 2 to 42 weeks and runcaciguat was applied orally in doses from 1 to 10 mg/kg/bid. In these different rat CKD models, runcaciguat significantly reduced proteinuria (urinary protein to creatinine ratio; uPCR). These effects were also significant at doses which did not or only moderately decrease systemic blood pressure. Moreover, runcaciguat significantly decreased kidney injury biomarkers and attenuated morphological kidney damages. In RenTG rats, runcaciguat improved survival rates and markers of heart injury. These data demonstrate that the sGC activator runcaciguat exhibits cardio-renal protection at doses which did not reduce blood pressure and was effective in hypertensive as well as diabetic and metabolic CKD models. These data, therefore, suggest that runcaciguat, with its specific mode of action, represents an efficient treatment approach for CKD and associated CV diseases. [ABSTRACT FROM AUTHOR]

As precursor cells of odontoblasts, dental papilla cells (DPCs) form the dentin–pulp complex during tooth development. Nitric oxide (NO) regulates the functions of multiple cells and organ tissues, including stem cell differentiation and bone formation. In this paper, we explored the involvement of NO in odontoblastic differentiation. We verified the expression of NO synthase (NOS) in rat odontoblasts by nicotinamide adenine dinucleotide phosphate–diaphorase (NADPH‐d) staining and immunohistochemistry in vivo. The expression of all three NOS isoforms in rat DPCs was confirmed by quantitative reverse‐transcription polymerase chain reaction (qRT‐PCR), immunofluorescence, and western blotting in vitro. The expression of neuronal NOS and endothelial NOS was upregulated during the odontoblastic differentiation of DPCs. Inhibition of NOS function by NOS inhibitor l‐NG‐monomethyl arginine (L‐NMMA) resulted in reduced formation of mineralized nodules and expression of dentin sialophosphoprotein (DSPP) and dentin matrix protein (DMP1) during DPC differentiation. The NO donor S‐nitroso‐N‐acetylpenicillamine (SNAP, 0.1, 1, 10, and 100 μM) promoted the viability of DPCs. Extracellular matrix mineralization and odontogenic markers expression were elevated by SNAP at low concentrations (0.1, 1, and 10 μM) and suppressed at high concentration (100 μM). Blocking the generation of cyclic guanosine monophosphate (cGMP) with 1H‐(1,2,4)oxadiazolo‐(4,3‐a)quinoxalin‐1‐one (ODQ) abolished the positive influence of SNAP on the odontoblastic differentiation of DPCs. These findings demonstrate that NO regulates the odontoblastic differentiation of DPCs, thereby influencing dentin formation and tooth development. [ABSTRACT FROM AUTHOR]

Purpose: Cyclic guanosine monophosphate (cGMP) is a second messenger for natriuretic peptide (NP) and nitric oxide pathways; its enhancement a target for heart failure and cardiovascular disease (CVD). We evaluated whether plasma cGMP was associated with change in left ventricular mass (LVM) among individuals free of CVD and if this differed by sex. Methods and Results: In 611 men and 612 women aged 45-84 years with plasma cGMP measured at baseline and cardiac MRI performed at baseline and 10 years later, we tested associations of cGMP [log-transformed, per 1 SD increment] with LVM, adjusting for CVD risk factors and N-terminal pro-Btype-NP (NT-proBNP). Participants had mean (SD) age of 63.1(8.5) years and cGMP 4.8(2.6) pmol/mL. Cross-sectionally, higher cGMP was associated with lesser LVM, non-lin-early. In contrast, longitudinally, higher cGMP was associated with increase in LVM [1.70g (0.61, 2.78)] over 10 years. Higher cGMP was associated with greater LVM change in men [2.68g (1.57, 3.79)] but not women [0.24g ((-0.92, 1.39); p-interaction < 0.001]. Conclusion: In conclusion, in a community-based cohort, higher cGMP levels were associated with increase in LVM over 10 years independent of CVD risk factors and NT-proBNP in men, perhaps reflecting compensatory changes. Further studies are needed to understand mechanistic roles of cGMP in LV remodelling and associated sex differences. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect of ischemic stroke (is) combined with hyperlipidemia (HLP) on erectile function in rats and its mechanism. Methods: Thirty male SD rats were randomly divided into normal group and HLP group. The model of is combined with HLP was established by feeding high-fat diet. The stroke model group and sham operation group were established by operation method. The contents of testosterone (T), D-Dimer (D-D) and cyclic guanosine (cGMP) were detected by ELISA. Western blot and real-time PCR were used to detect the expression of VEGF protein and mRNA, and hematoxylin and eosin (He) staining of penile tissue were observed to evaluate its erectile function. Results: Compared with group C, the levels of cGMP and T in group M decreased, while VEGF and D-D increased. He staining showed that the tissue structure of corpus cavernosum in model group was obviously damaged. Conclusion: The model of ischemic stroke combined with hyperlipidemia has certain effect on erectile function of rats, and the mechanism may be related to the expression of cGMP, VEGF related protein and mRNA. [ABSTRACT FROM AUTHOR]

The use of already-approved drugs to treat new or alternative diseases has proved to be beneficial in medicine, because it reduces both drug development costs and timelines. Most drugs can be used to treat different illnesses, due their mechanisms of action are not restricted to one molecular target, organ or illness. Diverging from its original intent offers an opportunity to repurpose previously approved drugs to treat other ailments. This is the case of sildenafil (Viagra), a phosphodiesterase-5 (PDE5) inhibitor, which was originally designed to treat systemic hypertension and angina but is currently commercialized as erectile dysfunction treatment. Sildenafil, tadalafil, and vardenafil are PDE5 inhibitors and potent vasodilators, that extend the physiological effects of nitric oxide and cyclic guanosine monophosphate (cGMP) signaling. Although most of the biological implications of these signaling regulations remain unknown, they offer a large therapeutic potential for several diseases. In addition, some PDE5 inhibitors' molecular effects seem to play a key role in different illnesses such as kidney disease, diabetes mellitus, and cancer. In this review, we discuss the molecular effects of PDE5 inhibitors and their therapeutic repurposing in different types of cancer. [ABSTRACT FROM AUTHOR]

The essential role of cyclic guanosine monophosphate (cGMP) signaling in regulating the oocyte meiotic cell cycle has been established. However, control of the level of cGMP in ovarian follicles is unclear. The cGMP-hydrolyzing phosphodiesterases (PDEs) are important in regulating the cellular cGMP level. We used zebrafish as a model to study the role of a cGMP-hydrolyzing phosphodiesterase-9a (PDE9a) in meiotic maturation of oocytes. Three PDE9a coding genes (PDE9aa, PDE9ab, and PDE9ac) were identified in zebrafish. Both pde9aa and pde9ac are expressed in most adult tissues including the ovary, but pde9ab is only expressed in the ovary, kidney, pituitary, and brain. All three pde9as mRNA exhibited different expression profiles during folliculogenesis. All of them are highly expressed in the oocyte but not in the follicular cell. The expression of both pde9aa and pde9ab , but not pde9ac , in ovarian follicles increases during oocyte maturation either in natural ovulatory cycle or induced by administration of hCG in vivo. We overexpressed pde9aa by injection of capped pde9aa mRNA into the oocytes. The cGMP level was decreased, and oocyte maturation was stimulated. When the activity of PDE9a was blocked by a specific inhibitor, Bay736691, the oocyte maturation was also stimulated. The stimulatory effect could be blocked by a gap junction blocker. However, the spontaneous oocyte maturation of denuded oocytes was not largely affected after treatment with Bay736691. All of the mature oocytes obtained by either treatment of Bay736691 or injection of pde9aa mRNA, could be fertilized in vitro. These results demonstrate the dual roles of PDE9a in oocyte maturation. The basal level of PDE9a is responsible for maintaining the meiotic arrest, and the increased level of PDE9a induced by LH signaling is helpful for stimulating meiotic maturation by hydrolyzing cGMP in oocytes. • Three PDE9a coding genes (PDE9aa, PDE9ab and PDE9ac) were identified in zebrafish. • All PDE9a mRNA are highly expressed in the oocyte of zebrafish. • The expression of both pde9aa and pde9ab is increased in oocyte during oocyte maturation. • PDE9a has dual roles in regulating the meiotic maturation of zebrafish oocytes. [ABSTRACT FROM AUTHOR]

The correlation between cell hydration and proliferation is one of the controversial subjects in the present cancer research because the detailed mechanism(s) of correlation between these two cell parameters are not evaluated yet. The fact that magnetic fields have antitumor effects and our previous data that the effect of 4 Hz pulsing magnetic field (PMF) is realized by the activation of Cyclic guanosine monophosphate (cGMP)-dependent Na/Ca exchange allow us to suggest that through the study of PMF effects on cell hydration and proliferation in soft tissues of sarcoma-180 tumor-carrying mice compared with those of healthy ones will be possible to evaluate the character of correlation between cell hydration and proliferation in norm and pathology. The daily 30-min PMF (0.2 mT) exposed on tumor-carrying mice has lifetime prolongation, time-dependent depression of tumor growth, decrease of thermal threshold, and lactate concentration in blood. In the initial (6 days) period tumorigenesis PMF leads to dehydration in spleen cells, which is accompanied by the activation of cell proliferation, while in late periods of tumorigenesis it leads to cell hydration accompanied with proliferation. We are suggesting that PMF-induced overhydration and the increase of cell proliferation in cancer tissue as a consequence of high [Ca]i-induced activation of Ca-calmoduline-NO-cGMP pathway leads to the activation of FNa/Ca exchange, while its antitumor effect expressed in initial period of tumorigenesis is due to the activation of cGMP-dependent FNa/Ca, where because of low [Ca]i, it brings to cell dehydration as a result of reactivation of Na/K pump. [ABSTRACT FROM AUTHOR]

In the inner ear, cyclic guanosine monophosphate (cGMP) signaling has been described as facilitating otoprotection, which was previously observed through elevated cGMP levels achieved by phosphodiesterase 5 inhibition. However, to date, the upstream guanylyl cyclase (GC) subtype eliciting cGMP production is unknown. Here, we show that mice with a genetic disruption of the gene encoding the cGMP generator GC-A, the receptor for atrial and B-type natriuretic peptides, display a greater vulnerability of hair cells to hidden hearing loss and noise- and age-dependent hearing loss. This vulnerability was associated with GC-A expression in spiral ganglia and outer hair cells (OHCs) but not in inner hair cells (IHCs). GC-A knockout mice exhibited elevated hearing thresholds, most pronounced for the detection of high-frequency tones. Deficits in OHC input–output functions in high-frequency regions were already present in young GC-A-deficient mice, with no signs of an accelerated progression of age-related hearing loss or higher vulnerability to acoustic trauma. OHCs in these frequency regions in young GC-A knockout mice exhibited diminished levels of KCNQ4 expression, which is the dominant K+ channel in OHCs, and decreased activation of poly (ADP-ribose) polymerase-1, an enzyme involved in DNA repair. Further, GC-A knockout mice had IHC synapse impairments and reduced amplitudes of auditory brainstem responses that progressed with age and with acoustic trauma, in contrast to OHCs, when compared to GC-A wild-type littermates. We conclude that GC-A/cGMP-dependent signaling pathways have otoprotective functions and GC-A gene disruption differentially contributes to hair-cell damage in a healthy, aged, or injured system. Thus, augmentation of natriuretic peptide GC-A signaling likely has potential to overcome hidden and noise-induced hearing loss, as well as presbycusis. [ABSTRACT FROM AUTHOR]

The cyclic guanosine monophosphate (cGMP) signaling system is one of the most prominent regulators of a variety of physiological and pathophysiological processes in many mammalian and non-mammalian tissues. Targeting this pathway by increasing cGMP levels has been a very successful approach in pharmacology as shown for nitrates, phosphodiesterase (PDE) inhibitors and stimulators of nitric oxide-guanylyl cyclase (NO-GC) and particulate GC (pGC). This is an introductory review to the cGMP signaling system intended to introduce those readers to this system, who do not work in this area. This article does not intend an in-depth review of this system. Signal transduction by cGMP is controlled by the generating enzymes GCs, the degrading enzymes PDEs and the cGMP-regulated enzymes cyclic nucleotide-gated ion channels, cGMP-dependent protein kinases and cGMP-regulated PDEs. Part A gives a very concise introduction to the components. Part B gives a very concise introduction to the functions modulated by cGMP. The article cites many recent reviews for those who want a deeper insight. [ABSTRACT FROM AUTHOR]

Cyclic guanosine monophosphate (cGMP) is a unique second messenger molecule formed in different cell types and tissues. cGMP targets a variety of downstream effector molecules and, thus, elicits a very broad variety of cellular effects. Its production is triggered by stimulation of either soluble guanylyl cyclase (sGC) or particulate guanylyl cyclase (pGC); both enzymes exist in different isoforms. cGMP-induced effects are regulated by endogenous receptor ligands such as nitric oxide (NO) and natriuretic peptides (NPs). Depending on the distribution of sGC and pGC and the formation of ligands, this pathway regulates not only the cardiovascular system but also the kidney, lung, liver, and brain function; in addition, the cGMP pathway is involved in the pathogenesis of fibrosis, inflammation, or neurodegeneration and may also play a role in infectious diseases such as malaria. Moreover, new pharmacological approaches are being developed which target sGC- and pGC-dependent pathways for the treatment of various diseases. Therefore, it is of key interest to understand this pathway from scratch, beginning with the molecular basis of cGMP generation, the structure and function of both guanylyl cyclases and cGMP downstream targets; research efforts also focus on the subsequent signaling cascades, their potential crosstalk, and also the translational and, ultimately, the clinical implications of cGMP modulation. This review tries to summarize the contributions to the "9th International cGMP Conference on cGMP Generators, Effectors and Therapeutic Implications" held in Mainz in 2019. Presented data will be discussed and extended also in light of recent landmark findings and ongoing activities in the field of preclinical and clinical cGMP research. [ABSTRACT FROM AUTHOR]

The hypothesis of decreased nitric oxide (NO) bioavailability in sickle cell disease (SCD) proposes that multiple factors leading to decreased NO production and increased consumption contributes to vaso-occlusion, pulmonary hypertension, and pain. The anion nitrite is central to NO physiology as it is an end product of NO metabolism and serves as a reservoir for NO formation. However, there is little data on nitrite levels in SCD patients and its relationship to pain phenotype. We measured nitrite in SCD subjects and examined its relationship to SCD pain. In SCD subjects, median whole blood, red blood cell and plasma nitrite levels were higher than in controls, and were not associated with pain burden. Similarly, Townes and BERK homozygous SCD mice had elevated blood nitrite. Additionally, in red blood cells and plasma from SCD subjects and in blood and kidney from Townes homozygous mice, levels of cyclic guanosine monophosphate (cGMP) were higher compared to controls. In vitro, hemoglobin concentration, rather than sickle hemoglobin, was responsible for nitrite metabolism rate. In vivo , inhibition of NO synthases and xanthine oxidoreductase decreased nitrite levels in homozygotes but not in control mice. Long-term nitrite treatment in SCD mice further elevated blood nitrite and cGMP, worsened anemia, decreased platelets, and did not change pain response. These data suggest that SCD in humans and animals is associated with increased nitrite/NO availability, which is unrelated to pain phenotype. These findings might explain why multiple clinical trials aimed at increasing NO availability in SCD patients failed to improve pain outcomes. • Sickle cell disease (SCD) is thought to be associated with nitric oxide (NO) deficit. • SCD subjects and SCD mouse models have elevated blood nitrite and cGMP levels. • Nitrite supplementation increases nitrite levels but does not change pain phenotype in mice. • SCD mice have increased bleeding time, which are decreased with NO scavengers. • These findings indicate that clinical trials seeking to increase nitrite in SCD should to be reconsidered. [ABSTRACT FROM AUTHOR]

Background: Episodic memory consists of different mnemonic phases, including acquisition and early and late consolidation. Each of these phases is characterised by distinct molecular processes. Although both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are implicated in the acquisition phase, early consolidation only depends on cGMP, whereas late consolidation is mediated by cAMP. Accordingly, the cGMP-selective phosphodiesterase 5 (PDE5) inhibitor vardenafil or the cAMP-selective PDE4 inhibitor rolipram can improve memory acquisition or consolidation when applied during their respective time windows.Aims: Considering the important role of glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) during normal memory function, we aimed to investigate whether the differential actions of these PDE inhibitors are mediated through AMPAR dynamics.Methods: For biochemical analysis, mice were treated with either vardenafil or rolipram and sacrificed shortly after injection. For the behavioural studies, mice received either of the inhibitors during the different mnemonic phases, while their spatial memory was tested using the object location task, and they were sacrificed 24 hours later.Results: Administration of either vardenafil or rolipram causes rapid changes in AMPARs. Moreover, treatment with vardenafil during the acquisition or early consolidation of spatial memory resulted in increased surface levels of AMPARs which were still augmented 24 hours after learning. Membrane levels of AMPARs were not affected anymore 24 hours after learning when rolipram was administrated at either the acquisition or late consolidation phase.Conclusions: These results suggest that dissociative molecular mechanisms could mediate the pro-cognitive function of different classes of PDE inhibitors, and in the case of vardenafil, this phenomenon could be explained by changes in AMPAR dynamics. [ABSTRACT FROM AUTHOR]

Phosphodiesterase type 5 (PDE5) is an important enzyme associated with the hydrolysis of cyclic guanosine monophosphate (cGMP) to guanosine monophosphate (GMP). Due to the relevant role of second messenger cGMP as a mediator in many physiological processes, efforts have been converged to find a safe pharmacological approach, seeking a specific, selective and potent inhibitor of the PDE5 enzyme. There are five commercial drugs with potential for clinical use: tadalafil, sildenafil, avanafil, udenafil and vardenafil. Here, we applied molecular modeling to obtain different profiles of protein-ligand interactions by adopting distinct PDE5 structures, specifically PDBid:1XOZ and two extracted from molecular dynamics (MD) simulations. The results generated by molecular docking showed several possibilities for inhibitor interactions with the catalytic pocket. Tadalafil, sildenafil and vardenafil were clearly stabilized by Gln817 via a well-oriented hydrogen bond. Another set of different interactions, such as polar, hydrophobic, π-stacking, metal-ligand and electrostatic, were responsible for accommodating avanafil and udenafil. All of the ligands are discussed in detail with consideration of the distinct protein structures, and a profile of the probability of residue-ligand contact is suggested, with the most frequently observed being: Tyr612, His613, Ser661, Thr723, Asp724, Asp764, Leu765, Val782 and Phe786. The molecular interactions displayed herein confirm findings achieved by previous authors and also present new contacts. In addition, the discussion can help researchers obtain a molecular basis for planning new selective PDE5 inhibitors, as well as explain an inhibitor's experimental assays by considering the specific interactions occurring at the catalytic site. [ABSTRACT FROM AUTHOR]

Objective: Migraine displays clinical heterogeneity of attack features and attack triggers. The question is whether this heterogeneity is explained by distinct intracellular signaling pathways leading to attacks with distinct clinical features. One well-known migraine-inducing pathway is mediated by cyclic adenosine monophosphate and another by cyclic guanosine monophosphate. Calcitonin gene-related peptide triggers migraine via the cyclic adenosine monophosphate pathway and sildenafil via the cyclic guanosine monophosphate pathway. To date, no studies have examined whether migraine induction mediated via the cyclic adenosine monophosphate and cyclic guanosine monophosphate pathways yields similar attacks within the same patients.Methods: Patients were subjected to migraine induction on two separate days using calcitonin gene-related peptide (1.5 µg/min for 20 minutes) and sildenafil (100 mg) in a double-blind, randomized, double-dummy, cross-over design. Data on headache intensity, characteristics and accompanying symptoms were collected until 24 hours after drug administration.Results: Thirty-four patients were enrolled and 27 completed both study days. Seventeen patients developed migraine after both study drugs (63%; 95% CI: 42-81). Eight patients developed migraine on one day only (seven after sildenafil and one after calcitonin gene-related peptide). Two patients did not develop migraine on either day. Headache laterality, nausea, photophobia and phonophobia were similar between drugs in 77%, 65%, 100%, and 94%, respectively, of the 17 patients who developed attacks on both days.Conclusion: A majority of patients developed migraine after both calcitonin gene-related peptide and sildenafil. This supports the hypothesis that the cyclic adenosine monophosphate and cyclic guanosine monophosphate intracellular signaling pathways in migraine induction converge in a common cellular determinator, which ultimately triggers the same attacks. Trial registration: ClinicalTrials.gov Identifier: NCT03143465. [ABSTRACT FROM AUTHOR]

Resumption of meiosis in mammalian oocytes, defined as oocyte maturation, is stimulated by luteinizing hormone (LH). Fully grown oocytes can also mature spontaneously, upon their release from the ovarian follicle. However, growing oocytes fail to resume meiosis in vitro and the mechanism underlying their meiotic incompetence is unknown. It is commonly accepted that a drop in intraoocyte cyclic guanosine monophosphate (cGMP) resulting in the elevated activity of the oocyte-specific PDE3A leads to a decrease in cAMP content, essential for reinitiation of meiosis. We explored the regulation of these cyclic nucleotides and their degrading PDE3A in growing oocytes. Our research addressed the LH-induced rather than spontaneous oocyte maturation. We examined 16–21 as compared to 25-day-old, PMSG-primed rats, treated with the LH analog, hCG. The effect of LH was also examined ex vivo, in isolated ovarian follicles. We found that hCG failed to induce oocyte maturation and ovulation in the younger animals and that ovulation-associated genes were not upregulated in response to this gonadotropin. Furthemore, the drop of intraoocyte cGMP and cAMP observed in fully grown oocytes upon exposure of the ovary to LH, was not detected in growing oocytes. Interestingly, whereas the global expression of PDE3A in growing and fully grown oocytes is similar, a significantly lower activity of this enzyme was determined in growing oocytes. Our findings show that meiotic incompetence is associated with a relatively high oocyte cGMP concentration and a low activity of PDE3A, which in follicle-enclosed oocytes may represent the failure of the somatic follicle cells to respond to LH. [ABSTRACT FROM AUTHOR]

Background: Atrial natriuretic peptide (ANP) inhibits TGF-β1-induced epithelial-mesenchymal transition (EMT) in human airway cells. We aim to explore the role and mechanism of ANP on EMT of bronchial epithelial cells from murine model of allergic asthma in vitro. Methods: Murine model of allergic asthma was established with BALB/c mice using ovalbumin (OVA). Bronchial epithelial cells were isolated from OVA-exposed mice, and then were cocultured with TGF-β1, ANP, natriuretic peptide receptor A antagonist, cGMP analog, cGMP inhibitor or/and protein kinase G (PKG) inhibitor, respectively. We assessed expressions of E-Cadherin, α-SMA, cGMP, Smad3 and p-Smad3 in the murine cells before and after Smad3 silence. Results: Compared with bronchial epithelial cells from controls and OVA-exposed mice without additional stimulation, the mRNA and protein expressions of E-Cadherin were decreased but α-SMA expressions were increased in cells with TGF-β1 stimulation from OVA-exposed mice in vitro. That could be reversed by ANP. The effect of ANP could be mimicked by the cGMP analog, which could be reversed by cGMP or PKG inhibitor. Moreover, the phosphorylated Smad3 expression was consistent with that of α-SMA. When Smad3 was silenced, Smad3 was mostly expressed in cytoplasm. In contrast, it is mostly expressed in nucleus of non-silenced cells during EMT. Conclusions: In a murine model of allergic asthma, ANP could inhibit TGF-β1-induced EMT of bronchial epithelial cells through cGMP/PKG signaling, targeting TGF-β1/Smad3 via attenuating phosphorylation of Smad3 in vitro, which may provide potential of ANP in treating allergic asthma with airway remodeling. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is a ubiquitous signalling molecule with widespread distribution in prokaryotes and eukaryotes where it is involved in countless physiological processes. While the mechanisms governing nitric oxide (NO) synthesis and signalling are well established in animals, the situation is less clear in the green lineage. Recent investigations have shown that NO synthase, the major enzymatic source for NO in animals, is absent in land plants but present in a limited number of algae. The first detailed analysis highlighted that these new NO synthases are functional but display specific structural features and probably original catalytic activities. Completing this picture, analyses were undertaken in order to investigate whether major components of the prototypic NO/cyclic GMP signalling cascades mediating many physiological effects of NO in animals were also present in plants. Only a few homologues of soluble guanylate cyclases, cGMP-dependent protein kinases, cyclic nucleotide-gated channels, and cGMP-regulated phosphodiesterases were identified in some algal species and their presence did not correlate with that of NO synthases. In contrast, S -nitrosoglutathione reductase, a critical regulator of S -nitrosothiols, was recurrently found. Overall, these findings highlight that plants do not mediate NO signalling through the classical NO/cGMP signalling module and support the concept that S -nitrosation is a ubiquitous NO-dependent signalling mechanism. [ABSTRACT FROM AUTHOR]

PDE9A is a cGMP-specific phosphodiesterase expressed in neurons throughout the brain that has attracted attention as a therapeutic target to treat cognitive disorders. Indeed, PDE9A inhibitors are under evaluation in clinical trials as a treatment for Alzheimer's disease and schizophrenia. However, little is known about the cGMP signaling cascades regulated by PDE9A. Canonical cGMP signaling in brain follows the activation of neuronal nitric oxide synthase (nNOS) and the generation of nitric oxide, which activates soluble guanylyl cyclase and cGMP synthesis. However, we show that in mice, PDE9A regulates a pool of cGMP that is independent of nNOS, specifically, and nitric oxide signaling in general. This PDE9A-regulated cGMP pool appears to be highly compartmentalized and independent of cGMP pools regulated by several PDEs. These findings provide a new foundation for study of the upstream and downstream signaling elements regulated by PDE9A and its potential as a therapeutic target for brain disease. [ABSTRACT FROM AUTHOR]

The native particulate guanylyl cyclase B receptor (pGC-B) activator, C-type natriuretic peptide (CNP), induces anti-remodeling actions in the heart and kidney through the generation of the second messenger 3′, 5′ cyclic guanosine monophosphate (cGMP). Indeed fibrotic remodeling, particularly in cardiorenal disease states, contributes to disease progression and thus, has been a key target for drug discovery and development. Although the pGC-B/cGMP system has been perceived as a promising anti-fibrotic pathway, its therapeutic potential is limited due to the rapid degradation and catabolism of CNP by neprilysin (NEP) and natriuretic peptide clearance receptor (NPRC). The goal of this study was to bioengineer and test in vitro and in vivo a novel pGC-B activator, C53. Here we established that C53 selectively generates cGMP via the pGC-B receptor and is highly resistant to NEP and has less interaction with NPRC in vitro. Furthermore in vivo, C53 had enhanced cGMP-generating actions that paralleled elevated plasma CNP-like levels, thus indicating a longer circulating half-life compared to CNP. Importantly in human cardiac fibroblasts (HCFs) and renal fibroblasts (HRFs), C53 exerted robust cGMP-generating actions, inhibited TGFβ-1 stimulated HCFs and HRFs proliferation chronically and suppressed the differentiation of HCFs and HRFs to myofibroblasts. The current findings advance innovation in drug discovery and highlight C53 as a novel pGC-B activator with sustained in vivo activity and anti-fibrotic actions in vitro. Future studies are warranted to explore the efficacy and therapeutic opportunity of C53 targeting fibrosis in cardiorenal disease states and beyond. • The bioengineering of a novel and selective pGC-B/cGMP activator, C53 • C53 is highly resistant to NEP degradation and has less interaction with NPRC compared to CNP in vitro • C53 has more sustained in vivo activity compared to CNP under normal conditions in rats • C53 treatment inhibits human cardiac and renal fibroblasts proliferation and differentiation chronically stimulated by TGFβ-1 [ABSTRACT FROM AUTHOR]

Abstract The development of small molecule modulators of NO/cGMP signaling for use in the CNS has lagged far behind the use of such clinical agents in the periphery, despite the central role played by NO/cGMP in learning and memory, and the substantial evidence that this signaling pathway is perturbed in neurodegenerative disorders, including Alzheimer's disease. The NO-chimeras, NMZ and Nitrosynapsin, have yielded beneficial and disease-modifying responses in multiple preclinical animal models, acting on GABA A and NMDA receptors, respectively, providing additional mechanisms of action relevant to synaptic and neuronal dysfunction. Several inhibitors of cGMP-specific phosphodiesterases (PDE) have replicated some of the actions of these NO-chimeras in the CNS. There is no evidence that nitrate tolerance is a phenomenon relevant to the CNS actions of NO-chimeras, and studies on nitroglycerin in the periphery continue to challenge the dogma of nitrate tolerance mechanisms. Hybrid nitrates have shown much promise in the periphery and CNS, but to date only one treatment has received FDA approval, for glaucoma. The potential for allosteric modulation of soluble guanylate cyclase (sGC) in brain disorders has not yet been fully explored nor exploited; whereas multiple applications of PDE inhibitors have been explored and many have stalled in clinical trials. Highlights • Allosteric modulation of soluble guanylate cyclase (sGC) in the CNS has unexploited therapeutic benefits. • Modulation of cGMP by PDE inhibitors has been explored in the CNS; however, many PDEi's have stalled in clinical trials. • Preclinical data on nitromemantines and nomethiazoles support clinical trials in neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Guanylate cyclase C (GUCY2C) is a transmembrane receptor expressed on the luminal aspect of the intestinal epithelium. Its ligands include bacterial heat-stable enterotoxins responsible for traveler's diarrhea, the endogenous peptide hormones uroguanylin and guanylin, and the synthetic agents, linaclotide, plecanatide, and dolcanatide. Ligand-activated GUCY2C catalyzes the synthesis of intracellular cyclic GMP (cGMP), initiating signaling cascades underlying homeostasis of the intestinal epithelium. Mouse models of GUCY2C ablation, and recently, human populations harboring GUCY2C mutations, have revealed the diverse contributions of this signaling axis to epithelial health, including regulating fluid secretion, microbiome composition, intestinal barrier integrity, epithelial renewal, cell cycle progression, responses to DNA damage, epithelial-mesenchymal cross-talk, cell migration, and cellular metabolic status. Because of these wide-ranging roles, dysregulation of the GUCY2C-cGMP signaling axis has been implicated in the pathogenesis of bowel transit disorders, inflammatory bowel disease, and colorectal cancer. This review explores the current understanding of cGMP signaling in the intestinal epithelium and mechanisms by which it opposes intestinal injury. Particular focus will be applied to its emerging role in tumor suppression. In colorectal tumors, endogenous GUCY2C ligand expression is lost by a yet undefined mechanism conserved in mice and humans. Further, reconstitution of GUCY2C signaling through genetic or oral ligand replacement opposes tumorigenesis in mice. Taken together, these findings suggest an intriguing hypothesis that colorectal cancer arises in a microenvironment of functional GUCY2C inactivation, which can be repaired by oral ligand replacement. Hence, the GUCY2C signaling axis represents a novel therapeutic target for preventing colorectal cancer. [ABSTRACT FROM AUTHOR]

Constipation is an important health burden that reduces the quality of life for countless millions of people. Symptom-centric therapeutics are often used to treat constipation due to unknown etiology, but in many cases, these drugs are either inadequate or have significant side effects. More recently, synthetic peptide agonists for epithelial guanylyl cyclase C (GC-C) have been developed which are effective at treating constipation in a sub-population of adult constipation patients. The first to market was linaclotide that is structurally related to the diarrheagenic enterotoxin, but this was followed by plecanatide, which more closely resembles endogenous uroguanylin. Both the drugs exhibit almost identical clinical efficacy in about 20% of patients, with diarrhea being a common side effect. Despite the potential for reduced side effects with plecanatide, detailed analysis suggests that clinically, they are very similar. Ongoing clinical and preclinical studies with these drugs suggest that treating constipation might be the tip of the iceberg in terms of clinical utility. The expression of cGMP signaling components could be diagnostic for functional bowel disorders, and increasing cGMP using GC-C agonists or phosphodiesterase inhibitors has huge potential for treating enteric pain, ulcerative colitis, and for the chemoprevention of colorectal cancer. [ABSTRACT FROM AUTHOR]

Alcohol use disorder (AUD), which combines the criteria of both alcohol abuse and dependence, contributes as an important causal factor to multiple health and social problems. Given the limitation of current treatments, novel medications for AUD are needed to better control alcohol consumption and maintain abstinence. It has been well established that the intracellular signal transduction mediated by the second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) crucially underlies the genetic predisposition, rewarding properties, relapsing features, and systemic toxicity of compulsive alcohol consumption. On this basis, the upstream modulators phosphodiesterases (PDEs), which critically control intracellular levels of cyclic nucleotides by catalyzing their degradation, are proposed to play a role in modulating alcohol abuse and dependent process. Here, we highlight existing evidence that correlates cAMP and cGMP signal cascades with the regulation of alcohol-drinking behavior and discuss the possibility that PDEs may become a novel class of therapeutic targets for AUD. [ABSTRACT FROM AUTHOR]

The roles of cyclic guanosine monophosphate (cGMP) signaling in oocyte maturation attracts much attention in mammals, but its roles in fish are still largely unknown. Using zebrafish as a model, we demonstrated for the first time in fish that cGMP is involved in oocyte maturation, and its functional model in oocyte maturation is different from that of mammals. The intracellular cGMP could be regulated by nitric oxide (NO), we found that all three NO synthase enzymes and four soluble guanylyl cyclases (sGC) are expressed in the zebrafish ovary. Intriguingly, either the activation or inhibition of the NO/sGC/cGMP pathway in fully grown follicles could lead to oocyte maturation. During oocyte maturation, cGMP levels increased in the follicular cell layer but decreased in oocytes, while NO levels increased in follicular cells but remained constant in oocytes. Based on these findings in zebrafish, we propose a hypothetical model on the dual role of cGMP in oocyte maturation: in follicular cells the LH signal could increase the level of NO and cGMP which induces oocyte maturation, while in the oocyte the decreased cGMP level can also induce oocyte maturation. These findings help us to understand the molecular mechanism of fish oocyte maturation. [ABSTRACT FROM AUTHOR]

The bryozoan Bugula neritina is a cosmopolitan marine fouling species that causes major fouling problems in sub-tropical waters. Settlement of B. neritina larvae can be triggered without an obvious external cue. Here, the negative regulatory role of nitric oxide (NO) during larval settlement of B. neritina was demonstrated to be mediated by cyclic guanosine monophosphate (cGMP). Although the regulatory role of the NO-p38 MAPK signaling axis in larval settlement was not evident, inhibition of nitric oxide synthase (NOS) led to the deactivation of p38 MAPK. Exclusive localization of NO and NO signaling components in sensory-related organs of the larvae is consistent with its signal transduction function in metamorphosis. Overall, this study provides new insights into the regulatory roles of the NO-p38MAPK/cGMP pathway in B. neritina settlement. [ABSTRACT FROM AUTHOR]