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Concept: Guanylate cyclase


The nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) signal-transduction pathway is impaired in many cardiovascular diseases, including pulmonary arterial hypertension (PAH). Riociguat (BAY 63-2521) is a stimulator of sGC that works both in synergy with and independently of NO to increase levels of cGMP. The aims of this study were to investigate the role of NO-sGC-cGMP signaling in a model of severe PAH and to evaluate the effects of sGC stimulation by riociguat and PDE5 inhibition by sildenafil on pulmonary hemodynamics and vascular remodeling in severe experimental PAH.

Concepts: Pulmonology, Myocardial infarction, Pulmonary artery, Nitric oxide, Pulmonary hypertension, Guanylate cyclase, Sildenafil, Riociguat


Mutations in GUCY2D are the cause of Leber congenital amaurosis type 1 (LCA1). GUCY2D encodes retinal guanylate cyclase-1 (retGC1), a protein expressed exclusively in outer segments of photoreceptors and essential for timely recovery from photoexcitation. Recent clinical data show that, despite a high degree of visual disturbance stemming from a loss of cone function, LCA1 patients retain normal photoreceptor architecture, except for foveal cone outer segment abnormalities and, in some patients, foveal cone loss. These results point to the cone-rich central retina as a target for GUCY2D replacement. LCA1 gene replacement studies thus far have been conducted in rod-dominant models (mouse) or with vectors and organisms lacking clinical translatability. Here we investigate gene replacement in the Nrl(-/-)Gucy2e(-/-) mouse, an all-cone model deficient in retGC1. We show that AAV-retGC1 treatment fully restores cone function, cone-mediated visual behavior, and guanylate cyclase activity, and preserves cones in treated Nrl(-/-)Gucy2e(-/-) mice over the long-term. A novel finding was that retinal function could be restored to levels above that in Nrl(-/-) controls, contrasting results in other models of retGC1 deficiency. We attribute this to increased cyclase activity in treated Nrl(-/-)Gucy2e(-/-) mice relative to Nrl(-/-) controls. Thus, Nrl(-/-)Gucy2e(-/-) mice possess an expanded dynamic range in ERG response to gene replacement relative to other models. Lastly, we show that a candidate clinical vector, AAV5-GRK1-GUCY2D, when delivered to adult Nrl(-/-)Gucy2e(-/-) mice, restores retinal function that persists for at least 6 months. Our results provide strong support for clinical application of a gene therapy targeted to the cone-rich, central retina of LCA1 patients.

Concepts: Gene, Retina, Photoreceptor cell, Rod cell, Guanylate cyclase, Leber's congenital amaurosis, GUCY2D, Amaurosis


Stimulation of cannabinoid CB1 receptors or inhibition of nitric oxide synthase (NOS) in the dorsolateral periaqueductal grey (dlPAG) decreases anxiety-like behavior. Moreover, activation of CB1 receptors attenuates flight responses induced by nitric oxide (NO) donors in the dlPAG, suggesting that endocannabinoids and NO could interact to control defensive responses such as anxiety-like behavior. To test this hypothesis male Wistar rats received intra-dlPAG microinjections of anandamide (AEA) or NO inhibitors and were tested in the elevated plus maze (EPM). Combined administration of low and ineffective doses of AEA and the NO scavenger (c-Ptio), the nNOS inhibitor (NPA) or the soluble guanylate cyclase inhibitor (ODQ) induced anxiolytic-like effects. The CB1 receptor antagonist AM251, but not the GABAA receptor antagonist bicuculline, attenuated the effect induced by AEA + c-Ptio combination. No effect, however, was found when anxiolytic doses of these same drugs were administered together. Combination of higher, ineffective doses of AEA and c-Ptio, NPA or ODQ was again anxiolytic. The effect of the former combination was prevented by low and ineffective doses of the GABAA receptor antagonist bicuculline or the GABA synthesis inhibitor L-allilglycine, suggesting that they depend on GABAA-mediated neurotransmission. AM251 was also able to attenuate this effect, indicating that in the presence of NO inhibition, the resultant anxiolytic-like effect could be due to AEA action on CB1 receptors. The present results suggest that the AEA and nitrergic systems exert a complex functional interaction in the dlPAG to modulate anxiety behavior, probably interfering, in addition to glutamate, also with GABAergic mechanisms.

Concepts: Receptor, Ligand, Receptor antagonist, Opioid receptor, Nitric oxide, Cannabinoid receptor, Guanylate cyclase, Schild regression


Nitric oxide (NO) is a highly reactive radical that acts as a direct or indirect cellular signalling molecule in plant growth, development and environmental responses. Here we studied the contribution of NO to the control of leaflet movements during nyctinastic closure. For this purpose, we tested the effect of NO donors and an NO scavenger, all supplied in light, on Albizia lophantha leaflet closure after transferral to darkness. Exogenous NO, applied as four donors [sodium nitroprusside (SNP), diethylammonium (Z)-1-(N,N-diethylamino) diazen-1-ium-1,2-diolate (DEA-NONOate), S-nitroso-N-acetylpenicillamine (SNAP) and S-nitrosoglutathione (GS-NO)], inhibited nyctinastic leaflet closure while the application of an NO scavenger [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO)] plus SNP cancelled the effect of the latter. The inclusion of Nω-nitro-l-arginine methyl ester (l-NAME) or sodium tungstate in the incubation media enhanced nyctinastic closure and also resulted in a decrease in the nitrate plus nitrite released by leaflets into the incubation solution. These results support the notion that NO is involved in regulating the nyctinastic closure of A. lophantha leaflets. Cellular perception of NO did not appear to be mediated by calcium. Pharmacological application of inhibitors of soluble guanylate cyclase (sGC) [1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ) and 6-anilino-5,8-quinolinequinone (Ly83583)], phosphodiesterase type 5 (PDE5) (Sildenafil) and the cyclic guanosine monophosphate (cGMP) analogue 8-bromoguanosine-3',5'-cyclomonophosphate sodium salt (8-Br-cGMP) indicated that cGMP was downstream of the NO signalling cascade during nyctinastic closure.

Concepts: Ammonia, Nitric oxide, Salt, Guanylate cyclase, Cyclic guanosine monophosphate, Phosphodiesterase, Sildenafil, Guanosine monophosphate


Nitric oxide (NO(•)) is a ubiquitous molecular mediator in biology. Many signalling actions of NO(•) generated by mammalian NO(•) synthase (NOS) result from targeting of the haem moiety of soluble guanylate cyclase. Some pathogenic and environmental bacteria also produce a NOS that is evolutionary related to the mammalian enzymes, but a bacterial haem-containing receptor for endogenous enzymatically generated NO(•) has not been identified previously. Here, we show that NOS of the human pathogen Staphylococcus aureus, in concert with an NO(•)-metabolizing flavohaemoprotein, regulates electron transfer by targeting haem-containing cytochrome oxidases under microaerobic conditions to maintain membrane bioenergetics. This process is essential for staphylococcal nasal colonization and resistance to the membrane-targeting antibiotic daptomycin and demonstrates the conservation of NOS-derived NO(•)-haem receptor signalling between bacteria and mammals.

Concepts: Bacteria, Evolution, Molecular biology, Microbiology, Staphylococcus aureus, Antibiotic resistance, Staphylococcus, Guanylate cyclase


Riociguat, a member of a new class of compounds (soluble guanylate cyclase stimulators), has been shown in previous clinical studies to be beneficial in the treatment of chronic thromboembolic pulmonary hypertension.

Concepts: Clinical trial, Pulmonary artery, Nitric oxide, Pulmonary hypertension, Member of Parliament, Guanylate cyclase, Riociguat


This trial sought to evaluate whether vericiguat, a novel oral soluble guanylate cyclase (sGC) stimulator, was superior to placebo, on a background of standard of care, in increasing the time to the first occurrence of the composite endpoints of cardiovascular (CV) death and heart failure (HF) hospitalization in patients with HF with reduced ejection fraction (HFrEF). Deficiency in sGC-derived cyclic guanosine monophosphate (cGMP) causes both myocardial dysfunction and impaired endothelium-dependent vasomotor regulation that includes the myocardial microcirculation. Experimental studies have suggested multiple potential benefits of sGC stimulators including prevention, or even reversal, of left ventricular hypertrophy and fibrosis, as well as reduction of ventricular afterload through both systemic and pulmonary vasodilation. Hence, restoration of sufficient nitric oxide (NO)-sGC-cGMP signaling has been proposed as an important treatment target in HF. Vericiguat has been shown to directly stimulate sGC and enhance sGC sensitivity to endogenous NO. Available phase IIb data in HFrEF patients indicate vericiguat is safe and well-tolerated, and exploratory analyses indicate that it results in a dose-dependent, clinically significant reduction in N-terminal pro-B-type natriuretic peptide (NT-proBNP) at the highest tested dose. VICTORIA (Vericiguat Global Study in Subjects With Heart Failure With Reduced Ejection Fraction) is a randomized, placebo-controlled, parallel group, multicenter, double-blind, event-driven phase 3 trial of vericiguat in subjects with HFrEF. Approximately 4,872 subjects will be randomized to evaluate the efficacy and safety of vericiguat compared with placebo on a background of standard of care. After a screening phase of up to 30 days, eligible subjects will be treated until the required number of cardiovascular deaths is observed. The estimated median follow-up duration is approximately 18 months. All subjects will be followed until study completion to assess for the occurrence of endpoint events. VICTORIA will establish the efficacy and safety of vericiguat on cardiovascular death and HF hospitalization in patients with HFrEF. (A Randomized Parallel-Group, Placebo-Controlled, Double-Blind, Event-Driven, Multi-Center Pivotal Phase III Clinical Outcome Trial of Efficacy and Safety of the Oral sGC Stimulator Vericiguat in Subjects With Heart Failure With Reduced Ejection Fraction [HFrEF]-VerICiguaT Global Study in Subjects With Heart Failure With Reduced Ejection Fraction [VICTORIA]; NCT02861534).

Concepts: Clinical trial, Myocardial infarction, Cardiology, Ejection fraction, Heart, Placebo, Guanylate cyclase, Cyclic guanosine monophosphate


Riociguat, a soluble guanylate cyclase stimulator, has been shown in a phase 2 trial to be beneficial in the treatment of pulmonary arterial hypertension.

Concepts: Myocardial infarction, Atherosclerosis, Hypertension, Coronary artery disease, Blood pressure, Solubility, Pulmonary artery, Guanylate cyclase


Network medicine utilizes common genetic origins, markers and co-morbidities to uncover mechanistic links between diseases. These links can be summarized in the diseasome, a comprehensive network of disease-disease relationships and clusters. The diseasome has been influential during the past decade, although most of its links are not followed up experimentally. Here, we investigate a high prevalence unmet medical need cluster of disease phenotypes linked to cyclic GMP. Hitherto, the central cGMP-forming enzyme, soluble guanylate cyclase (sGC), has been targeted pharmacologically exclusively for smooth muscle modulation in cardiology and pulmonology. Here, we examine the disease associations of sGC in a non-hypothesis based manner in order to identify possibly previously unrecognized clinical indications. Surprisingly, we find that sGC, is closest linked to neurological disorders, an application that has so far not been explored clinically. Indeed, when investigating the neurological indication of this cluster with the highest unmet medical need, ischemic stroke, pre-clinically we find that sGC activity is virtually absent post-stroke. Conversely, a heme-free form of sGC, apo-sGC, was now the predominant isoform suggesting it may be a mechanism-based target in stroke. Indeed, this repurposing hypothesis could be validated experimentally in vivo as specific activators of apo-sGC were directly neuroprotective, reduced infarct size and increased survival. Thus, common mechanism clusters of the diseasome allow direct drug repurposing across previously unrelated disease phenotypes redefining them in a mechanism-based manner. Specifically, our example of repurposing apo-sGC activators for ischemic stroke should be urgently validated clinically as a possible first-in-class neuroprotective therapy.

Concepts: Pharmacology, Medicine, Disease, Stroke, Neurology, Therapeutic hypothermia, Smooth muscle, Guanylate cyclase


The factors regulating the increase in skeletal muscle insulin sensitivity after exercise are unclear. We examined whether nitric oxide (NO) is required for the increase in insulin sensitivity after ex vivo contractions. Isolated C57BL/6J mouse EDL muscles were contracted for 10 min or remained at rest (basal) with or without the NO synthase (NOS) inhibition (L-NMMA; 100 μm). 3.5 h post contraction/basal, muscles were exposed to saline or insulin (120 μU ml(-1) ) with or without L-NMMA during the last 30 min. L-NMMA had no effect on basal skeletal muscle glucose uptake. The increase in muscle glucose uptake with insulin (57%) was significantly (P < 0.05) greater after prior contraction (140% increase). NOS inhibition during the contractions had no effect on this insulin-sensitizing effect of contraction but NOS inhibition during insulin prevented the increase in skeletal muscle insulin sensitivity post-contraction. Soluble guanylate cyclase inhibition, PKG inhibition or PDE5 inhibition each had no effect on the insulin-sensitizing effect of prior contraction. In conclusion, NO is required for increases in insulin sensitivity several hours after contraction of mouse skeletal muscle via a cGMP/PKG independent pathway. This article is protected by copyright. All rights reserved.

Concepts: Insulin, Glucose, Muscle, Glycogen, Acetylcholine, Nitric oxide, Guanylate cyclase, Copyright