Activation Of Soluble Guanylate Cyclase Research Articles

Constitutive LH receptor activity impairs NO-mediated penile smooth muscle relaxation.

Timely activation of the luteinizing hormone receptor (LHCGR) is critical for fertility. Activating mutations in LHCGR cause familial male-limited precocious puberty (FMPP) due to premature synthesis of testosterone. A mouse model of FMPP (KiLHRD582G), expressing a constitutively activating mutation in LHCGR, was previously developed in our laboratory. KiLHRD582G mice became progressively infertile due to sexual dysfunction and exhibited smooth muscle loss and chondrocyte accumulation in the penis. In this study, we tested the hypothesis that KiLHRD582G mice had erectile dysfunction due to impaired smooth muscle function. Apomorphine-induced erection studies determined that KiLHRD582G mice had erectile dysfunction. Penile smooth muscle and endothelial function were assessed using penile cavernosal strips. Penile endothelial cell content was not changed in KiLHRD582G mice. The maximal relaxation response to acetylcholine and the nitric oxide donor, sodium nitroprusside, was significantly reduced in KiLHRD582G mice indicating an impairment in the nitric oxide (NO)-mediated signaling. Cyclic GMP (cGMP) levels were significantly reduced in KiLHRD582G mice in response to acetylcholine, sodium nitroprusside and the soluble guanylate cyclase stimulator, BAY 41-2272. Expression of NOS1, NOS3 and PKRG1 were unchanged. The Rho-kinase signaling pathway for smooth muscle contraction was not altered. Together, these data indicate that KiLHRD582G mice have erectile dysfunction due to impaired NO-mediated activation of soluble guanylate cyclase resulting in decreased levels of cGMP and penile smooth muscle relaxation. These studies in the KiLHRD582G mice demonstrate that activating mutations in the mouse LHCGR cause erectile dysfunction due to impairment of the NO-mediated signaling pathway in the penile smooth muscle.

Nitric oxide in the insular cortex modulates baroreflex responses in a cGMP-independent pathway

Insular cortex is a brain structure involved in the modulation of autonomic activity and cardiovascular function. The nitric oxide/cyclic guanosine-3′,5′-monophosphate pathway is a prominent signaling mechanism in the central nervous system, controlling behavioral and physiological responses. Nevertheless, despite evidence regarding the presence of nitric oxide-synthesizing neurons in the insular cortex, its role in the control of autonomic and cardiovascular function has never been reported. Thus, the present study aimed to investigate the involvement of nitric oxide/cyclic guanosine-3′,5′-monophosphate pathway mediated by neuronal nitric oxide synthase (nNOS) activation within the insular cortex in the modulation of baroreflex responses in unanesthetized rats. For this, we evaluated the effect of bilateral microinjection of either the nitric oxide scavenger carboxy-PTIO, the selective neuronal nitric oxide synthase inhibitor Nω-Propyl-l-arginine or the soluble guanylate cyclase inhibitor ODQ into the insular cortex on the bradycardia evoked by blood pressure increases in response to intravenous infusion of phenylephrine, and the tachycardia caused by blood pressure decreases evoked by intravenous infusion of sodium nitroprusside. Bilateral microinjection of either NPLA or carboxy-PTIO into the insular cortex increased the reflex bradycardic response, whereas the reflex tachycardia was decreased by these treatments. Bilateral microinjection of the soluble guanylate cyclase inhibitor into the insular cortex did not affect any parameter of baroreflex function evaluated. Overall, our findings provide evidence that insular cortex nitrergic signaling, acting via neuronal nitric oxide synthase, plays a prominent role in control of baroreflex function. However, control of reflex responses seems to be independent of soluble guanylate cyclase activation.

Understanding metabolism related differences in ocular efficacy of MGV354

MGV354 was being developed as a novel ocular therapy for lowering of intraocular pressure, a key modifiable risk factor for glaucoma. MGV354 is an activator of soluble guanylate cyclase, an enzyme known to be involved in the regulation of IOP. MGV354 has been shown to robustly lower IOP over 24 h after a single topical ocular drop in rabbit and monkey pharmacology models. However, MGV354 failed to produce similar results in patients with ocular hypertension or open-angle glaucoma. With an objective of explaining the lack of efficacy in the clinic, we attempted to study whether human metabolism was significantly different from animal metabolism. The present study documents the investigation of metabolism of MGV354 in an effort to understand potential differences in biotransformation pathways of MGV354 in rabbits, monkeys, and humans. Overall twenty-six metabolites, formed via oxidative and conjugative pathways, were identified in vitro and in vivo. In vitro hepatic metabolism was qualitatively similar across species, with minor but distinct differences. There were no observable interspecies differences in the hepatic and ocular metabolism of MGV354. Although ocular metabolism was not as extensive as hepatic, the results do not explain the lack of efficacy of MGV354 in clinical studies.

Vascular dysfunction in aged mice contributes to persistent lung fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a progressive disease thought to result from impaired lung repair following injury and is strongly associated with aging. While vascular alterations have been associated with IPF previously, the contribution of lung vasculature during injury resolution and fibrosis is not well understood. To compare the role of endothelial cells (ECs) in resolving and non‐resolving models of lung fibrosis, we applied bleomycin intratracheally to young and aged mice. We found that injury in aged mice elicited capillary rarefaction, while injury in young mice resulted in increased capillary density. ECs from the lungs of injured aged mice relative to young mice demonstrated elevated pro‐fibrotic and reduced vascular homeostasis gene expression. Among the latter, Nos3 (encoding the enzyme endothelial nitric oxide synthase, eNOS) was transiently upregulated in lung ECs from young but not aged mice following injury. Young mice deficient in eNOS recapitulated the non‐resolving lung fibrosis observed in aged animals following injury, suggesting that eNOS directly participates in lung fibrosis resolution. Activation of the NO receptor soluble guanylate cyclase in human lung fibroblasts reduced TGFβ‐induced pro‐fibrotic gene and protein expression. Additionally, loss of eNOS in human lung ECs reduced the suppression of TGFβ‐induced lung fibroblast activation in 2D and 3D co‐cultures. Altogether, our results demonstrate that persistent lung fibrosis in aged mice is accompanied by capillary rarefaction, loss of EC identity, and impaired eNOS expression. Targeting vascular function may thus be critical to promote lung repair and fibrosis resolution in aging and IPF.

BAY60-2770 attenuates doxorubicin-induced cardiotoxicity by decreased oxidative stress and enhanced autophagy

BackgroundDoxorubicin (DOX) administration decreases cardiac soluble guanylate cyclase (sGC) activity. We hypothesized that bypassing impaired NO-sGC-cGMP pathway resulting from the activation of oxidized and heme-free soluble guanylate cyclase (sGC) could be a therapeutic target for DOX-mediated cardiomyopathy (DOX-CM). The present study investigated the therapeutic roles and mechanism of BAY60-2770, an activator of oxidized sGC, in alleviating DOX-CM. MethodsH9c2 cardiomyocytes were pretreated with BAY60-2770 followed by DOX. Cell viability and intracellular reactive oxygen species (ROS) were subsequently measured. To determine the role BAY60-2770 in mitochondrial ROS generation and mitochondrial membrane potential, we examined mitoSOX RED and TMRE fluorescence under DOX exposure. As animal experiments, rats were orally administered with 5 mg/kg of BAY60-2770 at 1 h prior to every DOX treatment and then assessed by echocardiography and apoptotic marker and autophagy. ResultsBAY60-2770 ameliorated cell viability and DOX-induced oxidative stress in H9c2 cells, which was mediated by PKG activation. Mitochondrial ROS and TMRE fluorescence were attenuated by BAY60-2770 in DOX-treated H9c2 cells. DOX-induced caspase-3 activation decreased after pretreatment with BAY60-2770 in vivo and in vitro. Echocardiography showed that BAY60-2770 significantly improved DOX-induced myocardial dysfunction. Autophagosome was increased by BAY60-2770 in vivo. ConclusionsBAY60-2770 appears to mitigate DOX-induced mitochondrial ROS, membrane potential loss, autophagy, and subsequent apoptosis, leading to protection of myocardial injury and dysfunction. These novel results highlighted the therapeutic potential of BAY60-2770 in preventing DOX-CM.

Soluble Guanylate Cyclase Stimulators and Activators: Where are We and Where to Go?

Soluble Guanylate Cyclase (sGC) is the intracellular receptor of Nitric Oxide (NO). The activation of sGC results in the conversion of Guanosine Triphosphate (GTP) to the secondary messenger cyclic Guanosine Monophosphate (cGMP). cGMP modulates a series of downstream cascades through activating a variety of effectors, such as Phosphodiesterase (PDE), Protein Kinase G (PKG) and Cyclic Nucleotide-Gated Ion Channels (CNG). NO-sGC-cGMP pathway plays significant roles in various physiological processes, including platelet aggregation, smooth muscle relaxation and neurotransmitter delivery. With the approval of an sGC stimulator Riociguat for the treatment of Pulmonary Arterial Hypertension (PAH), the enthusiasm in the discovery of sGC modulators continues for broad clinical applications. Notably, through activating the NO-sGC-cGMP pathway, sGC stimulator and activator potentiate for the treatment of various diseases, such as PAH, Heart Failure (HF), Diabetic Nephropathy (DN), Systemic Sclerosis (SS), fibrosis as well as other diseases including Sickle Cell Disease (SCD) and Central Nervous System (CNS) disease. Here, we review the preclinical and clinical studies of sGC stimulator and activator in recent years and prospect for the development of sGC modulators in the near future.

Allosteric activation of the nitric oxide receptor soluble guanylate cyclase mapped by cryo-electron microscopy.

Soluble guanylate cyclase (sGC) is the primary receptor for nitric oxide (NO) in mammalian nitric oxide signaling. We determined structures of full-length Manduca sexta sGC in both inactive and active states using cryo-electron microscopy. NO and the sGC-specific stimulator YC-1 induce a 71° rotation of the heme-binding β H-NOX and PAS domains. Repositioning of the β H-NOX domain leads to a straightening of the coiled-coil domains, which, in turn, use the motion to move the catalytic domains into an active conformation. YC-1 binds directly between the β H-NOX domain and the two CC domains. The structural elongation of the particle observed in cryo-EM was corroborated in solution using small angle X-ray scattering (SAXS). These structures delineate the endpoints of the allosteric transition responsible for the major cyclic GMP-dependent physiological effects of NO.

Protein Kinase G Is Involved in Acute but Not in Long-Term Regulation of Renin Secretion.

Pharmacological inhibition of the renin–angiotensin–aldosterone system (RAAS) is, in combination with diuretics, the first-choice treatment for hypertension, although 10–20% of patients do not respond adequately. Next to the RAAS, the nitric oxide/cGMP/protein kinase G (PKG) system is the second fundamental blood pressure regulator. Whether both systems influence each other is not well-studied. It has been shown that nitric oxide (NO) supports renin recruitment via activation of soluble guanylate cyclase (sGC) and subsequent generation of cGMP. Whether this leads to an ensuing activation of PKGs in this context is not known. PKGIα, as well as PKGII, is expressed in renin-producing cells. Hence, we analyzed whether these enzymes play a role regarding renin synthesis, secretion, or recruitment. We generated renin-cell-specific PKGI-knockout mice and either stimulated or inhibited the renin system in these mice by salt diets. To exclude the possibility that one kinase isoform can compensate the lack of the other, we also studied double-knockout animals with a conditional knockout of PKGI in juxtaglomerular cells (JG cells) and a ubiquitous knockout of PKGII. We analyzed blood pressure, renin mRNA and renal renin protein content as well as plasma renin concentration. Furthermore, we stimulated the cGMP system in these mice using BAY 41-8543, an sGC stimulator, and examined renin regulation either after acute administration or after 7 days (application once daily). We did not reveal any striking differences regarding long-term renin regulation in the studied mouse models. Yet, when we studied the acute effect of BAY 41-8543 on renin secretion in isolated perfused kidneys as well as in living animals, we found that the administration of the substance led to a significant increase in plasma renin concentration in control animals. This effect was completely abolished in double-knockout animals. However, after 7 days of once daily application, we did not detect a persistent increase in renin mRNA or protein in any studied genotype. Therefore, we conclude that in mice, cGMP and PKG are involved in the acute regulation of renin release but have no influence on long-term renin adjustment.

Cinaciguat in combination with insulin induces a favorable effect on implant osseointegration in type 2 diabetic rats

The osseointegration process of implant is seriously impaired in type 2 diabetes mellitus (T2DM) that causes high failure rate, and insufficiency exists in current insulin therapy, creating a demand for new bone-synergistic agent. Cinaciguat, a novel type of soluble guanylate cyclase (sGC) activator, plays a vital role in glucose metabolism, inflammation control and bone regeneration. We hypothesized that the combined application of cinaciguat and insulin could reverse poor implant osseointegration in diabetes. To test this hypothesis, streptozotocin-induced diabetic rats were placed implants in the femur, and divided into five groups: control, T2DM, cinaciguat-treated T2DM (7 μg/kg), insulin-treated T2DM (12 IU/kg), cinaciguat plus insulin combination-treated T2DM (7 μg/kg and 12 IU/kg respectively), according to different treatment received. The weight and glucose levels of rats were evaluated at fixed times, and plasma level of cyclic guanosine monophosphate (cGMP) was determined before euthanasia. Three months after therapy, the femurs were isolated for pull-out test, environmental scanning electron microscope observation, microscopic computerized tomography evaluation and various histology analysis. Results revealed that diabetic rats showed the highest blood glucose level and lowest cGMP content, which led to the worst structural damage and least osseointegration. Combined treatment could attenuate the diabetes induced hyperglycemia to be normal, restore the cGMP content, protein kinase G II (PKG II) expression, phosphodiesterase-5 (PDE5) activity and ameliorate the mechanical strength, the impaired bone microarchitecture and osseointegration to the highest level. Meanwhile, monotreatment (insulin or cinaciguat) also showed restorative effect, but less. Our findings demonstrated that the cGMP/PKG II signaling pathway activated by cinaciguat mediated the favorable effects of the combined application on improving implant fixation under T2DM condition.

Protective role of endothelial progenitor cells stimulated by riociguat in chronic thromboembolic pulmonary hypertension

BackgroundPulmonary endothelial damage has a negative impact on the maintenance of normal pulmonary vascular function. Such damage results in delayed thrombus dissolution and vascular remodeling in chronic thromboembolic pulmonary hypertension (CTEPH). Although endothelial progenitor cells (EPCs) may be incorporated into neovasculature during vascular repair, their function in CTEPH remains unclarified, especially under the augmentation of soluble guanylate cyclase (sGC) activity. Methods and resultsWe evaluated the effect of EPCs on endothelial function and compared the effect of riociguat, a sGC stimulator, on the number and function of circulating EPCs in two groups of CTEPH patients. The two groups consisted 16 CTEPH patients who were treatment naïve (Naïve group), and 14 CTEPH patients who were being treated with riociguat, a sGC stimulator (Riociguat group). The number of circulating EPCs in the Riociguat group was significantly higher than that in the Naïve group. Gene expression levels associated with angiogenesis were significantly higher in EPCs of the Riociguat group. EPC-stimulated tube formation and migration of human pulmonary microvascular endothelial cell (hPMVEC) in the Riociguat group exceeded that in the Naïve group. The angiogenic ability of hPMVECs stimulated by EPCs in the Riociguat group was enhanced compared to that of the sGC stimulator, BAY 41–2272. ConclusionThese findings indicate that riociguat may induce EPCs to play a protective role via modulation of endothelial functions associated with CTEPH. Translation aspect of the workEndothelial dysfunction exacerbates CTEPH. Riociguat enhanced the protective role of EPCs via neovascularization, which prevented vascular remodeling and alleviated CTEPH.

Soluble Guanylate Cyclase Activators Increase cGMP Expression and Improve Vascular Function and Placental Ischemia‐Induced Hypertension

Preeclampsia (PE) is a pregnancy specific disorder associated with maternal hypertension and endothelial dysfunction caused by the release of anti‐angiogenic and pro‐inflammatory factors from the ischemic placenta. In addition, nitric oxide (NO), which typically binds to soluble guanylate cyclase (sGC), and synthesizes cGMP, to facilitate vasodilation, is depleted in PE and contributes to vascular dysfunction. A novel class of drug, sGC activators, which are in clinical trials for pulmonary hypertension and heart failure, have been shown to bind to the sGC molecule and increase cGMP activity independently of NO. However, the therapeutic potential of sGC activators during PE is not known. We tested the hypothesis that sGC activators attenuate blood pressure in a placental ischemic rat model of PE by increasing cGMP production and improving vascular function. Sprague‐Dawley rats underwent Sham or RUPP (Reduced Uterine Perfusion Pressure) surgery on gestational day (GD) 14, where silver clips were placed on the abdominal aorta and branches of the ovarian artery to induce placental ischemia. Animals were then placed on placebo (P) or sGC activator (sGC‐A, 16 ppm, BAY 60‐2770) ‐supplemented diets, ad libitum, from GD14–19. On GD19, blood pressure was measured via indwelling catheter and uterine arteries were harvested to determine endothelium‐dependent vasorelaxation and cGMP expression. To determine the effect of sGC activator treatment on vascular function, uterine arteries from placebo or sGC activator‐supplemented rats were mounted on a wire myograph and pre‐constricted, followed by endothelium‐dependent vasorelaxation. A subset of uterine arteries from these rats were also prepared to determine expression of cGMP. RUPP surgery significantly increased mean arterial blood pressure (Sham+P, n=20, 105±9 mmHg; RUPP+P, n=19, 126±13 mmHg; P<0.05), and this was attenuated by treatment with the sGC activator (RUPP+sGC‐A, n=11, 107±8 mmHg; P<0.05). RUPP surgery induced endothelial dysfunction in uterine arteries (% relaxation, Sham+P, n=6, 92±2 %; RUPP+P, n=5, 34±12%, P<0.05), which was restored in the sGC activator treated group (RUPP+sGC‐A, n=5, 103±2%, P<0.05). Finally, cGMP was reduced in uterine arteries of RUPP‐operated animals (Sham+P, n=3, 0.11±0.009 pmol/mg; RUPP+P, n=3, 0.033±0.009 pmol/mg, P<0.05); however, sGC activation significantly increased cGMP production in the treated group (RUPP+sGC‐A, n=3, 0.127±0.013 pmol/mg, P<0.05). The results of this study demonstrate that activating sGC can reduce blood pressure by restoring cGMP production and improving vascular function in the RUPP rat. In conclusion, these findings suggest there could be a therapeutic potential for treating PE with sGC activators.Support or Funding InformationThis research was supported by the American Heart Association (18POST33990293) and the National Institutes of Health (P01HL051971, P20GM104357).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A novel soluble guanylate cyclase activator with reduced risk of hypotension by short-acting vasodilation.

Cinaciguat, a soluble guanylate cyclase (sGC) activator, was under clinical development for use in acute decompensated heart failure (ADHF), but was discontinued due to occurrence of hypotension. We hypothesized that short‐term activation of sGC in ADHF patients would exert a vasodilative effect without hypotension irrespective of disease state, using a novel short‐acting sGC activator, TY‐55002. The objective of this study was to investigate the vasodilation and hemodynamic effects of TY‐55002 in comparison with those of cinaciguat. TY‐55002 and cinaciguat activated both normal and heme‐oxidized sGC in a dose‐dependent manner and caused rapid relaxation of phenylephrine‐contracted rat aorta. However, TY‐55002 had a milder effect than cinaciguat in enhancing the dose‐activity response between normal and oxidized sGC. Therefore, we suggest that the pharmacological effect of TY‐55002 is less subject than cinaciguat to oxidative stress associated with complications such as cardiovascular disease or diabetes. In normal dogs, the effects of intravenous TY‐55002 or cinaciguat on blood pressure were evaluated in conjunction with the plasma concentrations of the compounds, and pharmacokinetic (PK)‐pharmacodynamic (PD) analyses were carried out. The plasma‐to‐effect‐site transfer rate constant (Ke0) for TY‐55002 was three times greater than for cinaciguat. On the other hand, there was a small difference in blood half‐life (T1/2) between the compounds. It is possible that the rapid fall in blood pressure after the initial administration of TY‐55002 and the quick recovery after cessation were due to the pharmacodynamic property of the compound. In heart failure‐model dogs, TY‐55002 and cinaciguat improved the condition to the same degree, and the short‐term action of TY‐55002 was replicated. In conclusion, TY‐55002 is a novel short‐acting sGC activator, which offers the possibility of easy dose management without excessive hypotension. It therefore holds potential to serve as an innovative drug in the pharmacotherapy of ADHF.

Effect of the B Subunit of the Cholera Toxin on the Raw 264.7 Murine Macrophage-Like Cell Line

The 125I-labeled B-subunit of the cholera toxin ([125I]CT-B with specific activity 98 Ci/mmol) was found to be bonded to the murine macrophage-like cells of the RAW 264.7 line with high affinity (Kd 2.3 nM). The binding of the 125I-labeled CT-B was inhibited by the unlabeled interferon-α2 (IFN-α2), thymosin-α1, (TM-α1), and the LKEKK synthetic peptide corresponding to the 16–20 sequence of human TM-α1 and 131–135 sequence of human IFN-α2 (Ki 0.9, 1.1, and 1.4 nM, respectively), but the KKEKL unlabeled synthetic peptide with the inverted sequence did not inhibit binding (Ki > 1 μM). In the concentration range from 10 to 1000 nM, CT-B and the LKEKK peptide dose-dependently increased the nitric oxide (NO) production by the cells, the activity of intracellular soluble guanylate cyclase (sGC), as well as the ability of the cells for adhesion, spreading, and digestion of bacteria of the 415 virulent strain of the Salmonella typhimurium in vitro. The KKEKL peptide was simultaneously tested and proved to be inactive. Thus, the binding of CT-B and the LKEKK peptide to the receptor on the RAW 264.7 cells resulted in an increase in their NO-synthase, guanylate-cyclase and phagocytic activity.

Nickel-catalyzed hydroalkylation and hydroalkenylation of 1,3-dienes with hydrazones.

Transition-metal-catalyzed hydrofunctionalization of 1,3-dienes is a useful and atom-economical method for constructing allylic compounds. Although substantial progress on hydroalkylation of dienes with stabilized carbon nucleophiles has been made, hydroalkylation of dienes with unstabilized carbon nucleophiles has remained a challenge. In this article, we report a protocol for nickel-catalyzed hydroalkylation of dienes with hydrazones, which serve as equivalents of alkyl carbon nucleophiles. In addition, we developed a protocol for hydroalkenylation of dienes with α,β-unsaturated hydrazones, providing a new method for the synthesis of 1,4-dienes. These hydroalkylation and hydroalkenylation reactions feature mild conditions and a wide substrate scope, and the utility of the reaction products is demonstrated by the preparation of an activator of soluble guanylate cyclase.

Correction to: Soluble Guanylate Cyclase Stimulators and Activators.

The chapter 'Soluble Guanylate Cyclase Stimulators and Activators' has now been made available open access under a CC BY 4.0 license.

Praliciguat. Soluble guanylate cyclase activator, Treatment of heart failure with preserved ejection fraction, Treatment of diabetic nephropathy

Praliciguat. Soluble guanylate cyclase activator, Treatment of heart failure with preserved ejection fraction, Treatment of diabetic nephropathy

Interaction of Cholera Toxin B Subunit with Rat Intestinal Epithelial Cells

We prepared 125I-labeled cholera toxin B subunit (125I-labeled CT-B, specific activity 98 Ci/mmol) and found that its binding to rat IEC-6 intestinal epithelial cells was high-affinity (Kd 1.9 nM). The binding of labeled protein was completely inhibited by unlabeled thymosin-α1 (TM-α1), interferon-α2 (IFN-α2), and synthetic peptide LKEKK, which corresponds to residues 16–20 in TM-α1 and 131–135 in IFN-α2 (Ki 1.2, 0.9, and 1.6 nM, respectively), but was not inhibited by synthetic peptide KKEKL with inverted amino acid sequence (Ki > 10 μM). Thus, TM-α1, IFN-α2, and the LKEKK peptide bind with high affinity and specificity to CT-B receptor on rIEC-6 cells. It was found that CT-B and the LKEKK peptide at concentrations of 10–1000 nM increased nitric oxide production and soluble guanylate cyclase activity in the cells in a dose-dependent manner.

Comparison of the anti-remodeling effect of pressure unloading and chronic soluble guanylate cyclase activation in rats with left ventricular myocardial hypertrophy

Comparison of the anti-remodeling effect of pressure unloading and chronic soluble guanylate cyclase activation in rats with left ventricular myocardial hypertrophy

A Randomized, Controlled Phase I/II Study to Evaluate the Safety and Efficacy of MGV354 for Ocular Hypertension or Glaucoma

To assess the clinical safety, tolerability, and efficacy of topically administered MGV354, a soluble guanylate cyclase (sGC) activator, in patients with ocular hypertension (OH) or glaucoma. Double-masked, randomized, and vehicle-controlled study. Parts 1 and 2 evaluated safety and tolerability to identify the maximum tolerated dose (MTD) of once-daily MGV354 in 32 healthy volunteers (Part 1) and 16 patients with OH or glaucoma (Part 2) at a single clinical site. Part 3 was a multisite trial that evaluated intraocular pressure (IOP)-lowering efficacy of the MTD administered nightly for 1week in 50 patients with minimum IOP of 24mm Hg at 8 AM, with a main outcome measure of mean diurnal IOP at day 8 compared to baseline (ClinicalTrials.govNCT02743780). There was no difference in favor of MGV354 for IOP lowering; change from baseline to day 8 in mean diurnal IOP was -0.6mm Hg for MGV354-treated patients and -1.1mm Hg for vehicle-treated patients in Part 3, with a confidence interval of -0.7 to 1.7. The most common adverse events reported after MGV354 administration were conjunctival and ocular hyperemia. Overall, MGV354 0.1% demonstrated no statistically significant effect compared to vehicle in lowering IOP based on the study's main outcome measure. MGV354 produced ocular hyperemia consistent with its pharmacology.

Soluble guanylate cyclase activation by nitric oxide

Since the discovery of nitric oxide (NO) formation in animals, it has become clear that this toxic, free radical, diatomic gas plays a central role in cellular function in eukaryotes. NO acts as a signaling agent in the cardiovascular system and other tissues. Using a low concentration of NO mitigates the toxicity problem but places a difficult chemical requirement on the NO receptor, the soluble isoform of guanylate cyclase (sGC). sGC contains a heme cofactor that binds and traps NO, thereby activating the enzyme to convert GTP to cGMP. The heme in sGC has unique ligand binding properties enabling sGC to act as a selective receptor for NO. The heme domain of sGC was found to be part of the H-NOX (Heme-Nitric oxide/Oxygen) family of proteins with homologues in both aerobic and anaerobic prokaryotes. Studies with H-NOX proteins has provided a molecular explanation for selective NO trapping at low concentrations. The structure/function picture that is emerging provides new clues to the activation mechanism. It is also become clear that the activation and deactivation of sGC is more complicated than the simple model of NO binding to the heme. As a physiological model is developed it must also account for activity properties of stimulators such as the FDA-approved Adempas®.