Activation Of Soluble Guanylyl Cyclase Research Articles

Airways Relaxant and Antiasthmatic Activity of Aconitum heterophyllum Wall ex Royle. Roots: A Mechanistic Insight.

Aconitum heterophyllum Wall ex Royle. (Ranunculaceae) is a traditional medicinal herb that has shown extensive pharmacological potential to treat cough, diarrhea, and infectious diseases but no scientific evidence is available to validate its antiasthmatic potential. In this study, we have investigated the tracheal relaxation and antiasthmatic activity of the selected bioactive fraction of A. heterophyllum. Chemical profiling of the most effective fraction obtained via bioassay-guided fractionation was done using LC-MS (Liquid chromatography-mass spectrometry, a technique utilized in the identification, separation, and quantification of known and unknown compounds). Molecular docking analysis of characterized constituents was performed to recognize the binding receptors, followed by an evaluation of the tracheal relaxation ability of active fraction. An acute oral toxicity study of the most effective fraction was done using OECD guidelines 423. Further, the therapeutic efficacy of the fraction was validated in asthma using a guinea pig model of ovalbumin (OVA) induced allergic asthma. The bio-guided activity revealed that hydro-methanolic extract of A. heterophyllum roots (F-1) was the most active fraction. LC-MS analysis of F-1 showed the presence of six major bioactive compounds in F-1. Molecular docking studies revealed strong binding affinities of identified constituents with histaminic receptor (H1) and muscarinic receptor (M3). The ex vivo study demonstrated smooth muscle relaxant activity of F-1 via dysregulating diverse signal transduction pathways viz. histaminic and muscarinic receptors antagonism (non-competitive), stimulation of β2-adrenergic receptor pathway, and soluble guanylyl cyclase activation. The findings of acute oral toxicity studies revealed that F-1 had no toxicity up to the dose of 2000 mg/Kg. The anti-asthmatic therapeutic efficacy of F-1 was further confirmed by the amelioration of respiratory hyperresponsiveness in asthmatic guinea pigs. This is the first evidence-based study showing the antiasthmatic therapeutic potential of the traditionally used herb A. heterophyllum through, computational and animal studies.

Molsidomine provides neuroprotection against vincristine-induced peripheral neurotoxicity through soluble guanylyl cyclase activation

Peripheral neurotoxicity is a dose-limiting adverse reaction of primary frontline chemotherapeutic agents, including vincristine. Neuropathy can be so disabling that patients drop out of potentially curative therapy, negatively impacting cancer prognosis. The hallmark of vincristine neurotoxicity is axonopathy, yet its underpinning mechanisms remain uncertain. We developed a comprehensive drug discovery platform to identify neuroprotective agents against vincristine-induced neurotoxicity. Among the hits identified, SIN-1—an active metabolite of molsidomine—prevents vincristine-induced axonopathy in both motor and sensory neurons without compromising vincristine anticancer efficacy. Mechanistically, we found that SIN-1’s neuroprotective effect is mediated by activating soluble guanylyl cyclase. We modeled vincristine-induced peripheral neurotoxicity in rats to determine molsidomine therapeutic potential in vivo. Vincristine administration induced severe nerve damage and mechanical hypersensitivity that were attenuated by concomitant treatment with molsidomine. This study provides evidence of the neuroprotective properties of molsidomine and warrants further investigations of this drug as a therapy for vincristine-induced peripheral neurotoxicity.

Hepatic improvement within 27 days of avenciguat treatment in Child-Pugh A cirrhosis detected by an oral cholate challenge test.

New methods for measuring hepatic improvement in clinical trials and the clinic are needed. One new method, HepQuant SHUNT, detected dose-dependent improvements in hepatic function and portal physiology in the phase 1b study (NCT03842761) of avenciguat, an activator of soluble guanylyl cyclase that is being developed for the treatment of portal hypertension. Herein, we examined whether HepQuant Duo, an easy-to-administer test version, could similarly detect the effects of avenciguat. Twenty-three patients with Child-Pugh A cirrhosis and liver stiffness >15kPa received either a placebo (n = 5) or a maximum twice-daily avenciguat dose of 1, 2, or 3mg (n = 6 per group) for 28 days. The DuO test was performed at baseline and on days 11 and 27 in each subject. The test involved administering 40mg of d4-cholate orally, measuring d4-cholate concentrations in serum at 20 and 60 minutes, and calculating portal hepatic filtration rate, disease severity index, portal-systemic shunting (SHUNT%), and hepatic reserve (HR%). Avenciguat demonstrated dose-dependent improvement in all test parameters. Changes from baseline in SHUNT% after 27 days' treatment were 0.1 ± 9.0% for placebo, 1.7 ± 5.5% for 1mg twice-daily, -3.2 ± 2.7% for 2mg twice-daily, and -6.1 ± 5.0% for 3mg twice-daily (paired t test for change from baseline p = 0.98, 0.48, 0.04, and 0.03, respectively). The changes detected by HepQuant DuO were similar to those previously observed and reported for HepQuant SHUNT. The results support further study of avenciguat in treating portal hypertension and spotlight the utility of HepQuant DuO in the development of drug therapy for liver disease. HepQuant DuO facilitates the use of function testing to measure hepatic improvement in clinical trials and the clinic.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of BI 685509, a soluble guanylyl cyclase activator, in healthy volunteers: Results from two randomized controlled trials

This study evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of BI 685509 after oral single rising doses (SRDs) or multiple rising doses (MRDs) in healthy volunteers. In the SRD trial (NCT02694354; February 29, 2016), within each of the three dose groups (DGs), six subjects received BI 685509 (1.0, 2.5, or 5.0 mg) and two received placebo (N = 24). In the MRD trial (NCT03116906; April 17, 2017), within each of the five DGs, nine subjects received BI 685509 (uptitrated to 1 mg once daily [qd; DG1], 2.5 mg twice daily [DG2], 5.0 mg qd [DG3]; 3.0 mg three times daily [tid; DG4] or 4.0 mg tid [DG5]) and three received placebo, for 14–17 days (N = 60). In the SRD trial, 7/24 subjects (29.2%) had ≥ 1 adverse event (AE), most frequently orthostatic dysregulation (n = 4). In the MRD trial, 26/45 subjects (57.8%) receiving BI 685509 had ≥ 1 AE, most frequently orthostatic dysregulation and fatigue (each n = 12). Tolerance development led to a marked decrease in orthostatic dysregulation events (DG3). BI 685509 was rapidly absorbed after oral administration, and exposure increased in a dose-proportional manner after single doses. Multiple dosing resulted in near–dose-proportional increase in exposure and limited accumulation. BI 685509 pharmacokinetics appeared linear with time; steady state occurred 3–5 days after each multiple-dosing period. Increased plasma cyclic guanosine monophosphate and decreased blood pressure followed by a compensatory increase in heart rate indicated target engagement. BI 685509 was generally well tolerated; orthostatic dysregulation may be appropriately countered by careful uptitration.

Flavoring Agents in E-cigarette Liquids: A Comprehensive Analysis of Multiple Health Risks.

The availability of a wide range of flavored e-cigarettes is one of the primary reasons for vaping initiation and persistent use among adolescents and young people. This plethora of flavors available on the market are crafted using different flavoring agents such as cinnamaldehyde, vanillin, benzaldehyde, ethyl maltol, menthol, and dimethylpyrazine. Recent studies have brought to light the potential risks associated with e-cigarette flavoring agents and their effects on various organ systems, both with and without nicotine. Research has demonstrated that flavoring agents can induce inflammation, endothelial dysfunction, epithelial barrier disruption, oxidative stress, DNA damage, electrophysiological alterations, immunomodulatory effects, and behavioral changes, even independently of nicotine. Notably, these negative outcomes adversely affect cardiovascular system by reducing cell viability, decreasing endothelial nitric oxide synthase, nitric oxide bioavailability, soluble guanylyl cyclase activity and cyclic guanosine monophosphate accumulation, impairing endothelial proliferation and tube formation, and altering vasoreactivity resulting in vascular dysfunction. In the heart, these agents decrease parasympathetic activity, induce depolarization of resting membrane potential, loss of rhythmicity, increase isovolumic relaxation time, and change in ventricular repolarization and ventricular tachyarrhythmias. It is found that the specific response elicited by flavoring agents in different organ systems varies depending on the flavor used, the concentration of the flavoring agent, and the duration of exposure. However, the literature on the effects of flavoring agents is currently limited, emphasizing the need for more preclinical and randomized clinical trials to gain a deeper understanding and provide further evidence of the harmful effects of flavored e-cigarette use. In summary, recent research suggests that flavoring agents themselves can have detrimental effects on the body. To fully comprehend these effects, additional preclinical and clinical studies are needed to explore the risks associated with flavored e-cigarette usage.

Platelet Cyclic GMP Levels Are Reduced in Patients with Primary Aldosteronism.

Nitric oxide inhibits platelet aggregation by increasing the second messenger cyclic guanosine-3',5'-monophosphate (cGMP) through the activation of soluble guanylyl cyclase in target cells. Within this context, the oxidative stress associated with the aldosterone excess impairs the nitric oxide availability. Thus, the aim of the present study was to assess the impact of chronic aldosterone excess on the platelet nitric oxide/cGMP pathway in humans. The levels of cGMP were evaluated in platelets of male patients, 12 with primary aldosteronism (PA) and 32 with uncomplicated essential hypertension (EH), matched for age and blood pressure (BP) values. PA and EH patients were 52.8 ± 3 years old and 51.6 ± 1.6 years old, respectively. Systolic and diastolic BP were 158 ± 5.0 mmHg and 105.9 ± 2.3 mmHg in PA and did not differ compared to EH patients (156.6 ± 2.4 mmHg and 104.7 ± 1.2 mmHg). Mean aldosterone levels were significantly higher in PA (25.5 ± 8.8 ng/dL) compared toEH (8.11 ± 0.73 ng/dL), whereas potassium was significantly lower in PA (3.52 ± 0.18 mEq/L) compared to EH (4.08 ± 0.04 mEq/L). Aldosterone and potassium were inversely related (r = -0.49, p = 0.0006) in the whole study population (n = 44). Platelet cGMP was significantly lower in PA (5.1 ± 0.36 pM/109 cells) than in EH (7.1 ± 0.53 pM/109 cells), and in the entire study cohort, it was directly related to plasma potassium (r = 0.43, p = 0.0321). These results show an impairment of nitric oxide/cGMP signaling in platelets of PA patients. This effect is likely related to the potassium-depleting effect of chronic aldosterone excess. Future studies are needed to understand whether the platelet nitric oxide/cGMP system is involved in the atherothrombotic events in these patients.

Signaling pathways upregulating glutathione‑specific γ‑glutamylcyclotransferase 1 by 3‑(5'‑hydroxymethyl‑2'‑furyl)‑1‑benzylindazole.

Glutathione‑specific γ‑glutamylcyclotransferase1 (CHAC1), is an unfolded protein response‑induced gene. Although it has been previously reported that CHAC1 transcription is regulated by activating transcription factor (ATF)4, ATF3 and CCAAT/enhancer‑binding protein β (C/EBPβ), the signaling pathways that regulate CHAC1 are largely unknown. It was revealed that 3‑(5'‑hydroxymethyl‑2'‑furyl)‑1‑benzylindazole (YC‑1; PubChem ID: 5712), a nitric oxide‑independent activator ofsoluble guanylyl cyclase (sGC), increases CHAC1 levels in cultured human kidney proximal tubular cells (HK‑2). Therefore, in the present study, the signaling pathways that induce CHAC1 by YC‑1 were investigated in HK‑2 cells. YC‑1 induced CHAC1 expression in a dose‑ and time‑dependent manner. KT5823, an inhibitor of cGMP‑dependent protein kinase (PKG), partially inhibited CHAC1 upregulation, indicating that the sGC‑cGMP‑PKG pathway participates in CHAC1 regulation. These results also suggested that other signaling pathways are involved in the regulation of CHAC1. Since antibody array analysis showed the activation of p38, mTOR and Akt, the involvement of these factors was further investigated. Although LY294002 and KU0063794 (inhibitors of Akt and mTOR, respectively) inhibited YC‑1‑induced CHAC1 expression, SB203580 (an inhibitor of p38) did not. These results indicated that CHAC1 is regulated by the Akt‑mTOR pathway. In addition, YC‑1 induced endoplasmic reticulum (ER) stress, a regulator of CHAC1 induction. These findings suggested that CHAC1 is regulated by YC‑1 through the sGC‑cGMP‑PKG, Akt‑mTOR and ER stress pathways. The present study demonstrated that CHAC1 induction reduced the intracellular glutathione concentration, indicating that CHAC1 plays an important role in intracellular redox homeostasis in tubular cells.

Varied effects of tobacco smoke and e-cigarette vapor suggest that nicotine does not affect endothelium-dependent relaxation and nitric oxide signaling

Chronic smoking causes dysfunction of vascular endothelial cells, evident as a reduction of flow-mediated dilation in smokers, but the role of nicotine is still controversial. Given the increasing use of e-cigarettes and other nicotine products, it appears essential to clarify this issue. We studied extracts from cigarette smoke (CSE) and vapor from e-cigarettes (EVE) and heated tobacco (HTE) for their effects on vascular relaxation, endothelial nitric oxide signaling, and the activity of soluble guanylyl cyclase. The average nicotine concentrations of CSE, EVE, and HTE were 164, 800, and 85 µM, respectively. At a dilution of 1:3, CSE almost entirely inhibited the relaxation of rat aortas and porcine coronary arteries to acetylcholine and bradykinin, respectively, while undiluted EVE, with a 15-fold higher nicotine concentration, had no significant effect. With about 50% inhibition at 1:2 dilution, the effect of HTE was between CSE and EVE. Neither extract affected endothelium-independent relaxation to an NO donor. At the dilutions tested, CSE was not toxic to cultured endothelial cells but, in contrast to EVE, impaired NO signaling and inhibited NO stimulation of soluble guanylyl cyclase. Our results demonstrate that nicotine does not mediate the impaired endothelium-dependent vascular relaxation caused by smoking.

Tylophora indica (Burm. f.) Merr alleviates tracheal smooth muscle hyperresponsiveness in ovalbumin-induced allergic-asthma model in guinea-pigs: Evidences from ex vivo, in silico and in vivo studies.

Tylophora indica (Burm. f.) Merr is a climbing perennial plant reported in Indian traditional system of medicine for its use in allergy and asthma. However, only few scientific studies have been performed in the past to validate its antiasthmatic potential. The present study deals with investigation of airway smooth muscle relaxant and antiasthmatic potential of extract and subsequent fractions prepared from T.indica. The most active fraction of T.indica leaves selected through bio-guided activity was subjected to liquid chromatography-mass spectrometry (LC-MS) analysis for chemical profiling. The binding affinity of identified compounds in fraction towards M3 and H1 receptors was determined by molecular docking study. F-2 (chloroform fraction prepared from methanolic extract of T.indica leaves) was examined for its smooth muscle relaxant properties using isolated trachea of guinea-pig. Further, F-2 was evaluated through in vivo studies employing ovalbumin-induced asthma model in guinea-pigs. F-2 was found most effective in bioassay-guided fractionation. Characterization by LC-MS analysis revealed presence of five major bioactive compounds in F-2 that showed good docking interactions with M3 and H1 receptors. The ex vivo study demonstrated that F-2 could significantly relax tracheal rings via targeting multiple signalling pathways videlicet, namely, noncompetitive antagonism of the histamine and muscarinic receptors, β2-adrenergic stimulation and activation of soluble guanylyl cyclase. In in vivo studies, F-2 ameliorated airway hyperresponsiveness and decreased broncho alveolar lavage fluid (BALF) levels of inflammatory cytokines and immunoglobulin E (IgE). These results confirm the traditional use of T.indica as an antiasthmatic agent which are evidenced through ex vivo, in silico and in vivo studies.

Soluble Guanylyl Cyclase Activator BI 685509 Reduces Portal Hypertension and Portosystemic Shunting in a Rat Thioacetamide-Induced Cirrhosis Model.

Portal hypertension (PT) commonly occurs in cirrhosis. Nitric oxide (NO) imbalance contributes to PT via reduced soluble guanylyl cyclase (sGC) activation and cGMP production, resulting in vasoconstriction, endothelial cell dysfunction, and fibrosis. We assessed the effects of BI 685509, an NO-independent sGC activator, on fibrosis and extrahepatic complications in a thioacetamide (TAA)-induced cirrhosis and PT model. Male Sprague-Dawley rats received TAA twice-weekly for 15 weeks (300-150 mg/kg i.p.). BI 685509 was administered daily for the last 12 weeks (0.3, 1, and 3 mg/kg p.o.; n = 8-11 per group) or the final week only (Acute, 3 mg/kg p.o.; n = 6). Rats were anesthetized to measure portal venous pressure. Pharmacokinetics and hepatic cGMP (target engagement) were measured by mass spectrometry. Hepatic Sirius Red morphometry (SRM) and alpha-smooth muscle actin (αSMA) were measured by immunohistochemistry; portosystemic shunting was measured using colored microspheres. BI 685509 dose-dependently increased hepatic cGMP at 1 and 3 mg/kg (3.92 ± 0.34 and 5.14 ± 0.44 versus 2.50 ± 0.19 nM in TAA alone; P < 0.05). TAA increased hepatic SRM, αSMA, PT, and portosystemic shunting. Compared with TAA, 3 mg/kg BI 685509 reduced SRM by 38%, αSMA area by 55%, portal venous pressure by 26%, and portosystemic shunting by 10% (P < 0.05). Acute BI 685509 reduced SRM and PT by 45% and 21%, respectively (P < 0.05). BI 685509 improved hepatic and extrahepatic cirrhosis pathophysiology in TAA-induced cirrhosis. These data support the clinical investigation of BI 685509 for PT in patients with cirrhosis. SIGNIFICANCE STATEMENT: BI 685509 is an NO-independent sGC activator that was tested in a preclinical rat model of TAA-induced nodular, liver fibrosis, portal hypertension, and portal systemic shunting. BI 685509 reduced liver fibrosis, portal hypertension, and portal-systemic shunting in a dose-dependent manner, supporting its clinical assessment to treat portal hypertension in patients with cirrhosis.

Safety, tolerability, pharmacodynamics and pharmacokinetics of the soluble guanylyl cyclase activator BI 685509 in patients with diabetic kidney disease: A randomized trial.

Albuminuria is associated with abnormalities in the nitric oxide (NO)-soluble guanylyl cyclase (sGC)-cyclic guanosine monophosphate pathway. We assessed safety and efficacy of the NO-independent sGC activator BI 685509 in patients with diabetic kidney disease and albuminuria. In this Phase Ib trial (NCT03165227), we randomized patients with type 1 or 2 diabetes, estimated glomerular filtration rate (eGFR) 20-75 mL/min/1.73 m2 and urinary albumin:creatinine ratio (UACR) 200-3500 mg/g to oral BI 685509 (1 mg three times daily, n = 20; 3 mg once daily, n = 19; 3 mg three times daily, n = 20, after final titration) or placebo (n = 15) for 28 days. Changes from baseline in UACR in first morning void (UACRFMV ) and 10-hour (UACR10h ) urine (3 mg once daily/three times daily only) were assessed. Baseline median eGFR and UACR were 47.0 mL/min/1.73 m2 and 641.5 mg/g, respectively. Twelve patients had drug-related adverse events (AEs; 16.2%: BI 685509, n = 9; placebo, n = 3), most frequently hypotension (4.1%: BI 685509, n = 2; placebo, n = 1) and diarrhoea (2.7%: BI 685509, n = 2; placebo, n = 0). Four patients experienced AEs leading to study discontinuation (5.4%: BI 685509, n = 3; placebo, n = 1). Placebo-corrected mean UACRFMV decreased from baseline in the 3-mg once-daily (28.8%, P = 0.23) and three-times-daily groups (10.2%, P = 0.71) and increased in the 1-mg three-times-daily group (6.6%, P = 0.82); changes were not significant. UACR10h decreased by 35.3% (3 mg once daily, P = 0.34) and 56.7% (3 mg three times daily, P = 0.09); ≥50.0% of patients (UACR10h 3 mg once daily/three times daily) responded (≥20% UACR decrease from baseline). BI 685509 was generally well tolerated. Effects on UACR lowering merit further investigation.

The rationale and study design of two phase II trials examining the effects of BI 685509, a soluble guanylyl cyclase activator, on clinically significant portal hypertension in patients with compensated cirrhosis

BackgroundClinically significant portal hypertension (CSPH) drives cirrhosis-related complications (i.e. hepatic decompensation). Impaired nitric oxide (NO) bioavailability promotes sinusoidal vasoconstriction, which is the initial pathomechanism of CSPH development. Activation of soluble guanylyl cyclase (sGC), a key downstream effector of NO, facilitates sinusoidal vasodilation, which in turn may improve CSPH. Two phase II studies are being conducted to assess the efficacy of the NO-independent sGC activator BI 685509 in patients with CSPH due to various cirrhosis aetiologies.MethodsThe 1366.0021 trial (NCT05161481) is a randomised, placebo-controlled, exploratory study that will assess BI 685509 (moderate or high dose) for 24 weeks in patients with CSPH due to alcohol-related liver disease. The 1366.0029 trial (NCT05282121) is a randomised, open-label, parallel-group, exploratory study that will assess BI 685509 (high dose) alone in patients with hepatitis B or C virus infection or non-alcoholic steatohepatitis (NASH) and in combination with 10 mg empagliflozin in patients with NASH and type 2 diabetes mellitus for 8 weeks. The 1366.0021 trial will enrol 105 patients, and the 1366.0029 trial will enrol 80 patients. In both studies, the primary endpoint is the change from baseline in hepatic venous pressure gradient (HVPG) until the end of treatment (24 or 8 weeks, respectively). Secondary endpoints include the proportion of patients with an HVPG reduction of >10% from baseline, the development of decompensation events and the change from baseline in HVPG after 8 weeks in the 1366.0021 trial. In addition, the trials will assess changes in liver and spleen stiffness by transient elastography, changes in hepatic and renal function and the tolerability of BI 685509.DiscussionThese trials will enable assessment of the short-term (8 weeks) and longer-term (24 weeks) safety of BI 685509, and the effect of sGC activation by BI 685509 on CSPH due to various cirrhosis aetiologies. The trials will use central readings of the diagnostic gold standard HVPG for the primary endpoint, and changes in established non-invasive biomarkers, such as liver and spleen stiffness. Ultimately, these trials will provide key information for developing future phase III trials.Trial registration1366.0021: EudraCT no. 2021–001285-38; ClinicalTrials.gov NCT05161481. Registered on 17 December 2021, https://www.clinicaltrials.gov/ct2/show/NCT05161481.1366.0029: EudraCT no. 2021–005171-40; ClinicalTrials.gov NCT05282121. Registered on 16 March 2022, https://www.clinicaltrials.gov/ct2/show/NCT05282121.

Cellular Factors That Shape the Activity or Function of Nitric Oxide-Stimulated Soluble Guanylyl Cyclase.

NO-stimulated guanylyl cyclase (SGC) is a hemoprotein that plays key roles in various physiological functions. SGC is a typical enzyme-linked receptor that combines the functions of a sensor for NO gas and cGMP generator. SGC possesses exclusive selectivity for NO and exhibits a very fast binding of NO, which allows it to function as a sensitive NO receptor. This review describes the effect of various cellular factors, such as additional NO, cell thiols, cell-derived small molecules and proteins on the function of SGC as cellular NO receptor. Due to its vital physiological function SGC is an important drug target. An increasing number of synthetic compounds that affect SGC activity via different mechanisms are discovered and brought to clinical trials and clinics. Cellular factors modifying the activity of SGC constitute an opportunity for improving the effectiveness of existing SGC-directed drugs and/or the creation of new therapeutic strategies.

A BODIPY-picolinium-cation conjugate as a blue-light-responsive caged group.

Caged compounds protected with photolabile protecting groups (PPGs) are useful for controlling various biological events with high spatiotemporal resolution. Most of the commonly used PPGs are controlled by ultraviolet light irradiation, but it is desirable to have PPGs controlled by visible light irradiation in order to minimize tissue damage. Here, we describe a boron-dipyrromethene (BODIPY)-picolinium conjugate (BPc group) that functions as a blue-light-controllable PPG. ESR experiments indicate that the photolysis mechanism is based on intramolecular photoinduced electron transfer. We illustrate the applicability of the BPc group to biologically active compounds by employing it firstly to photocontrol release of histamine, and secondly to photocontrol release of a soluble guanylyl cyclase (sGC) activator, GSK2181236A, which induces photovasodilation. The BPc group is expected to be a useful PPG for controlling various biological events with blue light irradiation.

Design, synthesis and biological evaluation of new 3,4-dihydroquinoxalin-2(1H)-one derivatives as soluble guanylyl cyclase (sGC) activators

Herein, we present the structure-based design, synthesis and biological evaluation of novel mono- and di-carboxylic 3,4-dihydroquinoxalin-2(1H)-one derivatives as potential heme-independent activators of soluble guanylate cyclase (sGC). Docking calculations of several known sGC agonists by utilizing both a homology model of human sGC β1 Η-ΝΟΧ domain and a recent cryo-EM structure of the same domain guided the structural optimization of various designed compounds. Among these, mono- and di-carboxylic 3,4-dihydroquinoxalin-2(1H)-one derivatives arose as promising candidate sGC activators. A series of such compounds was synthesized and assessed for their effect on sGC activity. None of them was able to trigger any detectable activation of native sGC in prostate cancer (LnCaP) or rat aortic smooth muscle (A7r5) cells, even after loss of heme by treatment with the heme oxidant ODQ. Furthermore, selected derivatives did not exhibit any antagonistic effect against the known heme-independent sGC activator BAY 60-2770 nor any additive or synergistic effect with the heme-dependent NO donor sodium nitroprusside (SNP) on heme-associated sGC in A7r5 cells. However, when tested in vitro using purified recombinant sGC enzyme, the dicarboxylic 3,4-dihydroquinoxalin-2(1H)-one derivative 30d was able to increase the enzymatic activity of both the wild-type α1/β1 sGC dimer (by 4.4-fold, EC50 = 0.77 μΜ) as well as the heme-free α1/β1 His105Ala mutant sGC (by 4.8-fold, EC50 = 1.8 μΜ). Notably, the activity of compound 30d towards the mutant α1/β1 Η105A enzyme was comparable with that previously reported by us for the bona fide activator BAY 60-2770, using the functionally equivalent wild-type sGC preparation treated with ODQ. These results indicate that compound 30d can indeed act as a promising sGC activator and may serve as a basic structure in the design of novel, optimized analogues with enhanced sGC agonistic activity and improved efficiency in cell-based and in vivo systems.

Responses in Blood Pressure and Kidney Function to Soluble Guanylyl Cyclase Stimulation or Activation in Normal and Diabetic Rats

Introduction: Agonists of soluble guanylate cyclase (sGC) are being developed as treatment for cardiovascular disease. Most effects of nitric oxide (NO) on glomerular and tubular function are mediated through sGC, but whether sGC agonists mimic these effects is unknown. Methods: Renal clearance and micropuncture studies were performed in Wistar-Froemter rats (WF), with or without streptozotocin diabetes (STZ-WF), and in Goto-Kakizaki rats (GK) with mild type 2 diabetes to test for acute effects of the sGC “stimulator” BAY 41-2272, which synergizes with endogenous NO, and the “activator” runcaciguat, which generates cGMP independent of NO. Results: Both sGC agonists reduced arterial blood pressure (MAP). For MAP reductions <10%, the drugs increased GFR in WF and STZ-WF but not in GK. Larger MAP reductions outweighed this effect and GFR declined, with better preserved GFR in STZ-WF. Changes in GFR could not be accounted for by changes in RBF, suggesting parallel changes in ultrafiltration pressure and/or ultrafiltration coefficient. The doses chosen for micropuncture in WF and GK reduced MAP by 2–10%, and the net effect on single nephron GFR and ultrafiltration pressure was neutral. The effects of the drugs on tubular reabsorption were dominated by declining MAP, and no natriuretic effect was observed at any dose. Discussion/Conclusion: sGC agonists impact kidney function directly and because they reduce MAP. The direct tendency to increase GFR is most apparent for MAP reductions <10%. The direct effect is otherwise subtle and overridden when MAP declines more. Effects of sGC agonists on tubular reabsorption are dominated by the effects on MAP.

SOLUBLE GUANYLYL CYCLASE ACTIVATION RESCUES HYPEROXIA-INDUCED DYSFUNCTION OF VASCULAR RELAXATION.

Introduction: Perioperative alterations in perfusion lead to ischemia and reperfusion injury, and supplemental oxygen is administered during surgery to limit hypoxic injury but can lead to hyperoxia. We hypothesized that hyperoxia impairs endothelium-dependent and endothelium-independent vasodilation but not the vasodilatory response to heme-independent soluble guanylyl cyclase activation. Methods: We measured the effect of oxygen on vascular reactivity in mouse aortas. Mice were ventilated with 21% (normoxia), 60% (moderate hyperoxia), or 100% (severe hyperoxia) oxygen during 30 minutes of renal ischemia and 30 minutes of reperfusion. After sacrifice, the thoracic aorta was isolated, and segments mounted on a wire myograph. We measured endothelium-dependent and endothelium-independent vasodilation with escalating concentrations of acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, and we measured the response to heme-independent soluble guanylyl cyclase activation with cinaciguat. Vasodilator responses to each agonist were quantified as the maximal theoretical response ( Emax ) and the effective concentration to elicit 50% relaxation (EC 50 ) using a sigmoid model and nonlinear mixed-effects regression. Aortic superoxide was measured with dihydroethidium probe and high-performance liquid chromatography quantification of the specific superoxide product 2-hydroxyethidium. Results: Hyperoxia impaired endothelium-dependent (ACh) and endothelium-independent (SNP) vasodilation compared with normoxia and had no effect on cinaciguat-induced vasodilation. The median ACh Emax was 76.4% (95% confidence interval = 69.6 to 83.3) in the normoxia group, 53.5% (46.7 to 60.3) in the moderate hyperoxia group, and 53.1% (46.3 to 60.0) in the severe hyperoxia group ( P &lt; 0.001, effect across groups), while the ACh EC 50 was not different among groups. The SNP Emax was 133.1% (122.9 to 143.3) in normoxia, 128.3% (118.1 to 138.6) in moderate hyperoxia, and 114.8% (104.6 to 125.0) in severe hyperoxia ( P &lt; 0.001, effect across groups), and the SNP EC 50 was 0.38 log M greater in moderate hyperoxia than in normoxia (95% confidence interval = 0.18 to 0.58, P &lt; 0.001). Cinaciguat Emax and EC 50 were not different among oxygen treatment groups (median range Emax = 78.0% to 79.4% and EC 50 = -18.0 to -18.2 log M across oxygen groups). Aorta 2-hydroxyethidium was 1419 pmol/mg of protein (25th-75th percentile = 1178-1513) in normoxia, 1993 (1831-2473) in moderate hyperoxia, and 2078 (1936-2922) in severe hyperoxia ( P = 0.008, effect across groups). Conclusions: Hyperoxia, compared with normoxia, impaired endothelium-dependent and endothelium-independent vasodilation but not the response to heme-independent soluble guanylyl cyclase activation, and hyperoxia increased vascular superoxide production. Results from this study could have important implications for patients receiving high concentrations of oxygen and at risk for ischemia reperfusion-mediated organ injury.

Nitric Oxide Signalling in Descending Vasa Recta after Hypoxia/Re-Oxygenation.

Reduced renal medullary oxygen supply is a key factor in the pathogenesis of acute kidney injury (AKI). As the medulla exclusively receives blood through descending vasa recta (DVR), dilating these microvessels after AKI may help in renoprotection by restoring renal medullary blood flow. We stimulated the NO-sGC-cGMP signalling pathway in DVR at three different levels before and after hypoxia/re-oxygenation (H/R). Rat DVR were isolated and perfused under isobaric conditions. The phosphodiesterase 5 (PDE5) inhibitor sildenafil (10−6 mol/L) impaired cGMP degradation and dilated DVR pre-constricted with angiotensin II (Ang II, 10−6 mol/L). Dilations by the soluble guanylyl cyclase (sGC) activator BAY 60-2770 as well as the nitric oxide donor sodium nitroprusside (SNP, 10−3 mol/L) were equally effective. Hypoxia (0.1% O2) augmented DVR constriction by Ang II, thus potentially aggravating tissue hypoxia. H/R left DVR unresponsive to sildenafil, yet sGC activation by BAY 60-2770 effectively dilated DVR. Dilation to SNP under H/R is delayed. In conclusion, H/R renders PDE5 inhibition ineffective in dilating the crucial vessels supplying the area at risk for hypoxic damage. Stimulating sGC appears to be the most effective in restoring renal medullary blood flow after H/R and may prove to be the best target for maintaining oxygenation to this vulnerable area of the kidney.

A physiologically relevant role for NO stored in vascular smooth muscle cells: A novel theory of vascular NO signaling

S-nitrosothiols (SNO), dinitrosyl iron complexes (DNIC), and nitroglycerine (NTG) dilate vessels via activation of soluble guanylyl cyclase (sGC) in vascular smooth muscle cells. Although these compounds are often considered to be nitric oxide (NO) donors, attempts to ascribe their vasodilatory activity to NO-donating properties have failed. Even more puzzling, many of these compounds have vasodilatory potency comparable to or even greater than that of NO itself, despite low membrane permeability. This raises the question: How do these NO adducts activate cytosolic sGC when their NO moiety is still outside the cell? In this review, we classify these compounds as ‘nitrodilators’, defined by their potent NO-mimetic vasoactivities despite not releasing requisite amounts of free NO. We propose that nitrodilators activate sGC via a preformed nitrodilator-activated NO store (NANOS) found within the vascular smooth muscle cell. We reinterpret vascular NO handling in the framework of this NANOS paradigm, and describe the knowledge gaps and perspectives of this novel model.

Isoflurane Disrupts Postsynaptic Density-95 Protein Interactions Causing Neuronal Synapse Loss and Cognitive Impairment in Juvenile Mice via Canonical NO-mediated Protein Kinase-G Signaling.

Inhalational anesthetics are known to disrupt PDZ2 domain-mediated protein-protein interactions of the postsynaptic density (PSD)-95 protein. The aim of this study is to investigate the underlying mechanisms in response to early isoflurane exposure on synaptic PSD-95 PDZ2 domain disruption that altered spine densities and cognitive function. The authors hypothesized that activation of protein kinase-G by the components of nitric oxide (NO) signaling pathway constitutes a mechanism that prevents loss of early dendritic spines and synapse in neurons and cognitive impairment in mice in response to disruption of PDZ2 domain of the PSD-95 protein. Postnatal day 7 mice were exposed to 1.5% isoflurane for 4 h or injected with 8 mg/kg active PSD-95 wild-type PDZ2 peptide or soluble guanylyl cyclase activator YC-1 along with their respective controls. Primary neurons at 7 days in vitro were exposed to isoflurane or PSD-95 wild-type PDZ2 peptide for 4 h. Coimmunoprecipitation, spine density, synapses, cyclic guanosine monophosphate-dependent protein kinase activity, and novel object recognition memory were assessed. Exposure of isoflurane or PSD-95 wild-type PDZ2 peptide relative to controls causes the following. First, there is a decrease in PSD-95 coimmunoprecipitate relative to N-methyl-d-aspartate receptor subunits NR2A and NR2B precipitate (mean ± SD [in percentage of control]: isoflurane, 54.73 ± 16.52, P = 0.001; and PSD-95 wild-type PDZ2 peptide, 51.32 ± 12.93, P = 0.001). Second, there is a loss in spine density (mean ± SD [spine density per 10 µm]: control, 5.28 ± 0.56 vs. isoflurane, 2.23 ± 0.67, P < 0.0001; and PSD-95 mutant PDZ2 peptide, 4.74 ± 0.94 vs. PSD-95 wild-type PDZ2 peptide, 1.47 ± 0.87, P < 0.001) and a decrease in synaptic puncta (mean ± SD [in percentage of control]: isoflurane, 41.1 ± 14.38, P = 0.001; and PSD-95 wild-type PDZ2 peptide, 50.49 ± 14.31, P < 0.001). NO donor or cyclic guanosine monophosphate analog prevents the spines and synapse loss and decline in the cyclic guanosine monophosphate-dependent protein kinase activity, but this prevention was blocked by soluble guanylyl cyclase or protein kinase-G inhibitors in primary neurons. Third, there were deficits in object recognition at 5 weeks (mean ± SD [recognition index]: male, control, 64.08 ± 10.57 vs. isoflurane, 48.49 ± 13.41, P = 0.001, n = 60; and female, control, 67.13 ± 11.17 vs. isoflurane, 53.76 ± 6.64, P = 0.003, n = 58). Isoflurane-induced impairment in recognition memory was preventable by the introduction of YC-1. Activation of soluble guanylyl cyclase or protein kinase-G prevents isoflurane or PSD-95 wild-type PDZ2 peptide-induced loss of dendritic spines and synapse. Prevention of recognition memory with YC-1, a NO-independent activator of guanylyl cyclase, supports a role for the soluble guanylyl cyclase mediated protein kinase-G signaling in countering the effects of isoflurane-induced cognitive impairment.