Olinciguat, a stimulator of soluble guanylyl cyclase, attenuates inflammation, vaso-occlusion and nephropathy in mouse models of sickle cell disease

Endothelial dysfunction in Sickle Cell Disease: Strategies for the treatment

Sickle Cell Anemia (SCA), is an inherited hemoglobinopathy characterized by the presence of an abnormal hemoglobin (HbS), being the most prevalent sickle cell disease (SCD). SCA is characterized by vascular endothelial dysfunction, which contributes significantly to various clinical conditions, including but not limited to pulmonary hypertension, priapism, cutaneous leg ulceration, and stroke. The pathophysiology of endothelial dysfunction (ED) in SCA is a multifaceted process involving a chronic inflammatory and hypercoagulable state. Key factors include hemolysis-associated elements like reduced arginine and nitric oxide (NO) availability, elevated levels of vascular adhesion molecules, the uncoupling effect of NO synthase, heightened arginase activity, an environment characterized by oxidative stress with the production of reactive oxygen and nitrogen species, and occurrences of ischemia-reperfusion injury, along with apolipoprotein A-1 depletion. The urgency for novel interventions addressing ED is evident. Presently, there is a focus on investigating small molecules that disrupt the arginine-nitric oxide pathway, exhibiting anti-inflammatory and antioxidant properties while diminishing levels of cellular and vascular adhesion molecules. In this mini-review article, we delve into the progress made in strategies for treating ED in SCD with the aim of cultivating insights for drug design.

Nitric Oxide Resistance in Priapism Associated with Sickle Cell Disease: Mechanisms, Therapeutic Challenges, and Future Directions

Patients with sickle cell disease (SCD) display priapism, a prolonged penile erection in the absence of sexual arousal. The current pharmacological treatments for SCD-associated priapism are limited and focused on acute interventions rather than prevention. Thus, there is an urgent need for new drug targets and preventive pharmacological therapies for this condition. This review focuses on the molecular mechanisms linked to the dysfunction of the NO-cyclic guanosine monophosphate (cGMP)-phosphodiesterase type 5 (PDE5) pathway implicated in SCD-associated priapism. In murine models of SCD, reduced nitric oxide (NO)-cGMP bioavailability in the corpus cavernosum is associated with elevated plasma hemoglobin levels, increased reactive oxygen species levels that inactive NO, and testosterone deficiency that leads to endothelial nitric oxide synthase downregulation. We discuss the consequences of the reduced cGMP-dependent PDE5 activity in response to these molecular changes, highlighting it as the primary pathophysiological mechanism leading to excessive corpus cavernosum relaxation, culminating in priapism. We also further discuss the impact of intravascular hemolysis on therapeutic approaches, present current pharmacological strategies targeting the NO-cGMP-PDE5 pathway in the penis, and identify potential pharmacological targets for future priapism therapies. In men with SCD and priapism, PDE5 inhibitor therapy and testosterone replacement have shown promising results. Recent preclinical research reported the beneficial effect of treatment with haptoglobin and NO donors. SIGNIFICANCE STATEMENT: This review discusses the molecular changes that reduce NO-cGMP bioavailability in the penis in SCD and highlights pharmacological targets and therapeutic strategies for the treatment of priapism, including PDE5 inhibitors, hormonal modulators, NO donors, hydroxyurea, soluble guanylate cyclase stimulators, haptoglobin, hemopexin, and antioxidants.

Riociguat in patients with sickle cell disease and hypertension or proteinuria (STERIO-SCD): a randomised, double-blind, placebo controlled, phase 1-2 trial

BACKGROUND

Although nitric oxide based therapeutics have been shown in preclinical models to reduce vaso-occlusive events and improve cardiovascular function, a clinical trial of a phosphodiesterase 5 inhibitor increased rates of admission to hospital for pain. We aimed to examine if riociguat, a direct stimulator of the nitric oxide receptor soluble guanylate cyclase, causes similar increases in vaso-occlusive events.

METHODS

This was a phase 1-2, randomised, double blind, placebo-controlled trial. Eligible patients were 18 years or older, had confirmed sickle cell disease documented by haemoglobin electrophoresis or HPLC fractionation (haemoglobin SS, SC, Sβ-thalassemia, SD, or SO-Arab), and stage 1 hypertension or proteinuria. Participants were randomly assigned 1:1 to receive either riociguat or matching placebo via a web-based system to maintain allocation concealment. Both treatments were administered orally starting at 1·0 mg three times a day up to 2·5 mg three times a day (highest tolerated dose) for 12 weeks. Dose escalation by 0·5 mg was considered every 2 weeks if systolic blood pressure was greater than 95 mm Hg and the participant had no signs of hypotension; otherwise, the last dose was maintained. The primary outcome was the proportion of participants who had at least one adjudicated treatment-emergent serious adverse event. The analysis was performed by the intention-to-treat. This trial is registered with ClinicalTrials.gov (NCT02633397) and was completed.

FINDINGS

Between April 11, 2017, and Dec 31, 2021, 165 participants were screened and consented to be enrolled into the study. Of these, 130 participants were randomly assigned to either riociguat (n=66) or placebo (n=64). The proportion of participants with at least one treatment-emergent serious adverse event was 22·7% (n=15) in the riociguat group and 31·3% (n=20) in the placebo group (difference -8·5% [90% CI -21·4 to 4·5]; p=0·19). A similar pattern emerged in other key safety outcomes, sickle cell related vaso-occlusive events (16·7 [n=11] vs 21·9% [n=14]; difference -5·2% [-17·2 to 6·5]; p=0·42), mean pain severity (3·18 vs 3·32; adjusted mean difference -0·14 [-0·70 to 0·42]; p=0·69), and pain interference (3·15 vs 3·12; 0·04 [-0·62 to 0·69]; p=0·93) at 12 weeks were similar between groups. Regarding the key clinical efficacy endpoints, participants taking riociguat had a blood pressure of -8·20 mm Hg (-10·48 to -5·91) compared with -1·24 (-3·58 to 1·10) in those taking placebo (-6·96 mm Hg (90% CI -10·22 to -3·69; p<0·001).

INTERPRETATION

Riociguat was safe and had a significant haemodynamic effect on systemic blood pressure. The results of this study provide measures of effect and variability that will inform power calculations for future trials.

FUNDING

Bayer Pharmaceuticals.

Soluble guanylate cyclase stimulators and activators: new horizons in the treatment of priapism associated with sickle cell disease

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.

Mouse models of sickle cell disease: Imperfect and yet very informative

The root cause of sickle cell disease (SCD) has been known for nearly a century, however, few therapies to treat the disease are available. Over several decades of work, with advances in gene editing technology and after several iterations of mice with differing genotype/phenotype relationships, researchers have developed humanized SCD mouse models. However, while a large body of preclinical studies has led to huge gains in basic science knowledge about SCD in mice, this knowledge has not led to the development of effective therapies to treat SCD-related complications in humans, thus leading to frustration with the paucity of translational progress in the SCD field. The use of mouse models to study human diseases is based on the genetic and phenotypic similarities between mouse and humans (face validity). The Berkeley and Townes SCD mice express only human globin chains and no mouse hemoglobin. With this genetic composition, these models present many phenotypic similarities, but also significant discrepancies that should be considered when interpreting preclinical studies results. Reviewing genetic and phenotypic similarities and discrepancies and examining studies that have translated to humans and those that have not, offer a better perspective of construct, face, and predictive validities of humanized SCD mouse models.

Decoding signaling mechanisms: unraveling the targets of guanylate cyclase agonists in cardiovascular and digestive diseases

Soluble guanylate cyclase agonists and guanylate cyclase C agonists are two popular drugs for diseases of the cardiovascular system and digestive systems. The common denominator in these conditions is the potential therapeutic target of guanylate cyclase. Thanks to in-depth explorations of their underlying signaling mechanisms, the targets of these drugs are becoming clearer. This review explains the recent research progress regarding potential drugs in this class by introducing representative drugs and current findings on them.

Vericiguat alleviates ventricular remodeling and arrhythmias in mouse models of myocardial infarction via CaMKII signaling

AIMS

Maladaptive ventricular remodeling is a major cause of ventricular arrhythmias following myocardial infarction (MI) and adversely impacts the quality of life of affected patients. Vericiguat is a new soluble guanylate cyclase (sGC) activator with cardioprotective properties. However, its effects on MI-induced ventricular remodeling and arrhythmias are not fully comprehended; hence, our research evaluated the effect of vericiguat on mice post-MI.

MATERIALS AND METHODS

Mice were divided into four treatment groups: Sham, Sham+Veri, MI, and MI + Veri. For the MI groups and MI + Veri groups, the left anterior descending (LAD) coronary artery was occluded to induce MI. Conversely, the Sham group underwent mock surgery. Vericiguat was administered orally daily for 28 days to the Sham+Veri and MI + Veri groups. Additionally, H9c2 cells were cultured for further mechanistic studies. Assessment methods included echocardiography, pathological analysis, electrophysiological analysis, and Western blotting.

KEY FINDINGS

Vericiguat reduced cardiac dysfunction and infarct size after MI. It also mitigated MI-induced left ventricular fibrosis and cardiomyocyte apoptosis. Vericiguat normalized the expression of ion channel proteins (Kv4.3, Kv4.2, Kv2.1, Kv1.5, Kv7.1, KCNH2, Cav1.2) and the gap junction protein connexin 43, reducing the susceptibility to ventricular arrhythmia. Vericiguat significantly inhibited MI-induced calcium/calmodulin-dependent protein kinase II (CaMKII) pathway activation in mice.

SIGNIFICANCE

Vericiguat alleviated MI-induced left ventricular adverse remodeling and arrhythmias through modulation of the CamkII signaling pathway.

Targeting Soluble Guanylyl Cyclase during Ischemia and Reperfusion

Ischemia and reperfusion (IR) damage organs and contribute to many disease states. Few effective treatments exist that attenuate IR injury. The augmentation of nitric oxide (NO) signaling remains a promising therapeutic target for IR injury. NO binds to soluble guanylyl cyclase (sGC) to regulate vasodilation, maintain endothelial barrier integrity, and modulate inflammation through the production of cyclic-GMP in vascular smooth muscle. Pharmacologic sGC stimulators and activators have recently been developed. In preclinical studies, sGC stimulators, which augment the reduced form of sGC, and activators, which activate the oxidized non-NO binding form of sGC, increase vasodilation and decrease cardiac, cerebral, renal, pulmonary, and hepatic injury following IR. These effects may be a result of the improved regulation of perfusion and decreased oxidative injury during IR. sGC stimulators are now used clinically to treat some chronic conditions such as heart failure and pulmonary hypertension. Clinical trials of sGC activators have been terminated secondary to adverse side effects including hypotension. Additional clinical studies to investigate the effects of sGC stimulation and activation during acute conditions, such as IR, are warranted.

Epicatechin exerts dual action to shield sickling and hydroxyurea-induced myelosuppression: Implication in sickle cell anemia management

Hydroxyurea (HU) is the key drug to treat Sickle cell anemia (SCA). However, its treatment is associated with the liability of myelosuppression. The present study aimed to investigate the potential of epicatechin as a supplementation therapy for the symptomatic management of SCA under HU therapy. A panel of experiments were performed at first to observe epicatechin's effect on sickling and hemolytic behaviour using SCA patient's blood (ex vivo). Thereafter, the effect of HU in the presence or absence of epicatechin was investigated on cytokine inhibition in rat splenocytes (ex vivo) as well as alterations in hematological parameters and kidney function tests in rats (in vivo). Then, any effect of epicatechin on pharmacokinetic modulation of HU in rats was elucidated along with the underlying mechanism using a battery of in vitro and in vivo models. Epicatechin exhibited potent action on anti-sickling, polymerization inhibition, and erythrocyte membrane stability. It did not show any inherent hemolytic activity and reduced TNF-α level during concomitant administration with HU. Based on hematological changes in rats, epicatechin treatment aided to the beneficial effect of HU and prevented the treatment-linked disadvantageous effects of HU like neutropenia. The plasma exposure of HU was significantly augmented in rats upon simultaneous oral administration of epicatechin with HU. Down-regulation of Oatp1b2 and catalase possibly contributed to the pharmacokinetic interaction of HU. Epicatechin is found to be a promising candidate and should be explored at a reduced dose level of HU towards offsetting the dose-dependent myelosuppressive effect of HU under the frame of supplementation therapy in SCA.

Limitations of mouse models for sickle cell disease conferred by their human globin transgene configurations

We characterized the human β-like globin transgenes in two mouse models of sickle cell disease (SCD) and tested a genome-editing strategy to induce red blood cell fetal hemoglobin (HbF; α₂γ₂). Berkeley SCD mice contain four to 22 randomly arranged, fragmented copies of three human transgenes (HBA1, HBG2-HBG1-HBD-HBB^S and a mini-locus control region) integrated into a single site of mouse chromosome 1. Cas9 disruption of the BCL11A repressor binding motif in the γ-globin gene (HBG1 and HBG2; HBG) promoters of Berkeley mouse hematopoietic stem cells (HSCs) caused extensive death from multiple double-strand DNA breaks. Long-range sequencing of Townes SCD mice verified that the endogenous Hbb genes were replaced by single-copy segments of human HBG1 and HBB^S including proximal but not some distal gene-regulatory elements. Townes mouse HSCs were viable after Cas9 disruption of the HBG1 BCL11A binding motif but failed to induce HbF to therapeutic levels, contrasting with human HSCs. Our findings provide practical information on the genomic structures of two common mouse SCD models, illustrate their limitations for analyzing therapies to induce HbF and confirm the importance of distal DNA elements in human globin regulation.

This article has an associated First Person interview with the first author of the paper.

Editor's choice: This study describes the genomic structures of two common sickle cell disease mouse models, illustrates their limitations for analyzing some genetic therapies and confirms the importance of distal DNA elements in human globin gene regulation.

Beneficial Metabolic Effects of Praliciguat, a Soluble Guanylate Cyclase Stimulator, in a Mouse Diet-Induced Obesity Model

Praliciguat is a soluble guanylate cyclase stimulator that elicits hemodynamic, anti-inflammatory, and antifibrotic effects in preclinical models of metabolic dysfunction. We assessed the metabolic effects of praliciguat in a mouse diet-induced obesity (DIO) model housed at thermoneutrality. At 6 weeks old, male C57BL/6N mice were either maintained on low-fat diet (LFD, lean mice) or placed on 60% high-fat diet (HFD, DIO mice). At 14 weeks old, the DIO mice were either maintained on HFD or switched to HFD with praliciguat (6-mg/kg). Day 28 samples were collected for biomarker analysis. In a second study under the same paradigm, indirect calorimetry was performed on days 8, 9, 20, 21, 32, and 33 and an oral lipid tolerance test (LTT) on day 38. Mice treated 28 days with praliciguat had lower levels of fasting plasma insulin, C-peptide, triglycerides, and HOMA-IR (homeostatic model assessment for insulin resistance) than DIO controls. In addition, energy expenditure was higher in praliciguat-treated than in DIO control mice on days 9, 20, 32, and 33; and day-38 triglycerides were lower. HFD-induced increases in gene expression of liver TNF-ɑ, lipoprotein lipase (Lpl), and patatin-like phospholipase domain-containing protein 3 (Pnpla3) in control DIO mice were attenuated in praliciguat-treated DIO mice. The positive metabolic effects observed in praliciguat-treated mice were associated with the restoration of liver PI3K (pAKT-Thr308) signaling, but not MAPK (pERK). In conclusion, praliciguat-treated DIO mice had increased energy utilization, improved insulin sensitivity, and lower plasma triglycerides. These results illustrate metabolic effects associated with praliciguat treatment in DIO mice.

The CNS-penetrant soluble guanylate cyclase stimulator CYR119 attenuates markers of inflammation in the central nervous system

Background

Inflammation in the central nervous system (CNS) is observed in many neurological disorders. Nitric oxide-soluble guanylate cyclase-cyclic guanosine monophosphate (NO–sGC–cGMP) signaling plays an essential role in modulating neuroinflammation. CYR119 is a CNS-penetrant sGC stimulator that amplifies endogenous NO–sGC–cGMP signaling. We evaluated target engagement and the effects of CYR119 on markers of neuroinflammation in vitro in mouse microglial cells and in vivo in quinolinic acid (QA)-induced and high-fat diet-induced rodent neuroinflammation models.

Methods

Target engagement was verified in human embryonic kidney (HEK) cells, rat primary neurons, mouse SIM-A9 cells, and in rats by measuring changes in cGMP and downstream targets of sGC signaling [phosphorylated vasodilator-stimulated phosphoprotein (pVASP), phosphorylated cAMP-response element binding (pCREB)]. In SIM-A9 cells stimulated with lipopolysaccharides (LPS), markers of inflammation were measured when cells were treated with or without CYR119. In rats, microinjections of QA and vehicle were administered into the right and left hemispheres of striatum, respectively, and then rats were dosed daily with either CYR119 (10 mg/kg) or vehicle for 7 days. The activation of microglia [ionized calcium binding adaptor molecule 1 (Iba1)] and astrocytes [glial fibrillary acidic protein (GFAP)] was measured by immunohistochemistry. Diet-induced obese (DIO) mice were treated daily with CYR119 (10 mg/kg) for 6 weeks, after which inflammatory genetic markers were analyzed in the prefrontal cortex.

Results

In vitro, CYR119 synergized with exogenous NO to increase the production of cGMP in HEK cells and in primary rat neuronal cell cultures. In primary neurons, CYR119 stimulated sGC, resulting in accumulation of cGMP and phosphorylation of CREB, likely through the activation of protein kinase G (PKG). CYR119 attenuated LPS-induced elevation of interleukin 6 (IL-6) and tumor necrosis factor (TNF) in mouse microglial cells. Following oral dosing in rats, CYR119 crossed the blood–brain barrier (BBB) and stimulated an increase in cGMP levels in the cerebral spinal fluid (CSF). In addition, levels of proinflammatory markers associated with QA administration or high-fat diet feeding were lower in rodents treated with CYR119 than in those treated with vehicle.

Conclusions

These data suggest that sGC stimulation could provide neuroprotective effects by attenuating inflammatory responses in nonclinical models of neuroinflammation.