Reduced cGMP signaling associated with neointimal proliferation and vascular dysfunction in late-stage atherosclerosis

The anti-inflammatory properties of vinpocetine mediates its therapeutic potential in management of atherosclerosis

Atherosclerosis (AS) formation is enhanced by different mechanisms including cytokine generation, vascular smooth muscle cell proliferation, and migration. One of the recent treatments towards endothelial dysfunction and AS is Vinpocetine (VPN). VPN is a potent inhibitor of phosphodiesterase enzyme 1 (PDE-1) and has anti-inflammatory and antioxidant effects through inhibition the expression of nuclear factor kappa B (NF-κB). VPN has been shown to be effective against the development and progression of AS. However, the underlying molecular mechanism was not fully clarified. Consequently, objective of the present review was to discuss the mechanistic role of VPN in the pathogenesis AS. Most of pro-inflammatory cytokines that released from macrophages are inhibited by action of VPN through NF-κB-dependent mechanism. VPN blocks monocyte adhesion and migration by constraining the expression and action of pro-inflammatory cytokines. As well, VPN is effective in reducing of oxidative stress a cornerstone in the pathogenesis of AS through inhibition of NF-κB and PDE1. VPN promotes plaque stability and prevents the erosion and rupture of atherosclerotic plaque. In conclusion, VPN through mitigation of inflammatory and oxidative stress, and improvement of plaque stability effects could be effective agent in the management of AS.

Loss of soluble guanylyl cyclase in platelets contributes to atherosclerotic plaque formation and vascular inflammation

Variants in genes encoding the soluble guanylyl cyclase (sGC) in platelets are associated with coronary artery disease (CAD) risk. Here, by using histology, flow cytometry and intravital microscopy, we show that functional loss of sGC in platelets of atherosclerosis-prone Ldlr^-/- mice contributes to atherosclerotic plaque formation, particularly via increasing in vivo leukocyte adhesion to atherosclerotic lesions. In vitro experiments revealed that supernatant from activated platelets lacking sGC promotes leukocyte adhesion to endothelial cells (ECs) by activating ECs. Profiling of platelet-released cytokines indicated that reduced platelet angiopoietin-1 release by sGC-depleted platelets, which was validated in isolated human platelets from carriers of GUCY1A1 risk alleles, enhances leukocyte adhesion to ECs. I mp or ta ntly, p ha rm ac ol ogical sGC stimulation increased platelet angiopoietin-1 release in vitro and reduced leukocyte recruitment and atherosclerotic plaque formation in atherosclerosis-prone Ldlr^-/- mice. Therefore, pharmacological sGC stimulation might represent a potential therapeutic strategy to prevent and treat CAD.

PDGF regulates guanylate cyclase expression and cGMP signaling in vascular smooth muscle

The nitric oxide-cGMP (NO-cGMP) pathway is of outstanding importance for vascular homeostasis and has multiple beneficial effects in vascular disease. Neointimal hyperplasia after vascular injury is caused by increased proliferation and migration of vascular smooth muscle cells (VSMCs). However, the role of NO-cGMP signaling in human VSMCs in this process is still not fully understood. Here, we investigate the interaction between platelet derived growth factor (PDGF)-signaling, one of the major contributors to neointimal hyperplasia, and the cGMP pathway in vascular smooth muscle, focusing on NO-sensitive soluble guanylyl cyclase (sGC). We show that PDGF reduces sGC expression by activating PI3K and Rac1, which in turn alters Notch ligand signaling. These data are corroborated by gene expression analysis in human atheromas, as well as immunohistological analysis of diseased and injured arteries. Collectively, our data identify the crosstalk between PDGF and NO/sGC signaling pathway in human VSMCs as a potential target to tackle neointimal hyperplasia.

PDGF reduces expression of nitric oxide-sensitive soluble guanylyl cyclase (NO-sGC) through PI3K-P-Rex1-Rac1 signaling in vascular smooth muscle cells. These insights provide possible avenues to prevent dysregulation of NO/cGMP signaling in vascular disease.

Activation mechanism of human soluble guanylate cyclase by stimulators and activators

Soluble guanylate cyclase (sGC) is the receptor for nitric oxide (NO) in human. It is an important validated drug target for cardiovascular diseases. sGC can be pharmacologically activated by stimulators and activators. However, the detailed structural mechanisms, through which sGC is recognized and positively modulated by these drugs at high spacial resolution, are poorly understood. Here, we present cryo-electron microscopy structures of human sGC in complex with NO and sGC stimulators, YC-1 and riociguat, and also in complex with the activator cinaciguat. These structures uncover the molecular details of how stimulators interact with residues from both β H-NOX and CC domains, to stabilize sGC in the extended active conformation. In contrast, cinaciguat occupies the haem pocket in the β H-NOX domain and sGC shows both inactive and active conformations. These structures suggest a converged mechanism of sGC activation by pharmacological compounds.

Soluble guanylate cyclase (sGC) is a validated drug target for cardiovascular diseases. Here, the authors report structures of human sGC in complex with NO and sGC stimulators or activator, providing insight into the mechanism of sGC activation by pharmacological compounds.

Alteration of the soluble guanylate cyclase system in coronary arteries of high cholesterol diet-fed rabbits

This study aimed to investigate how atherosclerosis affects the soluble guanylate cyclase (sGC) system in coronary arteries. Rabbits were fed a normal diet for 12 weeks (N group) or a diet containing high cholesterol (1%) for 4 weeks (S-HC group) and 12 weeks (L-HC group). Cholesterol deposition in the intima of coronary arteries was observed in the S-HC group, but the formation of an atherosclerotic plaque was not observed. In contrast, a major plaque developed in the L-HC group. The relaxant response of isolated coronary arteries to sodium nitroprusside (SNP, nitric oxide donor) was not different between the N and S-HC groups, whereas the response in the L-HC group was markedly attenuated. The relaxation induced by BAY 60-2770 (sGC activator) tended to be augmented in the S-HC group, but it was significantly impaired in the L-HC group compared to that in the N group. sGC β1 immunostaining was equally detected in the medial layer of the arteries among the N, S-HC, and L-HC groups. In addition, a strong staining was observed in the plaque region of the L-HC group. cGMP levels in the arteries stimulated with SNP were identical in the N and S-HC groups and slightly lower in the L-HC group than the other groups. BAY 60-2770-stimulated cGMP formation tended to be increased in the S-HC and L-HC groups. These findings suggest that the sGC system was not normal in atherosclerotic coronary arteries. The redox state of sGC and the distribution pattern are likely to change with the progression of atherosclerosis.

Vasorelaxing cell permeant phosphopeptide mimetics for subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) due to rupture of an intracranial aneurysm leads to vasospasm resulting in delayed cerebral ischemia. Therapeutic options are currently limited to hemodynamic optimization and nimodipine, which have marginal clinical efficacy. Nitric oxide (NO) modulates cerebral blood flow through activation of the cGMP-Protein Kinase G (PKG) pathway. Our hypothesis is that SAH results in downregulation of signaling components in the NO-PKG pathway which could explain why treatments for vasospasm targeting this pathway lack efficacy and that treatment with a cell permeant phosphopeptide mimetic of downstream effector prevents delayed vasospasm after SAH. Using a rat endovascular perforation model, reduced levels of NO-PKG pathway molecules were confirmed. Additionally, it was determined that expression and phosphorylation of a PKG substrate: Vasodilator-stimulated phosphoprotein (VASP) was downregulated. A family of cell permeant phosphomimetic of VASP (VP) was wasdesigned and shown to have vasorelaxing property that is synergistic with nimodipine in intact vascular tissuesex vivo. Hence, treatment targeting the downstream effector of the NO signaling pathway, VASP, may bypass receptors and signaling elements leading to vasorelaxation and that treatment with VP can be explored as a therapeutic strategy for SAH induced vasospasm and ameliorate neurological deficits.

Novel Approaches to Fine-Tune Therapeutic Targeting of Platelets in Atherosclerosis: A Critical Appraisal

The pathogenesis of atherosclerotic vascular disease is driven by a multitude of risk factors intertwining metabolic and inflammatory pathways. Increasing knowledge about platelet biology sheds light on how platelets take part in these processes from early to later stages of plaque development. Recent insights from experimental studies and mouse models substantiate platelets as initiators and amplifiers in atherogenic leukocyte recruitment. These studies are complemented by results from genetics studies shedding light on novel molecular mechanisms which provide an interesting prospect as novel targets. For instance, experimental studies provide further details how platelet-decorated von Willebrand factor tethered to activated endothelial cells plays a role in atherogenic monocyte recruitment. Novel aspects of platelets as atherogenic inductors of neutrophil extracellular traps and particularities in signaling pathways such as cyclic guanosine monophosphate and the inhibitory adaptor molecule SHB23/LNK associating platelets with atherogenesis are shared. In summary, it was our intention to balance insights from recent experimental data that support a plausible role for platelets in atherogenesis against a paucity of clinical evidence needed to validate this concept in humans.

B Vitamins and Fatty Acids: What Do They Share with Small Vessel Disease-Related Dementia?

Many studies have been written on vitamin supplementation, fatty acid, and dementia, but results are still under debate, and no definite conclusion has yet been drawn. Nevertheless, a significant amount of lab evidence confirms that vitamins of the B group are tightly related to gene control for endothelium protection, act as antioxidants, play a co-enzymatic role in the most critical biochemical reactions inside the brain, and cooperate with many other elements, such as choline, for the synthesis of polyunsaturated phosphatidylcholine, through S-adenosyl-methionine (SAM) methyl donation. B-vitamins have anti-inflammatory properties and act in protective roles against neurodegenerative mechanisms, for example, through modulation of the glutamate currents and a reduction of the calcium currents. In addition, they also have extraordinary antioxidant properties. However, laboratory data are far from clinical practice. Many studies have tried to apply these results in everyday clinical activity, but results have been discouraging and far from a possible resolution of the associated mysteries, like those represented by Alzheimer's disease (AD) or small vessel disease dementia. Above all, two significant problems emerge from the research: No consensus exists on general diagnostic criteria-MCI or AD? Which diagnostic criteria should be applied for small vessel disease-related dementia? In addition, no general schema exists for determining a possible correct time of implementation to have effective results. Here we present an up-to-date review of the literature on such topics, shedding some light on the possible interaction of vitamins and phosphatidylcholine, and their role in brain metabolism and catabolism. Further studies should take into account all of these questions, with well-designed and world-homogeneous trials.

Chronological Change of Vascular Reactivity to cGMP Generators in the Balloon-Injured Rat Carotid Artery

BACKGROUND/AIMS

Soluble guanylate cyclase (sGC) exists as reduced, oxidized, and heme-free forms. Currently, it is unclear whether endovascular mechanical stenosis has an impact on vascular tone control by drugs targeting sGC, namely cGMP generators.

METHODS

Pharmacological responses to acidified sodium nitrite (reduced sGC stimulant) and BAY 60-2770 (oxidized/heme-free sGC stimulant) were studied in balloon-injured rat carotid arteries at several time points. In addition, sGC expression was detected by immunohistochemistry.

RESULTS

At 1 day after injury, acidified sodium nitrite-induced relaxation was attenuated in the injured artery, whereas BAY 60-2770-induced relaxation was augmented. Similar attenuation of response to acidified sodium nitrite was seen at 7 and 14 days after injury. On the other hand, the augmentation of response to BAY 60-2770 disappeared at 7 and 14 days after injury. At 1 day after injury, the immunohistochemical expression pattern of sGC in the smooth muscle layer of the injured artery was not different from that of the uninjured artery. However, in the injured artery, the intensity of sGC staining was weak at 7 and 14 days after injury.

CONCLUSION

Balloon injury alters vascular responsiveness to cGMP generators, which seems to be associated with the form and/or expression of sGC.

Reactive Oxygen Comes of Age: Mechanism-Based Therapy of Diabetic End-Organ Damage

Reactive oxygen species (ROS) have been mainly viewed as unwanted by-products of cellular metabolism, oxidative stress, a sign of a cellular redox imbalance, and potential disease mechanisms, such as in diabetes mellitus (DM). Antioxidant therapies, however, have failed to provide clinical benefit. This paradox can be explained by recent discoveries that ROS have mainly essential signaling and metabolic functions and evolutionally conserved physiological enzymatic sources. Disease can occur when ROS accumulate in nonphysiological concentrations, locations, or forms. By focusing on disease-relevant sources and targets of ROS, and leaving ROS physiology intact, precise therapeutic interventions are now possible and are entering clinical trials. Their outcomes are likely to profoundly change our concepts of ROS in DM and in medicine in general.

Genetic alterations in the NO-cGMP pathway and cardiovascular risk

In the past ten years, several chromosomal loci have been identified by genome-wide association studies to influence the risk of coronary artery disease (CAD) and its risk factors. The GUCY1A3 gene encoding the α₁ subunit of the soluble guanylyl cyclase (sGC) resides at one of these loci and has been strongly associated with blood pressure and CAD risk. More recently, further genes in the pathway encoding the endothelial nitric oxide synthase, the phosphodiesterases 3A and 5A, and the inositol 1,4,5-trisphosphate receptor I-associated protein (IRAG), i.e., NOS3, PDE3A, PDE5A, and MRVI1, respectively, were likewise identified as CAD risk genes. In this review, we highlight the genetic findings linking variants in NO-cGMP signaling and cardiovascular disease, discuss the potential underlying mechanisms which might propagate the development of atherosclerosis, and speculate about therapeutic implications.

Chronic limb-threatening ischemia could benefit from growth hormone therapy for wound healing and limb salvage

Revascularization for chronic limb-threatening ischemia (CLTI) is necessary to alleviate symptoms and wound healing. When it fails or is not possible, there are few alternatives to avoid limb amputation in these patients. Although experimental studies with stem cells and growth factors have shown promise, clinical trials have demonstrated inconsistent results because CLTI patients generally need arteriogenesis rather than angiogenesis. Moreover, in addition to the perfusion of the limb, there is the need to improve the neuropathic response for wound healing, especially in diabetic patients. Growth hormone (GH) is a pleiotropic hormone capable of boosting the aforementioned processes and adds special benefits for the redox balance. This hormone has the potential to mitigate symptoms in ischemic patients with no other options and improves the cardiovascular complications associated with the disease. Here, we discuss the pros and cons of using GH in such patients, focus on its effects on peripheral arteries, and analyze the possible benefits of treating CLTI with this hormone.

Widespread Coronary Dysfunction in the Absence of HDL Receptor SR-B1 in an Ischemic Cardiomyopathy Mouse Model

Reduced clearance of lipoproteins by HDL scavenger receptor class B1 (SR-B1) plays an important role in occlusive coronary artery disease. However, it is not clear how much microvascular dysfunction contributes to ischemic cardiomyopathy. Our aim was to determine the distribution of vascular dysfunction in vivo in the coronary circulation of male mice after brief exposure to Paigen high fat diet, and whether this vasomotor dysfunction involved nitric oxide (NO) and or endothelium derived hyperpolarization factors (EDHF). We utilised mice with hypomorphic ApoE lipoprotein that lacked SR-B1 (SR-B1^−/−/ApoER61^h/h, n = 8) or were heterozygous for SR-B1 (SR-B1^+/−/ApoER61^h/h, n = 8) to investigate coronary dilator function with synchrotron microangiography. Partially occlusive stenoses were observed in vivo in SR-B1 deficient mice only. Increases in artery-arteriole calibre to acetylcholine and sodium nitroprusside stimulation were absent in SR-B1 deficient mice. Residual dilation to acetylcholine following L-NAME (50 mg/kg) and sodium meclofenamate (3 mg/kg) blockade was present in both mouse groups, except at occlusions, indicating that EDHF was not impaired. We show that SR-B1 deficiency caused impairment of NO-mediated dilation of conductance and microvessels. Our findings also suggest EDHF and prostanoids are important for global perfusion, but ultimately the loss of NO-mediated vasodilation contributes to atherothrombotic progression in ischemic cardiomyopathy.

Functional Characterization of the GUCY1A3 Coronary Artery Disease Risk Locus

BACKGROUND

A chromosomal locus at 4q32.1 has been genome-wide significantly associated with coronary artery disease risk. The locus encompasses GUCY1A3, which encodes the α₁ subunit of the soluble guanylyl cyclase (sGC), a key enzyme in the nitric oxide/cGMP signaling pathway. The mechanism linking common variants in this region with coronary risk is not known.

METHODS

Gene expression and protein expression were analyzed with quantitative polymerase chain reaction and immunoblotting, respectively. Putative allele-specific transcription factors were identified with in silico analyses and validated via allele-specific quantification of antibody-precipitated chromatin fractions. Regulatory properties of the lead risk variant region were analyzed with reporter gene assays. To assess the effect of zinc finger E box-binding homeobox 1 transcription factor (ZEB1), siRNA-mediated knockdown and overexpression experiments were performed. Association of GUCY1A3 genotype and cellular phenotypes was analyzed with vascular smooth muscle cell migration assays and platelet aggregation analyses.

RESULTS

Whole-blood GUCY1A3 mRNA levels were significantly lower in individuals homozygous for the lead (rs7692387) risk variant. Likewise, reporter gene assays demonstrated significantly lower GUCY1A3 promoter activity for constructs carrying this allele. In silico analyses located a DNase I hypersensitivity site to rs7692387 and predicted binding of the transcription factor ZEB1 rather to the nonrisk allele, which was confirmed experimentally. Knockdown of ZEB1 resulted in more profound reduction of nonrisk allele promoter activity and a significant reduction of endogenous GUCY1A3 expression. Ex vivo-studied platelets from homozygous nonrisk allele carriers displayed enhanced inhibition of ADP-induced platelet aggregation by the nitric oxide donor sodium nitroprusside and the phosphodiesterase 5 inhibitor sildenafil compared with homozygous risk allele carriers. Moreover, pharmacological stimulation of sGC led to reduced migration only in vascular smooth muscle cells homozygous for the nonrisk allele. In the Hybrid Mouse Diversity Panel, higher levels of GUCY1A3 expression correlated with less atherosclerosis in the aorta.

CONCLUSIONS

Rs7692387 is located in an intronic site that modulates GUCY1A3 promoter activity. The transcription factor ZEB1 binds preferentially to the nonrisk allele, leading to an increase in GUCY1A3 expression, higher sGC levels, and higher sGC activity after stimulation. Finally, human and mouse data link augmented sGC expression to lower risk of atherosclerosis.

The opposing roles of NO and oxidative stress in cardiovascular disease

Nitric oxide (NO) plays a pivotal role in the maintenance of cardiovascular homeostasis. A reduction in the bioavailability of endogenous NO, manifest as a decrease in the production and/or impaired signaling, is associated with many cardiovascular diseases including hypertension, atherosclerosis, stroke and heart failure. There is substantial evidence that reactive oxygen species (ROS), generated predominantly from NADPH oxidases (Nox), are responsible for the reduced NO bioavailability in vascular and cardiac pathologies. ROS can compromise NO function via a direct inactivation of NO, together with a reduction in NO synthesis and oxidation of its receptor, soluble guanylyl cyclase. Whilst nitrovasodilators are administered to compensate for the ROS-mediated loss in NO bioactivity, their clinical utility is limited due to the development of tolerance and resistance and systemic hypotension. Moreover, efforts to directly scavenge ROS with antioxidants has had limited clinical efficacy. This review outlines the therapeutic utility of NO-based therapeutics in cardiovascular diseases and describes the source and impact of ROS in these pathologies, with particular focus on the interaction with NO. Future therapeutic approaches in the treatment of cardiovascular diseases are highlighted with a focus on nitroxyl (HNO) donors as an alternative to traditional NO donors and the development of novel Nox inhibitors.

The impact of genome-wide association studies on the pathophysiology and therapy of cardiovascular disease

Cardiovascular diseases are leading causes for death worldwide. Genetic disposition jointly with traditional risk factors precipitates their manifestation. Whereas the implications of a positive family history for individual risk have been known for a long time, only in the past few years have genome-wide association studies (GWAS) shed light on the underlying genetic variations. Here, we review these studies designed to increase our understanding of the pathophysiology of cardiovascular diseases, particularly coronary artery disease and myocardial infarction. We focus on the newly established pathways to exemplify the translation from the identification of risk-related genetic variants to new preventive and therapeutic strategies for cardiovascular disease.

The Endothelium-Dependent Nitric Oxide-cGMP Pathway

Nitric oxide (NO)-cyclic 3'-5' guanosine monophosphate (cGMP) signaling plays a critical role on smooth muscle tone, platelet activity, cardiac contractility, renal function and fluid balance, and cell growth. Studies of the 1990s established endothelium dysfunction as one of the major causes of cardiovascular diseases. Therapeutic strategies that benefit NO bioavailability have been applied in clinical medicine extensively. Basic and clinical studies of cGMP regulation through activation of soluble guanylyl cyclase (sGC) or inhibition of cyclic nucleotide phosphodiesterase type 5 (PDE5) have resulted in effective therapies for pulmonary hypertension, erectile dysfunction, and more recently benign prostatic hyperplasia. This section reviews (1) how endothelial dysfunction and NO deficiency lead to cardiovascular diseases, (2) how soluble cGMP regulation leads to beneficial effects on disorders of the circulation system, and (3) the epigenetic regulation of NO-sGC pathway components in the cardiovascular system. In conclusion, the discovery of the NO-cGMP pathway revolutionized the comprehension of pathophysiological mechanisms involved in cardiovascular and other diseases. However, considering the expression "from bench to bedside" the therapeutic alternatives targeting NO-cGMP did not immediately follow the marked biochemical and pathophysiological revolution. Some therapeutic options have been effective and released on the market for pulmonary hypertension and erectile dysfunction such as inhaled NO, PDE5 inhibitors, and recently sGC stimulators. The therapeutic armamentarium for many other disorders is expected in the near future. There are currently numerous active basic and clinical research programs in universities and industries attempting to develop novel therapies for many diseases and medical applications.

Stimulators of the soluble guanylyl cyclase: promising functional insights from rare coding atherosclerosis-related GUCY1A3 variants

Stimulators of the soluble guanylyl cyclase (sGC) are emerging therapeutic agents in cardiovascular diseases. Genetic alterations of the GUCY1A3 gene, which encodes the α1 subunit of the sGC, are associated with coronary artery disease. Studies investigating sGC stimulators in subjects with CAD and carrying risk-related variants in sGC are, however, lacking. Here, we functionally investigate the impact of coding GUCY1A3 variants on sGC activity and the therapeutic potential of sGC stimulators in vitro. In addition to a known loss-of-function variant, eight coding variants in GUCY1A3 were cloned and expressed in HEK 293 cells. Protein levels and dimerization capability with the β1 subunit were analysed by immunoblotting and co-immunoprecipitation, respectively. All α1 variants found in MI patients dimerized with the β1 subunit. Protein levels were reduced by 72 % in one variant (p < 0.01). Enzymatic activity was analysed using cGMP radioimmunoassay after stimulation with a nitric oxide (NO) donor. Five variants displayed decreased cGMP production upon NO stimulation (p < 0.001). The addition of the sGC stimulator BAY 41-2272 increased cGMP formation in all of these variants (p < 0.01). Except for the variant leading to decreased protein level, cGMP amounts reached the wildtype NO-induced level after addition of BAY 41-2272. In conclusion, rare coding variants in GUCY1A3 lead to reduced cGMP formation which can be rescued by a sGC stimulator in vitro. These results might therefore represent the starting point for discovery of novel treatment strategies for patients at risk with coding GUCY1A3 variants.

Chronic Activation of Heme Free Guanylate Cyclase Leads to Renal Protection in Dahl Salt-Sensitive Rats

The nitric oxide (NO)/soluble guanylate cyclase (sGC)/cyclic guanosine monophasphate (cGMP)-signalling pathway is impaired under oxidative stress conditions due to oxidation and subsequent loss of the prosthetic sGC heme group as observed in particular in chronic renal failure. Thus, the pool of heme free sGC is increased under pathological conditions. sGC activators such as cinaciguat selectively activate the heme free form of sGC and target the disease associated enzyme. In this study, a therapeutic effect of long-term activation of heme free sGC by the sGC activator cinaciguat was investigated in an experimental model of salt-sensitive hypertension, a condition that is associated with increased oxidative stress, heme loss from sGC and development of chronic renal failure. For that purpose Dahl/ss rats, which develop severe hypertension upon high salt intake, were fed a high salt diet (8% NaCl) containing either placebo or cinaciguat for 21 weeks. Cinaciguat markedly improved survival and ameliorated the salt-induced increase in blood pressure upon treatment with cinaciguat compared to placebo. Renal function was significantly improved in the cinaciguat group compared to the placebo group as indicated by a significantly improved glomerular filtration rate and reduced urinary protein excretion. This was due to anti-fibrotic and anti-inflammatory effects of the cinaciguat treatment. Taken together, this is the first study showing that long-term activation of heme free sGC leads to renal protection in an experimental model of hypertension and chronic kidney disease. These results underline the promising potential of cinaciguat to treat renal diseases by targeting the disease associated heme free form of sGC.

Clinical Relevance of Biomarkers of Oxidative Stress

SIGNIFICANCE

Oxidative stress is considered to be an important component of various diseases. A vast number of methods have been developed and used in virtually all diseases to measure the extent and nature of oxidative stress, ranging from oxidation of DNA to proteins, lipids, and free amino acids.

RECENT ADVANCES

An increased understanding of the biology behind diseases and redox biology has led to more specific and sensitive tools to measure oxidative stress markers, which are very diverse and sometimes very low in abundance.

CRITICAL ISSUES

The literature is very heterogeneous. It is often difficult to draw general conclusions on the significance of oxidative stress biomarkers, as only in a limited proportion of diseases have a range of different biomarkers been used, and different biomarkers have been used to study different diseases. In addition, biomarkers are often measured using nonspecific methods, while specific methodologies are often too sophisticated or laborious for routine clinical use.

FUTURE DIRECTIONS

Several markers of oxidative stress still represent a viable biomarker opportunity for clinical use. However, positive findings with currently used biomarkers still need to be validated in larger sample sizes and compared with current clinical standards to establish them as clinical diagnostics. It is important to realize that oxidative stress is a nuanced phenomenon that is difficult to characterize, and one biomarker is not necessarily better than others. The vast diversity in oxidative stress between diseases and conditions has to be taken into account when selecting the most appropriate biomarker.

Pharmacology and Clinical Drug Candidates in Redox Medicine

SIGNIFICANCE

Oxidative stress is suggested to be a disease mechanism common to a wide range of disorders affecting human health. However, so far, the pharmacotherapeutic exploitation of this, for example, based on chemical scavenging of pro-oxidant molecules, has been unsuccessful.

RECENT ADVANCES

An alternative emerging approach is to target the enzymatic sources of disease-relevant oxidative stress. Several such enzymes and isoforms have been identified and linked to different pathologies. For some targets, the respective pharmacology is quite advanced, that is, up to late-stage clinical development or even on the market; for others, drugs are already in clinical use, although not for indications based on oxidative stress, and repurposing seems to be a viable option.

CRITICAL ISSUES

For all other targets, reliable preclinical validation and drug ability are key factors for any translation into the clinic. In this study, specific pharmacological agents with optimal pharmacokinetic profiles are still lacking. Moreover, these enzymes also serve largely unknown physiological functions and their inhibition may lead to unwanted side effects.

FUTURE DIRECTIONS

The current promising data based on new targets, drugs, and drug repurposing are mainly a result of academic efforts. With the availability of optimized compounds and coordinated efforts from academia and industry scientists, unambiguous validation and translation into proof-of-principle studies seem achievable in the very near future, possibly leading towards a new era of redox medicine.

Reactive Oxygen-Related Diseases: Therapeutic Targets and Emerging Clinical Indications

SIGNIFICANCE

Enhanced levels of reactive oxygen species (ROS) have been associated with different disease states. Most attempts to validate and exploit these associations by chronic antioxidant therapies have provided disappointing results. Hence, the clinical relevance of ROS is still largely unclear.

RECENT ADVANCES

We are now beginning to understand the reasons for these failures, which reside in the many important physiological roles of ROS in cell signaling. To exploit ROS therapeutically, it would be essential to define and treat the disease-relevant ROS at the right moment and leave physiological ROS formation intact. This breakthrough seems now within reach.

CRITICAL ISSUES

Rather than antioxidants, a new generation of protein targets for classical pharmacological agents includes ROS-forming or toxifying enzymes or proteins that are oxidatively damaged and can be functionally repaired.

FUTURE DIRECTIONS

Linking these target proteins in future to specific disease states and providing in each case proof of principle will be essential for translating the oxidative stress concept into the clinic.

Role of sGC-dependent NO signalling and myocardial infarction risk

The NO/cGMP pathway plays an important role in many physiological functions and pathophysiological conditions. In the last few years, several genetic and functional studies pointed to an underestimated role of this pathway in the development of atherosclerosis. Indeed, several genetic variants of key enzymes modulating the generation of NO and cGMP have been strongly associated with coronary artery disease and myocardial infarction risk. In this review, we aim to place the genomic findings on components of the NO/cGMP pathway, namely endothelial nitric oxide synthase, soluble guanylyl cyclase and phosphodiesterase 5A, in context of preventive and therapeutic strategies for treating atherosclerosis and its sequelae.

Oxidative stress associated with middle aging leads to sympathetic hyperactivity and downregulation of soluble guanylyl cyclase in corpus cavernosum

Impairment of nitric oxide (NO)-mediated cavernosal relaxations in middle age contributes to erectile dysfunction. However, little information is available about the alterations of sympathetic neurotransmission and contraction in erectile tissue at middle age. This study aimed to evaluate the alterations of the contractile machinery associated with tyrosine hydroxylase (TH) in rat corpus cavernosum (RCC) at middle age, focusing on the role of superoxide anion. Male Wistar young (3.5-mo) and middle-aged (10-mo) rats were used. Electrical-field stimulation (EFS)- and phenylephrine-induced contractions were obtained in RCC strips. Levels of reactive-oxygen species (ROS) and TH mRNA expression, as well as protein expressions for α1/β1-subunits of soluble guanylyl cyclase (sGC), in RCC were evaluated. The neurogenic contractile responses elicited by EFS (4–32 Hz) were greater in RCC from the middle-aged group that was accompanied by elevated TH mRNA expression ( P < 0.01). Phenylephrine-induced contractions were also greater in the middle-aged group. A 62% increase in ROS generation in RCC from middle-aged rats was observed. The mRNA expression for the α1A-adrenoceptor remained unchanged among groups. Protein levels of α1/β1-sGC subunits were decreased in RCC from the middle-aged compared with young group. The NADPH oxidase inhibitor apocynin (85 mg·rat−1·day−1, 4 wk) fully restored the enhanced ROS production, TH mRNA expressions, and α1/β1-subunit sGC expression, indicating that excess of superoxide anion plays a major role in the sympathetic hyperactivity and hypercontractility in erectile tissue at middle age. Reduction of oxidative stress by dietary antioxidants may be an interesting approach to treat erectile dysfunction in aging population.

Heparin responses in vascular smooth muscle cells involve cGMP-dependent protein kinase (PKG)

Published data provide strong evidence that heparin treatment of proliferating vascular smooth muscle cells results in decreased signaling through the ERK pathway and decreases in cell proliferation. In addition, these changes have been shown to be mimicked by antibodies that block heparin binding to the cell surface. Here, we provide evidence that the activity of protein kinase G is required for these heparin effects. Specifically, a chemical inhibitor of protein kinase G, Rp-8-pCPT-cGMS, eliminates heparin and anti-heparin receptor antibody effects on bromodeoxyuridine incorporation into growth factor-stimulated cells. In addition, protein kinase G inhibitors decrease heparin effects on ERK activity, phosphorylation of the transcription factor Elk-1, and heparin-induced MKP-1 synthesis. Although transient, the levels of cGMP increase in heparin treated cells. Finally, knock down of protein kinase G also significantly decreases heparin effects in growth factor-activated vascular smooth muscle cells. Together, these data indicate that heparin effects on vascular smooth muscle cell proliferation depend, at least in part, on signaling through protein kinase G.

Prolonged therapy with the soluble guanylyl cyclase activator BAY 60-2770 restores the erectile function in obese mice

INTRODUCTION

Cardiovascular and endocrine-metabolic diseases associated with increased oxidative stress such as obesity lead to erectile dysfunction (ED). Activators of soluble guanylyl cyclase (sGC) such as BAY 60-2770 reactivate the heme-oxidized sGC in vascular diseases.

AIM

This study aimed to evaluate the effects of 2-week oral intake with BAY 60-2270 on a murine model of obesity-associated ED.

METHODS

C57BL/6 male mice were fed for 12 weeks with standard chow or high-fat diet. Lean and obese mice were treated with BAY 60-2770 (1 mg/kg/day, 2 weeks).

MAIN OUTCOME MEASURES

Measurements of intracavernosal pressure (ICP), along with acetylcholine (10(-9) to 10(-5)  M) and electrical field stimulation (EFS; 4-10 Hz)-induced corpus cavernosum relaxations in vitro, were obtained. Levels of cyclic guanosine monophosphate (cGMP), reactive oxygen species (ROS), and sGC protein expressions in cavernosal tissues were measured.

RESULTS

Cavernous nerve stimulation caused frequency-dependent ICP increases, which were significantly lower in obese compared with lean mice (P < 0.05). Two-week therapy with BAY 60-2770 fully reversed the decreased ICP in obese group. Acetylcholine-induced cavernosal relaxations were 45% lower (P < 0.001) in obese mice, which were fully restored by BAY 60-2770 treatment. Likewise, the EFS-induced relaxations in obese mice were restored by BAY 60-2770. Basal cGMP content in erectile tissue was 68% lower (P < 0.05) in obese mice, an effect normalized by BAY 60-2770. Levels of ROS were 52% higher (P < 0.05) whereas protein expression of α1 sGC subunit was reduced in cavernosal tissue of obese mice, both of which were normalized by BAY 60-2770. In lean group, BAY 60-2770 did not significantly affect any functional, biochemical, or molecular parameter analyzed.

CONCLUSIONS

Two-week therapy with BAY 60-2770 restores the erectile function in obese mice that is associated with reduced ROS levels, up-regulation of α1 sGC subunit, and increased cGMP levels in the erectile tissue.

Hypertension alters phosphorylation of VASP in brain endothelial cells

Hypertension impairs cerebral vascular function. Vasodilator-stimulated phosphoprotein (VASP) mediates active reorganization of the cytoskeleton via membrane ruffling, aggregation and tethering of actin filaments. VASP regulation of endothelial barrier function has been demonstrated by studies using VASP(-/-) animals under conditions associated with tissue hypoxia. We hypothesize that hypertension regulates VASP expression and/or phosphorylation in endothelial cells, thereby contributing to dysfunction in the cerebral vasculature. Because exercise has direct and indirect salutary effects on vascular systems that have been damaged by hypertension, we also investigated the effect of exercise on maintenance of VASP expression and/or phosphorylation. We used immunohistochemistry, Western blotting and immunocytochemistry to examine the effect of hypertension on VASP expression and phosphorylation in brain endothelial cells in normotensive [Wistar-Kyoto (WKY)] and spontaneously hypertensive (SH) rats under normal and exercise conditions. In addition, we analyzed VASP regulation in normoxia- and hypoxia-induced endothelial cells. Brain endothelial cells exhibited significantly lower VASP immunoreactivity and phosphorylation at the Ser157 residue in SHR versus WKY rats. Exercise reversed hypertension-induced alterations in VASP phosphorylation. Western blotting and immunocytochemistry indicated reduction in VASP phosphorylation in hypoxic versus normoxic endothelial cells. These results suggest that diminished VASP expression and/or Ser157 phosphorylation mediates endothelial changes associated with hypertension and exercise may normalize these changes, at least in part, by restoring VASP phosphorylation.

Chemerin reduces vascular nitric oxide/cGMP signalling in rat aorta: a link to vascular dysfunction in obesity?

The adipokine chemerin has been implicated in cardiovascular complications associated with obesity and the metabolic syndrome. Chemerin has direct effects on the vasculature, augmenting vascular responses to contractile stimuli. As NO/cGMP signalling plays a role in vascular dysfunction associated with obesity and the metabolic syndrome, we hypothesized that chemerin induces vascular dysfunction by decreasing NO/cGMP signalling. Aortic rings from male Wistar rats (10-12 weeks of age) were incubated with chemerin (0.5 or 5 ng/ml for 1 h) or vehicle and isometric tension was recorded. Vasorelaxation in response to ACh (acetylcholine), SNP (sodium nitroprusside) and BAY 412272 [an sGC (soluble guanylate cyclase) stimulator] were decreased in chemerin-treated vessels. The NOS (NO synthase) cofactor BH4 (tetrahydrobiopterin), an O2- (superoxide anion) scavenger (tiron) and a SOD (superoxide dismutase) mimetic (tempol) abolished the effects of chemerin on ACh-induced vasodilation. eNOS (endothelial NOS) phosphorylation, determined by Western blotting, was increased in chemerin-treated vessels; however, the enzyme was mainly in the monomeric form, with decreased eNOS dimer/monomer ratio. Chemerin decreased the mRNA levels of the rate-limiting enzyme for BH4 biosynthesis GTP cyclohydrolase I. Chemerin-incubated vessels displayed decreased NO production, along with increased ROS (reactive oxygen species) generation. These effects were abrogated by BH4, tempol and L-NAME (NG-nitro-L-arginine methyl ester). sGC protein expression and cGMP levels were decreased in chemerin-incubated vessels. These results demonstrate that chemerin reduces NO production, enhances NO breakdown and also decreases NO-dependent cGMP signalling, thereby reducing vascular relaxation. Potential mechanisms mediating the effects of chemerin in the vasculature include eNOS uncoupling, increased O2- generation and reduced GC activity.

Activation of soluble guanylyl cyclase prevents foam cell formation and atherosclerosis

AIMS

Soluble guanylyl cyclase (sGC) is a key modulator in the regulation of vascular tone. However, its role and involving mechanism in cholesterol metabolism of macrophages and atherosclerosis remain unclear.

METHODS

Oil red O staining, Dil-oxidized low-density lipoprotein (oxLDL)-binding assay and cholesterol efflux assay were performed in biology of foam cells. Levels of cytokines or intracellular lipid were evaluated by ELISA or colorimetric kits. Expression of gene or protein was determined by quantitative real-time PCR or Western blotting. Histopathology was examined by haematoxylin and eosin staining.

RESULTS

Soluble guanylyl cyclase was expressed in macrophages of mouse atherosclerotic lesions. Treatment with 1H-[1, 2, 4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, sGC inhibitor) exacerbated oxLDL-induced cholesterol accumulation in macrophages. In contrast, 3-(5'-hydroxymethyl-2'furyl)-1-benzyl indazole (YC-1, sGC activator) attenuated the oxLDL-induced cholesterol accumulation because of increased cholesterol efflux. Additionally, YC-1 dose dependently increased the protein expression of ATP-binding cassette transporter A1 (ABCA1) but did not alter that of scavenger receptor class A (SR-A), CD36, SR-BI or ABCG1. Moreover, YC-1-upregulated ABCA1 level depended on liver X receptor α (LXRα). Inhibition of the LXRα-ABCA1 pathway by LXRα small interfering RNA (siRNA), ABCA1 neutralizing antibody or ABCA1 siRNA abolished the effect of YC-1 on cholesterol accumulation and cholesterol efflux. In vivo, YC-1 retarded the development of atherosclerosis, accompanied by reduced serum levels of cholesterol and pro-inflammatory cytokines, in apolipoprotein E-deficient mice.

CONCLUSION

Activation of sGC by YC-1 leads to LXRα-dependent upregulation of ABCA1 in macrophages and may confer protection against atherosclerosis.

Soluble guanylate cyclase: a potential therapeutic target for heart failure

The number of annual hospitalizations for heart failure (HF) and the mortality rates among patients hospitalized for HF remains unacceptably high. The search continues for safe and effective agents that improve outcomes when added to standard therapy. The nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway serves an important physiologic role in both vascular and non-vascular tissues, including regulation of myocardial and renal function, and is disrupted in the setting of HF, leading to decreased protection against myocardial injury, ventricular remodeling, and the cardio-renal syndrome. The impaired NO-sGC-cGMP pathway signaling in HF is secondary to reduced NO bioavailability and an alteration in the redox state of sGC, making it unresponsive to NO. Accordingly, increasing directly the activity of sGC is an attractive pharmacologic strategy. With the development of two novel classes of drugs, sGC stimulators and sGC activators, the hypothesis that restoration of NO-sGC-cGMP signaling is beneficial in HF patients can now be tested. Characterization of these agents in pre-clinical and clinical studies has begun with investigations suggesting both hemodynamic effects and organ-protective properties independent of hemodynamic changes. The latter could prove valuable in long-term low-dose therapy in HF patients. This review will explain the role of the NO-sGC-cGMP pathway in HF pathophysiology and outcomes, data obtained with sGC stimulators and sGC activators in pre-clinical and clinical studies, and a plan for the further clinical development to study these agents as HF therapy.

Novel vasodilators in heart failure

Heart failure is an important public health problem that is increasing in prevalence throughout the world. Not only is this condition common, but it is associated with significant morbidity and mortality as well as high costs to medical care systems. Vasodilator drugs help unload the heart and may have other effects that could benefit heart failure patients. Consequently, they have emerged as an important therapeutic approach for patients with this condition. Novel vasodilator therapies that are currently in development target new pathways, potentially giving clinicians alternate options for improving outcomes in this vulnerable population. This review focuses on investigational drugs that have the ability to dilate blood vessels amongst their therapeutic properties. These drugs include the natriuretic peptides that activate particulate guanylate cyclase, the novel agent cinaciguat that activates the soluble guanylate cyclase system, and finally a recombinant form of the naturally occurring vasodilating agent relaxin, a hormone that mediates many of the changes that allows the cardiovascular system to successfully adapt to pregnancy.

Regulation of metabolism by cGMP

The second messenger cyclic guanosine monophosphate (cGMP) mediates the physiological effects of nitric oxide and natriuretic peptides in a broad spectrum of tissues and cells. So far, the major focus of research on cGMP lay on the cardiovascular system. Recent evidence suggests that cGMP also plays a major role in the regulation of cellular and whole-body metabolism. Here, we focus on the role of cGMP in adipose tissue. In addition, other organs important for the regulation of metabolism and their regulation by cGMP are discussed. Targeting the cGMP signaling pathway could be an exciting approach for the regulation of energy expenditure and the treatment of obesity.

Transcriptional and post-transcriptional regulation of cGMP-dependent protein kinase (PKG-I): pathophysiological significance

The ability of the endothelium to produce nitric oxide, which induces generation of cyclic guanosine monophosphate (cGMP) that activates cGMP-dependent protein kinase (PKG-I), in vascular smooth muscle cells (VSMCs), is essential for the maintenance of vascular homeostasis. Yet, disturbance of this nitric oxide/cGMP/PKG-I pathway has been shown to play an important role in many cardiovascular diseases. In the last two decades, in vitro and in vivo models of vascular injury have shown that PKG-I is suppressed following nitric oxide, cGMP, cytokine, and growth factor stimulation. The molecular basis for these changes in PKG-I expression is still poorly understood, and they are likely to be mediated by a number of processes, including changes in gene transcription, mRNA stability, protein synthesis, or protein degradation. Emerging studies have begun to define mechanisms responsible for changes in PKG-I expression and have identified cis- and trans-acting regulatory elements, with a plausible role being attributed to post-translational control of PKG-I protein levels. This review will focus mainly on recent advances in understanding of the regulation of PKG-I expression in VSMCs, with an emphasis on the physiological and pathological significance of PKG-I down-regulation in VSMCs in certain circumstances.

Activation of haem-oxidized soluble guanylyl cyclase with BAY 60-2770 in human platelets lead to overstimulation of the cyclic GMP signaling pathway

BACKGROUND AND AIMS

Nitric oxide-independent soluble guanylyl cyclase (sGC) activators reactivate the haem-oxidized enzyme in vascular diseases. This study was undertaken to investigate the anti-platelet mechanisms of the haem-independent sGC activator BAY 60-2770 in human washed platelets. The hypothesis that sGC oxidation potentiates the anti-platelet activities of BAY 60-2770 has been tested.

METHODS

Human washed platelet aggregation and adhesion assays, as well as flow cytometry for α(IIb)β(3) integrin activation and Western blot for α1 and β1 sGC subunits were performed. Intracellular calcium levels were monitored in platelets loaded with a fluorogenic calcium-binding dye (FluoForte).

RESULTS

BAY 60-2770 (0.001-10 µM) produced significant inhibition of collagen (2 µg/ml)- and thrombin (0.1 U/ml)-induced platelet aggregation that was markedly potentiated by the sGC inhibitor ODQ (10 µM). In fibrinogen-coated plates, BAY 60-2770 significantly inhibited platelet adhesion, an effect potentiated by ODQ. BAY 60-2770 increased the cGMP levels and reduced the intracellular Ca(2+) levels, both of which were potentiated by ODQ. The cell-permeable cGMP analogue 8-Br-cGMP (100 µM) inhibited platelet aggregation and Ca(2+) levels in an ODQ-insensitive manner. The cAMP levels remained unchanged by BAY 60-2770. Collagen- and thrombin-induced α(IIb)β(3) activation was markedly inhibited by BAY 60-2770 that was further inhibited by ODQ. The effects of sodium nitroprusside (3 µM) were all prevented by ODQ. Incubation with ODQ (10 µM) significantly reduced the protein levels of α1 and β1 sGC subunits, which were prevented by BAY 60-2770.

CONCLUSION

The inhibitory effects of BAY 60-2770 on aggregation, adhesion, intracellular Ca(2+) levels and α(IIb)β(3) activation are all potentiated in haem-oxidizing conditions. BAY 60-2770 prevents ODQ-induced decrease in sGC protein levels. BAY 60-2770 could be of therapeutic interest in cardiovascular diseases associated with thrombotic complications.

Hypoxia induces downregulation of soluble guanylyl cyclase β1 by miR-34c-5p

Soluble guanylyl cyclase (sGC) is the principal receptor for nitric oxide (NO) and crucial for the control of various physiological functions. The β1 subunit of sGC is obligatory for the biological stability and activity of the sGC heterodimer. MicroRNAs (miRNAs) are important regulators of gene expression and exert great influences on diverse biological activities. The aim of the present study was to determine whether or not the expression of sGCβ1 is specifically regulated by miRNAs. We report that miR-34c-5p directly targets sGCβ1 under hypoxia. Bioinformatics analysis of the sGCβ1 3'-untranslated region (3'-UTR) revealed a putative binding site for miR-34b-5p and miR-34c-5p, but only miR-34c-5p inhibited luciferase activity through interaction with sGCβ1 3'-UTR in HEK293T cells. Site-directed mutagenesis of the putative miR-34c-5p binding site abolished the negative regulation of luciferase expression. Overexpression of miR-34c-5p repressed the expression of sGCβ1 in stable cell lines, which was reversed by miR-34c-5p-specific sponge. Inoculation of mouse lung tissues in vitro with lentivirus bearing miR-34c-5p significantly decreased both the expression of sGCβ1 and NO-stimulated sGC activity, which was also rescued by miR-34c-5p-specific sponge. Furthermore, we identified the putative Sp1-binding site in the promoter region of miR-34c-5p. Luciferase reporter constructs revealed that Sp1 directly binds to the wild-type promoter of miR-34c-5p, which was confirmed by chromatin immunoprecipitation. In summary, these findings reveal that miR-34c-5p directly regulates sGCβ1 expression, and they identify the key transcription factor Sp1 that governs miR-34c-5p expression during hypoxia.

NOX1, 2, 4, 5: counting out oxidative stress

For decades, oxidative stress has been discussed as a key mechanism of endothelial dysfunction and cardiovascular disease. However, attempts to validate and exploit this hypothesis clinically by supplementing antioxidants have failed. Nevertheless, this does not disprove the oxidative stress hypothesis. As a certain degree of reactive oxygen species (ROS) formation appears to be physiological and beneficial. To reduce oxidative stress therapeutically, two alternative approaches are being developed. One is the repair of key signalling components that are compromised by oxidative stress. These include uncoupled endothelial nitric oxide (NO) synthase and oxidized/heme-free NO receptor soluble guanylate cyclase. A second approach is to identify and effectively inhibit the relevant source(s) of ROS in a given disease condition. A highly likely target in this context is the family of NADPH oxidases. Animal models, including NOX knockout mice and new pharmacological inhibitors of NADPH oxidases have opened up a new era of oxidative stress research and have paved the way for new cardiovascular therapies.

Fluorescence dequenching makes haem-free soluble guanylate cyclase detectable in living cells

In cardiovascular disease, the protective NO/sGC/cGMP signalling-pathway is impaired due to a decreased pool of NO-sensitive haem-containing sGC accompanied by a reciprocal increase in NO-insensitive haem-free sGC. However, no direct method to detect cellular haem-free sGC other than its activation by the new therapeutic class of haem mimetics, such as BAY 58-2667, is available. Here we show that fluorescence dequenching, based on the interaction of the optical active prosthetic haem group and the attached biarsenical fluorophor FlAsH can be used to detect changes in cellular sGC haem status. The partly overlap of the emission spectrum of haem and FlAsH allows energy transfer from the fluorophore to the haem which reduces the intensity of FlAsH fluorescence. Loss of the prosthetic group, e.g. by oxidative stress or by replacement with the haem mimetic BAY 58-2667, prevented the energy transfer resulting in increased fluorescence. Haem loss was corroborated by an observed decrease in NO-induced sGC activity, reduced sGC protein levels, and an increased effect of BAY 58-2667. The use of a haem-free sGC mutant and a biarsenical dye that was not quenched by haem as controls further validated that the increase in fluorescence was due to the loss of the prosthetic haem group. The present approach is based on the cellular expression of an engineered sGC variant limiting is applicability to recombinant expression systems. Nevertheless, it allows to monitor sGC's redox regulation in living cells and future enhancements might be able to extend this approach to in vivo conditions.

RNA splicing in regulation of nitric oxide receptor soluble guanylyl cyclase

Soluble guanylyl cyclase (sGC) is a key protein in the nitric oxide (NO)/-cGMP signaling pathway. sGC activity is involved in a number of important physiological processes including smooth muscle relaxation, neurotransmission and platelet aggregation and adhesion. Regulation of sGC expression and activity emerges as a crucial factor in control of sGC function in normal and pathological conditions. Recently accumulated evidence strongly indicates that the regulation of sGC expression is a complex process modulated on several levels including transcription, post-transcriptional regulation, translation and protein stability. Presently our understanding of mechanisms governing regulation of sGC expression remains very limited and awaits systematic investigation. Among other ways, the expression of sGC subunits is modulated at the levels of mRNA abundance and transcript diversity. In this review we summarize available information on different mechanisms (including transcriptional activation, mRNA stability and alternative splicing) involved in the modulation of mRNA levels of sGC subunits in response to various environmental clues. We also summarize and cross-reference the information on human sGC splice forms available in the literature and in genomic databases. This review highlights the fact that the study of the biological role and regulation of sGC splicing will bring new insights to our understanding of NO/cGMP biology.

Vasorelaxant and antiaggregatory actions of the nitroxyl donor isopropylamine NONOate are maintained in hypercholesterolemia

Nitroxyl (HNO) displays pharmacological and therapeutic actions distinct from those of its redox sibling nitric oxide (NO(•)). It remains unclear, however, whether the vasoprotective actions of HNO are preserved in disease. The ability of the HNO donor isopropylamine NONOate (IPA/NO) to induce vasorelaxation, its susceptibility to tolerance development, and antiaggregatory actions were compared with those of a clinically used NO(•) donor, glyceryl trinitrate (GTN), in hypercholesterolemic mice. The vasorelaxant and antiaggregatory properties of IPA/NO and GTN were examined in isolated carotid arteries and washed platelets, respectively, from male C57BL/6J mice [wild-type (WT)] maintained on either a normal diet (WT-ND) or high fat diet (WT-HFD; 7 wk) as well as apolipoprotein E-deficient mice maintained on a HFD (ApoE(-/-)-HFD; 7 wk). In WT-ND mice, IPA/NO (0.1-30 μmol/l) induced concentration-dependent vasorelaxation and inhibition of collagen (30 μg/ml)-stimulated platelet aggregation, which was predominantly soluble guanylyl cyclase/cGMP dependent. Compared with WT-HFD mice, ApoE(-/-)-HFD mice displayed an increase in total plasma cholesterol levels (P < 0.001), vascular (P < 0.05) and platelet (P < 0.05) superoxide (O(2)(·-)) production, and reduced endogenous NO(•) bioavailability (P < 0.001). Vasorelaxant responses to both IPA/NO and GTN were preserved in hypercholesterolemia, whereas vascular tolerance developed to GTN (P < 0.001) but not to IPA/NO. The ability of IPA/NO (3 μmol/l) to inhibit platelet aggregation was preserved in hypercholesterolemia, whereas the actions of GTN (100 μmol/l) were abolished. In conclusion, the vasoprotective effects of IPA/NO were maintained in hypercholesterolemia and, thus, HNO donors may represent future novel treatments for vascular diseases.

Soluble guanylate cyclase activation with cinaciguat: a new approach to the treatment of decompensated heart failure

Heart failure (HF) remains a major cause of morbidity and mortality in the United States despite recent advances in its treatment. The nitric oxide -soluble guanylate cyclase (sGC)-cyclic 3', 5'-guanosine monophosphate pathway is a key signaling cascade involved in many physiologic processes. Derangements of the cascade may play an important role in the pathophysiology of HF and other diseases. Organic nitrates, which derive their action from their metabolic conversion to nitric oxide, exploit this pathway therapeutically. They are a mainstay of treatment for acute HF, but the development of tolerance with chronic administration limits their long-term efficacy. The development of a novel class of sGC activators has shown in both animal and preliminary clinical trials to improve hemodynamics without tolerance, while preserving renal function in patients with HF. A phase II clinical program using the sGC activator cinaciguat (BAY 58-2667) is now in progress in patients with symptomatic HF to further evaluate the efficacy and safety of this treatment approach.

Riociguat for the treatment of pulmonary hypertension

INTRODUCTION

Pulmonary hypertension (PH) is a severe condition with a poor prognosis despite recent treatment advances. Therapies with new mechanisms of action are needed.

AREAS COVERED

This review will help readers understand the mechanism of action of the soluble guanylate cyclase (sGC) stimulator riociguat (BAY 63-2521) and will provide a comprehensive summary regarding efficacy and safety of this drug in the management of PH. The most relevant publications up to December 2010 were used as sources for this review.

EXPERT OPINION

Cyclic guanosine monophosphate (cGMP) is an important mediator of the preferential perfusion of well-ventilated regions throughout the lung. Drugs that increase cGMP levels could promote pulmonary vasorelaxation while maintaining optimal gas exchange. cGMP is generated by sGC, which can be stimulated by nitric oxide (NO). Riociguat stimulates sGC independently of NO and increases the sensitivity of sGC to NO, resulting in increased cGMP levels. Results to date suggest rapid, potent and prolonged efficacy and good tolerability in different types of PH. Phase III clinical trials are evaluating the long-term safety and clinical effectiveness of riociguat in pulmonary arterial hypertension (PAH) and chronic thromboembolic PH. Riociguat has the potential to become an important drug for the treatment of patients with PH.

Combined superoxide dismutase mimetic and peroxynitrite scavenger protects against neointima formation after endarterectomy in association with decreased proliferation and nitro-oxidative stress

OBJECTIVE

Reactive oxygen and nitrogen species (e.g., peroxynitrite) may trigger neointima formation leading to restenosis. In a rat carotid endarterectomy (CEA) model, we investigated the effects of the manganese(III)tetrakis(4-benzoic acid)porphyrin (MnTBAP), a superoxide dismutase (SOD) mimetic and peroxynitrite scavenger on neointima formation.

METHODS

CEA was performed in male Sprague-Dawley rats. Animals received either vehicle (control group; n=15) or 15 mg kg(-1) day(-1) MnTBAP intraperitoneally for 3 weeks (treatment group; n=13). Four groups of carotids were analysed: the left, uninjured carotids (sham) and the right, injured carotids (control CEA) from the control group, the right, injured carotids from the treatment group (CEA+MnTBAP) and an additional group of carotids that were harvested 1h following endarterectomy. The analysis of carotid arteries was performed by histology, immunohistochemistry and real-time polymerase chain reaction (PCR). Plasma malondialdehyde (MDA) levels were measured by lipid hydroperoxidase assay.

RESULTS

Stenosis rate (10.5+/-8.1% vs. 45.4+/-28.3%), the percentage of proliferating cell nuclear antigen-positive cells (13.4+/-7.1% vs. 23.3+/-11.0%) and nitrotyrosine immunoreactivity (5.8+/-1.9 vs. 8.0+/-2.0) were significantly reduced in the vascular wall of the CEA+MnTBAP group compared with control CEA group. Ratio of Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL)-positive nuclei was significantly lower after antioxidant therapy (41.7+/-26.7% vs. 64.9+/-18.5%). Plasma MDA levels increased after endarterectomy (11.7+/-4.8 vs. 4.1+/-2.0 micromol l(-1)) and reduced in the treatment group (3.2+/-2.1 micromol l(-1)). No significant gene regulation after MnTBAP treatment could be noted.

CONCLUSIONS

MnTBAP decreased neointima formation, which was associated with reduced vascular smooth muscle cell proliferation and attenuated local and systemic nitro-oxidative stress.

[Restenosis following endovascular interventions: clinical and experimental studies]

Restenosis following endovascular interventions is the main limitation of their long-term success. The incidence of restenosis varies according to the method (stenting, endarterectomy) and the treated vascular region, but the pathomechanism and risk factors are similar. The current article reviews of the author's previous studies in this field. In clinical studies, we compared the restenosis rate after carotid artery stenting and carotid endarterectomy. We also analyzed the complement activation profile after these interventions. In another study, we investigated the role of two polymorphisms of the estrogen receptor alpha in the occurrence of carotid restenosis after either carotid artery stenting or carotid endarterectomy. In an animal model of carotid endarterectomy, we studied the role of the nitrite-oxide-cyclic guanosine monophosphate signaling and the effect of the phosphodiesterase-5 inhibitor therapy in neointimal hyperplasia. Our results suggest that higher incidence of restenosis following carotid endarterectomy can be correlated with the more highly expressed complement activation after this type of carotid intervention. Polymorphisms in the estrogen receptor alpha gene could contribute to the restenosis formation, especially in women. Neointimal hyperplasia can be attenuated by increased cyclic guanosine monophosphate signaling.