The soluble guanylate cyclase activator cinaciguat prevents cardiac dysfunction in a rat model of type-1 diabetes mellitus

Possible retinotoxicity of long-term vardenafil treatment

Phosphodiesterase (PDE) inhibitors - such as vardenafil - are used primarily for treating erectile dysfunction via increasing cyclic guanosine monophosphate (cGMP) levels. Recent studies have also demonstrated their significant cardioprotective effects in several diseases, including diabetes, upon long-term, continuous application. However, PDE inhibitors are not specific for PDE5 and also inhibit the retinal isoform. A sustained rise in cGMP in photoreceptors is known to be toxic; therefore, we hypothesized that long-term vardenafil treatment might result in retinotoxicity. The hypothesis was tested in a clinically relevant animal model of type 2 diabetes mellitus. Histological experiments were performed on lean and diabetic Zucker Diabetic Fatty rats. Half of the animals were treated with vardenafil for six months, and the retinal effects were evaluated. Vardenafil treatment alleviated rod outer segment degeneration but decreased rod numbers in some positions and induced changes in the interphotoreceptor matrix, even in control animals. Vardenafil treatment decreased total retinal thickness in the control and diabetic groups and reduced the number of nuclei in the outer nuclear layer. Müller cell activation was detectable even in the vardenafil-treated control animals, and vardenafil did not improve gliosis in the diabetic group. Vardenafil-treated animals showed complex retinal alterations with improvements in some parameters while deterioration in others. Our results point towards the retinotoxicity of vardenafil, even without diabetes, which raises doubts about the retinal safety of long-term continuous vardenafil administration. This effect needs to be considered when approving PDE inhibitors for alternative indications.

Role and molecular mechanisms of SGLT2 inhibitors in pathological cardiac remodeling (Review)

Cardiovascular diseases are caused by pathological cardiac remodeling, which involves fibrosis, inflammation and cell dysfunction. This includes autophagy, apoptosis, oxidative stress, mitochondrial dysfunction, changes in energy metabolism, angiogenesis and dysregulation of signaling pathways. These changes in heart structure and/or function ultimately result in heart failure. In an effort to prevent this, multiple cardiovascular outcome trials have demonstrated the cardiac benefits of sodium‑glucose cotransporter type 2 inhibitors (SGLT2is), hypoglycemic drugs initially designed to treat type 2 diabetes mellitus. SGLT2is include empagliflozin and dapagliflozin, which are listed as guideline drugs in the 2021 European Guidelines for Heart Failure and the 2022 American Heart Association/American College of Cardiology/Heart Failure Society of America Guidelines for Heart Failure Management. In recent years, multiple studies using animal models have explored the mechanisms by which SGLT2is prevent cardiac remodeling. This article reviews the role of SGLT2is in cardiac remodeling induced by different etiologies to provide a guideline for further evaluation of the mechanisms underlying the inhibition of pathological cardiac remodeling by SGLT2is, as well as the development of novel drug targets.

Empagliflozin treatment of cardiotoxicity: A comprehensive review of clinical, immunobiological, neuroimmune, and therapeutic implications

Cancer and cardiovascular disorders are known as the two main leading causes of mortality worldwide. Cardiotoxicity is a critical and common adverse effect of cancer-related chemotherapy. Chemotherapy-induced cardiotoxicity has been associated with various cancer treatments, such as anthracyclines, immune checkpoint inhibitors, and kinase inhibitors. Different methods have been reported for the management of chemotherapy-induced cardiotoxicity. In this regard, sodium-glucose cotransporter-2 inhibitors (SGLT2i), a class of antidiabetic agents, have recently been applied to manage heart failure patients. Further, SGLT2i drugs such as EMPA exert protective cardiac and systemic effects. Moreover, it can reduce inflammation through the mediation of major inflammatory components, such as Nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasomes, Adenosine 5'-monophosphate-activated protein kinase (AMPK), and c-Jun N-terminal kinase (JNK) pathways, Signal transducer and activator of transcription (STAT), and overall decreasing transcription of proinflammatory cytokines. The clinical outcome of EMPA administration is related to improving cardiovascular risk factors, including body weight, lipid profile, blood pressure, and arterial stiffness. Intriguingly, SGLT2 suppressors can regulate microglia-driven hyperinflammation affecting neurological and cardiovascular disorders. In this review, we discuss the protective effects of EMPA in chemotherapy-induced cardiotoxicity from molecular, immunological, and neuroimmunological aspects to preclinical and clinical outcomes.

Modulation of the nitric oxide/cGMP pathway in cardiac contraction and relaxation: Potential role in heart failure treatment

Evidence exists that heart failure (HF) has an overall impact of 1-2 % in the global population being often associated with comorbidities that contribute to increased disease prevalence, hospitalization, and mortality. Recent advances in pharmacological approaches have significantly improved clinical outcomes for patients with vascular injury and HF. Nevertheless, there remains an unmet need to clarify the crucial role of nitric oxide/cyclic guanosine 3',5'-monophosphate (NO/cGMP) signalling in cardiac contraction and relaxation, to better identify the key mechanisms involved in the pathophysiology of myocardial dysfunction both with reduced (HFrEF) as well as preserved ejection fraction (HFpEF). Indeed, NO signalling plays a crucial role in cardiovascular homeostasis and its dysregulation induces a significant increase in oxidative and nitrosative stress, producing anatomical and physiological cardiac alterations that can lead to heart failure. The present review aims to examine the molecular mechanisms involved in the bioavailability of NO and its modulation of downstream pathways. In particular, we focus on the main therapeutic targets and emphasize the recent evidence of preclinical and clinical studies, describing the different emerging therapeutic strategies developed to counteract NO impaired signalling and cardiovascular disease (CVD) development.

BNP protects against diabetic cardiomyopathy by promoting Opa1-mediated mitochondrial fusion via activating the PKG-STAT3 pathway

Brain natriuretic peptide (BNP) belongs to the family of natriuretic peptides, which are responsible for a wide range of actions. Diabetic cardiomyopathy (DCM) is often associated with increased BNP levels. This present research intends to explore the role of BNP in the development of DCM and the underlying mechanisms. Diabetes was induced in mice using streptozotocin (STZ). Primary neonatal cardiomyocytes were treated with high glucose. It was found that the levels of plasma BNP started to increase at 8 weeks after diabetes, which preceded the development of DCM. Addition of exogenous BNP promoted Opa1-mediated mitochondrial fusion, inhibited mitochondrial oxidative stress, preserved mitochondrial respiratory capacity and prevented the development of DCM, while knockdown of endogenous BNP exacerbated mitochondrial dysfunction and accelerated DCM. Opa1 knockdown attenuated the aforementioned protective action of BNP both in vivo and in vitro. BNP-induced mitochondrial fusion requires the activation of STAT3, which facilitated Opa1 transcription by binding to its promoter regions. PKG, a crucial signaling biomolecule in the BNP signaling pathway, interacted with STAT3 and induced its activation. Knockdown of NPRA (the receptor of BNP) or PKG blunted the promoting effect of BNP on STAT3 phosphorylation and Opa1-mediated mitochondrial fusion. The results of this study demonstrate for the first time that there is a rise in BNP during the early stages of DCM as a compensatory protection mechanism. BNP is a novel mitochondrial fusion activator in protecting against hyperglycemia-induced mitochondrial oxidative injury and DCM through the activation of NPRA-PKG-STAT3-Opa1 signaling pathway.

CYB5R3 in type II alveolar epithelial cells protects against lung fibrosis by suppressing TGF-β1 signaling

Type II alveolar epithelial cell (AECII) redox imbalance contributes to the pathogenesis of idiopathic pulmonary fibrosis (IPF), a deadly disease with limited treatment options. Here, we show that expression of membrane-bound cytochrome B5 reductase 3 (CYB5R3), an enzyme critical for maintaining cellular redox homeostasis and soluble guanylate cyclase (sGC) heme iron redox state, is diminished in IPF AECIIs. Deficiency of CYB5R3 in AECIIs led to sustained activation of the pro-fibrotic factor TGF-β1 and increased susceptibility to lung fibrosis. We further show that CYB5R3 is a critical regulator of ERK1/2 phosphorylation and the sGC/cGMP/protein kinase G axis that modulates activation of the TGF-β1 signaling pathway. We demonstrate that sGC agonists (BAY 41-8543 and BAY 54-6544) are effective in reducing the pulmonary fibrotic outcomes of in vivo deficiency of CYB5R3 in AECIIs. Taken together, these results show that CYB5R3 in AECIIs is required to maintain resilience after lung injury and fibrosis and that therapeutic manipulation of the sGC redox state could provide a basis for treating fibrotic conditions in the lung and beyond.

Emerging Therapy for Diabetic Cardiomyopathy: From Molecular Mechanism to Clinical Practice

Diabetic cardiomyopathy is characterized by abnormal myocardial structure or performance in the absence of coronary artery disease or significant valvular heart disease in patients with diabetes mellitus. The spectrum of diabetic cardiomyopathy ranges from subtle myocardial changes to myocardial fibrosis and diastolic function and finally to symptomatic heart failure. Except for sodium–glucose transport protein 2 inhibitors and possibly bariatric and metabolic surgery, there is currently no specific treatment for this distinct disease entity in patients with diabetes. The molecular mechanism of diabetic cardiomyopathy includes impaired nutrient-sensing signaling, dysregulated autophagy, impaired mitochondrial energetics, altered fuel utilization, oxidative stress and lipid peroxidation, advanced glycation end-products, inflammation, impaired calcium homeostasis, abnormal endothelial function and nitric oxide production, aberrant epidermal growth factor receptor signaling, the activation of the renin–angiotensin–aldosterone system and sympathetic hyperactivity, and extracellular matrix accumulation and fibrosis. Here, we summarize several important emerging treatments for diabetic cardiomyopathy targeting specific molecular mechanisms, with evidence from preclinical studies and clinical trials.

Nutraceutical Prevention of Diabetic Complications—Focus on Dicarbonyl and Oxidative Stress

Oxidative and dicarbonyl stress, driven by excess accumulation of glycolytic intermediates in cells that are highly permeable to glucose in the absence of effective insulin activity, appear to be the chief mediators of the complications of diabetes. The most pathogenically significant dicarbonyl stress reflects spontaneous dephosphorylation of glycolytic triose phosphates, giving rise to highly reactive methylglyoxal. This compound can be converted to harmless lactate by the sequential activity of glyoxalase I and II, employing glutathione as a catalyst. The transcription of glyoxalase I, rate-limiting for this process, is promoted by Nrf2, which can be activated by nutraceutical phase 2 inducers such as lipoic acid and sulforaphane. In cells exposed to hyperglycemia, glycine somehow up-regulates Nrf2 activity. Zinc can likewise promote glyoxalase I transcription, via activation of the metal-responsive transcription factor (MTF) that binds to the glyoxalase promoter. Induction of glyoxalase I and metallothionein may explain the protective impact of zinc in rodent models of diabetic complications. With respect to the contribution of oxidative stress to diabetic complications, promoters of mitophagy and mitochondrial biogenesis, UCP2 inducers, inhibitors of NAPDH oxidase, recouplers of eNOS, glutathione precursors, membrane oxidant scavengers, Nrf2 activators, and correction of diabetic thiamine deficiency should help to quell this.

Bibliometric study of soluble guanylate cyclase stimulators in cardiovascular research based on web of science from 1992 to 2021

Background: Several studies have shown that soluble guanylate cyclase (sGC) stimulators have cardiovascular (CV) benefits. However, few bibliometric analyses have examined this field systematically. Our study aimed to examine the publications to determine the trends and hotspots in CV research on sGC stimulators.

Methods: Publications on sGC stimulators in CV research were retrieved from the Web of Science Core Collection. VOSviewer and CiteSpace visualization software were used to analyze publication trends, countries (regions) and institutions, journals and cited journals, authors and cited references, as well as keywords.

Results: A total of 1,212 literatures were obtained. From its first appearance in 1992–2021 (based on WOSCC record), the overall volume of publications has shown a gradual increasing trend. Nearly one-third were authored by American scholars, and most were published in Circulation, Circulation Research, and Proceedings of the National Academy of Sciences of the United States of America. Bayer Agency in Germany was the leading driving force, and has a high academic reputation in this field. Stasch JP has published the most related articles and been cited most frequently. Half of the top 10 co-cited references were published in the leading highly co-cited journal Circulation and New England Journal of Medicine. “NO,” “allosteric regulation” and “free radicals” were the focus of previous research, “chronic thromboembolic pulmonary hypertension,” “pulmonary hypertension” and “heart failure” were the main research hotspots. The key words “chronic thromboembolic pulmonary hypertension,” “Pulmonary hypertension,” “preserved ejection fraction” and “heart failure” appeared most recently as research frontiers.

Conclusion: The research in the CV field of sGC stimulators was relatively comprehensive, and there was a close relationship among countries, research institutions and authors, but it is still in the exploratory stage in the treatment of CV disease. At present, most studies focus on the results of clinical trials. sGC stimulators in the treatment of heart failure, especially heart failure with preserved ejection fraction, may be the hotpots and Frontier at present and in the future, and should be closely monitored.

Effects of soluble guanylate cyclase stimulator on renal function in ZSF-1 model of diabetic nephropathy

BACKGROUND

Diabetic nephropathy is associated with endothelial dysfunction and oxidative stress, in which the nitric oxide-soluble guanylate cyclase-cyclic guanosine monophosphate (NO-sGC-cGMP) signaling pathway is impaired. We hypothesize that sGC stimulator Compound 1 can enhance NO signaling, reduce proteinuria in a diabetic nephropathy preclinical model with diminished NO bioavailability and increased oxidized sGC. Therefore, we evaluated the effect of sGC stimulator Compound 1 on the renal effect in obese ZSF1 (ZSF1 OB) rats.

MATERIALS AND METHODS

The sGC stimulator Compound 1, the standard of care agent Enalapril, and a combination of Compound 1 and Enalapril were administered chronically to obese ZSF1 rats for 6 months. Mean arterial pressure, heart rate, creatinine clearance for glomerular filtration rate (eGFR), urinary protein excretion to creatinine ratio (UPCR), and urinary albumin excretion ratio (UACR) were determined during the study. The histopathology of glomerular and interstitial lesions was assessed at the completion of the study.

RESULTS

While both Compound 1 and Enalapril significantly reduced blood pressure, the combination of Compound 1 and Enalapril normalized blood pressure levels. Compound 1 improved eGFR and reduced UPCR and UACR. A combination of Enalapril and Compound 1 resulted in a marked reduction in UPCR and UACR and improved GFR.

CONCLUSION

The sGC stimulator Compound 1 as a monotherapy slowed renal disease progression, and a combination of the sGC stimulator with Enalapril provided greater renal protection in a rodent model of diabetic nephropathy.

Soluble Klotho-integrin β1/ERK1/2 pathway ameliorates myocardial fibrosis in diabetic cardiomyopathy

Soluble Klotho (sKL) is closely related to insulin resistance, which is a major factor in the progression of diabetic cardiomyopathy (DCM). The purpose of this study was to investigate the role of sKL in the regulation of DCM and the mechanism involved. A mouse model of type 2 diabetes was induced by high-fat diet and streptozotocin injection. An insulin-resistant cardiac fibroblast model was established by high glucose and high insulin. KL gene overexpression was achieved in vivo and vitro through transfection with an adenovirus-harboring KL-cDNA. Gene overexpression was used to evaluate the role of sKL in the pathophysiologic characteristics of DCM. Insulin-resistant cardiac fibroblasts reduced sKL expression and collagen deposition. Diabetic mice constructed by streptozotocin exhibited severe insulin resistance, inflammation, fibrosis, left ventricular dysfunction, and sKL downregulation. The overexpression of sKL mitigated insulin resistance and metabolic disturbance; inflammation, fibrosis, and upregulated collagen I/III content ratio in diabetic state were significantly reduced. Our findings were accompanied by notable moderation of cardiac function. Further, blunted phosphorylation of Akt was restored with sKL gene overexpression, and activated phosphorylation of extracellular signal-regulated kinase 1/2 in DCM was reduced. Our results suggest that sKL protein overexpression exerts a defensive measure by ameliorating selective insulin resistance in mouse DCM, thus revealing its underlying mechanism for potential human DCM treatment.

Cardioprotective effect of icariin against myocardial fibrosis and its molecular mechanism in diabetic cardiomyopathy based on network pharmacology: Role of ICA in DCM

BACKGROUND

Diabetic cardiomyopathy (DCM) is one of the most severe symptoms of diabetes. It continues to be a major clinical problem, but our knowledge of its molecular mechanisms and effective treatments are limited. Traditional Chinese medicine has been shown to be a pool of novel drugs for diabetes.

PURPOSE

Herein, we aim to define the molecular mechanism of icariin (ICA), an extract from a traditional Chinese medicine herb, in protecting cardiac structures and restoring cardiac functions of in a rat model of type 2 diabetes mellitus (T2DM).

STUDY DESIGN AND METHODS

Candidate genes related to T2DM were identified through bioinformatics screening and their interactions were constructed by molecule docking technique, followed by pathway enrichment analyses of their cellular functions. A T2DM rat model was then established to evaluate the effects of ICA on cardiac structures, myocardial fibrosis, and cellular Ca²⁺ inflow, as reflected by HE and Masson staining, qRT-PCR and Western blot determination of related genes, and measurement of the L-type Ca²⁺ current.

RESULTS

Four potential target genes (Jun, p65, NOS3, and PDE5A) were identified. ICA ameliorated the structural damage and myocardial fibrosis in T2DM rats. Intracellular Ca2+ hyperactivities and dysfunction in myocardium of T2DM rats were also repressed by ICA treatment. Furthermore, ICA-induced inhibition of Jun and p65 ameliorated the irregular collagen metabolism and myocardial fibrosis. NOS3, PDE5A and the related sGC-cGMP-PKG signaling pathway mediated the ICA-induced improvement of intracellular Ca²⁺ inflow.

CONCLUSION

In conclusion, these results demonstrate the regulatory roles of potential target genes in DCM and suggest ICA as an effective treatment of DCM by targeting these genes specifically.

Endogenous asymmetric dimethylarginine accumulation precipitates the cardiac and mitochondrial dysfunctions in type 1 diabetic rats

Myocardial mitochondrial function and biogenesis are suppressed in diabetes, but the mechanisms are unclear. Increasing evidence suggests that asymmetric dimethylarginine (ADMA) is associated with diabetic cardiovascular complications. This study was to determine whether endogenous ADMA accumulation contributes to cardiac and mitochondrial dysfunctions of diabetic rats and elucidate the potential mechanisms. Diabetic rat was induced by single intraperitoneal injection of streptozotocin (50 mg/kg). N-acetylcysteine was given (250 mg/kg/d) by gavage for 12w. Cardiac function was detected by echocardiography. Left ventricle papillary muscles were isolated to examine myocardial contractility. Myocardial ATP and mitochondrial DNA contents were measured to evaluate mitochondrial function and biogenesis. Endogenous ADMA accumulation was augmented resulting in decreased nitric oxide (NO) production and increased oxidative stress, suggesting NO synthase (NOS) uncoupling in the myocardium of T1DM rats compared with control rats. ADMA augmentation was associated with cardiac and mitochondrial dysfunctions along with myocardial uncoupling protein-2 (UCP2) upregulation and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) downregulation in T1DM rats. Exogenous ADMA could directly inhibit myocardial contractility, mitochondrial function and biogenesis in parallel with decreasing NO content and PGC-1α expression while increasing oxidative stress and UCP2 expression in papillary muscles and cardiomyocytes. Treatment with antioxidant N-acetylcysteine, also an inhibitor of NOS uncoupling, either ameliorated ADMA-associated cardiac and mitochondrial dysfunctions or reversed ADMA-induced NO reduction and oxidative stress enhance in vivo and in vitro. These results indicate that myocardial ADMA accumulation precipitates cardiac and mitochondrial dysfunctions in T1DM rats. The underlying mechanism may be related to NOS uncoupling, resulting in NO reduction and oxidative stress increment, ultimate PGC-1α down-regulation and UCP2 up-regulation.

Current trends and future perspectives for heart failure treatment leveraging cGMP modifiers and the practical effector PKG

Cyclic guanosine monophosphate (cGMP), an intracellular second messenger molecule synthesized by guanylated cyclases (GCs), controls various myocardial properties, including cell growth and survival, interstitial fibrosis, endothelial permeability, cardiac contractility, and cardiovascular remodeling. These processes are mediated by the main cGMP effector protein kinase G (PKG) activation of which exerts intrinsic protective responses against the adverse effects of neurohormonal stimulation and pathological cardiac stress. Therapeutic strategies that enhance cGMP levels and PKG activation have been used for heart failure, which can be executed by reducing natriuretic peptide (NP) proteolysis, enhancing cGMP synthesis, or blocking cGMP hydrolysis. Among these, reducing NP clearance with neprilysin inhibitor combined with angiotensin receptor blocker has been shown to greatly improve the prognosis of patients with heart failure with reduced ejection fraction (HFrEF) compared to the prognosis of patients on standard therapy using angiotensin-converting enzyme inhibitors. Moreover, in a recent phase III clinical trial, soluble GC-derived cGMP generation was shown to have potential efficacy in the management of HFrEF. Despite the clinical significance of cGMP/PKG signaling activated by either soluble or particulate GCs in heart failure, the differential signaling events downstream of intracellular cGMP, which are precisely controlled not only by PKG activation but also by the changes in its targeting and compartmentalization depending on the pathophysiology of heart disease, are not yet completely understood. Hitherto, the importance of the latter PKG regulatory mechanisms in developing therapeutic strategies has not been elucidated. Further investigation of redox-based PKG modulation will aid in the successful development of clinical therapies and could also lead to the establishment of improved personalized treatments for patients with heart failure.

Targeted Delivery of Soluble Guanylate Cyclase (sGC) Activator Cinaciguat to Renal Mesangial Cells via Virus-Mimetic Nanoparticles Potentiates Anti-Fibrotic Effects by cGMP-Mediated Suppression of the TGF-β Pathway

Diabetic nephropathy (DN) ranks among the most detrimental long-term effects of diabetes, affecting more than 30% of all patients. Within the diseased kidney, intraglomerular mesangial cells play a key role in facilitating the pro-fibrotic turnover of extracellular matrix components and a progredient glomerular hyperproliferation. These pathological effects are in part caused by an impaired functionality of soluble guanylate cyclase (sGC) and a consequentially reduced synthesis of anti-fibrotic messenger 3′,5′-cyclic guanosine monophosphate (cGMP). Bay 58-2667 (cinaciguat) is able to re-activate defective sGC; however, the drug suffers from poor bioavailability and its systemic administration is linked to adverse events such as severe hypotension, which can hamper the therapeutic effect. In this study, cinaciguat was therefore efficiently encapsulated into virus-mimetic nanoparticles (NPs) that are able to specifically target renal mesangial cells and therefore increase the intracellular drug accumulation. NP-assisted drug delivery thereby increased in vitro potency of cinaciguat-induced sGC stabilization and activation, as well as the related downstream signaling 4- to 5-fold. Additionally, administration of drug-loaded NPs provided a considerable suppression of the non-canonical transforming growth factor β (TGF-β) signaling pathway and the resulting pro-fibrotic remodeling by 50–100%, making the system a promising tool for a more refined therapy of DN and other related kidney pathologies.

Activation of soluble guanylyl cyclase signalling with cinaciguat improves impaired kidney function in diabetic mice

BACKGROUND AND PURPOSE

Diabetic nephropathy is the leading cause for end-stage renal disease worldwide. Until now, there is no specific therapy available. Standard treatment with inhibitors of the renin-angiotensin system just slows down progression. However, targeting the NO/sGC/cGMP pathway using sGC activators does prevent kidney damage. Thus, we investigated if the sGC activator cinaciguat was beneficial in a mouse model of diabetic nephropathy, and we analysed how mesangial cells (MCs) were affected by related conditions in cell culture.

EXPERIMENTAL APPROACH

Type 1 diabetes was induced with streptozotocin in wild-type and endothelial NOS knockout (eNOS KO) mice for 8 or 12 weeks.. Half of these mice received cinaciguat in their chow for the last 4 weeks. Kidneys from the diabetic mice were analysed with histochemical assays and by RT-PCR and western blotting. . Additionally, primary murine MCs under diabetic conditions were stimulated with 8-Br-cGMP or cinaciguat to activate the sGC/cGMP pathway.

KEY RESULTS

The diabetic eNOS KO mice developed most characteristics of diabetic nephropathy, most marked at 12 weeks. Treatment with cinaciguat markedly improved GFR, serum creatinine, mesangial expansion and kidney fibrosis in these animals. We determined expression levels of related signalling proteins. Thrombospondin 1, a key mediator in kidney diseases, was strongly up-regulated under diabetic conditions and this increase was suppressed by activation of sGC/cGMP signalling.

CONCLUSION AND IMPLICATIONS

Activation of the NO/sGC/PKG pathway with cinaciguat was beneficial in a model of diabetic nephropathy. Activators of sGC might be an appropriate therapy option in patients with Type 1 diabetes.

Soluble Guanylate Cyclase Stimulators and Activators

When Furchgott, Murad, and Ignarro were honored with the Nobel prize for the identification of nitric oxide (NO) in 1998, the therapeutic implications of this discovery could not be fully anticipated. This was due to the fact that available therapeutics like NO donors did not allow a constant and long-lasting cyclic guanylyl monophosphate (cGMP) stimulation and had a narrow therapeutic window. Now, 20 years later, the stimulator of soluble guanylate cyclase (sGC), riociguat, is on the market and is the only drug approved for the treatment of two forms of pulmonary hypertension (PAH/CTEPH), and a variety of other sGC stimulators and sGC activators are in preclinical and clinical development for additional indications. The discovery of sGC stimulators and sGC activators is a milestone in the field of NO/sGC/cGMP pharmacology. The sGC stimulators and sGC activators bind directly to reduced, heme-containing and oxidized, heme-free sGC, respectively, which results in an increase in cGMP production. The action of sGC stimulators at the heme-containing enzyme is independent of NO but is enhanced in the presence of NO whereas the sGC activators interact with the heme-free form of sGC. These highly innovative pharmacological principles of sGC stimulation and activation seem to have a very broad therapeutic potential. Therefore, in both academia and industry, intensive research and development efforts have been undertaken to fully exploit the therapeutic benefit of these new compound classes. Here we summarize the discovery of sGC stimulators and sGC activators and the current developments in both compound classes, including the mode of action, the chemical structures, and the genesis of the terminology and nomenclature. In addition, preclinical studies exploring multiple aspects of their in vitro, ex vivo, and in vivo pharmacology are reviewed, providing an overview of multiple potential applications. Finally, the clinical developments, investigating the treatment potential of these compounds in various diseases like heart failure, diabetic kidney disease, fibrotic diseases, and hypertension, are reported. In summary, sGC stimulators and sGC activators have a unique mode of action with a broad treatment potential in cardiovascular diseases and beyond.

Cardiac cGMP Signaling in Health and Disease: Location, Location, Location

3',5'-Cyclic guanosine monophosphate (cGMP) is a ubiquitous second messenger, which critically regulates cardiac pump function and protects from the development of cardiac hypertrophy by acting in various subcellular microdomains. Although clinical studies testing the potential of cGMP elevating drugs in patients suffering from cardiac disease showed promising results, deeper insight into the local actions of these drugs at the subcellular level are indispensable to inspire novel therapeutic strategies. Detailed information on the spatio-temporal dynamics of cGMP production and degradation can be provided by the use of fluorescent biosensors that are capable of monitoring this second messenger at different locations inside the cell with high temporal and spatial resolution. In this review, we will summarize how these emerging new tools have improved our understanding of cardiac cGMP signaling in health and disease, and attempt to anticipate future challenges in the field.

Nitroxyl: A Novel Strategy to Circumvent Diabetes Associated Impairments in Nitric Oxide Signaling

Diabetes is associated with an increased mortality risk due to cardiovascular complications. Hyperglycemia-induced oxidative stress underlies these complications, leading to an impairment in endogenous nitric oxide (NO•) generation, together with reductions in NO• bioavailability and NO• responsiveness in the vasculature, platelets and myocardium. The latter impairment of responsiveness to NO•, termed NO• resistance, compromises the ability of traditional NO•-based therapeutics to improve hemodynamic status during diabetes-associated cardiovascular emergencies, such as acute myocardial infarction. Whilst a number of agents can ameliorate (e.g. angiotensin converting enzyme [ACE] inhibitors, perhexiline, statins and insulin) or circumvent (e.g. nitrite and sGC activators) NO• resistance, nitroxyl (HNO) donors offer a novel opportunity to circumvent NO• resistance in diabetes. With a suite of vasoprotective properties and an ability to enhance cardiac inotropic and lusitropic responses, coupled with preserved efficacy in the setting of oxidative stress, HNO donors have intact therapeutic potential in the face of diminished NO• signaling. This review explores the major mechanisms by which hyperglycemia-induced oxidative stress drives NO• resistance, and the therapeutic potential of HNO donors to circumvent this to treat cardiovascular complications in type 2 diabetes mellitus.

Therapeutic approaches to diabetic cardiomyopathy: Targeting the antioxidant pathway

The global epidemic of cardiovascular disease continues unabated and remains the leading cause of death both in the US and worldwide. We hereby summarize the available therapies for diabetes and cardiovascular disease in diabetics. Clearly, the current approaches to diabetic heart disease often target the manifestations and certain mediators but not the specific pathways leading to myocardial injury, remodeling and dysfunction. Better understanding of the molecular events determining the evolution of diabetic cardiomyopathy will provide insight into the development of specific and targeted therapies. Recent studies largely increased our understanding of the role of enhanced inflammatory response, ROS production, as well as the contribution of Cyp-P450-epoxygenase-derived epoxyeicosatrienoic acid (EET), Peroxisome Proliferator-Activated Receptor Gamma Coactivator-1α (PGC-1α), Heme Oxygenase (HO)-1 and 20-HETE in pathophysiology and therapy of cardiovascular disease. PGC-1α increases production of the HO-1 which has a major role in protecting the heart against oxidative stress, microcirculation and mitochondrial dysfunction. This review describes the potential drugs and their downstream targets, PGC-1α and HO-1, as major loci for developing therapeutic approaches beside diet and lifestyle modification for the treatment and prevention of heart disease associated with obesity and diabetes.

Downregulation of microRNA-873 attenuates insulin resistance and myocardial injury in rats with gestational diabetes mellitus by upregulating IGFBP2

Gestational diabetes mellitus (GDM) is a metabolic disorder characterized by insulin resistance, and patients with GDM have a higher risk of cardiovascular disease. Multiple microRNAs (miRNAs) are reported to be involved in the regulation of myocardial injury. Moreover, miR-873 was predicted to target insulin-like growth factor binding protein 2 (IGFBP2) through bioinformatic analysis, which was further confirmed using a luciferase assay. Thus, our objective was to assess whether microRNA-873 (miR-873) affects insulin resistance and myocardial injury in an established GDM rat model. The GDM rats were treated with miR-875 mimic or inhibitor or IGFBP2 siRNA. The effects of miR-875 and IGFBP2 on the cardiac function, insulin resistance, and myocardial injury were evaluated by hemodynamic measurements, determination of biochemical indices of myocardium and serum, and insulin homeostatic model assessment. The results indicated that downregulation of miR-873 upregulated the expression of IGFBP2 and promoted the activation of phosphatidylinositol-3 kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) axis. With downregulation of miR-873 in GDM rats, the cardiac function was improved and the myocardial apoptosis was inhibited, coupled with elevated activity of superoxide dismutase, carbon monoxide synthase, and the nitric oxide content. In addition, the inhibition of miR-873 in GDM rats modulated the insulin resistance and reduced myocardial apoptosis. Overall, the data showed that inhibition of miR-873 by targeting IGFBP2 may regulate the insulin resistance and curtail myocardial injury in GDM rats through activating the PI3K/AKT/mTOR axis, thus providing a potential means of impeding the progression of GDM.

Stimulation of soluble guanylate cyclase improves donor organ function in rat heart transplantation

Heart transplantation remains the definitive therapy of end-stage heart failure. Ischemia-reperfusion injury occurring during transplantation is a primary determinant of long-term outcome of heart transplantation and primary graft insufficiency. Modification of the nitric oxide/soluble guanylate cyclase/cyclic guanosine monophosphate signaling pathway appears to be one of the most promising among the pharmacological interventional options. We aimed at characterizing the cardio-protective effects of the soluble guanylate cyclase stimulator riociguat in a rat model of heterotopic heart transplantation. Donor Lewis rats were treated orally with either riociguat or placebo for two days (n = 9) in each transplanted group and (n = 7) in donor groups. Following explantation, hearts were heterotopically transplanted. After one hour reperfusion, left ventricular pressure-volume relations and coronary blood flow were recorded. Molecular biological measurements and histological examination were also completed. Left ventricular contractility (systolic pressure: 117 ± 13 vs. 48 ± 5 mmHg, p < 0.001; dP/dt_max: 2963 ± 221 vs. 1653 ± 159 mmHg/s, p < 0.001), active relaxation (dP/dt_min: −2014 ± 305 vs. −1063 ± 177 mmHg/s, p = 0.02; all at 120 µl of left ventricular volume), and alteration of coronary blood flow standardized to heart weight (2.55 ± 0.32 vs. 1.67 ± 0.22 ml/min/g, p = 0.03) were markedly increased following preconditioning with riociguat. Myocardial apoptosis markers were also significantly reduced in the riociguat pretreated group as well as the antioxidant markers were elevated. Pharmacological preconditioning with riociguat decreases ischemia-reperfusion injury and improves donor organ function in our animal model of heart transplantation. Therefore, riociguat might be a potential cardioprotective agent.

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

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

The importance of the nitric oxide-cGMP pathway in age-related cardiovascular disease: Focus on phosphodiesterase-1 and soluble guanylate cyclase

Among ageing-related illnesses, cardiovascular disease (CVD) remains the leading cause of morbidity and mortality causing one-third of all deaths worldwide. Ageing evokes a number of functional, pharmacological and morphological changes in the vasculature, accompanied by a progressive failure of protective and homeostatic mechanisms, resulting in target organ damage. Impaired vasomotor, proliferation, migration, antithrombotic and anti-inflammatory function in both the endothelial and vascular smooth muscle cells are parts of the vascular ageing phenotype. The endothelium regulates these functions by the release of a wide variety of active molecules including endothelium-derived relaxing factors such as nitric oxide, prostacyclin (PGI₂ ) and endothelium-derived hyperpolarization (EDH). During ageing, a functional decay of the nitric oxide pathway takes place. Nitric oxide signals to VSMC and other important cell types for vascular homeostasis through the second messenger cyclic guanosine monophosphate (cGMP). Maintenance of proper cGMP levels is an important goal in sustainment of proper vascular function during ageing. For this purpose, different components can be targeted in this signalling system, and among them, phosphodiesterase-1 (PDE1) and soluble guanylate cyclase (sGC) are crucial. This review focuses on the role of PDE1 and sGC in conditions that are relevant for vascular ageing.

Empagliflozin prevents cardiomyopathy via sGC-cGMP-PKG pathway in type 2 diabetes mice

Cardiovascular complications contribute to the major mortality and morbidity in type 2 diabetes. Diabetic cardiomyopathy (DCM) is increasingly recognized as an important cause of heart failure. EMPA-REG OUTCOME trial has reported that empagliflozin, the sodium-glucose cotransporter 2 inhibitor, exerts cardiovascular benefits on diabetic population. However, the mechanism by which empagliflozin alleviates DCM still remains unclear. In the current study, we investigated the cardiac protective effects of empagliflozin on spontaneous type 2 diabetic db/db mice and its potential mechanism. Eight weeks of empagliflozin treatment (10 mg/kg/day) decreased body weight and blood glucose level, and increased urinary glucose excretion (UGE) in diabetic mice. Echocardiography revealed that both systolic and diastolic functions of db/db mice were also obviously improved by empagliflozin. Furthermore, empagliflozin-treated diabetic mice presented with amelioration of cardiac hypertrophy and fibrosis. In addition, diabetic hearts exhibited the deterioration of oxidative stress, apoptosis and pyroptosis, while these effects were significantly counteracted after empagliflozin treatment. Moreover, empagliflozin rescued diabetes-induced suppression of sGC (soluble guanylate cyclase enzyme)-cGMP (cyclic guanosine monophosphate)-PKG (cGMP-dependent protein kinase) pathway. However, when sGC-β expression of hearts was inhibited by transvascular delivery of small interfering RNA, cardiac dysfunction was aggravated and the advantages of empagliflozin were reversed through inhibiting sGC-cGMP-PKG pathway. Collectively, these findings indicate that empagliflozin improves cardiac function involving the inhibition of oxidative stress-induced injury via sGC-cGMP-PKG pathway and may be a promising therapeutic option for DCM.

Selective Heart Irradiation Induces Cardiac Overexpression of the Pro-hypertrophic miR-212

Background: A deleterious, late-onset side effect of thoracic radiotherapy is the development of radiation-induced heart disease (RIHD). It covers a spectrum of cardiac pathology including also heart failure with preserved ejection fraction (HFpEF) characterized by left ventricular hypertrophy (LVH) and diastolic dysfunction. MicroRNA-212 (miR-212) is a crucial regulator of pathologic LVH via FOXO3-mediated pathways in pressure-overload-induced heart failure. We aimed to investigate whether miR-212 and its selected hypertrophy-associated targets play a role in the development of RIHD. Methods: RIHD was induced by selective heart irradiation (50 Gy) in a clinically relevant rat model. One, three, and nineteen weeks after selective heart irradiation, transthoracic echocardiography was performed to monitor cardiac morphology and function. Cardiomyocyte hypertrophy and fibrosis were assessed by histology at week 19. qRT-PCR was performed to measure the gene expression changes of miR-212 and forkhead box O3 (FOXO3) in all follow-up time points. The cardiac transcript level of other selected hypertrophy-associated targets of miR-212 including extracellular signal-regulated kinase 2 (ERK2), myocyte enhancer factor 2a (MEF2a), AMP-activated protein kinase, (AMPK), heat shock protein 40 (HSP40), sirtuin 1, (SIRT1), calcineurin A-alpha and phosphatase and tensin homolog (PTEN) were also measured at week 19. Cardiac expression of FOXO3 and phospho-FOXO3 were investigated at the protein level by Western blot at week 19. Results: In RIHD, diastolic dysfunction was present at every time point. Septal hypertrophy developed at week 3 and a marked LVH with interstitial fibrosis developed at week 19 in the irradiated hearts. In RIHD, cardiac miR-212 was overexpressed at week 3 and 19, and FOXO3 was repressed at the mRNA level only at week 19. In contrast, the total FOXO3 protein level failed to decrease in response to heart irradiation at week 19. Other selected hypertrophy-associated target genes failed to change at the mRNA level in RIHD at week 19. Conclusions: LVH in RIHD was associated with cardiac overexpression of miR-212. However, miR-212 seems to play a role in the development of LVH via FOXO3-independent mechanisms in RIHD. As a central regulator of pathologic remodeling, miR-212 might become a novel target for RIHD-induced LVH and heart failure.

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

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

Chronic kidney disease induces left ventricular overexpression of the pro-hypertrophic microRNA-212

Chronic kidney disease (CKD) is a public health problem that increases the risk of cardiovascular morbidity and mortality. Heart failure with preserved ejection fraction (HFpEF) characterized by left ventricular hypertrophy (LVH) and diastolic dysfunction is a common cardiovascular complication of CKD. MicroRNA-212 (miR-212) has been demonstrated previously to be a crucial regulator of pathologic LVH in pressure-overload-induced heart failure via regulating the forkhead box O3 (FOXO3)/calcineurin/nuclear factor of activated T-cells (NFAT) pathway. Here we aimed to investigate whether miR-212 and its hypertrophy-associated targets including FOXO3, extracellular signal-regulated kinase 2 (ERK2), and AMP-activated protein kinase (AMPK) play a role in the development of HFpEF in CKD. CKD was induced by 5/6 nephrectomy in male Wistar rats. Echocardiography and histology revealed LVH, fibrosis, preserved systolic function, and diastolic dysfunction in the CKD group as compared to sham-operated animals eight and/or nine weeks later. Left ventricular miR-212 was significantly overexpressed in CKD. However, expressions of FOXO3, AMPK, and ERK2 failed to change significantly at the mRNA or protein level. The protein kinase B (AKT)/FOXO3 and AKT/mammalian target of rapamycin (mTOR) pathways are also proposed regulators of LVH induced by pressure-overload. Interestingly, phospho-AKT/total-AKT ratio was increased in CKD without significantly affecting phosphorylation of FOXO3 or mTOR. In summary, cardiac overexpression of miR-212 in CKD failed to affect its previously implicated hypertrophy-associated downstream targets. Thus, the molecular mechanism of the development of LVH in CKD seems to be independent of the FOXO3, ERK1/2, AMPK, and AKT/mTOR-mediated pathways indicating unique features in this form of LVH.

Comparison of the Reverse-Remodeling Effect of Pharmacological Soluble Guanylate Cyclase Activation With Pressure Unloading in Pathological Myocardial Left Ventricular Hypertrophy

Background: Pressure unloading induces the regression of left ventricular myocardial hypertrophy (LVH). Recent findings indicate that pharmacological activation of the soluble guanylate cyclase (sGC) – cyclic guanosine monophosphate (cGMP) pathway may also exert reverse-remodeling properties in the myocardium. Therefore, we aimed to investigate the effects of the sGC activator cinaciguat in a rat model of LVH and compare it to the “gold standard” pressure unloading therapy.

Methods: Abdominal aortic banding was performed for 6 or 12 weeks. Sham operated animals served as controls. Pressure unloading was induced by removing the aortic constriction after week 6. The animals were treated from week 7 to 12, with 10 mg/kg/day cinaciguat or with placebo p.o., respectively. Cardiac function and morphology were assessed by left ventricular pressure-volume analysis and echocardiography. Additionally, key markers of myocardial hypertrophy, fibrosis, nitro-oxidative stress, apoptosis and cGMP signaling were analyzed.

Results: Pressure unloading effectively reversed LVH, decreased collagen accumulation and provided protection against oxidative stress and apoptosis. Regression of LVH was also associated with a full recovery of cardiac function. In contrast, chronic activation of the sGC enzyme by cinaciguat at sustained pressure overload only slightly influenced pre-established hypertrophy. However, it led to increased PKG activity and had a significant impact on interstitial fibrosis, nitro-oxidative stress and apoptosis. Amelioration of the pathological structural alterations prevented the deterioration of LV systolic function (contractility and ejection fraction) and improved myocardial stiffness.

Conclusion: Our results indicate that both cinaciguat treatment and pressure unloading evoked anti-remodeling effects and improved LV function, however in a differing manners.

Isosteviol ameliorates diabetic cardiomyopathy in rats by inhibiting ERK and NF-κB signaling pathways

Diabetes-induced injury of myocardium, defined as diabetic cardiomyopathy (DCM), accounts for significant mortality and morbidity in diabetic population. Alleviation of DCM by a potent drug remains considerable interests in experimental and clinical researches because hypoglycemic drugs cannot effectively control this condition. Here, we explored the beneficial effects of isosteviol sodium (STVNa) on type 1 diabetes-induced DCM and the potential mechanisms involved. Male Wistar rats were induced to diabetes by injection of streptozotocin (STZ). One week later, diabetic rats were randomly grouped to receive STVNa (STZ/STVNa) or its vehicle (STZ). After 11 weeks of treatment or 11 weeks treatment following 4 weeks of removal of the treatment, the cardiac function and structure were evaluated and related mechanisms were investigated. In diabetic rats, oxidative stress, inflammation, blood glucose and plasma advanced glycation end products (AGEs) were significantly increased, whereas superoxide dismutase 2 (SOD-2) expression and activity were decreased. STVNa treatment inhibited cardiac hypertrophy, fibrosis and inflammation, showed similar ratio of heart to body weight and antioxidant capacities almost similar to the normal controls, which can be sustained at least 4 weeks. Moreover, STVNa inhibited diabetes-inducted stimulation of both extracellular signal-regulated kinase (ERK) and nuclear factor κB (NF-κB) signal pathways. However, blood glucose, plasma AGE and insulin levels were not altered by STVNa treatment. These results indicate that STVNa may be developed into a potent therapy for DCM. The mechanism underlying this therapeutic effect involves the suppression of oxidative stress and inflammation by inhibiting ERK and NF-κB without changing blood glucose or AGEs.

Comparison of speckle-tracking echocardiography with invasive hemodynamics for the detection of characteristic cardiac dysfunction in type-1 and type-2 diabetic rat models

Background

Measurement of systolic and diastolic function in animal models is challenging by conventional non-invasive methods. Therefore, we aimed at comparing speckle-tracking echocardiography (STE)-derived parameters to the indices of left ventricular (LV) pressure–volume (PV) analysis to detect cardiac dysfunction in rat models of type-1 (T1DM) and type-2 (T2DM) diabetes mellitus.

Methods

Rat models of T1DM (induced by 60 mg/kg streptozotocin, n = 8) and T2DM (32-week-old Zucker Diabetic Fatty rats, n = 7) and corresponding control animals (n = 5 and n = 8, respectively) were compared. Echocardiography and LV PV analysis were performed. LV short-axis recordings were used for STE analysis. Global circumferential strain, peak strain rate values in systole (SrS), isovolumic relaxation (SrIVR) and early diastole (SrE) were measured. LV contractility, active relaxation and stiffness were measured by PV analysis.

Results

In T1DM, contractility and active relaxation were deteriorated to a greater extent compared to T2DM. In contrast, diastolic stiffness was impaired in T2DM. Correspondingly, STE described more severe systolic dysfunction in T1DM. Among diastolic STE parameters, SrIVR was more decreased in T1DM, however, SrE was more reduced in T2DM. In T1DM, SrS correlated with contractility, SrIVR with active relaxation, while in T2DM SrE was related to cardiac stiffness, cardiomyocyte diameter and fibrosis.

Conclusions

Strain and strain rate parameters can be valuable and feasible measures to describe the dynamic changes in contractility, active relaxation and LV stiffness in animal models of T1DM and T2DM. STE corresponds to PV analysis and also correlates with markers of histological myocardial remodeling.

Electronic supplementary material

The online version of this article (10.1186/s12933-017-0645-0) contains supplementary material, which is available to authorized users.

Pharmacological preconditioning with gemfibrozil preserves cardiac function after heart transplantation

While heart transplantation (HTX) is the definitive therapy of heart failure, donor shortage is emerging. Pharmacological activation of soluble guanylate cyclase (sGC) and increased cGMP-signalling have been reported to have cardioprotective properties. Gemfibrozil has recently been shown to exert sGC activating effects in vitro. We aimed to investigate whether pharmacological preconditioning of donor hearts with gemfibrozil could protect against ischemia/reperfusion injury and preserve myocardial function in a heterotopic rat HTX model. Donor Lewis rats received p.o. gemfibrozil (150 mg/kg body weight) or vehicle for 2 days. The hearts were explanted, stored for 1 h in cold preservation solution, and heterotopically transplanted. 1 h after starting reperfusion, left ventricular (LV) pressure-volume relations and coronary blood flow (CBF) were assessed to evaluate early post-transplant graft function. After 1 h reperfusion, LV contractility, active relaxation and CBF were significantly (p < 0.05) improved in the gemfibrozil pretreated hearts compared to that of controls. Additionally, gemfibrozil treatment reduced nitro-oxidative stress and apoptosis, and improved cGMP-signalling in HTX. Pharmacological preconditioning with gemfibrozil reduces ischemia/reperfusion injury and preserves graft function in a rat HTX model, which could be the consequence of enhanced myocardial cGMP-signalling. Gemfibrozil might represent a useful tool for cardioprotection in the clinical setting of HTX surgery soon.

Cinaciguat ameliorates glomerular damage by reducing ERK1/2 activity and TGF-ß expression in type-1 diabetic rats

Decreased soluble guanylate cyclase activity and cGMP levels in diabetic kidneys were shown to influence the progression of nephropathy. The regulatory effects of soluble guanylate cyclase activators on renal signaling pathways are still unknown, we therefore investigated the renal molecular effects of the soluble guanylate cyclase activator cinaciguat in type-1 diabetic (T1DM) rats. Male adult Sprague-Dawley rats were divided into 2 groups after induction of T1DM with 60 mg/kg streptozotocin: DM, untreated (DM, n = 8) and 2) DM + cinaciguat (10 mg/kg per os daily, DM-Cin, n = 8). Non-diabetic untreated and cinaciguat treated rats served as controls (Co (n = 10) and Co-Cin (n = 10), respectively). Rats were treated for eight weeks, when renal functional and molecular analyses were performed. Cinaciguat attenuated the diabetes induced proteinuria, glomerulosclerosis and renal collagen-IV expression accompanied by 50% reduction of TIMP-1 expression. Cinaciguat treatment restored the glomerular cGMP content and soluble guanylate cyclase expression, and ameliorated the glomerular apoptosis (TUNEL positive cell number) and podocyte injury. These effects were accompanied by significantly reduced TGF-ß overexpression and ERK1/2 phosphorylation in cinaciguat treated diabetic kidneys. We conclude that the soluble guanylate cyclase activator cinaciguat ameliorated diabetes induced glomerular damage, apoptosis, podocyte injury and TIMP-1 overexpression by suppressing TGF-ß and ERK1/2 signaling.

Supplementation with Phycocyanobilin, Citrulline, Taurine, and Supranutritional Doses of Folic Acid and Biotin-Potential for Preventing or Slowing the Progression of Diabetic Complications

Oxidative stress, the resulting uncoupling of endothelial nitric oxide synthase (eNOS), and loss of nitric oxide (NO) bioactivity, are key mediators of the vascular and microvascular complications of diabetes. Much of this oxidative stress arises from up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Phycocyanobilin (PhyCB), the light-harvesting chromophore in edible cyanobacteria such as spirulina, is a biliverdin derivative that shares the ability of free bilirubin to inhibit certain isoforms of NADPH oxidase. Epidemiological studies reveal that diabetics with relatively elevated serum bilirubin are less likely to develop coronary disease or microvascular complications; this may reflect the ability of bilirubin to ward off these complications via inhibition of NADPH oxidase. Oral PhyCB may likewise have potential in this regard, and has been shown to protect diabetic mice from glomerulosclerosis. With respect to oxidant-mediated uncoupling of eNOS, high-dose folate can help to reverse this by modulating the oxidation status of the eNOS cofactor tetrahydrobiopterin (BH4). Oxidation of BH4 yields dihydrobiopterin (BH2), which competes with BH4 for binding to eNOS and promotes its uncoupling. The reduced intracellular metabolites of folate have versatile oxidant-scavenging activity that can prevent oxidation of BH4; concurrently, these metabolites promote induction of dihydrofolate reductase, which functions to reconvert BH2 to BH4, and hence alleviate the uncoupling of eNOS. The arginine metabolite asymmetric dimethylarginine (ADMA), typically elevated in diabetics, also uncouples eNOS by competitively inhibiting binding of arginine to eNOS; this effect is exacerbated by the increased expression of arginase that accompanies diabetes. These effects can be countered via supplementation with citrulline, which efficiently enhances tissue levels of arginine. With respect to the loss of NO bioactivity that contributes to diabetic complications, high dose biotin has the potential to "pinch hit" for diminished NO by direct activation of soluble guanylate cyclase (sGC). High-dose biotin also may aid glycemic control via modulatory effects on enzyme induction in hepatocytes and pancreatic beta cells. Taurine, which suppresses diabetic complications in rodents, has the potential to reverse the inactivating impact of oxidative stress on sGC by boosting synthesis of hydrogen sulfide. Hence, it is proposed that concurrent administration of PhyCB, citrulline, taurine, and supranutritional doses of folate and biotin may have considerable potential for prevention and control of diabetic complications. Such a regimen could also be complemented with antioxidants such as lipoic acid, N-acetylcysteine, and melatonin-that boost cellular expression of antioxidant enzymes and glutathione-as well as astaxanthin, zinc, and glycine. The development of appropriate functional foods might make it feasible for patients to use complex nutraceutical regimens of the sort suggested here.

Prevention of the development of heart failure with preserved ejection fraction by the phosphodiesterase-5A inhibitor vardenafil in rats with type 2 diabetes

Aims

Heart failure with preserved ejection fraction (HFpEF) has a great epidemiological burden. The pathophysiological role of cyclic guanosine monophosphate (cGMP) signalling has been intensively investigated in HFpEF. Elevated levels of cGMP have been shown to exert cardioprotective effects in various cardiovascular diseases, including diabetic cardiomyopathy. We investigated the effect of long‐term preventive application of the phosphodiesterase‐5A (PDE5A) inhibitor vardenafil in diabetic cardiomyopathy‐associated HFpEF.

Methods and results

Zucker diabetic fatty (ZDF) rats were used as a model of HFpEF and ZDF lean rats served as controls. Animals received vehicle or 10 mg/kg body weight vardenafil per os from weeks 7 to 32 of age. Cardiac function, morphology was assessed by left ventricular (LV) pressure–volume analysis and echocardiography at week 32. Cardiomyocyte force measurements were performed. The key markers of cGMP signalling, nitro‐oxidative stress, apoptosis, myocardial hypertrophy and fibrosis were examined. The ZDF animals showed diastolic dysfunction (increased LV/cardiomyocyte stiffness, prolonged LV relaxation time), preserved systolic performance, decreased myocardial cGMP level coupled with impaired protein kinase G (PKG) activity, increased nitro‐oxidative stress, enhanced cardiomyocyte apoptosis, and hypertrophic and fibrotic remodelling of the myocardium. Vardenafil effectively prevented the development of HFpEF by maintaining diastolic function (decreased LV/cardiomyocyte stiffness and LV relaxation time), by restoring cGMP levels and PKG activation, by lowering apoptosis and by alleviating nitro‐oxidative stress, myocardial hypertrophy and fibrotic remodelling.

Conclusions

We report that vardenafil successfully prevented the development of diabetes mellitus‐associated HFpEF. Thus, PDE5A inhibition as a preventive approach might be a promising option in the management of HFpEF patients with diabetes mellitus.

Cinaciguat prevents the development of pathologic hypertrophy in a rat model of left ventricular pressure overload

Pathologic myocardial hypertrophy develops when the heart is chronically pressure-overloaded. Elevated intracellular cGMP-levels have been reported to prevent the development of pathologic myocardial hypertrophy, therefore we investigated the effects of chronic activation of the cGMP producing enzyme, soluble guanylate cyclase by Cinaciguat in a rat model of pressure overload-induced cardiac hypertrophy. Abdominal aortic banding (AAB) was used to evoke pressure overload-induced cardiac hypertrophy in male Wistar rats. Sham operated animals served as controls. Experimental and control groups were treated with 10 mg/kg/day Cinaciguat (Cin) or placebo (Co) p.o. for six weeks, respectively. Pathologic myocardial hypertrophy was present in the AABCo group following 6 weeks of pressure overload of the heart, evidenced by increased relative heart weight, average cardiomyocyte diameter, collagen content and apoptosis. Cinaciguat did not significantly alter blood pressure, but effectively attenuated all features of pathologic myocardial hypertrophy, and normalized functional changes, such as the increase in contractility following AAB. Our results demonstrate that chronic enhancement of cGMP signalling by pharmacological activation of sGC might be a novel therapeutic approach in the prevention of pathologic myocardial hypertrophy.

Loss of Nlrp3 Does Not Protect Mice from Western Diet-Induced Adipose Tissue Inflammation and Glucose Intolerance

We tested the hypothesis that loss of Nlrp3 would protect mice from Western diet-induced adipose tissue (AT) inflammation and associated glucose intolerance and cardiovascular complications. Five-week old C57BL6J wild-type (WT) and Nlrp3 knockout (Nlrp3-/-) mice were randomized to either a control diet (10% kcal from fat) or Western diet (45% kcal from fat and 1% cholesterol) for 24 weeks (n = 8/group). Contrary to our hypothesis that obesity-mediated white AT inflammation is Nlrp3-dependent, we found that Western diet-induced expression of AT inflammatory markers (i.e., Cd68, Cd11c, Emr1, Itgam, Lgals, Il18, Mcp1, Tnf, Ccr2, Ccl5 mRNAs, and Mac-2 protein) were not accompanied by increased caspase-1 cleavage, a hallmark feature of NLRP3 inflammasome activation. Furthermore, Nlrp3 null mice were not protected from Western diet-induced white or brown AT inflammation. Although Western diet promoted glucose intolerance in both WT and Nlrp3-/- mice, Nlrp3-/- mice were protected from Western diet-induced aortic stiffening. Additionally, Nlrp3-/- mice exhibited smaller cardiomyocytes and reduced cardiac fibrosis, independent of diet. Collectively, these findings suggest that presence of the Nlrp3 gene is not required for Western diet-induced AT inflammation and/or glucose intolerance; yet Nlrp3 appears to play a role in potentiating arterial stiffening, cardiac hypertrophy and fibrosis.

Chronic plus binge ethanol feeding induces myocardial oxidative stress, mitochondrial and cardiovascular dysfunction, and steatosis

Alcoholic cardiomyopathy in humans develops in response to chronic excessive alcohol consumption; however, good models of alcohol-induced cardiomyopathy in mice are lacking. Herein we describe mouse models of alcoholic cardiomyopathies induced by chronic and binge ethanol (EtOH) feeding and characterize detailed hemodynamic alterations, mitochondrial function, and redox signaling in these models. Mice were fed a liquid diet containing 5% EtOH for 10, 20, and 40 days (d) combined with single or multiple EtOH binges (5 g/kg body wt). Isocalorically pair-fed mice served as controls. Left ventricular (LV) function and morphology were assessed by invasive pressure-volume conductance approach and by echocardiography. Mitochondrial complex (I, II, IV) activities, 3-nitrotyrosine (3-NT) levels, gene expression of markers of oxidative stress (gp91phox, p47phox), mitochondrial biogenesis (PGC1α, peroxisome proliferator-activated receptor α), and fibrosis were examined. Cardiac steatosis and fibrosis were investigated by histological/immunohistochemical methods. Chronic and binge EtOH feeding (already in 10 days EtOH plus single binge group) was characterized by contractile dysfunction (decreased slope of end-systolic pressure-volume relationship and preload recruitable stroke work), impaired relaxation (decreased time constant of LV pressure decay and maximal slope of systolic pressure decrement), and vascular dysfunction (impaired arterial elastance and lower total peripheral resistance). This was accompanied by enhanced myocardial oxidative/nitrative stress (3-NT; gp91phox; p47phox; angiotensin II receptor, type 1a) and deterioration of mitochondrial complex I, II, IV activities and mitochondrial biogenesis, excessive cardiac steatosis, and higher mortality. Collectively, chronic plus binge EtOH feeding in mice leads to alcohol-induced cardiomyopathies (National Institute on Alcohol Abuse and Alcoholism models) characterized by increased myocardial oxidative/nitrative stress, impaired mitochondrial function and biogenesis, and enhanced cardiac steatosis.

Quickly promoting angiogenesis by using a DFO-loaded photo-crosslinked gelatin hydrogel for diabetic skin regeneration

A desferrioxamine (DFO)-loaded photo-crosslinked gelatin hydrogel was used to reconstruct vessel network and prompt skin regeneration in diabetic wounds.