Pharmacological activation of soluble guanylate cyclase protects the heart against ischemic injury

An ischemic area-targeting, peroxynitrite-responsive, biomimetic carbon monoxide nanogenerator for preventing myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion (MI/R) injury is common in patients who undergo revascularization therapy for myocardial infarction, often leading to cardiac dysfunction. Carbon monoxide (CO) has emerged as a therapeutic molecule due to its beneficial properties such as anti-inflammatory, anti-apoptotic, and mitochondrial biogenesis-promoting properties. However, its clinical application is limited due to uncontrolled release, potential toxicity, and poor targeting efficiency. To address these limitations, a peroxynitrite (ONOO^-)-triggered CO donor (PCOD585) is utilized to generate a poly (lactic-co-glycolic acid) (PLGA)-based, biomimetic CO nanogenerator (M/PCOD@PLGA) that is coated with the macrophage membrane, which could target to the ischemic area and neutralize proinflammatory cytokines. In the ischemic area, local produced ONOO^- triggers the continuous release of CO from M/PCOD@PLGA, which efficiently ameliorates MI/R injury by clearing harmful ONOO^-, attenuating the inflammatory response, inhibiting cardiomyocyte apoptosis, and promoting mitochondrial biogenesis. This study provides a novel insight into the safe therapeutic use of CO for MI/R injury by utilizing a novel CO donor combined with biomimetic technology. The M/PCOD@PLGA nanogenerator offers targeted delivery of CO to the ischemic area, minimizing potential toxicity and enhancing therapeutic efficacy.

Targeting Soluble Guanylyl Cyclase during Ischemia and Reperfusion

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

Benign prostatic hyperplasia/obstruction ameliorated using a soluble guanylate cyclase activator

Benign prostatic hyperplasia (BPH) is a feature of ageing males. Up to half demonstrate bladder outlet obstruction (BOO) with associated lower urinary tract symptoms (LUTS) including bladder overactivity. Current therapies to reduce obstruction, such as α1-adrenoceptor antagonists and 5α-reductase inhibitors, are not effective in all patients. The phosphodiesterase-5 inhibitor (PDE5I) tadalafil is also approved to treat BPH and LUTS, suggesting a role for nitric oxide (NO• ), soluble guanylate cyclase (sGC), and cGMP signalling pathways. However, PDE5I refractoriness can develop for reasons including nitrergic nerve damage and decreased NO• production, or inflammation-related oxidation of the sGC haem group, normally maintained in a reduced state by the cofactor cytochrome-b5-reductase 3 (CYB5R3). sGC activators, such as cinaciguat (BAY 58-2667), have been developed to enhance sGC activity in the absence of NO• or when sGC is oxidised. Accordingly, their effects on the prostate and LUT function of aged mice were evaluated. Aged mice (≥24 months) demonstrated a functional BPH/BOO phenotype, compared with adult animals (2-12 months), with low, delayed voiding responses and elevated intravesical pressures as measured by telemetric cystometry. This was consistent with outflow tract histological and molecular data that showed urethral constriction, increased prostate weight, greater collagen deposition, and cellular hyperplasia. All changes in aged animals were attenuated by daily oral treatment with cinaciguat for 2 weeks, without effect on serum testosterone levels. Cinaciguat had only transient (1 h) cardiovascular effects with oral gavage, suggesting a positive safety profile. The benefit of cinaciguat was suggested by its reversal of an overactive cystometric profile in CYB5R3 smooth muscle knockout mice that mirrors a profile of oxidative dysfunction where PDE5I may not be effective. Thus, the aged male mouse is a suitable model for BPH-induced BOO and cinaciguat has a demonstrated ability to reduce prostate-induced obstruction and consequent effects on bladder function. © 2021 The Pathological Society of Great Britain and Ireland.

Cardioprotective Role of Theobroma cacao against Isoproterenol-Induced Acute Myocardial Injury

BACKGROUND

Antioxidants are beneficial in myocardial infarction (MI). It is suggestive that Theobroma cacao (TC) with rich antioxidant properties can be of health benefits in myocardial injury.

AIM

The study investigated the effect of Theobroma cacao on cardioprotection in isoproterenol-induced myocardial infarction in rats.

MATERIAL AND METHODS

Male Wistar rats divided into four groups of 6 rats were used for the study. In group 1, 0.9% normal saline placebo was administered via oral gavage to the control. Group 2 was the MI induced group that was given 100 mg/kg body weight isoproterenol subcutaneously twice at an interval of 24 hours. Group 3 was administered TC for 2 weeks at 100 mg/kg bodyweight via the oral route. Group 4 was pretreated with TC (100 mg/kg) via oral route for 2 weeks, immediately followed by the administration of 100 mg/kg body weight isoproterenol subcutaneously twice at an interval of 24 hours. The rats were sacrificed using chloroform anesthesia, and blood samples collected via cardiac puncture. The serum was analyzed for troponin level, lactate dehydrogenase (LDH), and malondialdehyde (MDA) level.

RESULTS

The serum troponin, LDH, and MDA levels were found to be significantly (p<0.01) increased in the MI group compared with the control. Pretreatment with TC before MI induction significantly (p<0.01) prevented increased serum troponin, LDH, and MDA levels when compared with the MI group. There was also a significant (p<0.01) decrease in MDA in the TC group compared with the control.

CONCLUSION

These results suggest that Theobroma cacao protects against isoproterenol-induced myocardial injury, possibly by preventing oxidative stress and consequent lipid peroxidation.

Sex-related differences of early cardiac functional and proteomic alterations in a rat model of myocardial ischemia

BACKGROUND

Reduced cardiovascular risk in premenopausal women has been the focus of research in recent decades. Previous hypothesis-driven experiments have highlighted the role of sex hormones on distinct inflammatory responses, mitochondrial proteins, extracellular remodeling and estrogen-mediated cardioprotective signaling pathways related to post-ischemic recovery, which were associated with better cardiac functional outcomes in females. We aimed to investigate the early, sex-specific functional and proteomic changes following myocardial ischemia in an unbiased approach.

METHODS

Ischemia was induced in male (M-Isch) and female (F-Isch) rats with sc. injection of isoproterenol (85 mg/kg) daily for 2 days, while controls (M-Co, F-Co) received sc. saline solution. At 48 h after the first injection pressure-volume analysis was carried out to assess left ventricular function. FFPE tissue slides were scanned and analyzed digitally, while myocardial proteins were quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using isobaric labeling. Concentrations of circulating steroid hormones were measured with LC-MS/MS. Feature selection (PLS and PLS-DA) was used to examine associations among functional, proteomic and hormonal datasets.

RESULTS

Induction of ischemia resulted in 38% vs 17% mortality in M-Isch and F-Isch respectively. The extent of ischemic damage to surviving rats was comparable between the sexes. Systolic dysfunction was more pronounced in males, while females developed a more severe impairment of diastolic function. 2224 proteins were quantified, with 520 showing sex-specific differential regulation. Our analysis identified transcriptional, cytoskeletal, contractile, and mitochondrial proteins, molecular chaperones and the extracellular matrix as sources of disparity between the sexes. Bioinformatics highlighted possible associations of estrogens and their metabolites with early functional and proteomic alterations.

CONCLUSIONS

Our study has highlighted sex-specific alterations in systolic and diastolic function shortly after ischemia, and provided a comprehensive look at the underlying proteomic changes and the influence of estrogens and their metabolites. According to our bioinformatic analysis, inflammatory, mitochondrial, chaperone, cytoskeletal, extracellular and matricellular proteins are major sources of intersex disparity, and may be promising targets for early sex-specific pharmacologic interventions.

Dynamic Regulation of Cysteine Oxidation and Phosphorylation in Myocardial Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion (I/R) injury significantly alters heart function following infarct and increases the risk of heart failure. Many studies have sought to preserve irreplaceable myocardium, termed cardioprotection, but few, if any, treatments have yielded a substantial reduction in clinical I/R injury. More research is needed to fully understand the molecular pathways that govern cardioprotection. Redox mechanisms, specifically cysteine oxidations, are acute and key regulators of molecular signaling cascades mediated by kinases. Here, we review the role of reactive oxygen species in modifying cysteine residues and how these modifications affect kinase function to impact cardioprotection. This exciting area of research may provide novel insight into mechanisms and likely lead to new treatments for I/R injury.

Pharmacological activation of soluble guanylate cyclase improves vascular graft function

OBJECTIVES

Ischaemia-reperfusion injury impairs the nitric oxide/soluble guanylate cyclase/cyclic guanosine monophosphate (cGMP) signalling pathway and leads to vascular dysfunction. We assessed the hypothesis that the soluble guanylate cyclase activator cinaciguat would protect the vascular graft against ischaemia-reperfusion injury.

METHODS

In the treatment groups, rats (n = 8/group) were pretreated with either intravenous saline or intravenous cinaciguat (10 mg/kg) 2 h before an aortic transplant. Aortic grafts were stored for 2 h in saline and transplanted into the abdominal aorta of the recipients. Two hours after the transplant, the grafts were harvested and mounted in an organ bath. Vascular function of the grafts was investigated in the organ bath. Terminal deoxynucleotidyl transferase dUTP nick end labelling, cluster of differentiation 31, caspase-3, endothelial nitric oxide synthase, cGMP, nitrotyrosine and vascular cell adhesion molecule 1 immunochemical reactions were also investigated.

RESULTS

Pretreatment with cinaciguat significantly improved endothelium-dependent maximal relaxation 2 h after reperfusion compared with the saline group (maximal relaxation control: 96.5 ± 1%, saline: 40.4 ± 3% vs cinaciguat: 54.7 ± 2%; P < 0.05). Pretreatment with cinaciguat significantly reduced DNA fragmentation and nitro-oxidative stress; decreased the caspase-3 and vascular cell adhesion molecule 1 scores; and increased endothelial nitric oxide synthase, cGMP and cluster of differentiation 31 scores.

CONCLUSIONS

Our results demonstrated that enhancement of cGMP signalling by pharmacological activation of the soluble guanylate cyclase activator cinaciguat might represent a beneficial therapy for treating endothelial dysfunction of arterial bypass graft during cardiac surgery.

Cardiac-specific overexpression of HIF-1α during acute myocardial infarction ameliorates cardiomyocyte apoptosis via differential regulation of hypoxia-inducible pro-apoptotic and anti-oxidative genes

HIF-1α acts as the cellular rheostat for oxygen sensing in cardiomyocytes. Overexpression of HIF-1α in the heart during acute myocardial infarction (MI) is known to attenuate cardiac dysfunction by upregulating pro-angiogenic HIF-1α target genes. However, the effect of HIF-1α overexpression on hypoxic cardiomyocyte apoptosis still remains obscure. In this study, we report for the first time that myocardium-targeted nanotized HIF-1α overexpression during MI downregulates cardiomyocyte apoptosis. HIF-1α overexpression attenuates bnip3-mediated apoptosis indirectly by promoting HO-1-induced anti-oxidant response. Chromatin immunoprecipitation experiment revealed that HIF-1α overexpression in hypoxic cardiomyocytes increases binding of HIF-1α to the hypoxia-responsive element in the promoter of its target anti-oxidant gene ho-1 which is known to attenuate ROS accumulation. ROS accumulation in hypoxic cardiomyocytes causes cysteine oxidation of the DNA-binding p50 subunit of NFκB, which hampers NFκB binding to κB-responsive genes like bnip3. Downregulated oxidative stress due to HIF-1α overexpression leads to decline in cysteine oxidation of NFκBp50, causing NFκB to bind to the promoter of bnip3 as a transcriptional repressor. Therefore HIF-1α overexpression-mediated attenuation of cardiomyocyte apoptosis occurs by transcriptional repression of bnip3 by NFκB. Our study thus reveals that downregulation of bnip3-mediated cardiomyocyte apoptosis occurs via ho-1 upregulation upon HIF-1α overexpression during MI, despite both being HIF-1α target genes. The cross-regulation of HIF-1α and NFκB-mediated pathways effectively downregulates apoptosis due to HIF-1α overexpression during MI, which can be exploited for possible therapeutic intervention.

Severity and duration of hypoxic stress differentially regulates HIF-1α-mediated cardiomyocyte apoptotic signaling milieu during myocardial infarction

BACKGROUND

The severity and duration of hypoxia is known to determine apoptotic fate in heart; however, its implication during myocardial infarction (MI) remains unaddressed. Therefore the aim of the study was to determine apoptotic regulation in cardiomyocytes under varied hypoxic intensity and duration and to unravel the role of HIF-1α in such modulation.

METHODS

Treatment of cardiomyocytes to varied hypoxic intensity and duration was carried out in vitro, which was mimicked in vivo by dose-dependent Isoproterenol hydrochloride treatment for varied time-points. Myocardium-targeted HIF-1α knockdown in vivo was performed to decipher its role in cardiomyocyte apoptosis under varied stress. Signaling intermediates were analyzed by RT-PCR, immunoblotting and co-immunoprecipitation. DCFDA-based ROS assay, Griess assay for NO release and biochemical assays for estimating caspase activity were performed.

RESULTS

Severe stress resulted in cardiomyocyte apoptosis in both shorter and longer time-points. Moderate stress, on the other hand, induced apoptosis only in the shorter time-point which was downregulated in the longer time-point. ROS activity was upregulated under severe hypoxic stress for both time-points and only in the early time-point under moderate hypoxia. Increased ROS accumulation activated ERK-1/2 which stabilized nuclear HIF-1α, promoting bnip3-mediated apoptosis. Stable HSP90-IRE-1 association in such cells caused elevated endoplasmic reticulum stress-related caspase-12 activity. Sustained moderate hypoxia caused decline in ROS activity, but upregulated NFκB-dependent NO generation. NO-stabilized HIF-1α was predominantly cytosolic, since low ROS levels downregulated ERK-1/2 activity, thereby suppressing bnip3 expression. Cytosolic HIF-1α in such cells sequestered HSP90 from IRE-1, downregulating caspase-12 activity due to proteasomal degradation of IRE-1. Accordingly, myocardium-specific in vivo silencing of HIF-1α was beneficial at both time-points under severe stress as also for lesser duration of moderate stress. However, silencing of HIF-1α aggravated apoptotic injury during sustained moderate stress.

CONCLUSION

ROS-mediated HIF-1α stabilization promotes cardiomyocyte apoptosis on one hand while NO-mediated stabilization of HIF-1α disrupts apoptosis depending upon the severity and duration of hypoxia. Therefore the outcome of modulation of cardiac HIF-1α activity is regulated by both the severity and duration of ischemic stress.

Exogenous NO Therapy for the Treatment and Prevention of Atherosclerosis

Amyl nitrite was introduced in 1867 as the first molecule of a new class of agents for the treatment of angina pectoris. In the following 150 years, the nitric oxide pathway has been the subject of a number of pharmacological approaches, particularly since when this elusive mediator was identified as one of the most important modulators of vascular homeostasis beyond vasomotion, including platelet function, inflammation, and atherogenesis. While having potent antianginal and antiischemic properties, however, nitric oxide donors are also not devoid of side effects, including the induction of tolerance, and, as shown in the last decade, of oxidative stress and endothelial dysfunction. In turn, endothelial dysfunction is itself felt to be involved in all stages of atherogenesis, from the development of fatty streaks to plaque rupture and thrombosis. In the present review, we summarize the agents that act on the nitric oxide pathway, with a particular focus on their potentially beneficial antiatherosclerotic and unwanted pro-atherosclerotic effects.

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.

Nitric oxide for inhalation in ST-elevation myocardial infarction (NOMI): a multicentre, double-blind, randomized controlled trial

Aims

Inhalation of nitric oxide (iNO) during myocardial ischaemia and after reperfusion confers cardioprotection in preclinical studies via enhanced cyclic guanosine monophosphate (cGMP) signalling. We tested whether iNO reduces reperfusion injury in patients with ST-elevation myocardial infarction (STEMI; NCT01398384).

Methods and results

We randomized in a double-blind, placebo-controlled study 250 STEMI patients to inhale oxygen with (iNO) or without (CON) 80 parts-per-million NO for 4 h following percutaneous revascularization. Primary efficacy endpoint was infarct size as a fraction of left ventricular (LV) size (IS/LVmass), assessed by delayed enhancement contrast magnetic resonance imaging (MRI). Pre-specified subgroup analysis included thrombolysis-in-myocardial-infarction flow in the infarct-related artery, troponin T levels on admission, duration of symptoms, location of culprit lesion, and intra-arterial nitroglycerine (NTG) use. Secondary efficacy endpoints included IS relative to risk area (IS/AAR), myocardial salvage index, LV functional recovery, and clinical events at 4 and 12 months. In the overall population, IS/LVmass at 48-72 h was 18.0 ± 13.4% in iNO (n = 109) and 19.4 ± 15.4% in CON [n = 116, effect size -1.524%, 95% confidence interval (95% CI) -5.28, 2.24; P = 0.427]. Subgroup analysis indicated consistency across clinical confounders of IS but significant treatment interaction with NTG (P = 0.0093) resulting in smaller IS/LVmass after iNO in NTG-naïve patients (n = 140, P < 0.05). The secondary endpoint IS/AAR was 53 ± 26% with iNO vs. 60 ± 26% in CON (effect size -6.8%, 95% CI -14.8, 1.3, P = 0.09) corresponding to a myocardial salvage index of 47 ± 26% vs. 40 ± 26%, respectively, P = 0.09. Cine-MRI showed similar LV volumes at 48-72 h, with a tendency towards smaller increases in end-systolic and end-diastolic volumes at 4 months in iNO (P = 0.048 and P = 0.06, respectively, n = 197). Inhalation of nitric oxide was safe and significantly increased cGMP plasma levels during 4 h reperfusion. The Kaplan-Meier analysis for the composite of death, recurrent ischaemia, stroke, or rehospitalizations showed a tendency toward lower event rates with iNO at 4 months and 1 year (log-rank test P = 0.10 and P = 0.06, respectively).

Conclusions

Inhalation of NO at 80 ppm for 4 h in STEMI was safe but did not reduce infarct size relative to absolute LVmass at 48-72h. The observed functional recovery and clinical event rates at follow-up and possible interaction with nitroglycerine warrant further studies of iNO in STEMI.

Hydroalcoholic Extract from Rhizomes of Cynodon dactylon Improve Hemodynamic and Electrocardiogram Parameters in Myocardial Infarction in Rats

Background: Cynodon dactylon is a herbal medicine of interest in Iranian traditional medicine, which is used in cardiovascular diseases such as atherosclerosis and heart failure. The purpose of this study was to evaluate the effects of total extract of C. dactylon rhizomes on myocardial infarction and on post myocardial infarction (MI) heart tissue injuries. Methods: Isoproterenol (100 mg/kg) was injected subcutaneously for two consecutive days for induction of MI in rats and C. dactylon extract was administered orally twice daily started before isoproterenol injection for 4 consecutive days. Results: Histopathological analysis showed a marked increase in myocardial necrosis in rats with MI (p<0.001). Treatment with C. dactylon (200 mg/kg) significantly (P<0.05) decreased myocardial necrosis. Hemodynamic variables were significantly suppressed in MI group and treatment with C. dactylon improved the hemodynamic parameters (P<0.05). Our electrocardiogram analysis demonstrated that C. dactylon with all doses increased R-Amplitude and R-R Interval (p<0.05, p<0.01) which were suppressed in MI group. Furthermore in treated groups with 100 and 200 mg/kg, P-R interval was also significantly increased in compared to MI group. Conclusion: This study demonstrated that C. dactylon can improve hemodynamic and electrocardiogram parameters in isoproterenol-induced myocardial infarction and thereby suggest that it can be used as a cardioprotective agent in myocardial infarction.

Blood Leukocyte DNA Methylation Predicts Risk of Future Myocardial Infarction and Coronary Heart Disease

BACKGROUND

DNA methylation is implicated in coronary heart disease (CHD), but current evidence is based on small, cross-sectional studies. We examined blood DNA methylation in relation to incident CHD across multiple prospective cohorts.

METHODS

Nine population-based cohorts from the United States and Europe profiled epigenome-wide blood leukocyte DNA methylation using the Illumina Infinium 450k microarray, and prospectively ascertained CHD events including coronary insufficiency/unstable angina, recognized myocardial infarction, coronary revascularization, and coronary death. Cohorts conducted race-specific analyses adjusted for age, sex, smoking, education, body mass index, blood cell type proportions, and technical variables. We conducted fixed-effect meta-analyses across cohorts.

RESULTS

Among 11 461 individuals (mean age 64 years, 67% women, 35% African American) free of CHD at baseline, 1895 developed CHD during a mean follow-up of 11.2 years. Methylation levels at 52 CpG (cytosine-phosphate-guanine) sites were associated with incident CHD or myocardial infarction (false discovery rate<0.05). These CpGs map to genes with key roles in calcium regulation (ATP2B2, CASR, GUCA1B, HPCAL1), and genes identified in genome- and epigenome-wide studies of serum calcium (CASR), serum calcium-related risk of CHD (CASR), coronary artery calcified plaque (PTPRN2), and kidney function (CDH23, HPCAL1), among others. Mendelian randomization analyses supported a causal effect of DNA methylation on incident CHD; these CpGs map to active regulatory regions proximal to long non-coding RNA transcripts.

CONCLUSION

Methylation of blood-derived DNA is associated with risk of future CHD across diverse populations and may serve as an informative tool for gaining further insight on the development of CHD.

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.

Effects of nimodipine, vinpocetine and their combination on isoproterenol-induced myocardial infarction in rats

BACKGROUND

Myocardial infarction (MI) remains a major cause of morbidity and mortality worldwide. Nimodipine is a calcium (Ca²⁺⁾ channel blocker as well as a PDE1 inhibitor and primarily used in subarachnoid haemorrhage (SAH) due to its blood-brain barrier crossing property. Nimodipine and vinpocetine inhibit the degradation of phosphodiester bond which increases cGMP and cAMP levels causing vasodilation.

MATERIAL AND METHODS

We have divided rats randomly into Group I - Vehicle control; Group II - Toxic control (ISO 85 mg/kg, i.p.); Group III, IV and V - Nimodipine (5, 10 and 15 mg/kg, i.p. respectively) with ISO; Group VI- Nimodipine (15 mg/kg) alone; Group VII - Nimodipine + Vinpocetine (10 mg/kg + 10 mg/kg) with ISO; Group VIII - Nimodipine + Vinpocetine (10 mg/kg + 10 mg/kg) alone; Group IX- Diltiazem (25 mg/kg, p.o) with ISO; Group X- Diltiazem (25 mg/kg) alone and Group XI- Vinpocetine (10 mg/kg, p.o.) with ISO for 7 days. After 24 h of the last dose, haemodynamics were assessed then animals were sacrificed and biochemical, histopathological and ultrastructural changes were measured.

RESULTS

Treatment with ISO significantly deviated the haemodynamic parameters (HR, SAP, DAP and MAP), biochemical parameters (CK-MB, LDH, SGOT, cGMP and Troponin-T) and antioxidant markers (TBARS, SOD, CAT, GSH, GPx, GST and GR). Haemotoxylin and eosin staining of the cardiac tissue and ultrastructural study also indicated significant myocardial damage. Pretreatment with nimodipine (10 and 15 mg/kg, i.p), vinpocetine (10 mg/kg, p.o) and their combination significantly restored the antioxidant status, haemodynamic profile, cellular architecture and ultrastructural changes in the heart.

CONCLUSION

Nimodipine and vinpocetine both showed cardioprotection when given alone. However, their combination showed better restoration in terms of oxidative stress, cardiac membrane damage, haemodynamics, histopathology and ultrastructural changes.

Targeting Phosphodiesterase-5 by Vardenafil Improves Vascular Graft Function

OBJECTIVES

Ischaemia reperfusion (IR) injury occurs during vascular graft harvesting and implantation during vascular/cardiac surgery. Elevated intracellular cyclic guanosine monophosphate (cGMP) levels contribute to an effective endothelial protection in different pathophysiological conditions. The hypothesis that the phosphodiesterase-5 inhibitor vardenafil would protect vascular grafts against IR injury by upregulating the nitric oxide-cGMP pathway in the vessel wall of the bypass graft was investigated.

METHODS

Lewis rats (n = 6-7/group) were divided into Group 1, control; Group 2, donor rats received intravenous saline; Group 3, received intravenous vardenafil (30 μg/kg) 2 h before explantation. Whereas aortic arches of Group 1 were immediately mounted in an organ bath, aortic segments of Groups 2 and 3 were stored for 2 h in saline and transplanted into the abdominal aorta of the recipient. Two hours after transplantation, the implanted grafts were harvested. Endothelium dependent and independent vasorelaxations were investigated. TUNEL, CD-31, ICAM-1, VCAM-1, α-SMA, nitrotyrosine, dihydroethidium and cGMP immunochemistry were also performed.

RESULTS

Compared with the control, the saline group showed significantly attenuated endothelium dependent maximal relaxation (R_max) 2 h after reperfusion, which was significantly improved by vardenafil supplementation (R_max control, 91 ± 2%; saline 22 ± 2% vs. vardenafil 39 ± 4%, p < .001). Vardenafil pre-treatment significantly reduced DNA fragmentation (control 9 ± 1%, saline 66 ± 8% vs. vardenafil 13 ± 1%, p < .001), nitro-oxidative stress (control 0.8 ± 0.3, saline 7.6 ± 1.3 vs. vardenafil 3.8 ± 1, p = .036), reactive oxygen species level (vardenafil 36 ± 4, control 34 ± 2 vs. saline 43 ± 2, p = .049), prevented vascular smooth muscle cell damage (control 8.5 ± 0.7, saline 4.3 ± 0.6 vs. vardenafil 6.7 ± 0.6, p = .013), decreased ICAM-1 (control 4.1 ± 0.5, saline 7.0 ± 0.9 vs. vardenafil 4.4 ± 0.6, p = .031), and VCAM-1 score (control 4.4 ± 0.4, saline 7.3 ± 1.0 vs. vardenafil 5.2 ± 0.4, p = .046) and increased cGMP score in the aortic wall (control 11.2 ± 0.8, saline 6.5 ± 0.8 vs. vardenafil 8.9 ± 0.6, p = .016). The marker for endothelial integrity (CD-31) was also higher in the vardenafil group (control 74 ± 4%, saline 22 ± 2% vs. vardenafil 40 ± 3%, p = .008).

CONCLUSIONS

The results support the view that impairment of intracellular cGMP signalling plays a role in the pathogenesis of the endothelial dysfunction of an arterial graft after bypass surgery, which can effectively be prevented by vardenafil. Its clinical use as preconditioning drug could be a novel approach in vascular/cardiac surgery.

In utero and lactational exposure of DEHP increases the susceptibility of prostate carcinogenesis in male offspring through PSCA hypomethylation

As an ubiquitous environmental endocrine disruptor, di(2-ethylhexyl) phthalate (DEHP) has been shown to interfere with the development of reproductive organs and induce pathological changes in prostate. Our previous finding showed that in utero and lactational (IUL) DEHP exposure could disrupt the balance of testosterone and estrogen and increase the susceptibility of prostate carcinogenesis. The purpose of this study is to investigate whether the early-life specific epigenetic modifications could mediate the effect of DEHP exposure on prostate carcinogenesis in rodents, for epigenetic modifications play important roles in regulating prostate carcinogenesis. The pregnant rats were treated with corn oil (negative control) or DEHP at 0.01, 0.1 and 1 mg/kg BW/day from GD7 to PND21. On PND21, the expression and DNA methylation change of six prostate carcinogenesis-related genes (ESR2/GSTP1/NKX3.1/PSCA/PTGS2/Rassf1a) were assessed through SYBR-Green real-time PCR combined with pyrosequencing assay in F1 male offspring. On PND196, the relationship b(STP1, PSCA and PTGS2 in a dose-dependent manner, which were positively correlated with PIN scores, Gleason scores, serum PSA concentrations and negatively correlated with prostate/body weight ratio on PND196. Meanwhile, 1 mg/kg BW/day DEHP markedly reduced DNA methylation level of PSCA in all studied CpG sites. Significant inverse correlations between methylation levels of the promoter CpG site and PSCA mRNA expression were observed. These results indicated that transcriptional changes of GSTP1, PSCA and PTGS2 induced by DEHP exposure might be contribute to the increasing susceptibility of prostate carcinogenesis in late life. Moreover, hypomethylation of PSCA could mediate the effect of DEHP on prostate carcinogenesis in rats.

Cardioprotection by intermittent hypoxia conditioning: evidence, mechanisms, and therapeutic potential

The calibrated application of limited-duration, cyclic, moderately intense hypoxia-reoxygenation increases cardiac resistance to ischemia-reperfusion stress. These intermittent hypoxic conditioning (IHC) programs consistently produce striking reductions in myocardial infarction and ventricular tachyarrhythmias after coronary artery occlusion and reperfusion and, in many cases, improve contractile function and coronary blood flow. These IHC protocols are fundamentally different from those used to simulate sleep apnea, a recognized cardiovascular risk factor. In clinical studies, IHC improved exercise capacity and decreased arrhythmias in patients with coronary artery or pulmonary disease and produced robust, persistent, antihypertensive effects in patients with essential hypertension. The protection afforded by IHC develops gradually and depends on β-adrenergic, δ-opioidergic, and reactive oxygen-nitrogen signaling pathways that use protein kinases and adaptive transcription factors. In summary, adaptation to intermittent hypoxia offers a practical, largely unrecognized means of protecting myocardium from impending ischemia. The myocardial and perhaps broader systemic protection provided by IHC clearly merits further evaluation as a discrete intervention and as a potential complement to conventional pharmaceutical and surgical interventions.

Tiger nut and walnut extracts modulate extracellular metabolism of ATP and adenosine through the NOS/cGMP/PKG signalling pathway in kidney slices

BACKGROUND

Tiger nut (Cyperus esculentus L.) and walnut (Tetracarpidium conophorum Müll. Arg.) have been reportedly used in the treatment of inflammatory diseases such as atherosclerosis, prevent heart attack and improve blood circulation, reduce serum cholesterol level as well as inhibit oxidation reactions.

PURPOSE

This study investigated the effect of tiger nut and walnut hydro-alcoholic extracts on extracellular metabolism of ATP through the NOS/cGMP/PKG signaling pathway induced by Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME) in kidney slices.

METHODS

The plants were extracted for 24 h in 10 ml of 70% ethanol and 30% distilled water per gram milled material on a mechanical shaker and filtered using Whatman filter paper. The effect of the extracts on ecto-nucleotidases (NTPDase and 5' nucleotidase) and adenosine deaminase activities, nitrites and nitrates levels (NO, markers of NO production) as well as lipid and protein oxidation reactions in kidney slices were evaluated. Also, the phenolic components of the nut samples were determined using High Performance Liquid Chromatography (HPLC).

RESULTS

The results revealed a protective effect of tiger nut and walnut on co-incubation with L-NAME of the enzyme activities, increased NO significantly (P < 0.05) when compared to the vehicle. L-NAME also increased the thiobabituric reactive substances but co-incubation with the extracts caused a significant reduction while protein oxidation across groups showed no significant difference when compared to the vehicle group. HPLC finger printing revealed the presence of quercetin and kaempferol as the most abundant phenolic compounds in tiger nut and walnut respectively.

CONCLUSION

Tiger nut and walnut extracts showed a protective effect on L-NAME induced kidney slices by reducing the activities of NTPDase (ATP as substrate) and adenosine deaminase, increased NO levels as well as prevent oxidative damage. The effect observed may be attributed to the phenolic compounds present in both nuts as depicted by HPLC finger printing.

Sacubitril and valsartan protect from experimental myocardial infarction by ameliorating oxidative damage in Wistar rats

BACKGROUND

Sacubitril (SAC), a neprilysin inhibitor prevent degradation of neprilysin and activate cGMP signaling pathways leading to rise in blood volume concurrent to blood pressure by means of vasoactive peptides, adrenomedullin, and bradykinin.

OBJECTIVE

The aim of this study was to evaluate the anti-ischemic effects of SAC through inhibiting neprilysin in isoproterenol (ISO) induced myocardial infarction (MI) in Wistar albino rats. ISO (85 mg/kg) was injected subcutaneously at the end of 14 days pre-treatment with SAC and valsartan (VAL).

RESULT

Biochemical investigation revealed that SAC along with VAL significantly prevented the antioxidant enzymes (SOD, Catalase, GR, GPx, GST, and GSH) degradation and malondialdehyde (MDA) induced by ISO intoxication in Wistar rats. Along with this, cardiac biomarkers (LDH, CK-MB, ALT, AST, and ALP) were also significantly ameliorated by SACand VAL in ISO-treated rats. Concurrently, decreased infarction area (IA)and marked reduction in myofibril damage by SACand VAL further supported its protective benefits in MI.

CONCLUSION

Taken together, the results suggest that inhibition of enzyme neprilysin alleviated the ISO induces myocardial damage mediated by its strong antioxidant potential.

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.

Modulation of NFKB1/p50 by ROS leads to impaired ATP production during MI compared to cardiac hypertrophy

Pathological hypertrophy and myocardial infarction (MI) are two etiologically different cardiac disorders having differential molecular mechanisms of disease manifestation. However, no study has been conducted so far to analyze and compare the differential status of energy metabolism in these two disease forms. It was shown recently by our group that production of ATP is significantly impaired during MI along with inhibition of pyruvate dehydrogenase E1-β (PDHE1 B) by pyruvate dehydrogenase kinase 4 (PDK4). However, the ATP levels showed no significant change during pathological hypertrophy compared to control group. To seek a plausible explanation of this phenomenon, the peroxisome proliferator-activated receptor alpha (PPAR) pathway was studied in all the experimental groups which revealed that PGC1α- ERRα axis remains active in MI while the same remained inactive during pathological hypertrophy possibly by NF-κB that plays a significant role in deactivating this pathway during hypertrophy. At the same time, it was observed that reactive oxygen species (ROS) negatively regulates NF-κB activity during MI by oxidation of cysteine residues of p50- the DNA binding subunit of NF-κB. Thus, this study reports for the first time, a possible mechanism for the differential status of energy metabolism during two etiologically different cardiac pathophysiological conditions involving PGC1α-ERRα axis along with p50 subunit of NF-κB.

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.

Targeting vascular (endothelial) dysfunction

Cardiovascular diseases are major contributors to global deaths and disability-adjusted life years, with hypertension a significant risk factor for all causes of death. The endothelium that lines the inner wall of the vasculature regulates essential haemostatic functions, such as vascular tone, circulation of blood cells, inflammation and platelet activity. Endothelial dysfunction is an early predictor of atherosclerosis and future cardiovascular events. We review the prognostic value of obtaining measurements of endothelial function, the clinical techniques for its determination, the mechanisms leading to endothelial dysfunction and the therapeutic treatment of endothelial dysfunction. Since vascular oxidative stress and inflammation are major determinants of endothelial function, we have also addressed current antioxidant and anti-inflammatory therapies. In the light of recent data that dispute the prognostic value of endothelial function in healthy human cohorts, we also discuss alternative diagnostic parameters such as vascular stiffness index and intima/media thickness ratio. We also suggest that assessing vascular function, including that of smooth muscle and even perivascular adipose tissue, may be an appropriate parameter for clinical investigations.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

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.

Cyclic nucleotide imaging and cardiovascular disease

The universal second messengers cyclic nucleotides 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) play central roles in cardiovascular function and disease. They act in discrete, functionally relevant subcellular microdomains which regulate, for example, calcium cycling and excitation-contraction coupling. Such localized cAMP and cGMP signals have been difficult to measure using conventional biochemical techniques. Recent years have witnessed the advent of live cell imaging techniques which allow visualization of these functionally relevant second messengers with unprecedented spatial and temporal resolution at cellular, subcellular and tissue levels. In this review, we discuss these new imaging techniques and give examples how they are used to visualize cAMP and cGMP in physiological and pathological settings to better understand cardiovascular function and disease. Two primary techniques include the use of Förster resonance energy transfer (FRET) based cyclic nucleotide biosensors and nanoscale scanning ion conductance microscopy (SICM). These methods can provide deep mechanistic insights into compartmentalized cAMP and cGMP signaling.

Cardioprotective Effect of Ulmus wallichiana Planchon in β-Adrenergic Agonist Induced Cardiac Hypertrophy

Ulmus wallichiana Planchon (Family: Ulmaceae), a traditional medicinal plant, was used in fracture healing in the folk tradition of Uttarakhand, Himalaya, India. The present study investigated the cardioprotective effect of ethanolic extract (EE) and butanolic fraction (BF) of U. wallichiana in isoprenaline (ISO) induced cardiac hypertrophy in Wistar rats. Cardiac hypertrophy was induced by ISO (5 mg/kg/day, subcutaneously) in rats. Treatment was performed by oral administration of EE and BF of U. wallichiana (500 and 50 mg/kg/day). The blood pressure (BP) and heart rate (HR) were measured by non-invasive blood pressure measurement technique. Plasma renin, Ang II, NO, and cGMP level were estimated using an ELISA kit. Angiotensin converting enzyme activity was estimated. BP and HR were significantly increased in ISO group (130.33 ± 1.67 mmHg vs. 111.78 ± 1.62 mmHg, p < 0.001 and 450.51 ± 4.90 beats/min vs. 347.82 ± 6.91 beats/min, respectively, p < 0.001). The BP and HR were significantly reduced (EE: 117.53 ± 2.27 mmHg vs. 130.33 ± 1.67 mmHg, p < 0.001, BF: 119.74 ± 3.32 mmHg vs. 130.33 ± 1.67 mmHg, p < 0.001); HR: (EE: 390.22 ± 8.24 beats/min vs. 450.51 ± 4.90 beats/min, p < 0.001, BF: 345.38 ± 6.79 beats/min vs. 450.51 ± 4.90 beats/min, p < 0.001) after the treatment of EE and BF of U. wallichiana, respectively. Plasma renin, Ang II, ACE activity was decreased and NO, cGMP level were increased. The EE and BF of U. wallichiana down regulated the expression of ANP, BNP, TNF-α, IL-6, MMP9, β1-AR, TGFβ1 and up regulated NOS3, ACE2 and Mas expression level, respectively. Thus, this study demonstrated that U. wallichiana has cardioprotective effect against ISO induced cardiac hypertrophy.

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.

Acute Catecholamine Exposure Causes Reversible Myocyte Injury Without Cardiac Regeneration

RATIONALE

Catecholamines increase cardiac contractility, but exposure to high concentrations or prolonged exposures can cause cardiac injury. A recent study demonstrated that a single subcutaneous injection of isoproterenol (ISO; 200 mg/kg) in mice causes acute myocyte death (8%-10%) with complete cardiac repair within a month. Cardiac regeneration was via endogenous cKit(+) cardiac stem cell-mediated new myocyte formation.

OBJECTIVE

Our goal was to validate this simple injury/regeneration system and use it to study the biology of newly forming adult cardiac myocytes.

METHODS AND RESULTS

C57BL/6 mice (n=173) were treated with single injections of vehicle, 200 or 300 mg/kg ISO, or 2 daily doses of 200 mg/kg ISO for 6 days. Echocardiography revealed transiently increased systolic function and unaltered diastolic function 1 day after single ISO injection. Single ISO injections also caused membrane injury in ≈10% of myocytes, but few of these myocytes appeared to be necrotic. Circulating troponin I levels after ISO were elevated, further documenting myocyte damage. However, myocyte apoptosis was not increased after ISO injury. Heart weight to body weight ratio and fibrosis were also not altered 28 days after ISO injection. Single- or multiple-dose ISO injury was not associated with an increase in the percentage of 5-ethynyl-2'-deoxyuridine-labeled myocytes. Furthermore, ISO injections did not increase new myocytes in cKit(+/Cre)×R-GFP transgenic mice.

CONCLUSIONS

A single dose of ISO causes injury in ≈10% of the cardiomyocytes. However, most of these myocytes seem to recover and do not elicit cKit(+) cardiac stem cell-derived myocyte regeneration.

Administration of zinc complex of acetylsalicylic acid after the onset of myocardial injury protects the heart by upregulation of antioxidant enzymes

We recently demonstrated that the pre-treatment of rats with zinc and acetylsalicylic acid complex in the form of bis(aspirinato)zinc(II) [Zn(ASA)2] is superior to acetylsalicylic acid in protecting the heart from acute myocardial ischemia. Herein, we hypothesized that Zn(ASA)2 treatment after the onset of an acute myocardial injury could protect the heart. The rats were treated with a vehicle or Zn(ASA)2 after an isoproterenol injection. Isoproterenol-induced cardiac damage [inflammatory infiltration into myocardial tissue, DNA-strand breakage evidenced by TUNEL-assay, increased 11-dehydro thromboxane (TX)B2-levels, elevated ST-segment, widened QRS complex and prolonged QT-interval] was prevented by the Zn(ASA)2 treatment. In isoproterenol-treated rats, load-independent left ventricular contractility parameters were significantly improved after Zn(ASA)2. Furthermore, Zn(ASA)2 significantly increased the myocardial mRNA-expression of superoxide dismutase-1, glutathione peroxidase-4 and decreased the level of Na(+)/K(+)/ATPase. Postconditioning with Zn(ASA)2 protects the heart from acute myocardial ischemia. Its mechanisms of action might involve inhibition of pro-inflammatory prostanoids and upregulation of antioxidant enzymes.

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

BACKGROUND

Diabetes mellitus (DM) leads to the development of diabetic cardiomyopathy, which is associated with altered nitric oxide (NO)--soluble guanylate cyclase (sGC)--cyclic guanosine monophosphate (cGMP) signalling. Cardioprotective effects of elevated intracellular cGMP-levels have been described in different heart diseases. In the current study we aimed at investigating the effects of pharmacological activation of sGC in diabetic cardiomyopathy.

METHODS

Type-1 DM was induced in rats by streptozotocin. Animals were treated either with the sGC activator cinaciguat (10 mg/kg/day) or with placebo orally for 8 weeks. Left ventricular (LV) pressure-volume (P-V) analysis was used to assess cardiac performance. Additionally, gene expression (qRT-PCR) and protein expression analysis (western blot) were performed. Cardiac structure, markers of fibrotic remodelling and DNA damage were examined by histology, immunohistochemistry and TUNEL assay, respectively.

RESULTS

DM was associated with deteriorated cGMP signalling in the myocardium (elevated phosphodiesterase-5 expression, lower cGMP-level and impaired PKG activity). Cardiomyocyte hypertrophy, fibrotic remodelling and DNA fragmentation were present in DM that was associated with impaired LV contractility (preload recruitable stroke work (PRSW): 49.5 ± 3.3 vs. 83.0 ± 5.5 mmHg, P < 0.05) and diastolic function (time constant of LV pressure decay (Tau): 17.3 ± 0.8 vs. 10.3 ± 0.3 ms, P < 0.05). Cinaciguat treatment effectively prevented DM related molecular, histological alterations and significantly improved systolic (PRSW: 66.8 ± 3.6 mmHg) and diastolic (Tau: 14.9 ± 0.6 ms) function.

CONCLUSIONS

Cinaciguat prevented structural, molecular alterations and improved cardiac performance of the diabetic heart. Pharmacological activation of sGC might represent a new therapy approach for diabetic cardiomyopathy.

Superiority of zinc complex of acetylsalicylic acid to acetylsalicylic acid in preventing postischemic myocardial dysfunction

The pathophysiology of ischemic myocardial injury involves cellular events, reactive oxygen species, and an inflammatory reaction cascade. The zinc complex of acetylsalicylic acid (Zn(ASA)2) has been found to possess higher anti-inflammatory and lower ulcerogenic activities than acetylsalicylic acid (ASA). Herein, we studied the effects of both ASA and Zn(ASA)2 against acute myocardial ischemia. Rats were pretreated with ASA (75 mg/kg) or Zn(ASA)2 (100 mg/kg) orally for five consecutive days. Isoproterenol (85 mg/kg, subcutaneously [s.c.]) was applied to produce myocardial infarction. After 17-22 h, animals were anesthetized with sodium pentobarbital (60 mg/kg, intraperitoneally [i.p.]) and both electrical and mechanical parameters of cardiac function were evaluated in vivo. Myocardial histological and gene expression analyses were performed. In isoproterenol-treated rats, Zn(ASA)2 treatment normalized significantly impaired left-ventricular contractility index (Emax 2.6 ± 0.7 mmHg/µL vs. 4.6 ± 0.5 mmHg/µL, P < 0.05), increased stroke volume (30 ± 3 µL vs. 50 ± 6 µL, P < 0.05), decreased systemic vascular resistance (7.2 ± 0.7 mmHg/min/mL vs. 4.2 ± 0.5 mmHg/min/mL, P < 0.05) and reduced inflammatory infiltrate into the myocardial tissues. ECG revealed a restoration of elevated ST-segment (0.21 ± 0.03 mV vs. 0.09 ± 0.02 mV, P < 0.05) and prolonged QT-interval (79.2 ± 3.2 ms vs. 69.5 ± 2.5 ms, P < 0.05) by Zn(ASA)2. ASA treatment did not result in an improvement of these parameters. Additionally, Zn(ASA)2 significantly increased the mRNA-expression of superoxide dismutase 1 (+73 ± 15%), glutathione peroxidase 4 (+44 ± 12%), and transforming growth factor (TGF)-β1 (+102 ± 22%). In conclusion, our data demonstrate that oral administration of zinc and ASA in the form of bis(aspirinato)zinc(II) complex is superior to ASA in preventing electrical, mechanical, and histological changes after acute myocardial ischemia. The induction of antioxidant enzymes and the anti-inflammatory cytokine TGF-β1 may play a pivotal role in the mechanism of action of Zn(ASA)2.

TiProtec preserves endothelial function in a rat model

BACKGROUND

Coronary artery bypass surgery provides excellent patency rates; however, the early and/or late graft failure reduces the long-term benefit of myocardial revascularization. We investigated the effectiveness of generally used saline, Custodiol solutions and a new solution (TiProtec) at preserving endothelium after cold ischemia and warm reperfusion injury.

MATERIALS AND METHODS

Aortic transplantations were performed in Lewis rats. Aortic arches were stored in saline, Custodiol, and TiProtec solutions for 2 h then were transplanted into the abdominal aorta. Two, 24 hours and 1 week after transplantation, the implanted grafts were harvested. Endothelium-dependent and -independent vasorelaxations were investigated in organ bath. DNA strand breaks were assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-method, messenger RNA expressions by quantitative real-time polymerase chain reaction, and the expression of CD-31 and alpha smooth muscle actin by immunochemistry.

RESULTS

Severely impaired endothelial function and integrity of implanted aortic grafts were shown after 2 h in the saline, Custodiol group (maximal vasorelaxation to acetylcholine: control: 91 ± 2%, saline: 26 ± 5%, Custodiol: 24 ± 5%, CD-31-positive area control: 96 ± 2%, saline: 35 ± 13% Custodiol: 54 ± 5%, P < 0.05, respectively); however, a preserved endothelial function was observed in the TiProtec group when compared with the saline and Custodiol group (maximal vasorelaxation: 46 ± 7%, CD-31-positive area: 54 ± 10%, P < 0.05). After 1 wk, endothelial function was partially recovered in all groups; however, it was significantly better in the TiProtec group (maximal vasorelaxation to acetylcholine: saline: 42 ± 3%, Custodiol: 48 ± 3%, TiProtec: 56 ± 3%, CD-31-positive area: saline: 56 ± 5%, Custodiol: 54 ± 4%; TiProtec: 83 ± 6%, P < 0.05, respectively). In addition, messenger RNA levels of Bax, B-cell lymphoma-2, endothelial NOS, vascular endothelial growth factor 2, and caspase-3 were significantly altered in both groups.

CONCLUSIONS

TiProtec appears to be superior for the preservation of endothelial- and smooth muscle cells of bypass graft after cold storage and warm reperfusion in our murine model.

Effects of soluble guanylate cyclase activation on heart transplantation in a rat model

BACKGROUND

The nitric oxide (NO)/soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP) pathway is an important key mechanism to protect the heart from ischemia/reperfusion injury. However, this pathway is disrupted in several cardiovascular diseases as a result of decreased NO bioavailability and increased NO-insensitive forms of sGC. Cinaciguat preferentially activates these NO-insensitive, oxidized forms of sGC.

METHODS

We assessed the hypothesis that targeting NO-unresponsive sGC would protect the graft against ischemia/reperfusion injury in a rat heart transplantation model. Before explantation, donor Lewis rats received methylcellulose (1%) vehicle or cinaciguat 10 mg/kg. The hearts were excised, stored in cold preservation solution, and heterotopically transplanted. We evaluated in vivo left ventricular function of the graft.

RESULTS

After transplantation, decreased left ventricular systolic pressure (77 ± 3 mm Hg vs 123 ± 13 mm Hg, p < 0.05), dP/dt(max) (1,703 ± 162 mm Hg vs 3,350 ± 444 mm Hg, p < 0.05), and dP/dt(min) (995 ± 110 mm Hg vs 1,925 ± 332 mm Hg, p < 0.05) were significantly increased by cinaciguat. Coronary blood flow was significantly higher in the cinaciguat group compared with the control group. Additionally, cinaciguat increased adenosine triphosphate levels (1.9 ± 0.4 µmol/g vs 6.6 ± 0.8 µmol/g, p < 0.05) and improved energy charge potential. After transplantation, increased c-jun messenger RNA expression was downregulated, whereas superoxide dismutase-1 and cytochrome-c oxidase mRNA levels were upregulated by cinaciguat. Cinaciguat also significantly decreased myocardial DNA strand breaks induced by ischemia/reperfusion during transplantation and reduced death of cardiomyocytes in a cellular model of oxidative stress.

CONCLUSIONS

By interacting with NO-unresponsive sGC, cinaciguat enhances the protective effects of the NO/cGMP pathway at different steps of signal transduction after global myocardial ischemia/reperfusion. Its clinical use as pre-conditioning agent could be a novel approach in cardiac surgery.

The cGMP/PKG pathway as a common mediator of cardioprotection: translatability and mechanism

Cardiomyocyte cell death occurring during myocardial reperfusion (reperfusion injury) contributes to final infarct size after transient coronary occlusion. Different interrelated mechanisms of reperfusion injury have been identified, including alterations in cytosolic Ca(2+) handling, sarcoplasmic reticulum-mediated Ca(2+) oscillations and hypercontracture, proteolysis secondary to calpain activation and mitochondrial permeability transition. All these mechanisms occur during the initial minutes of reperfusion and are inhibited by intracellular acidosis. The cGMP/PKG pathway modulates the rate of recovery of intracellular pH, but has also direct effect on Ca(2+) oscillations and mitochondrial permeability transition. The cGMP/PKG pathway is depressed in cardiomyocytes by ischaemia/reperfusion and preserved by ischaemic postconditioning, which importantly contributes to postconditioning protection. The present article reviews the mechanisms and consequences of the effect of ischaemic postconditioning on the cGMP/PKG pathway, the different pharmacological strategies aimed to stimulate it during myocardial reperfusion and the evidence, limitations and promise of translation of these strategies to the clinical practice. Overall, the preclinical and clinical evidence suggests that modulation of the cGMP/PKG pathway may be a therapeutic target in the context of myocardial infarction.

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.

Comparative Proteome Profiling during Cardiac Hypertrophy and Myocardial Infarction Reveals Altered Glucose Oxidation by Differential Activation of Pyruvate Dehydrogenase E1 Component Subunit β

Cardiac hypertrophy and myocardial infarction (MI) are two etiologically different disease forms with varied pathological characteristics. However, the precise molecular mechanisms and specific causal proteins associated with these diseases are obscure to date. In this study, a comparative cardiac proteome profiling was performed in Wistar rat models for diseased and control (sham) groups using two-dimensional difference gel electrophoresis followed by matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry. Proteins were identified using Protein Pilot™ software (version 4.0) and were subjected to stringent statistical analysis. Alteration of key proteins was validated by Western blot analysis. The differentially expressed protein sets identified in this study were associated with different functional groups, involving various metabolic pathways, stress responses, cytoskeletal organization, apoptotic signaling and other miscellaneous functions. It was further deciphered that altered energy metabolism during hypertrophy in comparison to MI may be predominantly attributed to induced glucose oxidation level, via reduced phosphorylation of pyruvate dehydrogenase E1 component subunit β (PDHE1-B) protein during hypertrophy. This study reports for the first time the global changes in rat cardiac proteome during two etiologically different cardiac diseases and identifies key signaling regulators modulating ontogeny of these two diseases culminating in heart failure. This study also pointed toward differential activation of PDHE1-B that accounts for upregulation of glucose oxidation during hypertrophy. Downstream analysis of altered proteome and the associated modulators would enhance our present knowledge regarding altered pathophysiology of these two etiologically different cardiac disease forms.

Influence of cinaciguat on gastrointestinal motility in apo-sGC mice

BACKGROUND

Cinaciguat (BAY 58-2667), an NO- and heme-independent sGC activator, was shown to be more effective when the heme-group of sGC is oxidized in vascular tissue. In apo-sGC mice (sGCβ1 (His105Phe) knockin) both sGC isoforms (sGCα1 β1 and sGCα2 β1 ) are heme-deficient and can no longer be activated by NO; these mice, showing decreased gastrointestinal nitrergic relaxation and decreased gastric emptying, can be considered as a model to study the consequence of heme-oxidation in sGC. Our aim was to compare the influence of cinaciguat, on in vitro muscle tone of gastrointestinal tissues, and on gastric emptying in WT and apo-sGC mice.

METHODS

Gastrointestinal smooth muscle strips were mounted in organ baths for isometric force recording and cGMP levels were determined by enzyme immunoassay. Protein levels of sGC subunits were assessed by immunoblotting. Gastric emptying was determined by phenol red recovery.

KEY RESULTS

Although protein levels of the sGC subunits were lower in gastrointestinal tissues of apo-sGC mice, cinaciguat induced concentration-dependent relaxations and increased cGMP levels in apo-sGC fundus and colon to a similar or greater extent than in WT mice. The sGC inhibitor ODQ increased cinaciguat-induced relaxations and cGMP levels in WT fundus and colon. In apo-sGC antrum, pylorus and jejunum, cinaciguat was not able to induce relaxations. Cinaciguat did not improve delayed gastric emptying in apo-sGC mice.

CONCLUSIONS & INFERENCES

Cinaciguat relaxes the fundus and colon efficiently when sGC is in the heme-free condition; the non-effect of cinaciguat in pylorus explains its inability to improve the delayed gastric emptying in apo-sGC mice.

Total aortic arch replacement: superior ventriculo-arterial coupling with decellularized allografts compared with conventional prostheses

Background

To date, no experimental or clinical study provides detailed analysis of vascular impedance changes after total aortic arch replacement. This study investigated ventriculoarterial coupling and vascular impedance after replacement of the aortic arch with conventional prostheses vs. decellularized allografts.

Methods

After preparing decellularized aortic arch allografts, their mechanical, histological and biochemical properties were evaluated and compared to native aortic arches and conventional prostheses in vitro. In open-chest dogs, total aortic arch replacement was performed with conventional prostheses and compared to decellularized allografts (n = 5/group). Aortic flow and pressure were recorded continuously, left ventricular pressure-volume relations were measured by using a pressure-conductance catheter. From the hemodynamic variables end-systolic elastance (Ees), arterial elastance (Ea) and ventriculoarterial coupling were calculated. Characteristic impedance (Z) was assessed by Fourier analysis.

Results

While Ees did not differ between the groups and over time (4.1±1.19 vs. 4.58±1.39 mmHg/mL and 3.21±0.97 vs. 3.96±1.16 mmHg/mL), Ea showed a higher increase in the prosthesis group (4.01±0.67 vs. 6.18±0.20 mmHg/mL, P<0.05) in comparison to decellularized allografts (5.03±0.35 vs. 5.99±1.09 mmHg/mL). This led to impaired ventriculoarterial coupling in the prosthesis group, while it remained unchanged in the allograft group (62.5±50.9 vs. 3.9±23.4%). Z showed a strong increasing tendency in the prosthesis group and it was markedly higher after replacement when compared to decellularized allografts (44.6±8.3dyn·sec·cm⁻⁵ vs. 32.4±2.0dyn·sec·cm⁻⁵, P<0.05).

Conclusions

Total aortic arch replacement leads to contractility-afterload mismatch by means of increased impedance and invert ventriculoarterial coupling ratio after implantation of conventional prostheses. Implantation of decellularized allografts preserves vascular impedance thereby improving ventriculoarterial mechanoenergetics after aortic arch replacement.

Turning on cGMP-dependent pathways to treat cardiac dysfunctions: boom, bust, and beyond

cGMP inhibits hypertrophy, decreases fibrosis, and protects against cardiac ischemia-reperfusion (I/R) injury. Gene-targeting studies have not defined a clear role for its major downstream effector, cGMP-dependent protein kinase I (cGKI), in cardiac hypertrophy, but do implicate cGMP-cGKI signaling in fibrosis and I/R injury. No direct cGKI activators have advanced to clinical trials, whereas cardiac trials of agents that modulate cGMP via particulate or soluble guanylyl cyclases (GCs) and phosphodiesterase 5 (PDE5) are ongoing. Here we review concerns arising from preclinical and clinical studies that question whether targeting the cGMP pathway remains an encouraging concept for management of heart dysfunction. So far, trial results for GC modulators are inconclusive, and sildenafil, a PDE5 inhibitor, although cardioprotective in mouse models, has not shown positive clinical results. Preclinical cardioprotection observed for sildenafil may result from inhibition of PDE5 in non-cardiomyocytes or off-target effects, possibly on PDE1C. On the basis of such mechanistic considerations, re-evaluation of the cellular localization of drug target(s) and intervention protocols for cGMP-elevating agents may be needed.

Soluble guanylyl cyclase activation improves progressive cardiac remodeling and failure after myocardial infarction. Cardioprotection over ACE inhibition

Impaired nitric oxide (NO)-soluble guanylate cyclase (sGC)-cGMP signaling is involved in the pathogenesis of ischemic heart diseases, yet the impact of long-term sGC activation on progressive cardiac remodeling and heart failure after myocardial infarction (MI) has not been explored. Moreover, it is unknown whether stimulating the NO/heme-independent sGC provides additional benefits to ACE inhibition in chronic ischemic heart failure. Starting 10 days after MI, rats were treated with placebo, the sGC activator ataciguat (10 mg/kg/twice daily), ramipril (1 mg/kg/day), or a combination of both for 9 weeks. Long-term ataciguat therapy reduced left ventricular (LV) diastolic filling pressure and pulmonary edema, improved the rightward shift of the pressure-volume curve, LV contractile function and diastolic stiffness, without lowering blood pressure. NO/heme-independent sGC activation provided protection over ACE inhibition against mitochondrial superoxide production and progressive fibrotic remodeling, ultimately leading to a further improvement of cardiac performance, hypertrophic growth and heart failure. We found that ataciguat stimulating sGC activity was potentiated in (myo)fibroblasts during hypoxia-induced oxidative stress and that NO/heme-independent sGC activation modulated fibroblast-cardiomyocyte crosstalk in the context of heart failure and hypoxia. In addition, ataciguat inhibited human cardiac fibroblast differentiation and extracellular matrix protein production in response to TGF-β1. Overall, long-term sGC activation targeting extracellular matrix homeostasis conferred cardioprotection against progressive cardiac dysfunction, pathological remodeling and heart failure after myocardial infarction. NO/heme-independent sGC activation may prove to be a useful therapeutic target in patients with chronic heart failure and ongoing fibrotic remodeling.

Pathophysiology of hypertension in the absence of nitric oxide/cyclic GMP signaling

The nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling system is a well-characterized modulator of cardiovascular function, in general, and blood pressure, in particular. The availability of mice mutant for key enzymes in the NO-cGMP signaling system facilitated the identification of interactions with other blood pressure modifying pathways (e.g. the renin-angiotensin-aldosterone system) and of gender-specific effects of impaired NO-cGMP signaling. In addition, recent genome-wide association studies identified blood pressure-modifying genetic variants in genes that modulate NO and cGMP levels. Together, these findings have advanced our understanding of how NO-cGMP signaling regulates blood pressure. In this review, we will summarize the results obtained in mice with disrupted NO-cGMP signaling and highlight the relevance of this pathway as a potential therapeutic target for the treatment of hypertension.