Sildenafil inhibits beta-adrenergic-stimulated cardiac contractility in humans

Effect of phosphodiesterase type 5 inhibitors on surgical outcome of ventricular septal defect and pulmonary hypertension patients

BACKGROUND

Children with ventricular septal defect (VSD) and large systemic-to-pulmonary shunts eventually develop pulmonary hypertension (PH). The perioperative management of patients with VSD and PH is quite troublesome and still debatable, especially in developing countries where the different management options and standardization of treatment is not available. Oral phosphodiesterase type 5 (PDE-5) inhibitors are good treatment options being widely available, cheap, easy administration and do not require extensive monitoring. The aim of our study was to evaluate the effect of the PDE-5 inhibitors when given orally, early preoperative and continued for 3 months postoperative on controlling postoperative PH with its effect on right ventricle (RV) functions. Fifty-one patients were randomly assigned to either sildenafil or tadalafil, 1 week before and continued for 3 months after corrective surgery. The control group received a placebo.

RESULTS

There was no significant difference in the improvement in the right ventricle systolic pressure (RVSP) between both groups, early in the postoperative period (P = 0.255) and in follow-up (P = 0.259). There was also no significant difference in the changes in mean pulmonary artery pressure (mPAP), postoperatively and on follow-up (P = 0.788 and 0.059, respectively). There was a drop in RV functions in both groups postoperatively which improved on follow-up; however, it was not significant between both groups. The length of intensive care unit (ICU) stay was similar between both groups (P = 0.143).

CONCLUSION

Perioperative administration of PDE-5 inhibitors does not have an impact on the clinical course as regards improvement in pulmonary artery (PA) pressure, ventricular functions and ICU stay.

Phosphodiesterase in heart and vessels: from physiology to diseases

Phosphodiesterases (PDEs) are a superfamily of enzymes that hydrolyze cyclic nucleotides, including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both cyclic nucleotides are critical secondary messengers in the neurohormonal regulation in the cardiovascular system. PDEs precisely control spatiotemporal subcellular distribution of cyclic nucleotides in a cell- and tissue-specific manner, playing critical roles in physiological responses to hormone stimulation in the heart and vessels. Dysregulation of PDEs has been linked to the development of several cardiovascular diseases, such as hypertension, aneurysm, atherosclerosis, arrhythmia, and heart failure. Targeting these enzymes has been proven effective in treating cardiovascular diseases and is an attractive and promising strategy for the development of new drugs. In this review, we discuss the current understanding of the complex regulation of PDE isoforms in cardiovascular function, highlighting the divergent and even opposing roles of PDE isoforms in different pathogenesis.

Cardiac Effects of Phosphodiesterase-5 Inhibitors: Efficacy and Safety

The coexistence of cardiovascular disease and erectile dysfunction is widespread, possibly owing to underlying endothelial dysfunction in both diseases. Millions of patients with cardiovascular disease are prescribed phosphodiesterase-5 (PDE5) inhibitors for the management of erectile dysfunction. Although the role of PDE5 inhibitors in erectile dysfunction therapy is well established, their effects on the cardiovascular system are unclear. Preclinical studies investigating the effect of PDE5 inhibitors on ischemia-reperfusion injury, pressure overload-induced hypertrophy, and chemotoxicity suggested a possible clinical role for each of these medications; however, attempts to translate these findings to the bedside have resulted in mixed outcomes. In this review, we explore the biologic preclinical effects of PDE5 inhibitors in mediating cardioprotection. We then examine clinical trials investigating PDE5 inhibition in patients with heart failure, coronary artery disease, and ventricular arrhythmias and discuss why the studies likely have yet to show positive results and efficacy with PDE5 inhibition despite no safety concerns.

Cyclic nucleotide phosphodiesterases as therapeutic targets in cardiac hypertrophy and heart failure

Cyclic nucleotide phosphodiesterases (PDEs) modulate the neurohormonal regulation of cardiac function by degrading cAMP and cGMP. In cardiomyocytes, multiple PDE isozymes with different enzymatic properties and subcellular localization regulate local pools of cyclic nucleotides and specific functions. This organization is heavily perturbed during cardiac hypertrophy and heart failure (HF), which can contribute to disease progression. Clinically, PDE inhibition has been considered a promising approach to compensate for the catecholamine desensitization that accompanies HF. Although PDE3 inhibitors, such as milrinone or enoximone, have been used clinically to improve systolic function and alleviate the symptoms of acute HF, their chronic use has proved to be detrimental. Other PDEs, such as PDE1, PDE2, PDE4, PDE5, PDE9 and PDE10, have emerged as new potential targets to treat HF, each having a unique role in local cyclic nucleotide signalling pathways. In this Review, we describe cAMP and cGMP signalling in cardiomyocytes and present the various PDE families expressed in the heart as well as their modifications in pathological cardiac hypertrophy and HF. We also appraise the evidence from preclinical models as well as clinical data pointing to the use of inhibitors or activators of specific PDEs that could have therapeutic potential in HF.

The Effects of Different Doses of Sildenafil on Coronary Blood Flow and Oxidative Stress in Isolated Rat Hearts

The dose-response relationship of sildenafil effects on cardiac function is not completely elucidated. The aim of this study was to assess the effects of different doses of sildenafil on coronary flow and oxidative stress in isolated rat hearts. Coronary flow and markers of oxidative stress, including nitrite outflow, and superoxide anion production in coronary effluent, were determined for isolated rat hearts. The experiments were performed during control conditions and in the presence of sildenafil (10, 20, 50, 200 nM) alone or with Nω-nitro-L-arginine monomethyl ester (L-NAME) (30 μM). Sildenafil was shown to result in a significant increase in coronary flow at lower coronary perfusion pressure (CPP) values at all administered doses, whereas, with an increase in CPP, a reduction in coronary flow was observed. An increase in nitric oxide (NO) was most pronounced in the group treated with the lowest dose of sildenafil at the highest CPP value. After the inhibition of the NO-cyclic guanosine monophosphate (cGMP) signaling (NOS) system by L-NAME, only a dose of 200 nM sildenafil was high enough to overcome the inhibition and to boost release of O2-. That effect was CPP-dependent, with statistical significance reached at 80, 100 and 120 mmHg. Our findings indicate that sildenafil causes changes in heart vasculature in a dose-dependent manner, with a shift from a vasodilatation effect to vasoconstriction with a pressure increase. The highest dose administered is capable of producing superoxide anion radicals in terms of NOS system inhibition.

Effects of sildenafil on symptoms and exercise capacity for heart failure with reduced ejection fraction and pulmonary hypertension (The SilHF study): A randomised placebo-controlled multicentre trial

Aims

Pulmonary hypertension (PHT) may complicate heart failure with reduced ejection fraction (HFrEF) and is associated with a substantial symptom burden and poor prognosis. Sildenafil, a phosphodiesterase‐5 (PDE‐5) inhibitor, might have beneficial effects on pulmonary haemodynamics, cardiac function and exercise capacity in HFrEF and PHT. The aim of this study was to determine the safety, tolerability, and efficacy of sildenafil in patients with HFrEF and indirect evidence of PHT.

Methods and results

The Sildenafil in Heart Failure (SilHF) trial was an investigator‐led, randomized, multinational trial in which patients with HFrEF and a pulmonary artery systolic pressure (PASP) ≥40 mmHg by echocardiography were randomly assigned in a 2:1 ratio to receive sildenafil (up to 40 mg three times/day) or placebo. The co‐primary endpoints were improvement in patient global assessment by visual analogue scale and in the 6‐min walk test at 24 weeks. The planned sample size was 210 participants but, due to problems with supplying sildenafil/placebo and recruitment, only 69 patients (11 women, median age 68 (interquartile range [IQR] 62–74) years, median left ventricular ejection fraction 29% (IQR 24–35), median PASP 45 (IQR 42–55) mmHg) were included. Compared to placebo, sildenafil did not improve symptoms, quality of life, PASP or walk test distance. Sildenafil was generally well tolerated, but those assigned to sildenafil had numerically more serious adverse events (33% vs. 21%).

Conclusion

Compared to placebo, sildenafil did not improve symptoms, quality of life or exercise capacity in patients with HFrEF and PHT.

Outcomes With Phosphodiesterase-5 Inhibitor Use After Left Ventricular Assist Device: An STS-INTERMACS Analysis

BACKGROUND

Elevated right ventricular afterload following continuous-flow left ventricular assist device (CF-LVAD) may contribute to late right heart failure (LRHF). PDE5i (phosphodiesterase-5 inhibitors) are used to treat pulmonary hypertension and right heart dysfunction after CF-LVAD, but their impact on outcomes is uncertain.

METHODS

We queried Interagency Registry for Mechanically Assisted Circulatory Support from 2012 to 2017 for adults receiving a primary CF-LVAD and surviving ≥30 days from index discharge. Patients receiving early PDE5i (ePDE5i) at 1 month were propensity-matched 1:1 with controls. The primary outcome was the cumulative incidence of LRHF, defined using prevailing Interagency Registry for Mechanically Assisted Circulatory Support criteria; secondary outcomes included all-cause mortality and major bleeding.

RESULTS

Among 9627 CF-LVAD recipients analyzed, 2463 (25.6%) received ePDE5i and 1600 were propensity-matched 1:1 with controls. Before implant, ePDE5i patients had more severe RV dysfunction (13.1% versus 9.6%) and higher pulmonary vascular resistance (2.8±2.7 versus 2.2±2.4 WU), both P<0.001, but clinical factors were well-balanced after propensity-matching. In the unmatched cohort, ePDE5i patients had a higher 3-year cumulative incidence of LRHF, mortality, and major bleeding, but these differences were attenuated in the propensity-matched cohort: LRHF 40.8% versus 35.7% (hazard ratio, 1.14 [95% CI, 0.99-1.32]; P=0.07); mortality 38.6% versus 35.8% (hazard ratio, 0.99 [95% CI, 0.86-1.15]; P=0.93); major bleeding 51.2% versus 46.0% (hazard ratio, 1.12 [95% CI, 0.99-1.27]; P=0.06).

CONCLUSIONS

Compared with propensity-matched controls, adult CF-LVAD patients receiving ePDE5i had similar rates of LRHF, mortality, and major bleeding. While intrinsic patient risk factors likely account for more adverse outcomes with ePDE5i in the unmatched cohort, there is no obvious benefit of ePDE5i in the LVAD population.

Gene losses may contribute to subterranean adaptations in naked mole-rat and blind mole-rat

Background

Naked mole-rats (Heterocephalus glaber, NMRs) and blind mole-rats (Spalax galili, BMRs) are representative subterranean rodents that have evolved many extraordinary traits, including hypoxia tolerance, longevity, and cancer resistance. Although multiple candidate loci responsible for these traits have been uncovered by genomic studies, many of them are limited to functional changes to amino acid sequence and little is known about the contributions of other genetic events. To address this issue, we focused on gene losses (unitary pseudogenes) and systematically analyzed gene losses in NMRs and BMRs, aiming to elucidate the potential roles of pseudogenes in their adaptation to subterranean lifestyle.

Results

We obtained the pseudogene repertoires in NMRs and BMRs, as well as their respective aboveground relatives, guinea pigs and rats, on a genome-wide scale. As a result, 167, 139, 341, and 112 pseudogenes were identified in NMRs, BMRs, guinea pigs, and rats, respectively. Functional enrichment analysis identified 4 shared and 2 species-specific enriched functional groups (EFGs) in subterranean lineages. Notably, the pseudogenes in these EFGs might be associated with either regressive (e.g., visual system) or adaptive (e.g., altered DNA damage response) traits. In addition, several pseudogenes including TNNI3K and PDE5A might be associated with specific cardiac features observed in subterranean lineages. Interestingly, we observed 20 convergent gene losses in NMRs and BMRs. Given that the functional investigations of these genes are generally scarce, we provided functional evidence that independent loss of TRIM17 in NMRs and BMRs might be beneficial for neuronal survival under hypoxia, supporting the positive role of eliminating TRIM17 function in hypoxia adaptation. Our results also suggested that pseudogenes, together with positively selected genes, reinforced subterranean adaptations cooperatively.

Conclusions

Our study provides new insights into the molecular underpinnings of subterranean adaptations and highlights the importance of gene losses in mammalian evolution.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01243-0.

Phosphodiesterases and Compartmentation of cAMP and cGMP Signaling in Regulation of Cardiac Contractility in Normal and Failing Hearts

Cardiac contractility is regulated by several neural, hormonal, paracrine, and autocrine factors. Amongst these, signaling through β-adrenergic and serotonin receptors generates the second messenger cyclic AMP (cAMP), whereas activation of natriuretic peptide receptors and soluble guanylyl cyclases generates cyclic GMP (cGMP). Both cyclic nucleotides regulate cardiac contractility through several mechanisms. Phosphodiesterases (PDEs) are enzymes that degrade cAMP and cGMP and therefore determine the dynamics of their downstream effects. In addition, the intracellular localization of the different PDEs may contribute to regulation of compartmented signaling of cAMP and cGMP. In this review, we will focus on the role of PDEs in regulating contractility and evaluate changes in heart failure.

PDE5 Inhibition Suppresses Ventricular Arrhythmias by Reducing SR Ca2+ Content

[Figure: see text].

Predictors and prognosis of right ventricular function in pulmonary hypertension due to heart failure with reduced ejection fraction

Aims

Failure of right ventricular (RV) function worsens outcome in pulmonary hypertension (PH). The adaptation of RV contractility to afterload, the RV‐pulmonary artery (PA) coupling, is defined by the ratio of RV end‐systolic to PA elastances (Ees/Ea). Using pressure–volume loop (PV‐L) technique we aimed to identify an Ees/Ea cut‐off predictive for overall survival and to assess hemodynamic and morphologic conditions for adapted RV function in secondary PH due to heart failure with reduced ejection fraction (HFREF).

Methods and results

This post hoc analysis is based on 112 patients of the prospective Magdeburger Resynchronization Responder Trial. All patients underwent right and left heart echocardiography and a baseline PV‐L and RV catheter measurement. A subgroup of patients (n = 50) without a pre‐implanted cardiac device underwent magnetic resonance imaging at baseline. The analysis revealed that 0.68 is an optimal Ees/Ea cut‐off (area under the curve: 0.697, P < 0.001) predictive for overall survival (median follow up = 4.7 years, Ees/Ea ≥ 0.68 vs. <0.68, log‐rank 8.9, P = 0.003). In patients with PH (n = 76, 68%) multivariate Cox regression demonstrated the independent prognostic value of RV‐Ees/Ea in PH patients (hazard ratio 0.2, P < 0.038). Patients without PH (n = 36, 32%) and those with PH but RV‐Ees/Ea ≥ 0.68 showed comparable RV‐Ees/Ea ratios (0.88 vs. 0.9, P = 0.39), RV size/function, and survival. In contrast, secondary PH with RV‐PA coupling ratio Ees/Ea < 0.68 corresponded extremely close to cut‐off values that define RV dilatation/remodelling (RV end‐diastolic volume >160 mL, RV‐mass/volume‐ratio ≤0.37 g/mL) and dysfunction (right ventricular ejection fraction <38%, tricuspid annular plane systolic excursion <16 mm, fractional area change <42%, and stroke‐volume/end‐systolic volume ratio <0.59) and is associated with a dramatically increased short and medium‐term all‐cause mortality. Independent predictors of prognostically unfavourable RV‐PA coupling (Ees/Ea < 0.68) in secondary PH were a pre‐existent dilated RV [end‐diastolic volume >171 mL, odds ratio (OR) 0.96, P = 0.021], high pulsatile load (PA compliance <2.3 mL/mmHg, OR 8.6, P = 0.003), and advanced systolic left heart failure (left ventricular ejection fraction <30%, OR 1.23, P = 0.028).

Conclusions

The RV‐PA coupling ratio Ees/Ea predicts overall survival in PH due to HFREF and is mainly affected by pulsatile load, RV remodelling, and left ventricular dysfunction. Prognostically favourable coupling (RV‐Ees/Ea ≥ 0.68) in PH was associated with preserved RV size/function and mid‐term survival, comparable with HFREF without PH.

Pharmacological preconditioning with phosphodiestrase inhibitor: an answer to stem cell survival against ischemic injury through JAK/STAT signaling

Stem cell transplantation in regenerative medicine has been widely used in various disorders including cardiovascular diseases (CVD) and emerging next-generation therapy. However, transplanted stem cell encountered ischemia/reperfusion (IR) injury which is a major challenge for stem cell survival. During the acute phase after myocardial infarction (MI) cytokine-rich hostile microenvironment, extensive immune cell infiltration and lack of oxygen have been a bottleneck in cell-based therapy. During prolonged ischemia, intracellular pH and ATP level decrease results in anaerobic metabolism and lactate accumulation. Consequentially, ATPase-dependent ion transport becomes dysfunctional, contributing to calcium overload and cell death by apoptosis and necrosis. Although O₂ level revitalizes upon reperfusion, a surge in the generation of reactive oxygen species (ROS) occurs with neutrophil infiltration in ischemic tissues further aggravating the injury. Ischemic preconditioning (IPC) of stem cells with a repeated short cycle of IR results in the release of chemical signals such as NO, ROS, and adenosine which triggers a cascade of signaling events that activates protein kinase C (PKC), Src protein tyrosine kinases, and nuclear factor κB (NF-κB) and subsequently increased synthesis of inducible NO synthase (iNOS), cyclooxygenase-2 (COX-2), Heme oxygenase-1 [HO-1], aldose reductase, Mn superoxide dismutase, and anti-apoptotic genes (Mcl-1, BCl-x_L, c-FLIP_L, c-FLIP_S). Pharmacological preconditioning uses a phosphodiestrase inhibitor, another mode of protecting stem cell or heart per se from impending ischemic injury in two phases. During the early phase of cardioprotection (2 h), PC leads to increased expression of survival factors like BCl₂/Bax ratio while late phase (24 h) showed activation of the JAK/STAT survival pathway. Phosphorylation of STAT3 at two crucial residues, Tyr-705 and Ser-727, allows its entry inside the nucleus and upregulates the expression of protein kinase G-1 (PKG1) which evokes cardioprotective signaling. To confirm, heart-specific conditional STAT3 knockout mice undergone IR surgery, abolishing late-phase cardioprotective effects.

Effect of sildenafil on right ventricular performance in an experimental large-animal model of postcapillary pulmonary hypertension

Right ventricle (RV) dysfunction is a main determinant of morbidity and mortality in postcapillary pulmonary hypertension (PH). However, currently there are not available therapies. Since reduced nitric oxide (NO) availability and cyclic guanylate monophosphate (cGMP) levels are central in this disease, therapies targeting the NO pathway might have a beneficial effect on RV performance. In this regard, sildenafil has shown contradictory results. Our objective was to evaluate the effect of sildenafil on RV performance in an experimental pig model of postcapillary PH induced by a fixed banding of the venous pulmonary confluent. Animals were evaluated by right heart catheterization and cardiac magnetic resonance before randomization and after 8 weeks on sildenafil (n = 8) or placebo (n = 8), and myocardial tissues were analyzed with histology and molecular biology. At the end of the study, animals receiving sildenafil showed better RV performance as compared with those on placebo (improvement in RV ejection fraction of 7.3% ± 5.8% versus -0.6% ± 5.0%, P= 0.021) associated with less apoptotic cells and gene expression related with reduced oxidative stress and increased anti-inflammatory activity in the myocardium. No differences were observed in pulmonary hemodynamics. In conclusion, in a translational large animal model of chronic postcapillary PH, sildenafil improved RV systolic function independently of afterload. Further research with pharmacological approaches able to manipulate the NO-cGMP axis are needed to confirm this potential cardioprotective effect.

An update of cyclic nucleotide phosphodiesterase as a target for cardiac diseases

INTRODUCTION

Cyclic nucleotides, cAMP, and cGMP, are important second messengers of intracellular signaling and play crucial roles in cardiovascular biology and diseases. Cyclic nucleotide phosphodiesterases (PDEs) control the duration, magnitude, and compartmentalization of cyclic nucleotide signaling by catalyzing the hydrolysis of cyclic nucleotides. Individual PDEs modulate distinct signaling pathways and biological functions in the cell, making it a potential therapeutic target for the treatment of different cardiovascular disorders. The clinical success of several PDE inhibitors has ignited continued interest in PDE inhibitors and in PDE-target therapeutic strategies.

AREAS COVERED

This review concentrates on recent research advances of different PDE isoforms with regard to their expression patterns and biological functions in the heart. The limitations of current research and future directions are then discussed. The current and future development of PDE inhibitors is also covered.

EXPERT OPINION

Despite the therapeutic success of several marketed PDE inhibitors, the use of PDE inhibitors can be limited by their side effects, lack of efficacy, and lack of isoform selectivity. Advances in our understanding of the mechanisms by which cellular functions are changed through PDEs may enable the development of new approaches to achieve effective and specific PDE inhibition for various cardiac therapies.

Acute Unloading Effects of Sildenafil Enhance Right Ventricular-Pulmonary Artery Coupling in Heart Failure

BACKGROUND

Phosphodiesterase-5A inhibitors (PDE5i) are sometimes used in patients with advanced heart failure with reduced ejection fraction before heart transplant or left ventricular assist device implantation to decrease right ventricular (RV) afterload and mitigate the risk of right heart failure. Conflicting evidence exists regarding the impact of these drugs on RV contractility. The aim of this study was to explore the acute effects of PDE5i on ventricular-vascular coupling and load-independent RV contractility.

METHODS

Twenty-two patients underwent right heart catheterization and gated equilibrium blood pool single photon emission computed tomography, before and after 20 mg intravenous sildenafil. Single photon emission computed tomography and right heart catheterization-derived data were used to calculate RV loading and contractility.

RESULTS

PDE5i induced a decrease in the right atrial pressure (-43%), pulmonary artery (PA) mean pressure (-26%), and PA wedge pressure (PAWP; -23%), with favorable reductions in pulmonary vascular resistance (-41%) and PA elastance (-40%), and increased cardiac output (+13%) (all P < 0.01). The RV ejection fraction increased with sildenafil (+20%), with no change of RV contractility (P = 0.74), indicating that the improvement in the RV ejection fraction was related to enhanced RV-PA coupling (r = 0.59, P = 0.004) by a decrease in the ventricular load. RV diastolic compliance increased with sildenafil. The decrease in the PAWP correlated with RV end-diastolic volume decrease; no relationship was observed with the change in LV transmural pressure, suggesting decreased pericardial constraint.

CONCLUSIONS

Acute PDE5i administration has profound RV afterload-reducing effects, improves the RVEF, decreases RV volumes, and decreases the PAWP, predominantly through relief of pericardial constraint, without effects on RV chamber contractility. These findings support further study of PDE5i in protection of RV function in advanced heart failure with reduced ejection fraction who are at risk of RV failure.

Cardiac Cyclic Nucleotide Phosphodiesterases: Roles and Therapeutic Potential in Heart Failure

The cyclic nucleotides cyclic adenosine-3′,5′-monophosphate (cAMP) and cyclic guanosine-3′,5′-monophosphate (cGMP) maintain physiological cardiac contractility and integrity. Cyclic nucleotide–hydrolysing phosphodiesterases (PDEs) are the prime regulators of cAMP and cGMP signalling in the heart. During heart failure (HF), the expression and activity of multiple PDEs are altered, which disrupt cyclic nucleotide levels and promote cardiac dysfunction. Given that the morbidity and mortality associated with HF are extremely high, novel therapies are urgently needed. Herein, the role of PDEs in HF pathophysiology and their therapeutic potential is reviewed. Attention is given to PDEs 1–5, and other PDEs are briefly considered. After assessing the role of each PDE in cardiac physiology, the evidence from pre-clinical models and patients that altered PDE signalling contributes to the HF phenotype is examined. The potential of pharmacologically harnessing PDEs for therapeutic gain is considered.

Sildenafil Recovers Burn-Induced Cardiomyopathy

Background: Severe burn injury initiates a feedback cycle of inflammation, fibrosis, oxidative stress and cardiac mitochondrial damage via the PDE5A-cGMP-PKG pathway. Aim: To test if the PDE5A-cGMP-PKG pathway may contribute to burn-induced heart dysfunction. Methods: Sprague–Dawley rats were divided four groups: sham; sham/sildenafil; 24 h post burn (60% total body surface area scald burn, harvested at 24 h post burn); and 24 h post burn/sildenafil. We monitored heart function and oxidative adducts, as well as cardiac inflammatory, cardiac fibrosis and cardiac remodeling responses in vivo. Results: Sildenafil inhibited the burn-induced PDE5A mRNA level and increased the cGMP level and PKG activity, leading to the normalization of PKG down-regulated genes (IRAG, PLB, RGS2, RhoA and MYTP), a decreased ROS level (H2O2), decreased oxidatively modified adducts (malonyldialdehyde [MDA], carbonyls), attenuated fibrogenesis as well as fibrosis gene expression (ANP, BNP, COL1A2, COL3A2, αSMA and αsk-Actin), and reduced inflammation and related gene expression (RELA, IL-18 and TGF-β) after the burn. Additionally, sildenafil treatment preserved left ventricular heart function (CO, EF, SV, LVvol at systolic, LVPW at diastolic and FS) and recovered the oxidant/antioxidant balance (total antioxidant, total SOD activity and Cu,ZnSOD activity). Conclusions: The PDE5A-cGMP-PKG pathway mediates burn-induced heart dysfunction. Sildenafil treatment recovers burn-induced cardiac dysfunction.

Sildenafil Recovers Burn-Induced Cardiomyopathy

Background: Severe burn injury initiates a feedback cycle of inflammation, fibrosis, oxidative stress and cardiac mitochondrial damage via the PDE5A-cGMP-PKG pathway. Aim: To test if the PDE5A-cGMP-PKG pathway may contribute to burn-induced heart dysfunction. Methods: Sprague–Dawley rats were divided four groups: sham; sham/sildenafil; 24 h post burn (60% total body surface area scald burn, harvested at 24 h post burn); and 24 h post burn/sildenafil. We monitored heart function and oxidative adducts, as well as cardiac inflammatory, cardiac fibrosis and cardiac remodeling responses in vivo. Results: Sildenafil inhibited the burn-induced PDE5A mRNA level and increased the cGMP level and PKG activity, leading to the normalization of PKG down-regulated genes (IRAG, PLB, RGS2, RhoA and MYTP), a decreased ROS level (H2O2), decreased oxidatively modified adducts (malonyldialdehyde [MDA], carbonyls), attenuated fibrogenesis as well as fibrosis gene expression (ANP, BNP, COL1A2, COL3A2, αSMA and αsk-Actin), and reduced inflammation and related gene expression (RELA, IL-18 and TGF-β) after the burn. Additionally, sildenafil treatment preserved left ventricular heart function (CO, EF, SV, LVvol at systolic, LVPW at diastolic and FS) and recovered the oxidant/antioxidant balance (total antioxidant, total SOD activity and Cu,ZnSOD activity). Conclusions: The PDE5A-cGMP-PKG pathway mediates burn-induced heart dysfunction. Sildenafil treatment recovers burn-induced cardiac dysfunction.

Long-Term Hemodynamic Improvement after Transcatheter Mitral Valve Repair

BACKGROUND

Correction of mitral regurgitation (MR) alters the load on the left ventricle. There are few data on the long-term hemodynamic adaptations of the cardiovascular system after transcatheter mitral valve repair (TMVR). The aim of this study was to determine a comprehensive hemodynamic status using noninvasive pressure-volume analysis.

METHODS

Pressure-volume parameters were calculated from echocardiography with simultaneous arm-cuff blood pressure measurements at baseline before TMVR and 12 months after TMVR. Eighty-eight consecutive patients undergoing edge-to-edge mitral clip implantation because of grade 3+ or 4+, symptomatic (79.5% in New York Heart Association functional class ≥III) MR were prospectively enrolled. The mean left ventricular (LV) ejection fraction was 42 ± 14%. Sixty-seven percent of the patients had secondary MR.

RESULTS

Twelve months after TMVR, 17.7% of patients had died, and 19.0% were rehospitalized because of decompensated heart failure. MR grade was ≤2+ in 90% of surviving patients, and 77% were in New York Heart Association functional class ≤II. LV end-diastolic volume index decreased from 87 ± 38 to 77 ± 40 mL/m² (P < .0001), end-systolic volume index changed from 54 ± 34 to 50 ± 36 mL/m² (P = .018), hence total stroke volume index was reduced (from 34 ± 11 to 28 ± 7 ml/m², P < .0001). Ejection fraction and global longitudinal peak systolic strain remained unchanged. Increased forward ejection fraction (30 ± 14% vs 41 ± 20%, P < .0001), cardiac index (from 1.7 ± 0.4 to 1.9 ± 0.5 mL/min/m², P = .003), and peak power index (214 ± 114 vs 280 ± 149 mm Hg/sec, P = .0001) as well as similar end-systolic elastance at reduced LV volumes indicated improved LV performance. Cardiac efficiency, measured as cardiac index relative to myocardial energy, was improved (0.012 ± 0.008 vs 0.019 ± 0.010 mm Hg^-1, P = .002). Logistic regression analysis revealed baseline values of total ejection fraction and diastolic pulmonary pressure gradient as predictors of clinical improvement (odds ratios, 1.076 [P = .009] and 0.812 [P = .015], respectively) after TMVR.

CONCLUSIONS

One year after TMVR, patients showed reverse remodeling and improved LV performance that was associated with improved symptom status. This hemodynamic improvement supports TMVR as long-term effective therapy for patients with symptomatic MR.

Echocardiographic assessment of functional mitral regurgitation: opening Pandora's box?

Two recent trials of transcatheter mitral-valve repair in patients with functional mitral regurgitation (FMR) presented opposing results for the MitraClip® compared to medical therapy alone. The conflicting results gave rise to intensive discussions about assessment of mitral valve regurgitation (MR). A recent editorial viewpoint provided a potential explanation presenting a new pathophysiologic concept. However, the echocardiographic characterization of both trials' patients is inconsistent and the discussed concepts appear to suffer from plausibility weaknesses. It is well conceivable that limitations in the echocardiographic assessment of the trial patients introduced a bias regarding the selection of patients with severe (or less severe) MR that may be a more plausible explanation for the differences in outcome. We here illustrate our viewpoint regarding the two MitraClip trials and also illustrate the difficulties in assessing functional MR properly. It may indeed be "opening Pandora's box", but we will also make an attempt to provide a solution.

Diastology for the clinician

Diastolic filling of the heart is a complex sequence of multiple inter-related events consisting of processes such as ventricular relaxation, erectile coronary effect, visco-elastic forces of the myocardium, ventricular interaction, myocardial stress strain relationships, pericardial restraint, passive filling, and atrial contraction. However, in order to understand diastolic filling from a clinical aspect, a simplified foundation can be used which divides the cardiac cycle into contraction, relaxation, passive filling, and filling at atrial contraction. The mitral flow velocity curves are representative of the relative driving pressure between left atrium and left ventricle and allow one to grade the progression of diastolic dysfunction which occurs in disease states. Doppler tissue imaging is necessary as a surrogate of ventricular relaxation to further determine the stages of diastolic dysfunction in patients with preserved ejection fraction. These Doppler flow velocity curves can be applied to understanding diastolic filling of the heart in patients with both reduced ejection fraction and preserved ejection fraction.

Phosphodiesterase-5 inhibitors and the heart: compound cardioprotection?

Novel cardioprotective agents are needed in both heart failure (HF) and myocardial infarction. Increasing evidence from cellular studies and animal models indicate protective effects of phosphodiesterase-5 (PDE5) inhibitors, drugs usually reserved as treatments of erectile dysfunction and pulmonary arterial hypertension. PDE5 inhibitors have been shown to improve contractile function in systolic HF, regress left ventricular hypertrophy, reduce myocardial infarct size and suppress ischaemia-induced ventricular arrhythmias. Underpinning these actions are complex but increasingly understood cellular mechanisms involving the cyclic GMP activation of protein kinase-G in both cardiac myocytes and the vasculature. In clinical trials, PDE5 inhibitors improve symptoms and ventricular function in systolic HF, and accumulating epidemiological data indicate a reduction in cardiovascular events and mortality in PDE5 inhibitor users at high cardiovascular risk. Here, we focus on the translation of underpinning basic science to clinical studies and report that PDE5 inhibitors act through a number of cardioprotective mechanisms, including a direct myocardial action independent of the vasculature. We conclude that future clinical trials should be designed with these mechanisms in mind to identify patient subsets that derive greatest treatment benefit from these novel cardioprotective agents.

Roles of A-Kinase Anchoring Proteins and Phosphodiesterases in the Cardiovascular System

A-kinase anchoring proteins (AKAPs) and cyclic nucleotide phosphodiesterases (PDEs) are essential enzymes in the cyclic adenosine 3′-5′ monophosphate (cAMP) signaling cascade. They establish local cAMP pools by controlling the intensity, duration and compartmentalization of cyclic nucleotide-dependent signaling. Various members of the AKAP and PDE families are expressed in the cardiovascular system and direct important processes maintaining homeostatic functioning of the heart and vasculature, e.g., the endothelial barrier function and excitation-contraction coupling. Dysregulation of AKAP and PDE function is associated with pathophysiological conditions in the cardiovascular system including heart failure, hypertension and atherosclerosis. A number of diseases, including autosomal dominant hypertension with brachydactyly (HTNB) and type I long-QT syndrome (LQT1), result from mutations in genes encoding for distinct members of the two classes of enzymes. This review provides an overview over the AKAPs and PDEs relevant for cAMP compartmentalization in the heart and vasculature and discusses their pathophysiological role as well as highlights the potential benefits of targeting these proteins and their protein-protein interactions for the treatment of cardiovascular diseases.

The impact of ambrisentan and tadalafil upfront combination therapy on cardiac function in scleroderma associated pulmonary arterial hypertension patients: cardiac magnetic resonance feature tracking study

The aim of this study was to evaluate the effect of upfront combination therapy with ambrisentan and tadalafil on left ventricular (LV) and right ventricular (RV) function in patients with systemic sclerosis-associated pulmonary arterial hypertension (SSc-PAH). LV and RV peak longitudinal and circumferential strain and strain rate (SR), which consisted of peak systolic SR (SRs), peak early diastolic SR (SRe), and peak atrial-diastolic SR (SRa) were analyzed using cardiac magnetic resonance imaging (CMRI) data from the recently published ATPAHSS-O trial (ambrisentan and tadalafil upfront combination therapy in SSc-PAH). Twenty-one patients completed the study protocol. Measures of RV systolic function (RV free wall [RVFW] peak longitudinal strain [pLS], RVFW peak longitudinal SRs [pLSRs]) and RV diastolic function (RVFW peak longitudinal SRa [pLSRa], RVFW peak circumferential SRe) were improved after treatment. LV systolic function (LV peak global longitudinal strain [pGLS]) and diastolic function (LV peak global longitudinal SRe [pGLSRe]) were also significantly improved at follow-up. Increased 6-min walk distance was significantly correlated with RVFW pLS and pLSRs, while the decrease in N-terminal pro-brain natriuretic peptide was correlated with LV pGLS. Increased cardiac index was associated with improved LV pGLSRe, and reduction in mean right atrial pressure was correlated with improved RVFW pLS and pLSRa. Combination therapy was associated with a significant improvement in both RV and LV function as assessed by CMR-derived strain and SR. Importantly, the improvement in RV and LV strain and SR correlated with improvements in known prognostic markers of PAH. (Approved by clinicaltrials.gov [NCT01042158] before patient recruitment.)

Use of β-Blockers in Pulmonary Hypertension

Contrasting with the major attention that left heart failure has received, right heart failure remains understudied both at the preclinical and clinical levels. However, right ventricle failure is a major predictor of outcomes in patients with precapillary pulmonary hypertension because of pulmonary arterial hypertension, and in patients with postcapillary pulmonary hypertension because of left heart disease. In pulmonary hypertension, the status of the right ventricle is one of the most important predictors of both morbidity and mortality. Paradoxically, there are currently no approved therapies targeting the right ventricle in pulmonary hypertension. By analogy with the key role of β-blockers in the management of left heart failure, some authors have proposed to use these agents to support the right ventricle function in pulmonary hypertension. In this review, we summarize the current knowledge on the use of β-blockers in pulmonary hypertension.

The effects of pulmonary vasodilating agents on right ventricular parameters in severe group 3 pulmonary hypertension: a pilot study

Pulmonary arterial hypertension (PAH)-approved vasodilators improve right ventricular (RV) function in patients with PAH. However, whether PAH-approved drugs ameliorate RV morphology and function in lung disease-associated pulmonary hypertension (lung-PH) remains unclear. We aimed to prospectively evaluate the changes in RV volume and ejection fraction (RVEF) in 14 consecutive severe lung-PH patients treated with PAH-approved vasodilators. Severe lung-PH was defined as a mean pulmonary arterial pressure (MPAP) of ≥35 mmHg or an MPAP of ≥25 mmHg with a cardiac index (L/min/m²) of <2. Right heart catheterization and cardiac magnetic resonance (CMR) imaging were performed at baseline and at 3 months after starting sildenafil with or without other PAH-approved drugs. Follow-up was conducted at 3 months in 11 participants; compared with baseline values, MPAP and pulmonary vascular resistance (PVR) decreased by 18% and 37%, respectively. Baseline CMR imaging revealed an elevated RV end-diastolic volume index (RVEDVI; mL/m²) of 117.5 ± 35.9 and a below-average RVEF of 25.2% ± 7.2%; after 3 months, RVEDVI decreased by 23.7% (P = 0.0061) and RVEF increased by 32.9% (P = 0.0165). Among the 11 patients, 3 were thought to be a stable and homogenous subset in terms of background lung disease and medical management administered. These 3 patients exhibited similar ameliorations in PVR and RVEF, compared with the other 8 patients. PAH-approved drug treatment may improve RV dilatation and systolic function among patients with severe lung-PH. This study was approved by University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) on September 1, 2013 (UMIN000011541).

Ventricular-Arterial Function and Coupling in the Adult Fontan Circulation

Background

In adult Fontan patients, ventricular or arterial dysfunction may impact homeostasis of the Fontan circulation and predispose to heart failure. We sought to characterize ventricular‐arterial (VA) properties in adult Fontan patients.

Methods and Results

Adult Fontan patients (n=170), including those with right (SRV, n=57) and left (SLV, n=113) dominant ventricular morphology, were compared to age, sex, and body size matched controls (n=170). Arterial function, load‐insensitive measures of contractility, VA coupling, diastolic function, and ventricular efficiency were assessed. Compared to controls, Fontan patients had similar arterial (Ea), but lower end‐systolic ventricular (Ees), elastance, preload recruitable stroke work and peak power index, impaired VA coupling, eccentric remodeling, reduced ventricular efficiency and increased diastolic stiffness (P<0.05 for all). Ventricular efficiency declined steeply with higher heart rate in Fontan, but not control, patients. Among Fontan patients (n=123) and controls (n=162) with preserved cardiac index (CI; ≥2.5 L/min per m²), Fontan patients had worse contractility than controls, but CI was preserved owing to relative tachycardia, lower afterload, and eccentric remodeling. However, 25% of Fontan patients had reduced CI and were distinguished from those with preserved CI by less‐eccentric remodeling and worse diastolic function, rather than more‐impaired contractility.

Conclusions

Adult Fontan patients have contractile and diastolic dysfunction with normal afterload, impaired VA coupling, and reduced ventricular efficiency with heightened sensitivity to heart rate. Maintenance of CI is dependent on lower afterload, eccentric remodeling, and relative preservation of diastolic function. These data contribute to our understanding of circulatory physiology in adult Fontan patients.

Early Hemodynamic Improvement after Percutaneous Mitral Valve Repair Evaluated by Noninvasive Pressure-Volume Analysis

BACKGROUND

Mitral regurgitation represents a volume load on the left ventricle leading to congestion and symptoms of heart failure. The aim of this study was to characterize early hemodynamic adaptions after percutaneous mitral valve (MV) repair.

METHODS

Forty-six consecutive patients with symptomatic high-grade MV insufficiency (mean age, 72 years; 54% men) were prospectively included in the study and examined before and after successful catheter-based clip implantation. Seventy percent of patients had secondary mitral regurgitation. Noninvasive pressure-volume loops were reconstructed from echocardiography with simultaneous blood pressure measurements.

RESULTS

MV repair reduced left ventricular end-diastolic volume index from 87 ± 41 to 80 ± 40 mL/m(2) (P < .0001). End-systolic volume index was 55 ± 37 mL/m(2) before versus 54 ± 37 mL/m(2) after repair (P = .52). Hence, total stroke volume decreased from 60 ± 23 to 49 ± 16 mL (P < .0001), as did total ejection fraction (from 41 ± 14% to 37 ± 13%, P = .002) and global longitudinal strain (from -11 ± 4.9% to -9.1 ± 4.4%, P = .0001). Forward stroke volume, forward ejection fraction, and forward cardiac output remained constant (43 ± 12 mL vs 42 ± 11 mL, 33 ± 17% vs 35 ± 18%, and 3.2 ± 0.9 L/min vs 3.4 ± 0.8 L/min, respectively). Parameters of left ventricular contractility (end-systolic elastance and peak power index) and measurements of afterload (arterial elastance, end-systolic wall stress, and total peripheral resistance) were similar before and after MV repair. Forward ejection fraction correlated more strongly with end-systolic elastance (r = 0.61, P < .0001) than did total ejection fraction (r = 0.35, P = .0007) or global longitudinal strain (r = -0.38, P = .0002). Total mechanical energy (pressure-volume area) decreased from 10,903 ± 4,410 to 9,124 ± 2,968 mm Hg × mL (P = .0007) because of reduced stroke work (5,546 ± 2,241 mm Hg × mL vs 4,414 ± 1,412 mm Hg × mL, P < .0001). At 3 months, symptom status had improved (76% of patients in New York Heart Association classes I and II), and 97% of patients had mitral regurgitation grade ≤2+.

CONCLUSIONS

Left ventricular contractility and forward cardiac output remained unchanged after percutaneous MV repair despite decreases in total ejection fraction and global longitudinal strain. The left ventricle was unloaded through reduced end-diastolic volume. Thus, MV repair is associated with an improved hemodynamic state in noninvasive pressure-volume analysis.

Old dog, new tricks: novel cardiac targets and stress regulation by protein kinase G

The second messenger cyclic guanosine 3'5' monophosphate (cGMP) and its downstream effector protein kinase G (PKG) have been discovered more than 40 years ago. In vessels, PKG1 induces smooth muscle relaxation in response to nitric oxide signalling and thus lowers systemic and pulmonary blood pressure. In platelets, PKG1 stimulation by cGMP inhibits activation and aggregation, and in experimental models of heart failure (HF), PKG1 activation by inhibiting cGMP degradation is protective. The net effect of the above-mentioned signalling is cardiovascular protection. Yet, while modulation of cGMP-PKG has entered clinical practice for treating pulmonary hypertension or erectile dysfunction, translation of promising studies in experimental HF to clinical success has failed thus far. With the advent of new technologies, novel mechanisms of PKG regulation, including mechanosensing, redox regulation, protein quality control, and cGMP degradation, have been discovered. These novel, non-canonical roles of PKG1 may help understand why clinical translation has disappointed thus far. Addressing them appears to be a requisite for future, successful translation of experimental studies to the clinical arena.

Sildenafil in heart failure with reactive pulmonary hypertension (Sildenafil HF) clinical trial (rationale and design)

In this article, we present the rationale and design of the Sildenafil HF trial (ClinicalTrials.gov identifier: NCT02304705). We will randomize patients with heart failure and reactive pulmonary hypertension (pulmonary capillary wedge pressure > 15 mmHg, pulmonary vascular resistance > 3 Wood units) into two groups: the treatment group receiving sildenafil 20 mg 3 times a day and a matching placebo group. The duration of intervention will be 3 months. The primary outcome is 6-minute walk distance. Key features of this trial include (1) that reactive pulmonary hypertension is an inclusion criterion, (2) that patients will be enrolled regardless of left ventricular ejection fraction, and (3) that clinical stability in the 3 months preceding enrollment is not required.

Everything you ever wanted to know about phosphodiesterase 5 inhibitors and the heart (but never dared ask): How do they work?

INTRODUCTION

Phosphodiesterase 5 inhibitors (PDE5i) were developed while investigating novel treatments for coronary artery disease, but their andrological side effects shifted their indication toward the management of erectile dysfunction. Although PDE5i are now also indicated for pulmonary arterial hypertension and there are mounting preclinical and clinical evidences about their potentially beneficial cardiac effects, their use remains controversial and the involved mechanisms remain unclear.

MATERIALS AND METHODS

This review aimed to analyze the effects of PDE5i administration in various animal and humans models of cardiovascular diseases.

RESULTS

Animal studies have shown that PDE5i have protective effects in several models of cardiac disease. In humans, some studies showed that PDE5i improves microvascular and endothelial dysfunction and exerts positive effects in different samples of cardiovascular (CV) impairment. In contrast, other studies found no benefit (and no harm) in heart failure with preserved ejection fraction. The discrepancies in these findings are likely related to the fact that the mechanisms targeted by PDE5i in human disease are still poorly understood and the target population not yet identified. The mechanisms of actions herein reviewed suggest that hypertrophy, microvascular impairment, and inflammation, should be variably present for PDE5i to work. All these conditions frequently coexist in diabetes. A gender responsiveness has also been recently proposed.

CONCLUSIONS

Continuous PDE5 inhibition may exert cardioprotective effects, improving endothelial function and counteracting cardiac remodeling in some but not all conditions. A better patient selection could help to clarify the controversies on PDE5i use for CV disorders.

Pulmonary Hypertension in Heart Failure Patients Presenting at OAUTHC, Ile-Ife, Nigeria

Background

Pulmonary hypertension (PH) is common in heart failure patients. Literature on PH in heart failure is sparse in Nigeria. This study was carried out to determine the prevalence of PH in heart failure patients and ascertain the relationship between left ventricular systolic and diastolic function and the degree of PH.

Methods

A total of 125 heart failure patients had echocardiography done. PH was diagnosed using tricuspid regurgitation jet and pulmonary ejection jet profile.

Results

PH was present in 70.4% of heart failure patients. Estimated mean pulmonary arterial pressure increased with increasing severity of systolic and diastolic dysfunction and had significantly negative correlation with ejection fraction, fractional shortening, and early mitral annular tissue diastolic velocity ( E′), but positive correlation with left ventricular end-systolic volume, right ventricular dimension, transmitral E to A ratio, and E/E′ ratio.

Conclusion

PH is very common in heart failure and has significant relationship with left ventricular function.

Cardiac Adrenergic Nervous System and Left Ventricular Remodeling

Heightened cardiac adrenergic nervous system (ANS) activity and progression of left ventricular (LV) remodeling are temporally related in patients with systolic heart failure. Whether cardiac ANS activation directly contributes to or merely accompanies LV remodeling remains an unresolved issue. Human and experimental data that directly link cardiac ANS activation to LV remodeling and worsening heart failure are first reviewed, including cardiac norepinephrine spillover. Alterations of beta adrenergic receptor signaling pathways are then addressed with emphasis on the mechanisms that may mediate the beneficial effect of beta adrenergic receptor blockade on LV remodeling. Lastly, alternative approaches to beta adrenergic receptor blockade for lessening cardiac ANS activation and reversing cardiac ANS-induced LV remodeling are discussed. A large body of work now links LV remodeling to cardiac ANS activation. However, the precise mechanisms that link cardiac ANS activation to LV remodeling are still to be fully understood. Fully understanding of these mechanisms may uncover new therapeutic approaches.

Sepiapterin prevents left ventricular hypertrophy and dilatory remodeling induced by pressure overload in rats

Uncoupling of nitric oxide (NO) synthase (NOS) has been implicated in left ventricular (LV) hypertrophy (LVH) and dilatory remodeling induced by pressure overload. We investigated whether administration of sepiapterin, a substrate of the salvage pathway of tetrahydrobiopterin synthesis, prevents LVH and dilatory LV remodeling by inhibiting NOS uncoupling and increasing bioavailable NO. Pressure overload was induced in rats by transverse aortic constriction (TAC). Concentric LVH developed during 8 wk after TAC, and dilatory LV remodeling and dysfunction developed between 8 and 16 wk after TAC associated with a decrease in capillary density. Oral administration of sepiapterin or the superoxide/peroxynitrite scavenger N-(2-mercaptopropionyl)-glycine for 8 wk after TAC inhibited oxidative stress, but only sepiapterin increased bioavailable NO and inhibited cardiomyocyte hypertrophy associated with a further increase in capillary density. When sepiapterin was administered between 8 and 16 wk after TAC, cardiomyocyte hypertrophy was regressed and capillary density was restored. This was associated with the inhibition of interstitial fibrosis and dilatory LV remodeling. N-nitro-l-arginine methyl ester abrogated all the beneficial effects of sepiapterin in rats with TAC. These results suggest that sepiapterin prevents concentric LVH and dilatory remodeling after TAC primarily by increasing the bioavailability of NO.

[Phosphodiesterase-5 inhibitors for the treatment of pulmonary arterial hypertension]

In experimental and clinical cardiology, phosphodiesterase type 5 (PDE-5) inhibitors have brought scientific interest as a therapeutic tool in pulmonary arterial hypertension (PAH) management in recent years. Phosphodiesterases are a superfamily of enzymes that inactivate cyclic adenosine monophosphate and cyclic guanosine monophosphate, the second messengers of prostacyclin and nitric oxide. The rationale for the use of PDE-5 inhibitors in PAH is based on their capacity to overexpresss the nitric oxide pathway pursued inhibition of cyclic guanosine monophosphate hydrolysis. By increasing cyclic guanosine monophosphate levels it promotes vasodilation, antiproliferative and pro-apoptotic effects that may reverse pulmonary vascular remodeling. There is also evidence that these drugs may directly enhance right ventricular contractility through an increase in cyclic adenosine monophosphate mediated by the inhibition of the cyclic guanosine monophosphate -sensitive PDE-3. Sildenafil, tadalafil and vardenafil are 3 specific PDE-5 inhibitors in current clinical use, which share similar mechanisms of action but present some significant differences regarding potency, selectivity for PDE-5 and pharmacokinetic properties. Sildenafil received approval in 2005 by the Food and Drug Administration and the European Medicines Agency and tadalafil in 2009 by the Food and Drug Administration and the European Medicines Agency for the treatment of PAH in patients classified as NYHA/WHO functional class II and III. In Mexico, sildenafil and tadalafil were approved by Comisión Federal de Protección contra Riesgos Sanitarios for this indication in 2010 and 2011, respectively.

Inhibition of type 5 phosphodiesterase counteracts β2-adrenergic signalling in beating cardiomyocytes

AIMS

Compartmentalization of cAMP and PKA activity in cardiac muscle cells plays a key role in maintaining basal and enhanced contractility stimulated by sympathetic nerve activity. In cardiomyocytes, activation of adrenergic receptor increases cAMP production, which is countered by the hydrolytic activity of selective phosphodiesterases (PDEs). The intracellular regional dynamics of cAMP production and hydrolysis modulate downstream signals resulting in different biological responses. The interplay between beta receptors (βARs) signalling and phosphodiesterase 5 (PDE5) activity remains to be addressed.

METHODS AND RESULTS

Using combined strategies with pharmacological inhibitors and genetic deletion of PDEs and βAR isoforms, we revealed a specific pool of cAMP that is under dual regulation by PDE2 and, indirectly, PDE5 activity. Inhibition of PDE5 with sildenafil produces a cGMP-dependent activation of PDE2 that attenuates cAMP generation induced by βAR agonists, with concomitant modulation of stimulated contraction rate and calcium transients. PDE2 haploinsufficiency abolished the effects of sildenafil. The negative chronotropic effect of PDE5 inhibition through PDE2 activation was also observed in sinoatrial node tissue from adult mice. PDE5 inhibition selectively lowered contraction rate stimulated by β2AR, but not β1AR activation, supporting a compartmentalization of the cGMP-modulated pool of cAMP.

CONCLUSION

These data identify a new effect of PDE5 inhibitors on the modulation of cardiomyocyte response to adrenergic stimulation via PDE5-PDE2-mediated cross-talk.

Therapeutic effects of udenafil on pressure-overload cardiac hypertrophy

This study was performed to determine whether the newly developed phosphodiesterase type 5 (PDE5) inhibitor udenafil had beneficial effects on pressure-overload cardiac hypertrophy. Pressure overload cardiac hypertrophy was created by using suprarenal aortic constriction (SAC) in male Sprague-Dawley rats. Rats were divided into three groups: sham (n=19), SAC (n=18) and SAC+udenafil (n=14) groups. Three-week periods of SAC provoked significant left ventricular (LV) hypertrophy. Udenafil was administered (20 mg kg(-1) PO, daily) between the 3rd and 20th weeks after SAC in the SAC+udenafil group. Udenafil improved the survival rate (log-rank P=0.012) and exercise capacity (maximal exercise duration at the 20th week after surgery: 448±54 s for the SAC+udenafil group versus 317±73 s for the SAC group, P<0.05) of the rats with SAC. Serial echocardiographic examinations showed that udenafil attenuated LV remodeling processes following SAC (mean LV end-diastolic dimension at the 20th week after surgery: 9.84±0.59 mm for SAC and 9.05±0.58 mm for SAC+udenafil group, P<0.05). Invasive hemodynamic studies showed that udenafil improved the LV performance. Udenafil-attenuated myocardial fibrosis and apoptosis. Udenafil also decreased myocardial matrix metalloproteinase-9 expression and augmented serum interleukin-10 concentration. Long-term udenafil use prevented cardiac remodeling and improved exercise capacity and survival in rats exposed to pressure-overload cardiac hypertrophy.

Effects of sildenafil on ventricular and vascular function in heart failure with preserved ejection fraction

BACKGROUND

Early studies showed beneficial effects of phosphodiesterase 5 inhibitors on cardiovascular function in heart failure (HF) patients, but the RELAX trial observed no improvement in exercise capacity with sildenafil treatment in subjects with HF and preserved ejection fraction.

METHODS AND RESULTS

A subgroup of participants in the RELAX trial (n=48) underwent comprehensive noninvasive cardiovascular assessment before and after treatment with sildenafil or placebo in a prospective ancillary study. Left ventricular contractility was assessed by peak power index and stroke work index. Systemic arterial load was assessed by arterial elastance (Ea) and right ventricular afterload by pulmonary artery systolic pressure. Endothelial function was assessed by reactive hyperemia index after upper arm cuff occlusion. Compared with placebo (n=25), sildenafil (n=23) decreased Ea (-0.29±0.28 mm Hg/mL versus +0.02±0.29, P=0.008) and tended to improve reactive hyperemia index (+0.30±0.45 versus -0.17±0.30, P=0.054). In contrast, left ventricular contractility was reduced by 11% to 16% with sildenafil compared with placebo (ΔPWR/EDV -52±70 versus +0±40 mm Hg/s, P=0.006; ΔSW/EDV +0.3±5.8 versus -6.0±5.1 mm Hg, P=0.04). Sildenafil had no effect on pulmonary artery systolic pressure.

CONCLUSIONS

In subjects with HF and preserved ejection fraction, sildenafil displayed opposing effects on ventricular and vascular function. We speculate that beneficial effects of phosphodiesterase 5 inhibitors in the systemic vasculature and endothelium were insufficient to improve clinical status or that the deleterious effects on left ventricular function offset any salutary vascular effects, contributing to the absence of benefit observed with sildenafil in subjects with HF and preserved ejection fraction in the RELAX trial.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00094302.

A novel in vivo approach to assess radial and axial distensibility of large and intermediate pulmonary artery branches

Pulmonary arteries (PAs) distend to accommodate increases in cardiac output. PA distensibility protects the right ventricle (RV) from excessive increases in pressure. Loss of PA distensibility plays a critical role in the fatal progression of pulmonary arterial hypertension (PAH) toward RV failure. However, it is unclear how PA distensibility is distributed across the generations of PA branches, mainly because of the lack of appropriate in vivo methods to measure distensibility of vessels other than the large, conduit PAs. In this study, we propose a novel approach to assess the distensibility of individual PA branches. The metric of PA distensibility we used is the slope of the stretch ratio-pressure relationship. To measure distensibility, we combined invasive measurements of mean PA pressure with angiographic imaging of the PA network of six healthy female dogs. Stacks of 2D images of the PAs, obtained from either contrast enhanced magnetic resonance angiography (CE-MRA) or computed tomography digital subtraction angiography (CT-DSA), were used to reconstruct 3D surface models of the PA network, from the first bifurcation down to the sixth generation of branches. For each branch of the PA, we calculated radial and longitudinal stretch between baseline and a pressurized state obtained via acute embolization of the pulmonary vasculature. Our results indicated that large and intermediate PA branches have a radial distensibility consistently close to 2%/mmHg. Our axial distensibility data, albeit affected by larger variability, suggested that the PAs distal to the first generation may not significantly elongate in vivo, presumably due to spatial constraints. Results from both angiographic techniques were comparable to data from established phase-contrast (PC) magnetic resonance imaging (MRI) and ex vivo mechanical tests, which can only be used in the first branch generation. Our novel method can be used to characterize PA distensibility in PAH patients undergoing clinical right heart catheterization (RHC) in combination with MRI.

Effects of PDE type 5 inhibitors on left ventricular diastolic dysfunction in resistant hypertension

Resistant hypertension (RHTN) is a multifactorial disease characterized by blood pressure (BP) levels above goal (140/90 mmHg) in spite of the concurrent use of three or more antihypertensive drugs of different classes. Moreover, it is well known that RHTN subjects have high prevalence of left ventricular diastolic dysfunction (LVDD), which leads to increased risk of heart failure progression. This review gathers data from studies evaluating the effects of phosphodiesterase-5 (PDE-5) inhibitors (administration of acute sildenafil and short-term tadalafil) on diastolic function, biochemical and hemodynamic parameters in patients with RHTN. Acute study with sildenafil treatment found that inhibition of PDE-5 improved hemodynamic parameters and diastolic relaxation. In addition, short-term study with the use of tadalafil demonstrated improvement of LVDD, cGMP and BNP-32 levels, regardless of BP reduction. No endothelial function changes were observed in the studies. The findings of acute and short-term studies revealed potential therapeutic effects of IPDE-5 drugs on LVDD in RHTN patients.

Is chronic inhibition of phosphodiesterase type 5 cardioprotective and safe? A meta-analysis of randomized controlled trials

BACKGROUND

The myocardial effects of phosphodiesterase type 5 inhibitors (PDE5i) have recently received consideration in several preclinical studies. The risk/benefit ratio in humans remains unclear.

METHODS

We performed a meta-analysis of randomized, placebo-controlled trials (RCTs) to evaluate the efficacy and safety of PDE5i on cardiac morphology and function. From March 2012 to December 2013 (update: May 2014), we searched English-language studies from MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials and SCOPUS-selecting RCTs of continuous PDE5i administration that reported cardiovascular outcomes: cardiac geometry and performance, afterload, endothelial function and safety. The pooled estimate of a weighted mean difference between treatment and placebo was obtained for all outcomes using a random effects model. A test for heterogeneity was performed and the I2 statistic calculated.

RESULTS

Overall, 1,622 subjects were treated, with 954 randomized to PDE5i and 772 to placebo in 24 RCTs. According to our analysis, sustained PDE5 inhibition produced: (1) an anti-remodeling effect by reducing cardiac mass (-12.21 g/m2, 95% confidence interval (CI): -18.85; -5.57) in subjects with left ventricular hypertrophy (LVH) and by increasing end-diastolic volume (5.00 mL/m2; 95% CI: 3.29; 6.71) in non-LVH patients; (2) an improvement in cardiac performance by increasing cardiac index (0.30 L/min/m2, 95% CI: 0.202; 0.406) and ejection fraction (3.56%, 95% CI: 1.79; 5.33). These effects are parallel to a decline of N-terminal-pro brain natriuretic peptide (NT-proBNP) in subjects with severe LVH (-486.7 pg/ml, 95% CI: -712; -261). PDE5i administration also produced: (3) no changes in afterload parameters and (4) an improvement in flow-mediated vasodilation (3.31%, 95% CI: 0.53; 6.08). Flushing, headache, epistaxis and gastric symptoms were the commonest side effects.

CONCLUSIONS

This meta-analysis suggests for the first time that PDE5i have anti-remodeling properties and improve cardiac inotropism, independently of afterload changes, with a good safety profile. Given the reproducibility of the findings and tolerability across different populations, PDE5i could be reasonably offered to men with cardiac hypertrophy and early stage heart failure. Given the limited gender data, a larger trial on the sex-specific response to long-term PDE5i treatment is required.

Sildenafil does not improve cardiomyopathy in Duchenne/Becker muscular dystrophy

OBJECTIVE

Duchenne and Becker muscular dystrophies (DBMD) are allelic disorders caused by mutations in dystrophin. Adults with DBMD develop life-threatening cardiomyopathy. Inhibition of phosphodiesterase 5 (PDE5) improves cardiac function in mouse models of DBMD. To determine whether the PDE5-inhibitor sildenafil benefits human dystrophinopathy, we conducted a randomized, double-blind, placebo-controlled trial (ClinicalTrials.gov, number NCT01168908).

METHODS

Adults with DBMD and cardiomyopathy (ejection fraction ≤ 50%) were randomized to receive sildenafil (20mg 3× daily) or placebo for 6 months. All subjects received an additional 6 months of open-label sildenafil. The primary endpoint was change in left ventricular end-systolic volume (LVESV) on cardiac magnetic resonance imaging. Secondary cardiac endpoints, skeletal muscle function, and quality of life were also assessed.

RESULTS

An interim analysis (performed after 15 subjects completed the blinded phase) revealed that 29% (4 of 14) of subjects had a ≥10% increase in LVESV after 6 months of sildenafil compared to 13% (1 of 8) of subjects receiving placebo. Subjects with LVESV > 120ml at baseline were more likely to worsen at 12 months regardless of treatment assignment (p = 0.035). Due to the higher number of subjects worsening on sildenafil, the data and safety monitoring board recommended early termination of the study. There were no statistically significant differences in outcome measures between treatment arms.

INTERPRETATION

Due to the small sample size, comparisons between groups must be interpreted with caution. However, this trial suggests that sildenafil is unlikely to improve cardiac function in adults with DBMD.

PDE5 inhibitor efficacy is estrogen dependent in female heart disease

Inhibition of cGMP-specific phosphodiesterase 5 (PDE5) ameliorates pathological cardiac remodeling and has been gaining attention as a potential therapy for heart failure. Despite promising results in males, the efficacy of the PDE5 inhibitor sildenafil in female cardiac pathologies has not been determined and might be affected by estrogen levels, given the hormone's involvement in cGMP synthesis. Here, we determined that the heart-protective effect of sildenafil in female mice depends on the presence of estrogen via a mechanism that involves myocyte eNOS-dependent cGMP synthesis and the cGMP-dependent protein kinase Iα (PKGIα). Sildenafil treatment failed to exert antiremodeling properties in female pathological hearts from Gαq-overexpressing or pressure-overloaded mice after ovary removal; however, estrogen replacement restored the effectiveness of sildenafil in these animals. In females, sildenafil-elicited myocardial PKG activity required estrogen, which stimulated tonic cardiomyocyte cGMP synthesis via an eNOS/soluble guanylate cyclase pathway. In contrast, eNOS activation, cGMP synthesis, and sildenafil efficacy were not estrogen dependent in male hearts. Estrogen and sildenafil had no impact on pressure-overloaded hearts from animals expressing dysfunctional PKGIα, indicating that PKGIα mediates antiremodeling effects. These results support the importance of sex differences in the use of PDE5 inhibitors for treating heart disease and the critical role of estrogen status when these agents are used in females.

Therapeutic potential of PDE modulation in treating heart disease

Altered cyclic nucleotide-mediated signaling plays a critical role in the development of cardiovascular pathology. By degrading cAMP/cGMP, the action of cyclic nucleotide PDEs is essential for controlling cyclic nucleotide-mediated signaling intensity, duration, and specificity. Altered expression, localization and action of PDEs have all been implicated in causing changes in cyclic nucleotide signaling in cardiovascular disease. Accordingly, pharmacological inhibition of PDEs has gained interest as a treatment strategy and as an area of drug development. While targeting of certain PDEs has the potential to ameliorate cardiovascular disease, inhibition of others might actually worsen it. This review will highlight recent research on the physiopathological role of cyclic nucleotide signaling, especially with regard to PDEs. While the physiological roles and biochemical properties of cardiovascular PDEs will be summarized, the primary emphasis will be pathological. Research into the potential benefits and hazards of PDE inhibition will also be discussed.