The effects of intravenous sildenafil on hemodynamics and cardiac sympathetic activity in chronic human heart failure

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.

PDE5 Inhibitors in Type 2 Diabetes Cardiovascular Complications

Pharmacological inhibition of Phosphodiesterase type 5 (PDE5) proved its efficacy treating several pathological conditions, such as erectile dysfunction and pulmonary hypertension. Nowadays, its benefits on cardiovascular diseases are well documented, particularly in the treatment of type 2 diabetes (T2DM)-related cardiovascular complications. In this context, treatment of T2DM with PDE5 inhibitors, such as sildenafil, tadalafil or vardenafil ameliorates endothelial dysfunction both in patients and animal models through an augmented flow mediated dilation rate and an up-regulation of endothelial markers; it also reduces the inflammatory state by down-regulating inflammatory cytokines expression and improves diabetic cardiomyopathy and ischemia-reperfusion injury mainly through the activation of NO-cGMP-PKG pathway. The present review summarizes the state of art on PDE5 inhibition in the treatment of cardiovascular complications in T2DM.

Effects of phosphodiestrase type 5 inhibitors in epinephrine-induced arrhythmia in rats: Involvement of lactate dehydrogenase and creatine kinase downregulation and adiponectin expression

Cardiac arrhythmia is a common cause of mortality, and its progression may be due to abnormal sympathetic nerve activity and catecholamine release. Besides, lactate dehydrogenase (LDH) and creatine kinase (CK) downregulation and adiponectin expression play important roles in promoting coronary artery disease. The study aimed to examine the possible cardioprotective effect of members of phosphodiesterase type 5 (PDE-5) inhibitors in epinephrine-induced arrhythmia in rats. Arrhythmia was induced by cumulative boluses of epinephrine (4, 8, 16, 32, 64, and 128 mg/kg) given at 10-min intervals. Rats were randomly allocated into five groups. Group I: Normal control group received only saline. Group II: Rats injected with epinephrine and served as arrhythmia group. Groups III, IV, and V: Rats received daily oral sildenafil (0.5 mg/kg), vardenafil (3 mg/kg), and tadalafil (10 mg/kg), respectively, for 30 days prior to epinephrine injections. Injection of epinephrine to rats decreased heart rate and QTc interval but increased RR interval and duration of arrhythmia. Epinephrine group had lower serum reduced glutathione (GSH) and adiponectin levels and higher serum malondialdehyde (MDA), nitric oxide (NO), heart LDH, and CK contents. Histopathological investigations of epinephrine group provoked necrotic changes with strong positive immunoreactivity for caspases-3. While pretreatment of rats with PDE-5 inhibitors improved GSH and adiponectin contents, ameliorated serum MDA and NO levels and heart LDH and CK contents and corrected epinephrine-induced histopathological changes. PDE-5 inhibitors may delay epinephrine-induced arrhythmia through expression of adiponectin and downregulation of heart LDH and CK.

Inhaled therapy for the management of perioperative pulmonary hypertension

Patients with pulmonary hypertension (PH) are at high risk for complications in the perioperative setting and often receive vasodilators to control elevated pulmonary artery pressure (PAP). Administration of vasodilators via inhalation is an effective strategy for reducing PAP while avoiding systemic side effects, chiefly hypotension. The prototypical inhaled pulmonary-specific vasodilator, nitric oxide (NO), has a proven track record but is expensive and cumbersome to implement. Alternatives to NO, including prostanoids (such as epoprostenol, iloprost, and treprostinil), NO-donating drugs (sodium nitroprusside, nitroglycerin, and nitrite), and phosphodiesterase inhibitors (milrinone, sildenafil) may be given via inhalation for the purpose of treating elevated PAP. This review will focus on the perioperative therapy of PH using inhaled vasodilators.

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.

Sildenafil increases sympathetically mediated vascular tone in humans

BACKGROUND

Sildenafil, a selective phosphodiesterase-type-5 (PDE-5) inhibitor, produces vasodilation that improves erectile dysfunction and pulmonary hypertension. Sildenafil could also cause baroreflex sympathetic activation that would enhance vascular tone and oppose direct vasodilation. We tested the hypothesis that sildenafil administration increases sympathetically mediated vascular tone in healthy middle-aged men.

METHODS

We randomized 9 healthy, middle-aged, male volunteers (mean age 45±2 years) in a double-blind, crossover fashion to receive a single oral dose of sildenafil 100mg or placebo on 2 separate study days. Hemodynamics and forearm blood flow responses were measured at baseline, at 30 and 45 minutes after study drug administration, and then during intra-arterial infusions of vasoactive drugs. After sildenafil and placebo administration, intrabrachial medications were infused to test forearm alpha receptor sensitivity (norepinephrine), cyclic-AMP-mediated vasodilation (isoproterenol), and sympathetically mediated vascular tone (phentolamine) (adenosine was a control vasodilator). Blood samples were taken before and 60 minutes after study drug administration and at the end of the intrabrachial infusions for measurement of plasma norepinephrine concentrations.

RESULTS

Forearm vascular responses to norepinephrine, isoproterenol, and adenosine were not different after placebo and sildenafil administration. Percentage reduction in forearm vascular resistance during phentolamine was significantly lower after sildenafil than placebo (-73% ± 3% vs -63% ± 3%; P = 0.0002). Sildenafil significantly increased plasma norepinephrine compared with placebo 60 minutes after study drug administration and at the end of the study session (P = 0.02).

CONCLUSIONS

Sildenafil increased sympathetically mediated vascular tone in middle-aged healthy men. Alpha-adrenergic-mediated vasoconstriction may offset vasodilation during PDE-5 inhibition and may explain the significant hypotension observed in patients taking alpha-blockers with sildenafil.

Phosphodiesterase 5 inhibition-induced coronary vasodilation is reduced after myocardial infarction

The balance between the production and removal of cGMP in coronary vascular smooth muscle is of critical importance in determining coronary vasomotor tone and thus in the regulation of coronary blood flow. cGMP production by soluble guanylyl cyclase is activated by nitric oxide (NO), whereas cGMP breakdown occurs through phosphodiesterase 5 (PDE5). We hypothesized that myocardial infarction (MI) alters the balance between the production and removal of cGMP in the coronary vasculature and thereby alters the control of coronary vasomotor tone. Chronically instrumented swine with and without a 2-wk-old MI were exercised on a treadmill in the absence and presence of the PDE5 inhibitor EMD-360527 (300 μg·kg−1·min−1 iv). Inhibition of PDE5 produced coronary resistance vessel dilation, which was more pronounced at rest than during exercise in normal swine. PDE5 gene expression was markedly reduced in coronary resistance vessels isolated from the remote myocardium of MI swine, which was accompanied by a similarly marked attenuation of coronary vasodilation by PDE5 inhibition in MI swine. The coronary vasoconstriction produced by inhibition of NO synthesis with Nω-nitro-l-arginine (20 mg/kg iv) was only slightly smaller in swine with MI. Interestingly, inhibition of NO synthesis reduced the vasodilator response to subsequent PDE5 inhibition in normal swine but not in MI swine. Conversely, PDE5 inhibition enhanced the coronary vasoconstriction produced by NO synthesis inhibition in normal swine but not in MI swine, suggesting that downregulation of PDE5 mitigated the loss of NO vasodilator influence. In conclusion, the expression and vasoconstrictor influence of PDE5 are markedly attenuated in coronary resistance vessels in the remote myocardium after MI, which appears to serve as a compensatory mechanism to mitigate the loss of NO vasodilator influence.

Effect of sildenafil on ventricular arrhythmias in post-infarcted rat hearts

We have demonstrated that activation of ATP-sensitive potassium (K(ATP)) channels can attenuate sympathetic hyperinnervation. Sildenafil, a phosphodiesterase-5 inhibitor, has been shown to provide a preconditioning-like cardioprotective effect via opening of K(ATP) channels. The aim of this study was to investigate whether chronic administration of sildenafil attenuates cardiac sympathetic hyperinnervation after myocardial infarction through activation of K(ATP) channels and to compare it with the nitric oxide donor isosorbide dinitrate. Male Wistar infarcted rats induced by ligation of the anterior descending artery were randomized to either vehicle, nicorandil, sildenafil, isosorbide dinitrate, glibenclamide, or a combination of nicorandil and glibenclamide, or sildenafil and glibenclamide. Myocardial norepinephrine levels revealed a significant elevation in vehicle-treated rats compared with sham-operated rats, consistent with sympathetic hyperinnervation after infarction assessed by immunohistochemical analysis for tyrosine hydroxylase, growth associated factor 43 and neurofilament and by protein expression and mRNA of nerve growth factor. Sympathetic hyperinnervation was reduced after administering either nicorandil or sildenafil. Arrhythmic scores during programmed stimulation in the sildenafil-treated rats were significantly lower than those treated with the vehicle. Furthermore, the beneficial effects of sildenafil-induced were reversed by the addition of either glibenclamide or 5-hydroxydecanoate, implicating mitochondrial K(ATP) channels as the relevant target. Isosorbide dinitrate failed to confer similar antiarrhythmia. 1H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one, a soluble guanylyl cyclase inhibitor, did not influence the effect of sildenafil on the nerve growth factor. These data indicate that sildenafil after infarction attenuated sympathetic hyperinnervation and arrhythmias by activation of mitochondrial K(ATP) channels through a guanylyl cyclase-cGMP-independent pathway.

The effect of sildenafil on cisplatin nephrotoxicity in rats

Sildenafil, the first drug for erectile dysfunction, has cardiopulmonary protective actions. A recent study has reported that sildenafil given intraperitoneally (i.p.) attenuated cisplatin (CP)-induced nephrotoxicity. Here, we evaluated whether sildenafil, given by two different routes and at two different doses, can attenuate CP-induced nephrotoxicity and would also affect renal haemodynamics in CP-treated rats. Six groups of rats were treated with saline (controls), CP [5 mg/kg, intraperitoneally (i.p.) once], sildenafil (0.4 mg/kg/day, i.p. for 5 days), sildenafil (0.4 mg/kg/day i.p. for 5 days) plus CP (5 mg/kg, i.p., once), sildenafil [10 mg/kg/day, subcutaneous (s.c.) for 5 days] or sildenafil (10 mg/kg/day, s.c. for 5 days) plus CP (5 mg/kg, i.p. once). Five days after the end of the treatments, urine was collected from all rats, which were then anaesthetized for blood pressure and renal blood flow monitoring. This was followed by intravenous (i.v.) injection of norepinephrine for the measurement of renal vasoconstrictor responses. Thereafter, blood and kidneys were collected for measurement of several biochemical, functional and structural parameters. CP reduced body-weight and renal blood flow but did not affect norepinephrine-induced renal vasoconstriction. It increased the plasma concentrations of urea and creatinine, and reduced creatinine clearance. CP caused extensive renal tubular necrosis, increased urine volume and N-acetyl-β-D-glucosaminidase activity. When sildenafil (0.4 mg/kg/day, i.p. for 5 days) was combined with cisplatin, there was a dramatic improvement in renal histopathology, reduction in N-acetyl-β-D-glucosaminidase and increase in renal blood flow. However, sildenafil (10 mg/kg/day, s.c. for 5 days) did not affect CP nephrotoxicity, suggesting the importance of dose and route selection of sildenafil as a nephroprotectant.

Sildenafil Is More Selective Pulmonary Vasodilator Than Prostaglandin E1 in Patients With Pulmonary Hypertension Due to Heart Failure

In some patients, heart failure (HF) is associated with increased pulmonary vascular resistance (PVR). The magnitude and the reversibility of PVR elevation affect the HF management. Sildenafil has been recently recognized as potent PVR-lowering drug in HF. The aim of the study was to compare hemodynamic effects and pulmonary selectivity of sildenafil to prostaglandin E1 (PGE1). Right-heart catheterization was performed in 13 euvolemic advanced HF patients with elevated PVR (6.3±2 Wood´s units). Hemodynamic parameters were measured at the baseline, during i.v. infusion of PGE1 (alprostadil 200 ng∙kg-1∙min-1) and after 40 mg oral dose of sildenafil. Both drugs similarly reduced systemic vascular resistance (SVR), but sildenafil had higher effect on PVR (–28 % vs. –49 %, p=0.05) and transpulmonary pressure gradient than PGE1. The PVR/SVR ratio – an index of pulmonary selectivity, did not change after PGE1 (p=0.7) but it decreased by –32 % (p=0.004) after sildenafil. Both drugs similarly reduced pulmonary artery mean and wedge pressures and increased cardiac index (+27 % and +28 %). Sildenafil led more often to transplant-acceptable PVR while causing smaller drop of mean systemic pressure than PGE1. In conclusion, vasodilatatory effects of sildenafil in patients with heart failure are more pronounced in pulmonary than in systemic circulation.

Transpulmonary B-type natriuretic peptide uptake and cyclic guanosine monophosphate release in heart failure and pulmonary hypertension: the effects of sildenafil

OBJECTIVES

We sought to identify factors that discriminate heart failure (HF) patients with normal and elevated pulmonary vascular resistance (PVR) and to elucidate the role of cyclic guanosine monophosphate (cGMP)-dependent vasodilation.

BACKGROUND

Mechanisms of PVR increase in patients with chronic HF are incompletely understood.

METHODS

Twenty-two HF patients with high pulmonary vascular resistance (H-PVR) (>200 dyn.s.cm(-5)) were compared with 24 matched low pulmonary vascular resistance (L-PVR) patients of similar age, sex, body size, HF severity, and volume status who were undergoing invasive hemodynamic study. Pulmonary arterial (PA) and venous blood samples from a wedged PA catheter were used to calculate transpulmonary B-type natriuretic peptide (BNP) uptake and cGMP release. The H-PVR patients were re-examined 1 h after a 40-mg oral dose of sildenafil.

RESULTS

Although transpulmonary BNP uptake was similar (p = 0.2), cGMP release was diminished in the H-PVR patients (-1.9 vs. 27.8 nmol.min(-1); p = 0.005). Transpulmonary BNP uptake and cGMP release correlated in the L-PVR patients (R = 0.6, p = 0.004) but not in the H-PVR. The H-PVR patients also had lower PA compliance, systemic arterial compliance (by 47% and 20%, p < 0.001 and p < 0.03), and cardiac index. Sildenafil reduced PVR (-47%), systemic resistance (-24%) and heart rate (-8%), increased cardiac index (+24%), and PA compliance (+87%, all p < 0.001), with a parallel increase of cGMP release (from -5.6 to 16.5 nmol.min(-1), p = 0.047), without affecting BNP uptake or norepinephrine(PA). The PVR response was not dependent on PA wedge pressure or pulmonary hypertension reversibility with prostaglandin E(1).

CONCLUSIONS

The H-PVR patients have stiffening of both pulmonary and systemic arteries, preserved transpulmonary BNP uptake, but diminished cGMP release, which is reversible by the administration of sildenafil. This study provides in vivo evidence that phosphodiesterase 5A inhibition restores sensitivity of pulmonary vasculature to endogenous cGMP-dependent vasodilators.

Acute hemodynamic effects of intravenous sildenafil citrate in congestive heart failure: comparison of phosphodiesterase type-3 and -5 inhibition

BACKGROUND

The reversibility of elevated pulmonary vascular resistance in heart failure bears an important relation to outcome after cardiac transplantation. The phosphodiesterase 3 (PDE3) and PDE5 inhibitors both increase levels of cyclic nucleotides in the vascular smooth muscle, causing vasodilatation. PDE3 inhibitors also have direct inotropic effects. We contrasted the acute hemodynamic responses to intravenous PDE3 and PDE5 inhibitors in patients with congestive cardiac failure to assess their relative suitability for reversibility testing in this setting.

METHODS

Thirty patients undergoing assessment for cardiac transplantation underwent right heart catheterization. Patients were randomized to receive an intravenous bolus of milrinone (0.05 mg/kg) or sildenafil citrate at a high (0.43 mg/kg) or low dose (0.05 mg/kg).

RESULTS

Differences between low- and high-dose sildenafil were not significant. Both agents caused similar reductions in systemic and pulmonary vascular resistance. Milrinone caused significantly greater reductions in pulmonary artery wedge and mean pulmonary artery pressure, and increases in heart rate. In all study groups, greater increases in cardiac index (>25%) were seen in patients with a higher pulmonary artery wedge pressure at baseline (29 +/- 1 vs 20 +/- 2 mm Hg; p < 0.001).

CONCLUSIONS

In end-stage congestive cardiac failure, intravenous milrinone and sildenafil both cause similar reductions in systemic and pulmonary vascular resistance; however, milrinone has more cardiac selective effects on left ventricular filling and heart rate. Both agents appear to have a suitable hemodynamic profile for testing of reversibility of secondary pulmonary hypertension in congestive cardiac failure. Larger studies are needed to confirm these results.

Erectile dysfunction and heart failure: the role of phosphodiesterase type 5 inhibitors

The phosphodiesterase type 5 (PDE-5) inhibitors are effective in treating erectile dysfunction (ED). ED and heart failure (HF) share similar risk factors, and commonly present together. This association has led to questions ranging from the safety and efficacy of PDE-5 inhibitors in HF patients to a possible role for this class of medication to treat HF patients with or without ED. In addition to endothelial dysfunction, there are causes of ED specific to patients with HF including low exercise tolerance, depression and HF medications. Before treating HF patients with PDE-5 inhibitors, patients should be assessed for their risk of a cardiac event during sexual activity. PDE-5 inhibitors are safe and effective in treating ED in HF patients. An improvement in erectile function by PDE-5 inhibitors was associated with an improvement in quality of life and reduction in depression. Several studies demonstrated the effect of PDE-5 inhibitors on HF per se. PDE-5 inhibitors improved endothelial dysfunction, increased exercise tolerance, decreased pulmonary vascular resistance and pulmonary artery pressure, and increased cardiac index. Several mechanisms whereby PDE-5 inhibitors improve HF have been proposed. PDE-5 inhibitors already have a role in treating primary pulmonary hypertension; however additional studies are needed to determine if they will become a standard therapy for HF patients.