Hemodynamic and exercise effects of phosphodiesterase 5 inhibitors

Safety of Phosphodiesterase-5 Inhibitors in Valvular Heart Disease

ABSTRACT

Erectile dysfunction is a common entity in clinical practice. Primary erectile dysfunction, not related to vasculopathy or psychiatric disorder, can be readily treated with phosphodiesterase inhibitors. These drugs have many physiologic effects that can alter a patient's hemodynamic profile considerably, especially in the presence of concomitant structural heart disease, specifically valvular heart disease. Although some contraindications to the use of PDE5 inhibitors in patients with cardiovascular disease are defined, the effect of these drugs in the presence of valvular heart disease is not well documented. The purpose of this review is to analyze the data regarding the safety of PDE5 inhibitors in patients with valvular heart disease.

The effect of tadalafil on functional capacity and echocardiographic parameters in patients with repaired Tetralogy of Fallot

BACKGROUND

Tetralogy of Fallot (TOF) is one of the most common cyanotic congenital heart diseases (CHD) in children. Various surgical procedures including palliative shunts and TOF total correction (TFTC) were done with some complications, of which, the most common is pulmonary valve regurgitation (PR). Tadalafil is a phosphodiesterase 5 inhibitor which reduces pulmonary vascular resistance, and improves right ventricular function and vascular endothelium, and may have some beneficial effects after TFTC.

METHODS

We studied 18 patients with TOF and PR, with some impaired right ventricular function after TFTC. Tadalafil tablets at a dose of 1 mg per kg (maximum 40 mg) per day as a single dose was administered orally for 8 weeks. In all patients, before and after taking tadalafil, functional class assessment, electrocardiography (ECG) changes, some echocardiographic and endothelial function parameters [flow-mediated dilation (FMD) and intima-media thickness (IMT) of carotid artery], and exercise test were determined.

RESULTS

The patient's mean age was 10.11 ± 4.03 years, and the mean age of operation was 2.52 ± 1.12 years. The effect of tadalafil on different echocardiographic parameters and also on tricuspid valve regurgitation (TR) and PR severity and gradient was not significant. Moreover, it had no effects on QRS duration. Tadalafil had a significant effect on improving FMD and exercise test (P = 0.01). The effect of tadalafil on echocardiographic parameters, carotid artery IMT, and ECG parameters was not significant (P > 0.05). Tadalafil was tolerated well, and the most common side effects were headache and myalgia.

CONCLUSION

This study showed that tadalafil is a safe and well-tolerated drug. It might improve exercise performance, endothelial function, and functional class, and possibly could allow patients a longer period of well-being and could possibly delay the need for pulmonary valve replacement (PVR).

Effect of Tadalafil on Myocardial and Endothelial Function and Exercise Performance After Modified Fontan Operation

Better postoperative management of patients who have undergone single ventricle (SV) Fontan procedure could potentially reduce long-term complications and improve the quality of life for patients. The present study determined the effect of tadalafil on myocardial and endothelial function and exercise performance after modified Fontan operation. Patients who had undergone SV modified Fontan operation were enrolled in this clinical trial. The demographic characteristics of the patients were recorded. Before administration of tadalafil and after the trial, ventricular function (MPI, EF, FS, E/A, VTI), exercise performance, and endothelial function were evaluated for sonographic and biochemical markers (FMD, IMT, ICAM, VCAM, NO) using echocardiography, exercise testing, vascular ultrasonography, and biochemical measurements, respectively. A single dose of tadalafil of 1 mg/kg was administered daily for 6 weeks, and the functional class of the patients before and after tadalafil was determined. A total of 15 patients completed this clinical trial. Tadalafil was shown to have a significant effect on myocardial function, exercise performance, and improvement in NYHA functional class (p < 0.05) of study population. It had no significant effect on the biochemical variables and endothelial function except for IMT (p > 0.05), which decreased significantly after tadalafil administration (p < 0.05). The findings indicate that tadalafil is a safe, well-tolerated agent for the use after modified Fontan operation to improve myocardial function and exercise performance and possibly reduce long-term morbidity and mortality of patients. More conclusive results could be obtained from further study with a larger sample size and long-term follow-up.

Mechanism of endothelial cyto-protective and thrombo-resistance effects of sildenafil, vardenafil and tadalafil in male rabbit

INTRODUCTION

PDE5 inhibitors (PDE5inhs) have proven to be of great impact in the treatment of numerous human extra-sexual diseases and their chronic use may induce endothelial rehabilitation. This study aimed to assess the effects of PDE5inhs at chronic administration to explore the possible endothelial cyto-protective and thrombo-resistance effects.

MATERIAL AND METHODS

One hundred New Zealand white male rabbits were divided into four groups. The first group (control, C) received 1 ml saline/kg, the second group (S) received 10 mg/kg sildenafil, the third group (V) received 2 mg/kg vardenafil, and the fourth group (T) received 2 mg/kg tadalafil in saline I.P. three times weekly for 4 weeks. Blood samples were collected and plasma was isolated for determination of 2,3-dinor-6-keto-prostaglandin F-1α (PGF1α), 11-dehydro-TXB2 (TXB2), fibrinogen, calcium levels, prothrombin (PT), and thrombin times (TT).

RESULTS

PDE5inhs significantly increase PGF1α, calcium levels, PT and TT (p < 0.001) when compared with baseline data or with the saline group at the end of treatment. In contrast, PDE5inhs significantly decrease TXB2 and fibrinogen levels (p < 0.001) when compared either with their baseline data or with the saline group at the end of treatment. The tadalafil group showed a lower increase in PGF1α (p < 0.001), lower decrease in TXB2 (p < 0.001), and higher increase in calcium levels (p < 0.01, p < 0.05), lower increase in PT and TT levels (p < 0.001) when compared with sildenafil or vardenafil.

CONCLUSIONS

The prolonged use of PDE5inhs has time-dependent mild to moderate endothelial cyto-protective, thrombo-resistance anti-inflammatory and anti-nociception effects via activation of endothelial NOS (eNOS), increase of PGI2 synthesis and decrease of fibrinogen with significant increase in PT and TT.

Prediction of Cardiovascular Events With Aortic Stiffness in Patients With Erectile Dysfunction

Erectile dysfunction confers an independent risk for cardiovascular events and total mortality. Aortic pulse wave velocity (PWV) is an important predictor of cardiovascular events and all-cause mortality. We investigated whether PWV predicts major adverse cardiovascular events (MACEs) in patients with erectile dysfunction beyond traditional risk factors. MACEs in relation to PWV were analyzed with proportional hazards models in 344 patients (mean age, 56 years) without established cardiovascular disease. During a mean follow-up of 4.7 years (range, 1–8.5 years), 24 of 344 participants (7.0%) experienced a MACE. Subjects in the highest PWV tertile (>8.8 m/s) had a 4-fold higher risk of MACEs compared with those in the lowest PWV tertile (<7.6 m/s; adjusted hazard ratio, 3.97; P =0.035). A PWV value of 7.81 m/s was associated with a negative predictive value (ability to rule out MACE) of 98.1%. Addition of PWV to standard risk factor model yielded correct patient reclassification to higher or lower risk category by 27.6% ( P =0.0332) in the whole cohort. Our results show that higher aortic stiffness is associated with increased risk for a MACE in patients with erectile dysfunction without known cardiovascular disease. Aortic PWV improves risk prediction when added to standard risk factors and may represent a valuable biomarker of prediction of cardiovascular disease risk in these patients.

Sildenafil enhances locomotor activity in young mice and exerts anxiogenic effects in both young and aged mice

Background

Sildenafil is a selective PDE5 inhibitor that increases cGMP levels in the target tissues and is an effective treatment agent for erectile dysfunction. The nitric oxide-cGMP pathway might be implicated in regulation of certain CNS functions, including locomotor activity and anxiety.

Material/Methods

The aim of the current study was to investigate effects of sildenafil (3 and 10 mg/kg) on anxiety and locomotor activity in open field and elevated plus maze (EPM) tests in young and aged mice.

Results

Sildenafil (3 and 10 mg/kg) significantly decreased the percent of time spent in the open arms compared to the control group in young animals in the EPM test, but only the 10 mg/kg dose significantly decreased the percentage of total number of entries to the open arms in young animals. Sildenafil (3 and 10 mg/kg) significantly decreased the percentage of total number of entries to the open arms in aged animals in the EPM test, but it significantly increased total distance moved and speed of the animals in the locomotor activity test in young animals. The total distance moved and the speed of the animals significantly decreased in aged animals compared to the young control group, although sildenafil (3 and 10 mg/kg) did not alter these parameters in aged mice.

Conclusions

Our results show that sildenafil had anxiogenic effects in young as well as aged mice, but it enhanced locomotor activity only in the young mice in the EPM test. Thus, sildenafil seems to exert different effects on anxiety and locomotion in young and aged animals.

cGMP-dependent protein kinases and cGMP phosphodiesterases in nitric oxide and cGMP action

To date, studies suggest that biological signaling by nitric oxide (NO) is primarily mediated by cGMP, which is synthesized by NO-activated guanylyl cyclases and broken down by cyclic nucleotide phosphodiesterases (PDEs). Effects of cGMP occur through three main groups of cellular targets: cGMP-dependent protein kinases (PKGs), cGMP-gated cation channels, and PDEs. cGMP binding activates PKG, which phosphorylates serines and threonines on many cellular proteins, frequently resulting in changes in activity or function, subcellular localization, or regulatory features. The proteins that are so modified by PKG commonly regulate calcium homeostasis, calcium sensitivity of cellular proteins, platelet activation and adhesion, smooth muscle contraction, cardiac function, gene expression, feedback of the NO-signaling pathway, and other processes. Current therapies that have successfully targeted the NO-signaling pathway include nitrovasodilators (nitroglycerin), PDE5 inhibitors [sildenafil (Viagra and Revatio), vardenafil (Levitra), and tadalafil (Cialis and Adcirca)] for treatment of a number of vascular diseases including angina pectoris, erectile dysfunction, and pulmonary hypertension; the PDE3 inhibitors [cilostazol (Pletal) and milrinone (Primacor)] are used for treatment of intermittent claudication and acute heart failure, respectively. Potential for use of these medications in the treatment of other maladies continues to emerge.

Usefulness of noninvasive estimate of pulmonary vascular resistance to predict mortality, heart failure, and adverse cardiovascular events in Patients With stable coronary artery disease (from the Heart and Soul Study)

Pulmonary vascular resistance (PVR) is an important hemodynamic variable that affects prognosis and therapy in a wide range of cardiovascular and pulmonary conditions. We sought to determine whether a noninvasive estimate of PVR predicts adverse outcomes in patients with stable coronary artery disease. Using Doppler echocardiography we measured the estimated PVR (defined as the ratio of the tricuspid regurgitant velocity [TRV] to the velocity-time integral [VTI] of the right ventricular outflow tract [RVOT]) in 795 ambulatory patients with stable coronary artery disease. Participants were categorized by quartiles of the TRV/VTI RVOT ratio. Hazard ratios (HRs) and 95% confidence intervals were calculated for all-cause mortality, heart failure hospitalization, and adverse cardiovascular events (cardiovascular death, nonfatal myocardial infarction, or stroke). After 4.3 years of follow-up there were 161 deaths, 44 deaths from cardiovascular causes, 103 heart failure hospitalizations, and 120 adverse cardiovascular events. Compared with patients in the lowest TRV/VTI RVOT quartile, those in the highest quartile were at increased risk of all-cause mortality (unadjusted HR 1.8, 95% confidence interval 1.3 to 2.5), heart failure hospitalization (unadjusted HR 2.9, 95% confidence interval 2.0 to 4.3), and adverse cardiovascular events (unadjusted HR 2.0, 95% confidence interval 1.4 to 2.9). After multivariate adjustment, patients in the highest quartile were at increased risk of heart failure hospitalizations (adjusted HR 2.5, 95% confidence interval 1.3 to 4.7). In conclusion, a noninvasive estimate of PVR (TRV/VTI RVOT ratio) predicts mortality, heart failure hospitalization, and adverse cardiovascular events in patients with stable coronary artery disease.

Acute effects of a single dose of phosphodiesterase type 5 inhibitor (sildenafil) on systemic arterial blood pressure during exercise and 24-hour ambulatory blood pressure monitoring in heart transplant recipients

BACKGROUND

Arterial systemic hypertension (SH) can be associated with a decrease in endothelium-dependent nitric oxide (NO). Sildenafil increases cyclic guanosine monophosphate (cGMP), a mediator of NO. However, little is known about the effects of PDE5 inhibition on 24-hour ambulatory pressure (ABP) and exercise blood pressure, noreprinephrine (Nor), and exercise capacity, especially after orthotopic heart transplantation (OHT).

METHODS

We studied 22 OHT patients who on the 1st day underwent a cardiopulmonary (CP) self-controlled treadmill 6' walk test (6') and, then, an ECG monitored CP treadmill maximal exercise test (Ex) within 60 and 90 minutes after oral Sildenafil (Sil; 50 mg) or placebo (Pl) given at random, and ABP. We determined at basal position (b), in the last minute of the 6' and at the peak Ex, the HR (bpm), Systolic blood pressure (SBP), and diastolic blood pressure (DBP), (mm Hg), VO2 (mL/kg/min), Slope VE/VCO2, exercise time (ET, min), distance (D; miles), and Nor (pg/mL). Also, after CP tests, 24-h SBP and DBP, the measurements were repeated on the 2nd day when the cross-over was done.

RESULTS

Sil significantly reduced blood pressure in the basal position and during exercise. It also promoted a significant reduction in SBP and DBP during 24 hours, daytime and nighttime. Sil did not change exercise capacity.

CONCLUSION

The NO-cGMP pathway seems to play a role in blood pressure control in OHT. In addition to antihypertensive therapy, PDE5 inhibition may have potential beneficial effects on hypertensive OHT.

Daily Administration of Phosphodiesterase Type 5 Inhibitors for Urological and Nonurological Indications

OBJECTIVES

Although the discovery of phosphodiesterases (PDEs) was made soon after the identification of cyclic adenosine monophosphate nearly half a century ago, their true importance in medicine has taken many decades to be realised. The recognition of the important role PDE enzymes play and the impact of altering intracellular cyclic nucleotide levels became significant for most urologists and clinicians in the early 1990s with the discovery of sildenafil, a PDE5 inhibitor (PDE5-I). Once approved around the world, on-demand use of PDE5-Is became the gold standard. Recently, the potential beneficial effects of PDE5-Is on the pulmonary, vascular, and other systems has led to examination of alternative dosing regimens. In this review, we have synthesised the available published peer-reviewed literature to provide a critical contemporary view of evolving indications for PDE5-Is and how alternative dosing regimens may impact on sexual and other functions.

METHODS

MEDLINE search of all peer-reviewed English literature for the period 1990-2007.

RESULTS

The plethora of articles detailing potential uses of PDE5-I in multiple fields of medicine was uncovered. Use of alternative dosing regimens shows great promise across a number of clinical indications, including post-radical retropubic prostatectomy, pulmonary hypertension, endothelial dysfunction, and salvage of on-demand PDE5-I nonresponders.

CONCLUSIONS

Use of PDE5-I on a daily basis may evolve into a major form of drug administration both for men with erectile dysfunction and for those with a myriad of other conditions shown to benefit from this approach.

Expression of the PDE5 enzyme on human retinal tissue: new aspects of PDE5 inhibitors ocular side effects

OBJECTIVE

We tested the effect of two phosphodiesterase type-5 (PDE5) inhibitors, sildenafil and tadalafil, on ophthalmic artery (OA) blood flow velocity and investigated the presence of the PDE5 enzyme on human retinal tissue in comparison with the PDE6 enzyme localization.

METHODS

Using Colour Doppler ultrasonography (CDU) we investigated, in 30 healthy young subjects (27.8 years of age; range, 24.3-33.7 years), the effects of a single oral dose of sildenafil (100 mg), tadalafil (20 mg), and placebo on OA blood flow velocity. Western blot for PDE6 and PDE5 protein expression was performed on frozen samples of human retina, testis, sperm, skin, and corpus cavernosum. Immunohistochemistry was performed on two ocular globes from dead donors.

RESULTS

CDU showed a relationship between the administration of PDE5 inhibitors and OA blood flow velocity modifications in a time-dependent manner. Western blot and immunohistochemical analysis showed PDE6 and PDE5 presence in human retinal tissue and gave a map of its distribution.

CONCLUSION

We demonstrated that (a) tadalafil and sildenafil are able to modify the OA flux in a time-dependent manner; (b) the PDE5 enzyme is expressed on retinal and choroid vasculature (smooth muscle and endothelial cells), on ganglion and bipolar cells; (c) human retinal tissues express the PDE6 enzyme in the rod and cone photoreceptors; (d) visual side effects after PDE5 inhibitors administration may be linked to a specific effect on the PDE5 enzyme; and (e) the PDE5 enzyme may have a physiologic role on ganglion and bipolar cells that need to be further investigated.