Inhibition of angiotensin-converting enzyme and phosphodiesterase type 5 improves endothelial function in heart failure

Molecular Mechanisms and Therapeutic Implications of Endothelial Dysfunction in Patients with Heart Failure

Heart failure is a complex medical syndrome that is attributed to a number of risk factors; nevertheless, its clinical presentation is quite similar among the different etiologies. Heart failure displays a rapidly increasing prevalence due to the aging of the population and the success of medical treatment and devices. The pathophysiology of heart failure comprises several mechanisms, such as activation of neurohormonal systems, oxidative stress, dysfunctional calcium handling, impaired energy utilization, mitochondrial dysfunction, and inflammation, which are also implicated in the development of endothelial dysfunction. Heart failure with reduced ejection fraction is usually the result of myocardial loss, which progressively ends in myocardial remodeling. On the other hand, heart failure with preserved ejection fraction is common in patients with comorbidities such as diabetes mellitus, obesity, and hypertension, which trigger the creation of a micro-environment of chronic, ongoing inflammation. Interestingly, endothelial dysfunction of both peripheral vessels and coronary epicardial vessels and microcirculation is a common characteristic of both categories of heart failure and has been associated with worse cardiovascular outcomes. Indeed, exercise training and several heart failure drug categories display favorable effects against endothelial dysfunction apart from their established direct myocardial benefit.

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.

Endothelial Dysfunction in Patients with Advanced Heart Failure Treated with Levosimendan Periodic Infusion Compared with Optimal Medical Therapy: A Pilot Study

Endothelial dysfunction (ED) is frequently found in patients with heart failure (HF). Among several pharmacological agents reported to improve endothelial function, levosimendan seems to be a promising one, even though, to date, only two previously published studies have evaluated its effects on ED in these patients. The aim of our pilot study was to further investigate the role of periodic levosimendan infusion on endothelial function in patients affected by advanced HF. In this cross-sectional study, three different groups were enrolled: 20 patients with advanced HF treated with periodic levosimendan (LEVO), 20 patients with HF on optimal medical therapy (OMT), and 20 healthy subjects (control group). ED was evaluated through flow-mediated dilation (FMD) at the level of the brachial artery. The three groups presented similar ages with significant differences in gender distribution, systolic blood pressure, and chronic kidney disease (eGFR < 30 mL/min). In HF patients, ischaemic aetiology was more prevalent in the LEVO group than in the OMT group (60 vs. 40%, p < 0.001). The New York Heart Association (NYHA) functional class was worse in the LEVO group, as well as in NT-proBNP (5636.7 ± 6164.6 ng/dL and 1243.7 ± 1487.2 ng/dL, in the LEVO and OMT groups, respectively, p = 0.005). The FMD was significantly higher in the healthy control group compared to that of the OMT group (15.7 ± 6.4 vs. 9.1 ± 6.0%, p = 0.007) while it showed an intermediate value in LEVO patients (12.4 ± 7.1%) (ANOVA p = 0.010). In conclusion, levosimendan therapy seems to ameliorate endothelial dysfunction related to heart failure. Longitudinal studies in patients on periodic therapy are needed in order to confirm the long-term effects of levosimendan on ED.

Influence of lemon (Citrus limon) and lime (Citrus aurantifolia) juices on the erectogenic properties of sildenafil in rats with L-NAME-induced erectile dysfunction

The use of lemon (Citrus limon) and lime (Citrus aurantifolia) juices for the treatment of erectile dysfunction (ED) is fast becoming common practice, even though there is dearth of information on the effect of such functional food and drug combination in the management of ED. This study evaluated the effect of lemon and lime juices on the erectogenic properties of sildenafil. ED was induced with L-NAME (40 mg/kg body weight). The rats were divided into 11 groups (n = 6) and given various doses of the test samples. Immediately after the sexual behavior studies, the animals were sacrificed and the penile and brain tissues were isolated. The results revealed that lime and lemon juices improved sexual behavior in rats by improving NO production and inhibiting the activities of PDE-5, arginase, ACE, MAO, ATPdase, AMPdase, and activated antioxidant enzymes. Furthermore, lime at 1.0 ml/kg significantly improved the therapeutic properties of sildenafil. While, lemon (0.5 and 1.0 ml/kg) and lime (0.5 ml/kg) did not show any synergistic effect. This study revealed that lime and lemon juices could improve erectile function and combining lime juice with sildenafil could be very effective in the management of ED. PRACTICAL APPLICATIONS: The therapeutic management of erectile dysfunction has involved maximizing NO production through the modulation of macromolecules such as phosphodiesterase-5 and arginase with the use of drugs such as sildenafil. Combining such drugs with functional foods such as lime and lemon juices is becoming common practice. However, there is dearth of report on the effect of lime and lemon juices on the erectogenic potentials of sildenafil. The present study shows that combining 1 ml/kg lime juice (got from 2 lime fruits) with sildenafil will boost the erectogenic properties of the drug. While combining lime (0.5 ml/kg) and lemon (0.5 and 1.0 ml/kg) juices with the drug did not have any synergistic effect.

Fig (Ficus exasperata and Ficus asperifolia)-Supplemented diet improves sexual function, endothelial nitric oxide synthase and suppresses tumour necrosis factor-alpha genes in hypertensive rats

We measured the effect of varieties of Fig leaves, Ficus exasperata Vahl. (FE) and Ficus asperifolia Miq (FA), commonly found in Sub-sahara Africa for managing hypertension on sexual performance in hypertensive rats, which is unknown. Hypertensive rats experienced erectogenic damage after exposure to 40 mg kg^-1  bw^-1 , N(G)-nitro-l-arginine-methyl-ester (L-NAME). Experimental rats were grouped into eight groups (n = 6) namely: control rats, hypertensive rats, hypertensive treatment groups with atenolol (10 mg kg^-1  day^-1 ) and sildenafil (5.0 mg/kg), rats treated with FE- and FA-formulated biscuits at proportions of 2.5 g and 5.0 g respectively. Furthermore, we measured the level of sexual performance (Intromission number, latency, Mounting number, and latency), hormonal levels, phosphodiesterase-5 enzyme (PDE-5) activity and genes expressed using real-time quantitative polymerase chain reaction (RT-qPCR) in hypertensive rats. The result deduced revealed that treated hypertensive rats showed significantly reduced follicle-stimulating hormone, luteinising hormone levels, PDE-5 enzyme activity, tumour necrosis factor-alpha (TNF-α) expression while having a marked increase in testosterone level, sexual performance and endothelial nitric oxide synthase (eNOS) expression. Therefore, this study revealed the comparative dietary enhancing effect of FE- and FA-formulated biscuit on sexual behaviour activity, hormonal levels and the level of eNOS and TNF-α genes expressed in hypertensive rats.

Nox2+ myeloid cells drive vascular inflammation and endothelial dysfunction in heart failure after myocardial infarction via angiotensin II receptor type 1

AIMS

Heart failure (HF) ensuing myocardial infarction (MI) is characterized by the initiation of a systemic inflammatory response. We aimed to elucidate the impact of myelomonocytic cells and their activation by angiotensin II on vascular endothelial function in a mouse model of HF after MI.

METHODS AND RESULTS

HF was induced in male C57BL/6J mice by permanent ligation of the left anterior descending coronary artery. Compared to sham, HF mice had significantly impaired endothelial function accompanied by enhanced mobilization of Sca-1+c-Kit+ haematopoietic stem cells and Sca-1-c-Kit+ common myeloid and granulocyte-macrophage progenitors in the bone marrow as well as increased vascular infiltration of CD11b+Ly6G-Ly6Chigh monocytes and accumulation of CD11b+ F4/80+ macrophages, assessed by flow cytometry. Using mice with Cre-inducible expression of diphtheria toxin receptor in myeloid cells, we selectively depleted lysozyme M+ myelomonocytic cells for 10 days starting 28 days after MI. While the cardiac phenotype remained unaltered until 38 days post-MI, myeloid cell depletion attenuated vascular accumulation of Nox2+CD45+ cells, endothelial dysfunction, oxidative stress, and vascular expression of adhesion molecules and angiotensin II receptor type 1 (AT1R). Pharmacological blockade of this receptor for 4 weeks did not significantly alter cardiac function, but mimicked the effects of myeloid cell depletion: telmisartan (20 mg/kg/day, fed to C57BL/6J mice) diminished bone marrow myelopoesis and myeloid reactive oxygen species production, attenuated endothelial leucocyte rolling and vascular accumulation of CD11b+Ly6G-Ly6Chigh monocytes and macrophages, resulting in improved vascular function with less abundance of Nox2+CD45+ cells.

CONCLUSION

Endothelial dysfunction in HF ensuing MI is mediated by inflammatory Nox2+ myeloid cells infiltrating the vessel wall that can be targeted by AT1R blockade.

Endothelial dysfunction and heart failure: A review of the existing bibliography with emphasis on flow mediated dilation

Heart failure affects 1–2% of the population worldwide, and it is characterized by episodes of decompensation often requiring hospitalization. Although targeted treatment has reduced the prevalence of rehospitalizations to 30–50%, mortality rates remain high. A complex blend of structural and functional alterations accounts for the genesis and progression of heart failure, but the exact underlying pathophysiology remains poorly understood. The aim of this review is to summarize endothelial dysfunction and its role in the pathogenesis and progression of heart failure. Moreover, it sums up all the appropriate methods of assessing endothelial dysfunction emphasizing on flow-mediated dilation and introduces endothelium as a potential target for new therapeutic development and research in the wide spectrum of the syndrome called heart failure.

Potentiation of the NO-cGMP pathway and blood flow responses during dynamic exercise in healthy humans

PURPOSE

Previous work has shown nitric oxide (NO) contributes to ~15% of the hyperemic response to dynamic exercise in healthy humans. This NO-mediated vasodilation occurs, in part, via increases in intracellular cyclic guanosine monophosphate (cGMP), which is catabolized by phosphodiesterase. We sought to examine the effect of phosphodiesterase-5 (PDE-5) inhibition on forearm blood flow (FBF) responses to dynamic handgrip exercise in healthy humans and the role of NO. We hypothesized exercise hyperemia would be augmented by sildenafil citrate (SDF, PDE-5 inhibitor). We further hypothesized any effect of SDF on exercise hyperemia would be abolished with intra-arterial infusion of the NO synthase (NOS) inhibitor L-N^G-monomethyl arginine (L-NMMA).

METHODS

FBF (Doppler ultrasound) was assessed at rest and during 5 min of dynamic forearm handgrip exercise at 15% of maximal voluntary contraction under control (saline) conditions and during 3 experimental protocols: (1) oral SDF (n = 10), (2) intra-arterial L-NMMA (n = 20), (3) SDF and L-NMMA (n = 10). FBF responses to intra-arterial sodium nitroprusside (NTP, NO donor) were also assessed.

RESULTS

FBF increased with exercise (p < 0.01). Intra-arterial infusion of L-NMMA resulted in a reduction in exercise hyperemia (17 ± 1 to 15 ± 1 mL/dL/min, p < 0.01). Although the hyperemic response to NTP was augmented by SDF (area under the curve: 41 ± 7 vs 61 ± 11 AU, p < 0.01), there was no effect of SDF on exercise hyperemia (p = 0.33).

CONCLUSIONS

Despite improving NTP-mediated vasodilation, oral SDF failed to augment exercise hyperemia in young, healthy adults. These observations reflect a minor contribution of NO and the cGMP pathway during exercise hyperemia in healthy young humans.

Additional use of a phosphodiesterase 5 inhibitor in patients with pulmonary hypertension secondary to chronic systolic heart failure: a meta-analysis

AIMS

Increased indiscriminate use of pulmonary artery hypertension-targeted drugs has been observed in patients with pulmonary hypertension (PH) secondary to heart failure. We performed a meta-analysis to evaluate the chronic effects of using phosphodiesterase 5 (PDE5) inhibitors to treat patients with PH secondary to chronic systolic heart failure.

METHODS AND RESULTS

PubMed, EMBASE, and the Cochrane Library were searched up to October 2013 for randomized controlled trials (RCTs) assessing PDE5 inhibitor treatments in PH patients secondary to chronic heart failure. Six RCTs involving 206 chronic systolic heart failure patients with PH complications were included. Sildenafil was used in all trials. Sildenafil treatment resulted in fewer hospital admissions compared with the placebo treatment (3.15% vs. 12.20%; risk ratio 0.29; 95% confidence interval 0.11-0.77). Various haemodynamic parameters were improved with additional sildenafil treatment, including reduced mean pulmonary artery pressure [weighted mean difference (WMD) -5.71 mmHg, P<0.05] and pulmonary vascular resistance (WMD -81.5 dynes/cm(-5), P<0.00001), increased LVEF (WMD 3.95%, P<0.01), and unchanged heart rate and blood pressure. The exercise capacity improved (oxygen consumption at peak exercise, WMD 3.20 mL/min(-1)/kg(-1), P<0.00001; ventilation to CO2 production slope, WMD -5.89, P<0.00001), and the clinical symptoms were relieved based on the breathlessness (WMD 7.72, P<0.00001), fatigue (WMD 2.28, P<0.05), and emotional functioning (WMD 5.92, P<0.00001) scores.

CONCLUSIONS

Additional sildenafil treatment is a potential therapeutic method to improve pulmonary exercise capacity and quality of life by ameliorating PH in patients with chronic systolic heart failure.

Comparative Effects of Preoperative Angiotensin-converting Enzyme In-hibitor, Statin and Beta-blocker Treatment on Human Internal Mammary Artery Reactivity in Patients with Coronary Artery Disease: A Pilot Study

PURPOSE

We investigated the effect of angiotensin-converting enzyme (ACE)- inhibitor, statin, and beta-blocker usage before coronary bypass surgery (CABG) on vascular reactivity of the internal mammary artery (IMA).

METHODS

Patients, who underwent elective CABG were evaluated. Samples of IMA obtained from 22 patients were divided into 4 groups in respect of drugs used by patients before bypass surgery (control group, ACE inhibitor + statin group, ACE inhibitor + statin + beta-blocker group, and ACE inhibitor + beta-blocker group). The discarded, distal end section of IMA was carefully removed, and the vasoreactivity of IMA rings was evaluated in vitro using an organ chamber. Smooth muscle contractile function was tested on artery segments exposed to 10-80 mM KCl and norepinephrine. The endothelial function of IMA rings was assessed with acetylcholine (ACh) and bradykinin, while endothelium-independent vasorelaxation was evaluated by sodium nitroprusside (SNP).

RESULTS

Both ACh and bradykinin caused concentration-dependent relaxation in endothelium-intact IMA rings. However, the maximal effect produced by endothelium-dependent agents in all treatment groups was more prominent when compared with the control group. There was no significant difference in the endothelium-dependent relaxation response of IMA between ACE inhibitor + statin, ACE inhibitor + beta-blocker and ACE inhibitor + statin + beta-blocker groups. The vasodilatory potency of SNP was similar in all groups. Similarly, contractile response to KCl or norepinephrine was not significantly different between groups.

CONCLUSION

Use of ACE inhibitors and statins before bypass surgery may influence IMA vasoreactivity by improving endothelial control of vascular tone.

Phosphodiesterase type 5 inhibitors as adjunctive therapy in the management of systolic heart failure

OBJECTIVE

To review the efficacy and safety of phosphodiesterase-5 (PDE5) inhibitors in the treatment of patients with chronic systolic heart failure (HF).

DATA SOURCES

Literature was retrieved through MEDLINE (1966-September 2011) and EMBASE (1980-September 2011), using the medical subject heading terms heart failure and phosphodiesterase-5 inhibitors, sildenafil, tadalafil, and vardenafil. Focus was placed on multidose trials of patients with systolic HF, because of these trials' greater strength of clinical evidence.

STUDY SELECTION AND DATA EXTRACTION

All English-language, peer-reviewed publications were analyzed for relevance. Studies appropriate to the objective were evaluated, including 4 multidose trials investigating the effect of sildenafil on cardiovascular function.

DATA SYNTHESIS

In patients with New York Heart Association class II or III HF, treatment with sildenafil was associated with improvements in cardiac index, right ventricular ejection fraction, and other markers of cardiovascular function, as well as reduced pulmonary arterial pressure. Study durations ranged from 4 weeks to 1 year, and the studies used varying doses of sildenafil, ranging from 75 to 225 mg/day, in divided doses. The most common adverse effects associated with sildenafil therapy were headache and flushing.

CONCLUSIONS

Based on current studies, sildenafil appears to be well tolerated and can improve markers of cardiovascular and pulmonary function in patients with HF. PDE5 inhibitors may be a therapeutic option for patients who cannot tolerate standard therapy for HF or who remain symptomatic with standard therapy. Larger long-term trials are necessary to better understand the role of PDE5 inhibitors in HF.

Acute effects of sildenafil on flow mediated dilatation and cardiovascular autonomic nerve function in type 2 diabetic patients

BACKGROUND

Sildenafil, frequently used as on demand medication for the treatment of erectile dysfunction (ED), has been suggested to improve endothelial function but also to alter blood pressure (BP) and induce sympathetic activation. In people with type 2 diabetes mellitus (T2DM), a high-risk population, the safety profile and the effects on endothelial function of a maximal sildenafil dose (100 mg) have not been investigated and therefore constituted the aim of our study.

METHODS

A double-blind, placebo-controlled, cross-over trial using a single dose of 100 mg sildenafil or placebo has been conducted in 40 subjects with T2DM without known CVD. Haemodynamic parameters, flow mediated dilatation (FMD) in brachial artery, cardiovascular autonomic function tests and spontaneous baroreflex sensitivity (BRS) were measured.

RESULTS

Sixty minutes after administration of sildenafil but not placebo, a fall of supine systolic blood pressure (SBP) (-5.41 +/- 1.87 vs. + 0.54 +/- 1.71 mmHg) and diastolic blood pressure (DBP) (-4.46 +/- 1.13 vs. + 0.89 +/- 0.94 mmHg), as well as orthostatic SBP (-7.41 +/- 2.35 vs. + 0.94 +/- 2.06 mmHg) and DBP (-5.65 +/- 1.45 vs. + 1.76 +/- 1.00 mmHg) during standing occurred, accompanied by an increase in heart rate (+1.98 +/- 0.69 vs. - 2.42 +/- 0.59 beats/min) (all p < 0.01 vs. placebo). Changes in BP to standing up, FMD, time domain and frequency domain indices of heart rate variability (HRV) and BRS were comparable between sildenafil and placebo.

CONCLUSIONS

Sildenafil administered at a maximum single dose to T2DM men results in a mild increase in heart rate and decrease in BP, but it induces neither an acute improvement of FMD nor any adverse effects on orthostatic BP regulation, HRV and BRS.

Oral phosphodiesterase type 5 inhibitors: nonerectogenic beneficial uses

INTRODUCTION

Phosphodiesterase type 5 (PDE5) hydrolyses cyclic guanylate monophosphate (cGMP) specifically to 5' GMP. PDE5 inhibitors were a breakthrough medication that addressed a previously unfulfilled medical need. They promoted vascular relaxation in the corpora cavernosa and penile erection during sexual stimulation. Sildenafil, vardenafil, and tadalafil were approved then introduced as effective treatments for male erectile dysfunction. This impact has stimulated academic, clinical, and industrial research.

AIM

To highlight the nonerectogenic beneficial uses of oral PDE5 inhibitors.

METHOD

A systematic review of published studies in this affair based on a Pubmed and medical subject heading databases search of all concerned articles.

MAIN OUTCOME MEASURES

Demonstrated beneficial as well as applicable uses of oral PDE5 inhibitors.

RESULTS

As chemical molecules, these drugs were shown to exert potential nonerectogenic beneficial effects. They showed efficacy as a useful adjunct in the management of pulmonary hypertension. Additional uses were extended to different utilities: essential hypertension, benign prostatic hyperplasia, gastrointestinal disorders, endothelial dysfunction, female sexual dysfunction, genital blood flow, exercise capacity, Raynaud's phenomenon, sperm motility, etc.

CONCLUSION

Exploring PDE5 inhibitors for their possible medical applications in diverse specialties seems to be beneficial in making use of these molecules for the welfare of humanity.

Effects of 5'-phosphodiesterase four-week long inhibition with sildenafil in patients with chronic heart failure: a double-blind, placebo-controlled clinical trial

BACKGROUND

The effects of chronic inhibition of 5'-phosphodiesterase with sildenafil on functional capacity, ventilatory efficiency, oxygen uptake, pulmonary hypertension, and endothelial function in chronic heart failure (CHF) are unknown.

METHODS

We conducted a randomized, double-blind, placebo-controlled trial to assess the acute (1 hour after 50 mg by mouth) and chronic (4 weeks after 50 mg 3 times per day by mouth) effects of sildenafil in outpatients with CHF. The outcomes were cardiopulmonary exercise test parameters (chronic effect), echocardiographic-derived pulmonary artery systolic pressure, and plethysmography-derived forearm blood flow (acute and chronic effects).

RESULTS

Nineteen patients with CHF (48 +/- 12 years) with an ejection fraction of 28% +/- 6% were studied. Patients who received sildenafil (n = 11) showed improved maximal oxygen uptake, ventilatory efficiency, and oxygen uptake kinetics. Sildenafil decreased pulmonary artery systolic pressure levels at 60 minutes and at 4 weeks compared with changes after placebo (P = .004 for group and time interaction). Improvement in ventilatory efficiency was positively associated with reductions in pulmonary artery systolic pressure. Patients allocated to placebo demonstrated a trend toward decreased forearm blood flow after reactive hyperemia, whereas this remained unchanged in patients allocated to sildenafil.

CONCLUSIONS

Sildenafil administration for 4 weeks in stable outpatients with CHF improves functional capacity, ventilatory efficiency, oxygen uptake kinetics, and pulmonary hypertension. These effects may be mediated in part by improvements in endothelial function.

Improvement of vascular function by acute and chronic treatment with the PDE-5 inhibitor sildenafil in experimental diabetes mellitus

BACKGROUND AND PURPOSE

Diabetes-associated vascular dysfunction contributes to increased cardiovascular risk. We investigated whether the phosphodiesterase-5 inhibitor sildenafil would improve vascular function in diabetic rats.

EXPERIMENTAL APPROACH

Male Wistar rats were injected with streptozotocin (50 mg kg(-1), i.v.) to induce insulin-deficient diabetes. Direct effects of sildenafil as well as modification of endothelium-dependent and -independent vasorelaxation were investigated in vitro. The effects of acute and chronic (2 week) treatment in vivo of sildenafil on vascular function were also characterized in isolated aortic segments in organ bath chambers 4 weeks after diabetes induction.

KEY RESULTS

Sildenafil induced a concentration-dependent vasorelaxation, which was attenuated by the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine. Acetylcholine-induced endothelium-dependent as well as endothelium-independent relaxation induced by the NO donor, DEA-NONOate, was significantly reduced in aortae from diabetic rats. Incubation with sildenafil in vitro normalized both endothelium-dependent and -independent relaxation in aortae from diabetic rats. Acute as well as chronic in vivo treatment with sildenafil resulted in enhanced endothelium-dependent and -independent vasorelaxation. Superoxide formation was increased in diabetes, associated with enhanced membrane expression of the NAD(P)H oxidase subunit gp91(phox) and Rac, which were both reduced by chronic treatment with sildenafil.

CONCLUSIONS AND IMPLICATIONS

We demonstrate that sildenafil treatment rapidly and chronically improves vascular relaxation in diabetic rats. Treatment with sildenafil might provide a similarly beneficial effect in diabetic patients.

PDE5 inhibitors beyond erectile dysfunction

The phosphodiesterase type-5 (PDE5) inhibitors sildenafil, vardenafil and tadalafil are widely used first-line therapy for erectile dysfunction (ED). Since the advent of sildenafil in 1998, more than 40 million men worldwide have been successfully treated with these compounds. The safety and high tolerability of PDE5 inhibitors make them an attractive tool to investigate further physiological functions of PDE5, for example the modulation of intracellular cyclic GMP (cGMP) pools. As cGMP is a key component of intracellular signaling this may provide novel therapeutic opportunities beyond ED even for indications in which chronic administration is necessary. The approval of sildenafil for the treatment of pulmonary hypertension in 2005 was a notable success in this area of research. A number of other potential new indications are currently in various phases of preclinical research and development. In recent years, extensive but very heterogeneous information has been published in this field. The aim of this review is to summarize existing preclinical and clinical knowledge and critically discuss the evidence to support potential future indications for PDE5 inhibitors.

The erectile–endothelial dysfunction nexus: new opportunities for cardiovascular risk prevention

Erectile and endothelial dysfunction are common in individuals with multiple cardiovascular risk factors and are longitudinal predictors of cardiovascular events. The pathogenesis of both endothelial and erectile dysfunction is intimately linked through increased expression and activation of endothelial nitric oxide synthase, and the subsequent physiological actions of nitric oxide. Endothelial production of nitric oxide by endothelial nitric oxide synthase in the corpus cavernosum is involved in the maintenance of penile erection. Erectile dysfunction can be detected clinically using systematic questioning and could potentially be employed as an independent predictor of cardiovascular risk to target treatment of cardiovascular risk factors. Both erectile and endothelial dysfunction respond to lifestyle modifications, particularly in individuals with the metabolic syndrome. Drugs that improve endothelial dysfunction can also improve erectile dysfunction, but responses are not always concordant. Phosphodiesterase type 5 inhibitors, however, are powerful agents that commonly improve erectile and endothelial dysfunction, with potential cardiac applications. The recent Princeton consensus requires more extensive implementation and evaluation in clinical practice. The judicious diagnosis of erectile dysfunction, nevertheless, provides a unique opportunity for the prevention of cardiovascular disease.

Sildenafil improves endothelial function in patients with pulmonary hypertension

BACKGROUND

Sildenafil has been shown to be effective in the treatment of pulmonary hypertension, and has favourable effects on endothelial function. Our hypothesis is that a part of the beneficial effects of sildenafil in patients with pulmonary hypertension is due to the improvement of the endothelial function.

METHODS

Nine patients (seven females, age 67+/-9 years) with thromboembolic pulmonary hypertension were treated with sildenafil, at a mean dose of 150+/-75 mg/die. At baseline and after 6 months all patients underwent: right-heart catheterization, 6-min walking distance, and a study of endothelial function, including the measure of the flow-mediated vasodilation of the brachial artery, and the dosage of plasma levels of endothelin-1 and von Willebrand factor.

RESULTS

During follow-up we found a significant reduction of mean pulmonary artery pressure and arteriolar resistances. Accordingly, the functional capacity improved (an average of+37 m). Sildenafil improved endothelial-dependent vasodilation and reduced plasma concentrations of endothelin-1 (from 4.5+/-0.6 to 3.1+/-0.7 pg/mL; p<0.0001) and von Willebrand factor (from 183.1+/-10.1 to 149.1+/-17.6 mU/mL; p<0.0001).

CONCLUSION

Improvement of the endothelial function may represents one of the mechanisms able to explain the favourable effects sildenafil has shown in patients with pulmonary hypertension.

Beneficial effects of combined benazepril-amlodipine on cardiac nitric oxide, cGMP, and TNF-alpha production after cardiac ischemia

The aim of this study was to determine if myocardial inflammation is increased after myocardial ischemia and whether angiotensin-converting enzyme inhibitors, calcium channel blockers, or diuretics decrease mediators of inflammation in rats with induced myocardial ischemia. Changes in cardiac interstitial fluid (CIF) levels of nitric oxide metabolites (NOX), cyclic guanosine 3',5'-monophosphate (cGMP), angiotensin II (Ang II), and tumor necrosis factor-alpha (TNF-alpha) were monitored with/without oral administration of benazepril, amlodipine, combined benazepril-amlodipine, or hydrochlorothiazide. Using a microdialysis technique, levels of several mediators of inflammation were measured after sham operation or 30-minute occlusion of the left anterior descending coronary artery. Compared with sham animals, levels of CIF NOX and cGMP were decreased in animals with ischemia (P < 0.001). Benazepril or amlodipine significantly increased NOX levels (P < 0.05 vs. untreated ischemia), but only benazepril significantly increased cGMP (P < 0.05). Combined benazepril-amlodipine further increased CIF NOX and cGMP (P < 0.001), compared with either drug alone. CIF Ang II and TNF-alpha in sham animals did not change significantly. In animals with ischemia, CIF Ang II and TNF-alpha increased progressively. Amlodipine alone, benazepril alone, or combined benazepril-amlodipine significantly reduced TNF-alpha (P < 0.01 for monotherapies and P < 0.001 for combination therapy). Hydrochlorothiazide did not cause significant changes in NOX, cGMP, or TNF-alpha. Combination benazepril-amlodipine may be beneficial for managing cardiac ischemia.

Effect of Regular Phosphodiesterase Type 5 Inhibition in Hypertension

There are no published controlled clinical trials of regular phosphodiesterase type 5 inhibitor therapy as a long-term treatment of hypertension. In a randomized, double-blind, 2-way crossover study, 25 otherwise untreated hypertensive subjects were administered 50 mg of sildenafil or matched placebo 3 times daily for 16 days, and the effects on ambulatory blood pressure (BP), clinic BP, arterial wave reflection, carotid-femoral pulse wave velocity, and brachial artery flow-mediated dilatation were assessed. Three subjects were withdrawn because of adverse effects, and the data from the remaining 22 subjects were analyzed. Sildenafil reduced ambulatory BP (mean [SE] change from baseline for average daytime BP: systolic -8 [2] mm Hg versus 2 [2] mm Hg with placebo, P<0.01; diastolic -6 [1] mm Hg versus 0 [1] mm Hg, P<0.01) and clinic BP (change from baseline to 1 hour after drug administration on day 16: systolic -5 [2] mm Hg versus 4 [2] mm Hg, P<0.01; diastolic -5 [1] mm Hg versus 2 [2] mm Hg, P<0.01). Compared with baseline, sildenafil, but not placebo, reduced arterial wave reflection both acutely and after chronic treatment, but the chronic change in arterial wave reflection was not statistically different from the chronic change with placebo. Sildenafil did not affect pulse wave velocity or flow-mediated dilatation. The main adverse effects of sildenafil, which were generally transient and rated as mild or moderate in severity, were dyspepsia, headache, and myalgia. In conclusion, regular sildenafil constitutes effective antihypertensive therapy. Further studies are warranted to evaluate the role of longer-acting phosphodiesterase type 5 inhibitors as antihypertensive agents in clinical practice.

Effect of sildenafil on cardiac performance in patients with heart failure

Sildenafil is rarely used in patients with heart failure despite a high prevalence of erectile dysfunction, and the theoretic possibility that by increasing nitric oxide availability, it may improve left ventricular (LV) load and performance. This study aimed to determine the peak effects of sildenafil on LV load and performance in patients with heart failure caused by systolic LV dysfunction. Twenty patients with controlled LV failure and ejection fractions <35% received sildenafil 50 mg or a matching placebo when not receiving regular medication for > or =12 hours, in a randomized, placebo-controlled, double-blind, 2-way crossover fashion. Cardiac output was measured by Doppler echocardiography. The aortic pressure waveform was determined using generalized transfer function from radial artery applanation tonometry. Aortic and femoral arterial stiffness was determined as carotid-femoral and femoral-pedal pulse-wave velocity (PWV); wave reflection was measured as an augmentation index (AIx). Cardiac index increased significantly (by 0.37 L/min.m(2), p <0.0001), with the peak effect 60 minutes after sildenafil administration. Compared with the baseline value, total systemic resistance showed a reduction of 479 dynes.s.cm(-5) (p <0.0001). Aortic and lower limb PWV decreased significantly (by 0.89 and 1.14 m/s, respectively, p <0.0001 for both), as did AIx (by 3.6% absolute, p <0.0001); these remained significant after adjustment for mean pressure and heart rate changes. In conclusion, sildenafil improves cardiac performance because of a decrease in LV load, which is caused by decreases in peripheral resistance, in aortic and large artery stiffness, and in wave reflection from peripheral sites. This can explain the increase in cardiac output and in exercise capacity with sildenafil in patients with heart failure.