Comparative analysis of phosphodiesterase type 5 inhibitors and usnic acid: exploring therapeutic potential in pulmonary arterial hypertension

Evidence for the use of combination targeted therapeutic approaches for the management of pulmonary arterial hypertension

Sildenafil was recently approved for the treatment of pulmonary arterial hypertension. The beneficial effects of phosphodiesterase type 5 (PDE5) inhibitors in pulmonary arterial hypertension are thought to result from relatively selective vasodilatory and antiproliferative effects on the pulmonary vasculature and, on the basis of early data showing lack of significant PDE5 expression in the normal heart, are thought to spare the myocardium. We studied surgical specimens from 9 patients and show here for the first time that although PDE5 is not expressed in the myocardium of the normal human right ventricle (RV), mRNA and protein are markedly upregulated in hypertrophied RV (RVH) myocardium. PDE5 also is upregulated in rat RVH. PDE5 inhibition (with either MY-5445 or sildenafil) significantly increases contractility, measured in the perfused heart (modified Langendorff preparation) and isolated cardiomyocytes, in RVH but not normal RV. PDE5 inhibition leads to increases in both cGMP and cAMP in RVH but not normal RV. Protein kinase G activity is suppressed in RVH, explaining why the PDE5 inhibitor-induced increase in cGMP does not lead to inhibition of contractility. Rather, it leads to inhibition of the cGMP-sensitive PDE3, explaining the increase in cAMP and contractility. This is further supported by our findings that, in RVH protein kinase A, inhibition completely inhibits PDE5-induced inotropy, whereas protein kinase G inhibition does not. The ability of PDE5 inhibitors to increase RV inotropy and to decrease RV afterload without significantly affecting systemic hemodynamics makes them ideal for the treatment of diseases affecting the RV, including pulmonary arterial hypertension.

Oral Treprostinil for the Treatment of Pulmonary Arterial Hypertension in Patients on Background Endothelin Receptor Antagonist and/or Phosphodiesterase Type 5 Inhibitor Therapy (The FREEDOM-C Study): A Randomized Controlled Trial

The role of calcium channel blockers for the treatment of pulmonary arterial hypertension: How much do we actually know and how could they be positioned today?

Oral Treprostinil for the Treatment of Pulmonary Arterial Hypertension in Patients Receiving Background Endothelin Receptor Antagonist and Phosphodiesterase Type 5 Inhibitor Therapy (The FREEDOM-C2 Study): A Randomized Controlled Trial

Treatment of Pulmonary Arterial Hypertension: A Step Forward

Has the 6-Min Walk Distance Run Its Course?

Tadalafil is a selective inhibitor of phosphodiesterase type-5 (PDE-5) that was originally developed for the treatment of male erectile dysfunction and recently approved for the treatment of pulmonary arterial hypertension (PAH). The antipulmonary hypertensive effects of nitric oxide and the natriuretic peptides are mediated via increasing intracellular cGMP and enzymatic degradation by PDE-5 is the major route of cGMP inactivation in the lung. Evidence is accruing that PDE-5 activity is increased in pulmonary vascular diseases and may contribute to the pathogenesis of PAH. The longer half-life of tadalafil allows for once-daily dosing as compared with three-times daily dosing for sildenafil, the only other PDE-5 inhibitor currently approved for treatment of PAH. This article reviews the role of cGMP and PDE-5 in PAH, presents the results of recent clinical trials and discusses the role of tadalafil in the treatment of this rare but difficult-to-treat disease.

Echocardiography in Pulmonary Arterial Hypertension: An Essential Tool

The study of rare diseases is limited by just that, their infrequency. Pulmonary arterial hypertension (PAH), for example, has a prevalence of 15 cases per million.1 Although there has been an explosion in knowledge of and therapies for this life-threatening disease over the past decade, most of our insight is based on small studies. The first therapy that was approved by the Food and Drug Administration in 1995, intravenous epoprostenol, was based on the results of an 81-patient trial.2 The most recently approved therapy, inhaled treprostinil, in 2009, was based on the results of a 235-patient trial.3 Similarly, our understanding of the natural history of this disease is based on small observational series. Articles see pp 156 and 164 To further our comprehension of rare diseases, we often turn to “registries,” constructed as multicenter cohorts of patients who have the disease with longitudinal follow-up. Despite the inherent limitations of their observational and uncontrolled nature, which also represent strengths, these cohorts are useful to describe and compare patient characteristics, practice patterns, and outcomes. Observations from such registries can generate hypotheses that subsequently form the basis of further studies. Lastly, such cohorts facilitate the study of the prognostic profile of the disease via the derivation and validation of clinical prediction tools. In this issue of Circulation , data from the 2 of the most important present-day registries in PAH give us the opportunity to better understand the prognosis of PAH, its determinants, and outcomes in the current treatment era. Humbert and colleagues4 share data from the French National Registry, in which 354 consecutive idiopathic, heritable, and anorexigen-associated patients with PAH were enrolled from October 2002 to October 2003. They report 1-, 2-, and 3-year survival rates of 82.9%, 67.1%, and 58.2%, respectively. Sadly, despite the many advances in …

A Novel Vascular Homing Peptide Strategy to Selectively Enhance Pulmonary Drug Efficacy in Pulmonary Arterial Hypertension

Oral targeted therapies in the treatment of pulmonary arterial hypertension: A meta-analysis of clinical trials

Phosphodiesterase type-5 (PDE-5) inhibitors are novel and important options for the treatment of pulmonary arterial hypertension (PAH). Therefore, we aimed to examine effects of vardenafil, a PDE-5 inhibitor, on the pulmonary arteries isolated from rats with monocrotaline- (MCT-) induced pulmonary hypertension. MCT (60 mg/kg) or its vehicle was administered by a single intraperitoneal injection to 6-week-old male Sprague Dawley rats. Rats were sacrificed 21 days after MCT injection, and the main pulmonary arteries were isolated and then mounted in 20 mL organ baths. Concentration-response curves for vardenafil (10−10–10−5 M) were constructed in phenylephrine- (Phe-) precontracted rings. PAH caused marked rightward shift in the curves to vardenafil whereas maximal responses were not affected. Inhibition of NO synthase (L-NAME, 10−4 M) or guanylyl cyclase (ODQ, 10−5 M) caused similar attenuation in responses evoked by vardenafil. Moreover, contraction responses induced by CaCl2 (3×10−5–3×10−2 M) were significantly reduced in concentration-dependent manner by vardenafil. In conclusion, vardenafil induced pulmonary vasodilatation via inhibition of extracellular calcium entry in addition to NO-cGMP pathway activation. These results provide evidence that impaired arterial relaxation in PAH can be prevented by vardenafil. Thus, vardenafil represents a valuable therapeutic approach in PAH besides other PDE-5 inhibitors.

Riociguat is a soluble guanylate cyclase stimulator approved for the treatment of pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. We studied the clinical and hemodynamics effects of transitioning 12 pulmonary hypertension patients from Phosphodiesterase type 5 inhibitor (PDE5i) to riociguat, and demonstrated a significant increase in cardiac index, fall in pulmonary vascular resistance, and improvement in functional class with this switch. Switch from PDE5i to riociguat appeared to be safe and fairly well tolerated in most patients.

After launching of Sildenafil Citrate, the last invention of 20th century, in 1998, oral PDE5 inhibitor has been established as first line treatment of erectile dysfunction (ED) and shift new paradigm of diagnosis and treatment of ED. The big success of sildenafil in pharmaceutical R&D induced the consecutive development of the so-called ‘The second viagra’, e.g., Tadalafil and Vardenafil in 2003. Currently, these 3 kinds of PDE5 inhibitors are most famous and well-known PDE5 inhibitors worldwide. In Korea, another 3 kinds of PDE5 inhibitors, Udenafil (2005), Mirodenafil (2007) and Avanafil (2011) have been developed and 6 kinds of PDE5 inhibitors were used in the competitive market. In last 10 years, the evolution of PDE5 inhibitors competition has changed the dosage concept from on-demand to daily low-dose and applied for other indications beyond ED such as pulmonary hypertension in Sildenafil, and BPH/LUTS in Tadalafil and penile rehabilitation with daily low dose. For the preparations of PDE5 inhibitors, the termination of Korean patent of sildenafil in 2012 released 4 preparations of PDE5 inhibitors, tablet, oro-disposable film, granule and chewable of 60 generic Sildenafil from 49 companies. The oro-disposable film and chewable are favorable from patients. In Korea, patent of Cialis will be terminated in near future and the development of generic drugs like Viagra will go in the right way and as expected. The long half-life of Tadalafil enabled the approval for BPH/LUTS with daily low dose usage. In turn, the generic Cialis also will be developed as various preparations including oro-disposable film and as combination with antihypertensive for ED/HT, PDE5 inhibitor with alpha blockers for ED/LUTS and PDE5 inhibitor with antidepressant for ED/PE. The present lecture review the evolution of PDE5 inhibitors from the development of sildenafil citrate in 1998 to combination in 2015, Korea.