Effect of sildenafil on platelet function and platelet cGMP of patients with erectile dysfunction

Future perspectives for PDE5 inhibitors bridging the gap between cardiovascular health and psychological status

The serendipitous discovery that inhibiting type 5 phosphodiesterase (PDE5) using sildenafil, a potent PDE5 inhibitor (PDE5i) initially developed for cardioprotection, introduced the possibility of orally managing erectile dysfunction (ED) led to an increase in research data, which are currently considered groundbreaking for the new discipline of sexual medicine. Findings from a number of laboratories and clinics around the world unanimously demonstrated the following: (i) the major cause of ED is directly or indirectly related to cardiovascular disease (CVD); (ii) ED and CVDs share the same risk factors, which are related mainly to lifestyle choices; (iii) the first therapeutic approach to both ED and CVDs is to transform harmful lifestyles into virtuous lifestyles; and (iv) PDE5is in general, particularly sildenafil, are very safe, if not protective, for use in CVD patients. However, the use of PDE5is has faced several challenges. Many patients and some healthcare providers (HCPs) often share the misconception that using these drugs can increase the risk of CVD. Some patients might desire to fulfill the unmet need for privacy linked to the stigma of being treated for ED or might be enticed by the idea of buying drugs online, either because of shame or cheaper prices, without knowing the risks associated with counterfeit drugs. The aim of this narrative revision of the current literature is to demonstrate that (i) the orodispersible film of sildenafil is safe from a CV perspective; (ii) it is a discreet formulation that respects the need for privacy; and (iii) it is virtually the unique PDE5i formulation too expensive to produce outside the correct channels, making it impossible to be counterfeit.

Off-target effect of high-dose sildenafil on adenosine 5'- diphosphate and collagen-induced platelet activation through mitogen-activated protein kinase pathway in treated BALB/C mice and in vitro experiments: A preliminary study

ABSTRACT

Sildenafil, a common over-the-counter pill often self-administered at high doses for erectile dysfunction, has been reported to rarely cause prothrombotic events and sudden cardiac death in a few case reports. Therefore, we investigated the in vitro and in vivo effect of sildenafil treatment and dosage on platelet activation and mitogen-activated protein kinase (MAPK) phosphorylation. BALB/C mice were segregated into four groups, each having four mice each (control, low [3.25 mg/kg], medium [6.5 mg/kg], and high [13 mg/kg] sildenafil), and after the treatment, blood was drawn from each mouse and washed platelets prepared. Washed platelets were incubated with CD41 PE-Cy7 and Phospho-p38 MAPK PE antibodies and analyzed using a flow cytometer for platelet activation and adenosine 5'- diphosphate (ADP)/collagen-induced MAPK phosphorylation. Washed platelets obtained from the venous blood of 18 human volunteers, were incubated with PAC-1 FITC and Phospho-p38 MAPK PE antibodies, and platelet activation (ADP and collagen), followed by flow cytometry analysis. There was a significant increase in both platelet activation as well as MAPK phosphorylation in the presence of collagen in the high-dose (13 mg/kg) sildenafil group (P = 0.000774). Further, increased platelet activation was observed in samples that were treated with high-dose sildenafil as compared to the untreated samples (P < 0.00001). These studies show the risk of prothrombotic episodes in patients on high-dose sildenafil (100 mg), in those with even mild endothelial dysfunction due to ADP, and collagen-induced platelet activation through MAPK phosphorylation, which was not seen in the low-and intermediate-dose cohorts.

Progress in the development of antiplatelet agents: Focus on the targeted molecular pathway from bench to clinic

Antiplatelet drugs serve as a first-line antithrombotic therapy for the management of acute ischemic events and the prevention of secondary complications in vascular diseases. Numerous antiplatelet therapies have been developed; however, currently available agents are still associated with inadequate efficacy, risk of bleeding, and variability in individual response. Understanding the mechanisms of platelet involvement in thrombosis and the clinical development process of antiplatelet agents is critical for the discovery of novel agents. The functions of platelets in thrombosis are regulated by two major mechanisms: the interaction between surface receptors and their ligands, and the downstream intracellular signaling pathways. Recently, most of the progress made in antiplatelet drug development has been achieved with P2Y receptor antagonists. Additionally, the usage of GP IIb/IIIa receptor antagonists has decreased, because it is associated with a higher risk of bleeding and thrombocytopenia. Agents targeting other platelet surface receptors such as PARs, TP receptor, EP3 receptor, GPIb-IX-V receptor, P-selectin, as well as intracellular signaling factors, such as PI3Kβ, have been evaluated in an attempt to develop the next generation of antiplatelet drugs, reduce or eliminate interpatient variability of drug efficacy and significantly lower the risk of drug-induced bleeding. The aim of this review is to describe the pathways of platelet activation in thrombosis, and summarize the development process of antiplatelet agents, as well as the preclinical and clinical evaluations performed on these agents.

The Phosphodiesterase-5 Inhibitors and Prostate Cancer – What We Rely Know About It?

Phosphodiesterase-5 inhibitors (PDE5Is) represent a group of drugs that are registered for the treatment of erectile dysfunctions predominantly, but recently also for treatment of pulmonary hypertension and benign prostatic hypertrophy. However, more and more research deals with possible antitumor potential of PDE5Is in different types of cancers, including prostate cancer. Prostate cancer represents the one of the most common carcinoma in the male population, whose incidence is continuously increasing. Early detection combined with radical prostatectomy increases the survival rate, but also it is necessary to keep in mind the quality of life of patients undergoing prostatectomy in light of bladder control and erectile function. Authors of various clinical studies presented the results that often lead to totally opposing conclusions. For example, Chavez and colleagues have shown that use of PDE5Is in men with erectile dysfunction decreases the risk of developing prostate cancer, while, on the other hand, Michl and colleagues pointed out the adversely effect of PDE5Is on biochemical recurrence after bilateral nerve sparing radical prostatectomy. In that sense, the aim of this review was to present as many as possible of existing results dealing with of action of PDE5Is in the field of prostatic carcinoma. Taking into account all presented data, it can be concluded that eff ect of PDE5Is on formation, development and outcome of treatment in patients with prostate carcinoma is very intriguing question, whose response requires additional both experimental and clinical research.

Platelet indices and erectile dysfunction: A systematic review and meta-analysis

Elevated platelet levels have been postulated to be associated with cardiovascular diseases, conditions closely linked to erectile dysfunction (ED). The current systematic review and meta-analysis was performed to assess the platelet indices, which including platelet count (PLT), mean platelet volume (MPV) and platelet distribution width (PDW) in subjects with ED compared to controls in an attempt to clarify the possible role of platelet indices in the pathogenesis of ED. We initially screened the candidate studies observing the possible association between platelet indices and ED following literature search of database Cochrane Library, PubMed, EMBASE and MEDLINE and therefore included the studies based on the pre-defined inclusion and exclusion criteria. Two independent investigators extracted the related information on article data and outcome measures from the qualified studies, and a meta-analysis was therefore performed using Stata 12.0 software. Subgroup analyses were conducted by the different ED aetiology obtained from the eligible studies. The standard mean difference (SMD) and the corresponding 95% confidence intervals (95% CIs) were applied to estimate the outcome measures. A total of 14 articles were qualified in our meta-analysis with a total of 1595 cases and 987 controls included. Pooled estimate was in favour of increased MPV levels in subjects with ED with a SMD of 0.651 fl, 95% CI 0.567-0.735, p = 0.000. Subgroup analysis showed that vasculogenic ED had a higher MPV levels than controls as well (SMD [95% CI] = 1.026 [0.823-1.228], p = 0.000). However, pooled analysis based on PLT and PDW levels has produced inconsistent results and not strong evidence on platelet level and ED correlation. In conclusion, vasculogenic ED patients had a higher MPV level in our study. However, the results need further interpretation with caution and more high-quality studies are warranted.

Effects of Two Different Dosages of Sildenafil on Patients With Erectile Dysfunction

To investigate the effects of two different dosages of sildenafil on patients with erectile dysfunction (ED), a total of 3,674 patients with ED were recruited to answer questionnaires designed specifically for this study. There were 977 patients in the 50 mg group and there were 2,697 patients in the 100 mg group. Both 50 mg and 100 mg of sildenafil therapy increased the ED patients' average monthly frequency of sexual intercourse, improved erectile function state in self-assessment, and elevated sexual satisfaction and enjoyment. Despite a higher rate of concomitant diseases, patients in the higher dosage of sildenafil group had a better outcome in the average monthly frequency of sexual intercourse and sexual enjoyment compared with those in the lower dosage. Such a study might be helpful for health care providers to choose sildenafil dosage for patients with ED.