The future of the oral pharmacotherapy of male erectile dysfunction: things to come

Erectile Dysfunction: Key Role of Cavernous Smooth Muscle Cells

Erectile dysfunction is increasingly affecting men, from the elderly to young adults, being a sexual disorder related to the inability to generate or maintain a penile erection. This disorder is related to psychosocial factors such as anxiety, depression, and low self-esteem, to organic factors such as the presence of preexisting conditions like hypertension, diabetes and dyslipidemia. The pathophysiology of the disease is related to changes in the neurotransmission of the autonomic or the non-cholinergic non-adrenergic nervous system, as well as the release of local mediators, such as thromboxane A₂ and endothelin, and hormonal action. These changes lead to impaired relaxation of cavernous smooth muscle, which reduces local blood flow and impairs penile erection. Currently, therapy is based on oral vasodilation, such as sildenafil, tadalafil, vardenafil and iodenafil, or by direct administration of these agents into the corpus cavernosum or by intraurethral route, such as alprostadil and papaverine. Despite this, studies that consolidate the understanding of its pathophysiological process contribute to the discovery of new more efficient drugs for the treatment of erectile dysfunction. In this sense, in the present work an extensive survey was carried out of the mechanisms already consolidated and the most recent ones related to the development of erectile dysfunction.

Influencing Factors for Erectile Dysfunction of Young Adults with No Response to PDE5i

Erectile dysfunction (ED) is a common male disorder. Although orally-administered phosphodiesterase type 5 inhibitors (PDE5 inhibitors) are now recognized as the primary pharmacological treatment method for ED, 20%-30% of the patients treated with PDE5 inhibitors exhibit no significant effects. This study aims to investigate the influencing factors of ED in young adults with no response to PDE5 inhibitors. ED patients who would take PDE5 inhibitors were included and investigated with a questionnaire. Patients with no response to PDE5 inhibitors (tadalafil and sildenafil) served as study group, and those with response to PDE5 inhibitors as control group. Then Chi square test and logistic regression analysis were applied to find the potential influencing factors. In total, 378 ED patients were included. Ninety-three (24.6%) cases were non-responsive to PDE5 inhibitors, and the remaining 285 (75.4%) responded to PDE5 inhibitors. In multiple logistic regression analysis, we found that history of drinking (OR=3.152; 95%CI 1.672-6.975), spousal noncooperation (OR=2.994; 95%CI 1.589-5.638), number of fixed sex partners (OR=0.358; 95%CI 0.132-0.651), duration of ED (OR=3.356; 95%CI 1.352-8.333), and depression (OR=3.689; 95%CI 1.579-8.979) could be the influencing factors for ED patients' non-response to PDE5 inhibitors. In conclusion, history of drinking, spousal noncooperation, number of fixed sex partner, long duration of ED, and depression could be the influencing factors for ED patients' non-response to PDE5 inhibitors. Patients and doctors should pay attention to these factors.

Intracavernous Injection of Autologous Platelet-Rich Plasma Ameliorates Hyperlipidemia-Associated Erectile Dysfunction in a Rat Model

Introduction

Hyperlipidemia is associated with an increased risk of erectile dysfunction (ED) mediated by endothelial damage. Platelet-rich plasma (PRP) contains numerous angiogenic growth factors. Currently, evidence supporting the use of PRP for ED treatment is limited.

Aim

We investigated PRP in a rat model of hyperlipidemia-associated ED.

Methods

Thirty 2-month-old male Sprague–Dawley rats were randomly divided into 3 groups. 20 rats were fed a high-fat diet for 5 months and were randomly divided into 2 groups: (i) rats in the H group received supernatant injection into the corpus cavernosum weekly for 4 weeks; (ii) rats in the H + PRP group received PRP injection into the corpus cavernosum weekly for 4 weeks. 10 rats were fed a standard diet for 5 months and received supernatant injection into the corpus cavernosum weekly for 4 weeks (N group). 7 days after the 4th injection, all rats underwent erectile function testing and then euthanasia.

Main outcome measures

Erectile function was evaluated by measuring intracavernous pressure (ICP) and mean arterial pressure (MAP). Serum and penile tissue were collected for metabolic variable assessment and histochemical examination, respectively.

Results

Intracavernous pressure/MAP and area under the curve/MAP ratios were significantly higher in the N and H + PRP groups than in the H group. Insulin-like growth factor-1, brain-derived neurotrophic factor, and vascular endothelial growth factor levels were significantly higher in the H + PRP group than in the N and H groups. Corporal neuronal nitric oxide synthase, endothelial nitric oxide synthase, and endothelial cells were weakly expressed in the H group compared with the N and H + PRP groups. Intracorporal oxidative stress and apoptotic index were significantly higher in the H group than in the N and H + PRP groups.

Conclusions

This preclinical evidence suggests that clinical trials of PRP in men with ED should be considered. PRP may play a role in ED management.

Huang YC, Wu CT, Chen MF, et al. Intracavernous Injection of Autologous Platelet-Rich Plasma Ameliorates Hyperlipidemia-Associated Erectile Dysfunction in a Rat Model. Sex Med 2021;9:100317.

Relationship between penile erection and the ratio of estradiol to testosterone: A retrospective study

Previous studies have found that the ratio of estradiol to testosterone (E2/T ratio) has a negative effect on sexual function, but the relationship between the E2/T ratio and erection of the penis is not clarified. We conducted a retrospective study of 183 patients with erectile dysfunction and 52 healthy men to investigate the relationship between penis base erection and tip erection. All participants underwent nocturnal penile tumescence tests and medical history checks and had relevant biochemical and endocrine indicators measured. The ratio of estradiol to testosterone was calculated. The relationship between E2/T ratio and erectile time of penile tip and penile base was determined by univariate analysis, multivariate analysis and stratification analysis. After adjusting for mixed factors, the results showed that the E2/T ratio had a more significant negative effect on the base of the penis compared with the tip of the penis (Hazard ratio: -4.34 95% CI: -6.52, -2.16 p = .0001). Moreover, when the effective erection time was ≥10 min, the negative effect of E2/T on penile root erection was more obvious (HR ratio: -4.46 95% CI: -6.50, -2.43 p < .0001). In summary, our study demonstrated a negative relationship between E2/T ratio and penile erection, particularly at the root of the penis.

Novel PDE4 inhibitors derived from Chinese medicine forsythia

Cyclic adenosine monophosphate (cAMP) is a crucial intracellular second messenger molecule that converts extracellular molecules to intracellular signal transduction pathways generating cell- and stimulus-specific effects. Importantly, specific phosphodiesterase (PDE) subtypes control the amplitude and duration of cAMP-induced physiological processes and are therefore a prominent pharmacological target currently used in a variety of fields. Here we tested the extracts from traditional Chinese medicine, Forsythia suspense seeds, which have been used for more than 2000 years to relieve respiratory symptoms. Using structural-functional analysis we found its major lignin, Forsynthin, acted as an immunosuppressant by inhibiting PDE4 in inflammatory and immune cell. Moreover, several novel, selective small molecule derivatives of Forsythin were tested in vitro and in murine models of viral and bacterial pneumonia, sepsis and cytokine-driven systemic inflammation. Thus, pharmacological targeting of PDE4 may be a promising strategy for immune-related disorders characterized by amplified host inflammatory response.

Emerging tools for erectile dysfunction: a role for regenerative medicine

Erectile dysfunction (ED) is the most common sexual disorder reported by men to their health-care providers and the most investigated male sexual dysfunction. Currently, the treatment of ED focuses on 'symptomatic relief' of ED and, therefore, tends to provide temporary relief rather than providing a cure or reversing the cause. The identification of a large population of "difficult-to-treat" patients has triggered researchers to identify novel treatment approaches, which focus on cure and restoration of the underlying cause of ED. Regenerative medicine has developed extensively in the past few decades and preclinical trials have emphasized the benefit of growth factor therapy, gene transfer, stem cells and tissue engineering for the restoration of erectile function. Development of clinical trials involving immunomodulation in postprostatectomy ED patients and the use of maxi-K channels for gene therapy are illustrative of the advances in the field. However, the search for novel treatment targets and a wealth of preclinical studies represent a dynamic and continuing field of enquiry.

Bacterial vaginosis: what is physiological in vaginal bacteriology? An update and opinion

Bacterial vaginosis (BV) was originally described as a sexually transmitted infection caused by a single microbe. The prevailing concept describes BV as a polymicrobial coitus-associated disease of uncertain origin. In this overview the natural history of BV as a monobacterial and polymicrobial entity is examined with respect to the physiological concept of BV in relation to sexual behavior before and after introduction of the hormonal contraceptive pill. Bacterial vaginosis, characterized by low vaginal acidity (elevated pH) and replacement of vaginal Lactobacillus by Gardnerella vaginalis flora, could be caused by unprotected intercourse when a low pH changes through the neutralizing power of male ejaculate, vaginal coital transudate and vaginal neurogenic transudate. A monobacterial form, G. vaginalis vaginitis, could be a physiological post-coital condition for protection of ejaculated spermatozoa, characterized by 'pure'Gardnerella flora and elevated pH as an immediate result of an incidental unprotected coital act through neutralization of vaginal acid and replacement of Lactobacillus by Gardnerella flora. A polymicrobial form of BV could be autoinfection of the post-coital physiological G. vaginalis flora, characterized by a mixture of G. vaginalis, Mycoplasma hominis and anaerobic bacteria at lower vaginal acidity, possibly resulting from suppression of normal vaginal acidity through repeated sexual acts, with a resultant higher pH and transfer of enteric bacteria from the perianal region. Monobacterial and polymicrobial auto-infectious forms of BV may be clinically distinct and share a common origin. The understanding of BV as a basic physiological entity could influence the prophylaxis and treatment of the largely therapy-resistant polymicrobial BV.

Evaluation and treatment of erectile dysfunction in the aging male: a mini-review

Before the 20th century, individuals often did not live beyond the reproductive years, and sexuality of the elderly was not an issue. However, in the current era it is known that as life expectancy improves, both men and women are seeking to preserve their sexuality into old age. While the appreciation of sexuality persists with aging, a decline in sexual activity is typically seen with, and can be attributed to both general health problems as well as specific sexual dysfunctions. Erectile dysfunction is the most frequently diagnosed sexual dysfunction in the older male population. This mini-review provides an overview of contemporary literature concerning epidemiology, pathophysiology, assessment and treatment of erectile dysfunction in the aging male.

Effects of arginase inhibitors on the contractile and relaxant responses of isolated human penile erectile tissue

OBJECTIVES

An impairment in the local availability of nitric oxide (NO) may impair male erectile function. The activity of l-arginine-degrading arginase enzymes may attenuate the relaxation of cavernous smooth muscle by reducing local NO production. Arginase enzymes compete with the nitric oxide synthases for the common substrate, the amino acid l-arginine. Very little data are available regarding the significance of arginase enzymes in the control of human penile erectile tissue. The aim of the present study was to elucidate the effects of drugs known to inhibit arginase activity on the relaxation of isolated human corpus cavernosum (HCC) and the production of cyclic GMP.

METHODS

Using the organ bath technique, the effects of the arginase inhibitors DFMO, H-Orn-OH·HCl, H-lle-OH and nor-NOHA (10 nM–10 μM) on the tension induced by NE (1 μM) and the relaxation induced by electrical field stimulation (EFS) of HCC were investigated. HCC strips were also exposed to increasing concentrations of the compounds, and the production of cGMP was determined by means of a radioimmunoassay.

RESULTS

Only marginal effects of the arginase inhibitors were registered on the tension induced by NE and the relaxation exerted by EFS. Mean reversion of tension ranged from 18 to 8%. Only DFMO and nor-NOHA amplified the EFS-induced relaxation by 11 and 29%, respectively. These effects were not paralleled by an increase in tissue levels of cGMP.

CONCLUSION

Arginase inhibitors appeared to be ineffective in reversing the adrenergic tension and increasing the electrically induced relaxation of isolated HCC.

Evaluation and treatment of erectile dysfunction

Erectile dysfunction (ED) is a prevalent and important disease that has been associated with various comorbidities. The evaluation of patients with ED should include a general health assessment followed by a discussion of reversible factors and lifestyle changes that might help preserve erectile capacity. Numerous effective treatment options are currently available. A frank discussion about use and side effects of these therapies is required to optimize success. Although oral pharmacologic treatments can be initiated and monitored by the primary care physician, patients who do not experience response to these treatments may be best served by referral to a sexual medicine specialist for further assessment and consideration of other treatment options. This article discusses the physiology and pathophysiology of erectile function in men, how the primary care physician may address the clinical problem of ED in practice, and when specialty referral is indicated.

The future is today: emerging drugs for the treatment of erectile dysfunction

IMPORTANCE OF THE FIELD

Erectile dysfunction (ED) is the most common male sexual dysfunction presented for treatment affecting between 10 and 20% of men. PDE type 5 inhibitors (PDE5I) now account for the largest segment of the ED market. While these drugs are highly efficacious for many men, a relatively large subset of ED patients who do not respond to PDE5I is increasingly recognized.

AREAS COVERED IN THIS REVIEW

In this review, we discuss clinical and preclinical evidence supporting various emerging compounds that regulate penile erection both centrally (clavulanic acid, dopamine and melanocortin receptor agonists) and peripherally (novel PDE5I, soluble and particulate guanylil cyclase activators, rho-kinase inhibitors and maxi-K channel openers).

WHAT THE READER WILL GAIN

The reader will gain a broad understanding of erectile (patho-)physiology and gain insights in the mechanisms of action, efficacy and adverse events of various compounds under development for the treatment of ED.

TAKE HOME MESSAGE

We expect emerging drugs to allow treatment protocols tailored to the specific needs of each individual patient, taking into consideration the efficacy of erectile performance enhancement and the potential for adverse events. This tailored approach may include combination of various emerging drugs to enhance efficacy in difficult-to-treat patients.

Expression of cyclic AMP-dependent protein kinase isoforms in human cavernous arteries: functional significance and relation to phosphodiesterase type 4

INTRODUCTION

The cyclic adenosine monophosphate-dependent protein kinase (cAK) is considered a key protein in the control of smooth muscle tone in the cardiovascular system. There is evidence that erectile dysfunction might be linked to systemic vascular disorders and arterial insufficiency, subsequently resulting in structural changes in the penile tissue. The expression and significance of cAK in human cavernous arteries (HCA) have not been evaluated.

AIMS

To evaluate the expression of cAK isoforms in HCA and examine the role of cAK in the cyclic adenosine monophosphate (cAMP)- and cyclic guanosine monophosphate (cGMP)-mediated control of penile vascular smooth muscle.

METHODS

The expression and distribution of phosphodiesterase type 4 (PDE4) and cAK isoforms in sections of HCA were investigated by means of immunohistochemistry and Western blot analysis. The effects of the cAK inhibitor Rp-8-CPT-cAMPS on the relaxation of isolated preparations of HCA (diameter > 100 µm) induced by rolipram, sildenafil, tadalafil, and vardenafil were studied using the organ bath technique.

MAIN OUTCOME MEASURES

Investigate the expression of cAK in relation to α-actin and PDE4 in HCA and evaluate the effects of an inhibition of cAK on the relaxation induced by inhibitors of PDE4 and PDE5 of isolated penile arteries.

RESULTS

Immunosignals specific for cAKIα, IIα, and IIβ were observed within the wall of HCA. Double stainings revealed colocalization of cAK with α-actin and PDE4. The expression of cAK isoforms was confirmed by Western blot analysis. The reversion of tension induced by inhibitors of PDE4 and PDE5 of isolated penile vascular tissue were attenuated significantly by Rp-8-CPT-cAMPS.

CONCLUSIONS

Our results demonstrate the expression of cAK isoforms in the smooth musculature of HCA and its colocalization with PDE4. A significant role for cAK in the regulation mediated by cAMP and cGMP of vascular smooth muscle tone in HCA can also be assumed.

The nitric oxide pathway in the human prostate: clinical implications in men with lower urinary tract symptoms

To date, there is an increasing interest in the nitric oxide (NO) pathway as a potential pharmacological target to treat male lower urinary tract symptomatology (LUTS). In the transition zone of the human prostate, a dense nitrinergic innervation has been shown of the fibromuscular stroma, glandular epithelium and blood vessels. The expression of key proteins of the NO pathway, such as the endothelial and neuronal nitric oxide synthase (eNOS, nNOS), cGMP-degrading phosphodiesterase type 5 (PDE5) and cGMP-binding protein kinase (cGK), has also been demonstrated. The hypothesis that an impaired NO/cGMP-signaling may contribute to the pathophysiology of benign prostatic hyperplasia (BPH) is supported by the results from randomized, placebo-controlled clinical studies, indicating that NO donor drugs and PDE5-inhibitors sildenafil, tadalafil and vardenafil may be useful to treat storage and voiding dysfunctions resulting from LUTS in men. Thus, given a potential role of the NO-pathway in the prostate and/or in other parts of lower urinary tract (e.g. bladder), the enhancement of the NO signaling by NO donor drugs, PDE5 inhibitors or activators of the soluble guanylyl cyclase (sGC) may represent a new therapeutic strategy for the treatment of LUTS. This review serves to focus on the role of NO and the NO-dependent signaling in the control of smooth muscle function in the human prostate. Results from clinical trials in men with LUTS/BPH are also discussed.