Followup results of a combination of calcitonin gene-related peptide and prostaglandin E1 in the treatment of erectile dysfunction

A comprehensive history of injection therapy for erectile dysfunction, 1982-2023

INTRODUCTION

Although oral phosphodiesterase 5 inhibitors represent a first choice and long-term option for about half of all patients with erectile dysfunction (ED), self-injection therapy with vasoactive drugs remains a viable alternative for all those who are not reacting or cannot tolerate oral drug therapy. This current injection therapy has an interesting history beginning in 1982.

OBJECTIVES

To provide a comprehensive history of self-injection therapy from the very beginnings in 1982 by contemporary witnesses and some members of the International Society for Sexual Medicine's History Committee, a complete history of injection therapy is prepared from eyewitness accounts and review of the published literature on the subject, as well as an update of the current status of self-injection therapy.

METHODS

Published data on injection therapy, as a diagnostic and therapeutic tool for ED, were reviewed thoroughly by PubMed and Medline research from 1982 until June 2023. Early pioneers and witnesses added firsthand details to this historical review. Therapeutic reports of injection therapy were reviewed, and results of side effects and complications were thoroughly reviewed.

RESULTS

The pioneers of the first hours were Ronal Virag (1982) for papaverine, Giles Brindley (1983) for cavernosal alpha-blockade (phentolamine and phenoxybenzamine), Adrian Zorgniotti (1985) for papaverine/phentolamine, and Ganesan Adaikan and N. Ishii (1986) for prostaglandin E1. Moxisylyte (thymoxamine) was originally marketed but later withdrawn. The most common side effect is priapism, with the greatest risk of this from papaverine, which has modified its use for therapy. Currently, prostaglandin E1 and trimixes continue to be the agents of choice for diagnostic and therapeutic use in ED. A recent agent is a mixture of a vasoactive intestinal polypeptide (aviptadil) and phentolamine.

CONCLUSIONS

After 40 years, self-injection therapy represents the medication with the highest efficacy and reliability rates and remains a viable option for many couples with ED. The history of this therapy is rich.

Emerging gene and stem cell therapies for the treatment of erectile dysfunction

Erectile dysfunction is a prevalent condition that leads to significant morbidity and distress, not just for affected men but also for their partners. Very few currently available treatments ameliorate the underlying causes of the disorder and 'cure' the disease state. Much recent effort has been focused on the development of gene and cell-based approaches to rectify the molecular and tissue defects responsible for ED. Gene therapy has been investigated in animal models as a means to restore normal function to the penis; at this time, however, only one human trial has been published in the peer-reviewed literature. Recent gene therapy studies have focused on the modulation of enzymes associated with the NOS/cGMP pathway, and supplementation of trophic factors, peptides and potassium channels. Stem cell therapy has been a topic of interest in more recent years but there are currently very few published reports in animal models and none in human men. Although stem cell therapy offers the potential for restoration of functional tissues, legitimate concerns remain regarding the long-term fate of stem cells. The long-term safety of both gene and stem cell therapy must be thoroughly investigated before large-scale human studies can be considered.

Gene and stem cell therapy for erectile dysfunction

Erectile dysfunction (ED) is defined as the inability to attain and/or maintain penile erection sufficient for satisfactory sexual performance. ED is a highly prevalent health problem with considerable impact on the quality of life of men and their partners. Although the treatment of ED with oral phosphodiesterase type V (PDE5) inhibitors is effective in a wide range of individuals, it is not efficacious in all patients. The failure of PDE5 inhibitors happens mainly in men with diabetes, non-nerve sparing radical prostatectomy, and high disease severity. Therefore, improved therapies based on a better understanding of the fundamental issues in erectile physiology and pathophysiology have recently been proposed. Here, we summarize studies on ED treatment using gene and stem cell therapies. Adenoviral-mediated intracavernosal transfer of therapeutic genes, such as endothelial nitric oxide synthase (eNOS), calcitonin gene-related peptide (CGRP), superoxide dismutase (SOD), and RhoA/Rho kinase and mesenchymal stem cell-based cell and gene therapy strategy for the treatment of age- and diabetes-related ED are the focus of this review.

Engineering ex vivo-expanded marrow stromal cells to secrete calcitonin gene-related peptide using adenoviral vector

Calcitonin gene-related peptide (CGRP) is a target for cardiovascular gene therapy. Marrow stromal cells (MSCs) hold promise for use in adult stem cell-based cell and gene therapy. To determine the feasibility of adenoviral-mediated CGRP gene transfer into ex vivo-expanded MSCs, rat MSCs were isolated, ex vivo expanded, and transduced with adenoviruses. Adprepro-CGRP and AdntlacZ, adenoviral vectors containing prepro-CGRP or nuclear-targeted beta-galactosidase reporter gene ntlacZ under the control of Rous sarcoma virus promoter, were used. In this study, it can be shown that transduction efficiency of adenoviral-mediated gene transfer into ex vivo-expanded MSCs is dose dependent, transgene expression persists for more than 21 days in culture, and adenoviral transduction does not alter the proliferation or viability of MSCs. Transduced MSCs retain multipotentiality and transgene expression after cell differentiation. The expression and secretion of CGRP by Adprepro- CGRP-transduced MSCs was confirmed by Western blot analysis and enzyme immunoassay. The secretion of CGRP by Adprepro-CGRP-transduced MSCs is dose dependent, and the transduced cells release as much as 9.5 +/- 0.4 pmol CGRP/1 x 10(6) cells/48 hours (mean +/- standard error of mean, n = 3) into culture medium at a multiplicity of infection of 300. Furthermore, culture supernatant from Adprepro-CGRP-transduced MSCs increases intracellular cyclic AMP levels in pulmonary artery smooth muscle cells in culture. These findings suggest that replication-deficient recombinant adenovirus can be used to gene engineer ex vivo-expanded MSCs and that high-level secretion of biologically active CGRP can be achieved, underscoring the clinical potential of using this novel adult stem cell-based cell and gene therapy strategy for the treatment of cardiovascular diseases.

Nitric oxide-cyclic GMP pathway with some emphasis on cavernosal contractility

Nitric oxide (NO) is formed from the conversion of L-arginine by nitric oxide synthase (NOS), which exists in three isoforms: neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). nNOS is expressed in penile neurons innervating the corpus cavernosum, and eNOS protein expression has been identified primarily in both cavernosal smooth muscle and endothelium. NO is released from nerve endings and endothelial cells and stimulates the activity of soluble guanylate cyclase (sGC), leading to an increase in cyclic guanosine-3',5'-monophosphate (cGMP) and, finally, to calcium depletion from the cytosolic space and cavernous smooth muscle relaxation. The effects of cGMP are mediated by cGMP dependent protein kinases, cGMP-gated ion channels, and cGMP-regulated phosphodiesterases (PDE). Thus, cGMP effect depends on the expression of a cell-specific cGMP-receptor protein in a given cell type. Numerous systemic vasculature diseases that cause erectile dysfunction (ED) are highly associated with endothelial dysfunction, which has been shown to contribute to decreased erectile function in men and a number of animal models of penile erection. Based on the increasing knowledge of intracellular signal propagation in cavernous smooth muscle tone regulation, selective PDE inhibitors have recently been introduced in the treatment of ED. Phosphodiesterase 5 (PDE5) inactivates cGMP, which terminates NO-cGMP-mediated smooth muscle relaxation. Inhibition of PDE5 is expected to enhance penile erection by preventing cGMP degradation. Development of pharmacologic agents with this effect has closely paralleled the emerging science.

Vasoconstriction and vasodilation in erectile physiology

Recent studies have demonstrated that vasoconstriction in the erectile vasculature of the penis is mediated in part by RhoA/Rho-kinase signaling. However, this constrictor activity must be overcome to permit the vasodilation essential for erection. We hypothesize that the primary action of nitric oxide and other agents that cause penile erection is inhibition of the RhoA/Rho-kinase pathway, thereby allowing vasodilation and erection. This hypothesis, as well as experiments using hypogonadal and hypertensive animal models, are discussed in terms of the potential clinical value of Rho-kinase inhibitors for the treatment of erectile dysfunction.

Gene transfer of prepro-calcitonin gene-related peptide restores erectile function in the aged rat

Erectile dysfunction in the aging male is caused, in part, by inadequate relaxation of the corpora cavernosal smooth musculature. Calcitonin gene-related peptide (CGRP), a peptide neurotrasmitter localized in the corpora cavernosa, is down-regulated in the aging rat penis. We examined the hypothesis that this reduction in CGRP may contribute to decreased cavernosal smooth muscle relaxation. Therefore, we sought to determine whether adenoviral-mediated gene transfer of prepro-CGRP (AdRSVCGRP) could enhance erectile responses in aged rats. We found a significant decrease in CGRP concentrations and in cAMP and cGMP levels in aged rat cavernosal tissue compared to younger rats. Aged rats also had significantly lower erectile function as determined by cavernosal nerve stimulation compared to younger rats. Five days after transfection with AdRSVCGRP, these aged rats had an approximately threefold increase in cavernosal CGRP levels compared to animals transfected with adenoviruses encoding nuclear-targeted beta-galactosidase (AdRSV beta gal). The AdRSVCGRP-transfected animals also demonstrated an increase in CGRP mRNA and immunohistochemical localization of CGRP in the smooth muscle of the corpora cavernosa. In addition, cAMP levels in the corpora cavernosa were significantly increased, whereas cGMP levels remained unchanged. Adenoviral transduction efficiency of beta-galactosidase reporter gene was measured by chemiluminescence and was observed in cavernosal tissue 5 days after transfection with AdRSV beta gal. More importantly, 5 days after administration of AdRSVCGRP, a significant increase was observed in the erectile response to cavernosal nerve stimulation in the aged rat, similar to the response observed in younger rats. These data suggest that in vivo adenoviral gene transfer of CGRP can physiologically improve erectile function in the aged rat.

Nitric oxide-mediated erectile effects of galantide but not galanin in vivo

The purpose of this study was to investigate the in vivo effects of intracavernosal injections of galanin and galantide (a specific galanin receptor antagonist) on penile erection in the anesthetized cat. Erectile responses to galanin and galantide were compared with responses to a standard triple drug combination [1.65 mg papaverine, 25 microg phentolamine, and 0.5 microg prostaglandin E(1) (PGE(1))]. Intracavernosal injections of galanin (3-100 nmol) and galantide (0. 1-3 nmol) induced penile erection in a dose-dependent manner. In terms of relative potency, galantide was approximately 100-fold more potent than galanin at increasing cavernosal pressure. The maximal increases in intracavernosal pressure in response to galanin and galantide were 83 and 95%, respectively, of the control triple drug combination. The total durations of erectile response caused by these peptides were significantly shorter (P<0.05) than those by the triple drug combination. The nitric oxide synthase inhibitor L-NAME (20 mg) significantly decreased the erectile response in the cat to galantide but not to galanin, while the K(+)(ATP) channel antagonist U-37883A (3 mg) had no effect on the erectile response to galanin nor galantide. The results of the present study demonstrate that galantide, a putative antagonist for the galanin receptor, has more potent agonist activity than galanin in increasing intracavernosal pressure in the cat. Moreover, these data suggest that galantide, but not galanin, causes penile erection by an NO/cGMP-dependent mechanism. This is the first study to demonstrate that galanin may play a role in the physiology of penile erection.

Non-surgical management of erectile dysfunction

Erectile dysfunction is a common and distressing medical condition that is now highly amenable to treatment almost irrespective of the cause. Safe, non-surgical treatments with unequivocal efficacy are psychological therapy, intracorporeal injection of vasoactive drugs, transurethral vasodilators and oral sildenafil, all of which have been reported to have a 50-70% overall response rate. Vacuum constriction devices are acceptable for some, usually older patients and oral yohimbine is thought to have marginal efficacy. Local creams to induce or enhance erectile function are currently being investigated. There is no place for androgen supplementation unless the patient is profoundly hypogonadal. Treatment of hyperprolactinaemia is very effective but is a rare cause of erectile dysfunction. As intercourse may entail an unfamiliar level of physical activity, it is sensible to ensure that the patient is able to climb a flight or two of stairs comfortably without provoking undue breathlessness or chest pain and to provide suitable advice about technique before commencing treatment. Once it is clear to the patients that erectile dysfunction can be satisfactorily overcome, the long-term use of treatments to do so tends to wane. Thus, although the prospect of effective treatment for what had been for many a distressing life sentence has the potential to place new demands on the health service, there is no evidence that restrictions on prescribing will prove economically rational.

Physiology and pathophysiology of erection: consequences for present medical therapy of erectile dysfunction

Smooth muscle relaxation of the corpus cavernosum is the key mechanism of erection. It depends on a cascade of consecutive regulatory systems starting in the central nervous system, and proceeding via peripheral neurotransmission to intracellular signal transmission within the cavernous smooth muscle cells. Knowledge of these interacting mechanisms of erection is fundamental for understanding of the mode of action of new and possibly selective pharmacological agents that are presently available or under evaluation for treatment of erectile dysfunction.

Vasoactive cocktails for erectile dysfunction: chemical stability of PGE1, papaverine and phentolamine

PURPOSE

Vasoactive cocktails are widely used in diagnosing and treating erectile dysfunction, especially in poor responders to prostaglandin E1 (PGE1). However, very little information as to their chemical interactions and stability is available, despite the huge amount of published work regarding their clinical efficacy. Obviously, medical and legal problems are involved.

MATERIALS AND METHODS

We analyzed four kinds of vasoactive cocktails, composed of papaverine, phentolamine and PGE1 in different combinations, using High Performance Liquid Chromatography analysis after 5 to 60 days of storage at temperatures between 2 and 8C. SPSS MANOVA analysis and a t-test for paired samples were used for statistical purposes.

RESULTS

Papaverine and phentolamine concentrations showed no significant variations during the 2 month study, ranging from a minimum of 96.75+/-1.20 to a maximum of 103.00+/-0.20% of the starting values. In the same period, PGE1 showed an accelerated degradation profile, reaching concentration values, after 60 days, of 76.00+/-2.28% and 70.20+/-2.02% when added to phentolamine or papaverine respectively and 70.00+/-2.40% with both.

CONCLUSIONS

Papaverine and phentolamine are characterized by chemical stability when blended together or with PGE1. Papaverine and/or phentolamine increase the naturally occurring degradation of PGE1 in physiological solution. This effect is most evident in the first 10 days. Papaverine has the greatest deteriorating effect on PGE1. A safe and proper use of these cocktails should take into account the variations of PGE1 concentration.

Medical treatment of erectile dysfunction

There has been a tremendous increase in demand for the treatment of erectile dysfunction in the last 10 years. This has occurred partly because of a greater understanding and awareness by both the general public and clinicians, and also because there now exists a range of effective treatments. The choice of treatments is increasing rapidly and novel delivery systems which may be more patient-friendly than intracavernosal injections are now becoming available. We review the published data on effectiveness and safety of the currently available treatments and discuss recent advances in oral therapy, as these drugs are likely to become available in the near future.

Intracavernous pharmacotherapy

Intracavernous application of vasoactive substances not only has enhanced our understanding of penile hemodynamics, the physiology of penile erection, and the pathophysiology of erectile dysfunction but also has revolutionized the diagnosis and treatment of erectile dysfunction in the last 15 years. Virag was the first to report on the erectile effect of papaverine in humans, and Brindley later reported the effect of intracavernous application of alpha-receptor-blocking agents on cavernous tissue. These reports led to numerous basic and clinical investigations and ultimately established a new treatment alternative for patients with erectile dysfunction that is now considered to be the treatment of choice for most patients. Changes in penile hemodynamics include the relaxation of cavernous smooth musculature and arteries, which leads to an increase in arterial blood flow and a restriction of venous outflow through a compression of subtunical veins. These hemodynamic changes are the prerequisite for the induction and maintenance of penile erection. With the intracavernous application of vasoactive substances it was possible to influence penile hemodynamics at a local level and to induce an erection despite alterations in the nervous system, penile arterial blood flow, cavernous musculature, or neurotransmitter status. In addition, the local application of pharmacologically active substances directly to the end organ enabled the achievement of high local drug concentrations without severe systemic side effects. The commonly used substances are papaverine the combination of papaverine and phentolamine, and prostaglandin E1 (alprostadil). In addition to these established substances, several other regimens, such as linsidomine (SIN-1), calcitonin gene-related peptide (CGRP), moxisylyte, and various triple- or quadruple-drug mixtures have been described. In addition, several other compounds as well as different routes of administration are on the horizon and may prove to be effective in the future diagnosis and treatment of erectile dysfunction.

Role of the nitric oxide donor linsidomine chlorhydrate (SIN-1) in the diagnosis and treatment of erectile dysfunction

OBJECTIVES

Recently, nitric oxide was shown to be a mediator of penile erection in men and the nitric oxide donor linsidomine chlorhydrate (SIN-1) was introduced as a novel treatment option in patients with erectile dysfunction. We now present our follow-up results with the intracavernous application of SIN-1.

METHODS

One hundred thirteen patients with erectile dysfunction of various etiologies and 10 normal control subjects underwent intracavernous pharmacotesting with 1 mg SIN-1. Of the 113 patients, 71 (62.8%) underwent additional pharmacotesting with a mixture of papaverine (15 mg/mL) and phentolamine (0.5 mg/mL) (P/P). Forty-eight responders to SIN-1 were enrolled in an autoinjection program with this substance.

RESULTS

All normal control subjects had full rigid erections lasting 40 to 70 minutes. Of 113 patients, 78 (69%) had responses sufficient for intercourse with SIN-1, and the other 35 patients (31%) demonstrated inadequate responses. All 44 responders to SIN-1 who also received P/P had erections sufficient for intercourse with P/P in doses of 0.25 to 2 mL (mean, 0.6 +/- 0.3 mL). Six patients (13.6%) had prolonged erections with minimal to moderate doses of P/P. From the total of 27 patients who had erections insufficient for intercourse with SIN-1, 20 (74.1%) had good responses with 0.25 to 2.0 mL P/P (mean, 1.5 +/- 0.5 mL). One patient (4%) had a prolonged erection with 1.0 mL P/P: After 10 to 150 injections/patient (total of 1160 injections; mean, 24.1 injections), no significant side effects were noted with SIN-1.

CONCLUSIONS

Our data suggest that intracavernous SIN-1 is safe and efficacious in the majority of patients with erectile dysfunction; however, it has a lower smooth muscle relaxing effect than a combination of P/P. The absence of severe side effects, including priapisms, may be explained by the use of a physiologic pathway for induction of the erectile response and the rapid intracavernous decomposition of SIN-1.

Impotence: diagnosis and management of male erectile dysfunction

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Prognostic factors for the postoperative outcome of penile venous surgery for venogenic erectile dysfunction

Since penile venous surgery is usually associated with a poor postoperative outcome, a study was done to evaluate possible prognostic factors for this procedure. A total of 77 patients with erectile dysfunction underwent ligation of all dorsal penile veins and resection of the deep dorsal penile vein for venous incompetence. In all patients a comprehensive evaluation was done preoperatively. All patients did not respond to pharmacotherapy and had a venous leak. After a followup of 6 months, patients were classified as having full spontaneous erections, failure and response to pharmacotherapy. Of the 77 patients 31 (40.3%) had full spontaneous erections, 8 (10.3%) were currently responding to pharmacotherapy and 38 (49.4%) failed. The maintenance flow was 75 +/- 45 ml. per minute in the group with spontaneous erections and 103 +/- 60 ml. per minute in the failure group (p = 0.20). Mean patient age was 49.8 +/- 11.7 and 49.1 +/- 10.2 years, respectively (p = 0.23). Of the 41 patients wih normal single potential analysis of cavernous electrical activity 28 had full erections postoperatively, 5 responded to pharmacotherapy and 8 failed, compared to 3, 3 and 30, respectively, of the 36 patients with abnormal single potential analysis of cavernous electrical activity. After a mean followup of 21 months (range 6 to 47 months), 4 patients with full erections at 6 months postoperatively currently require intracavernous pharmacotherapy. Our results indicate that single potential analysis of cavernous electrical activity seems to be an important prognostic factor for the postoperative outcome of penile venous surgery for venogenic impotence.