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

Current Knowledge on Radiation-Therapy-Induced Erectile Dysfunction in Prostate-Cancer Patients: A Narrative Review

Prostate cancer is the most frequently diagnosed cancer in men in the United States. Among the different available treatment options, radiation therapy is recommended for localized or even advanced disease. Erectile dysfunction (ED) often occurs after radiation therapy due to neurological, vascular, and endocrine mechanisms resulting in arterial tone alteration, pudendal-nerve neuropraxia, and lastly fibrosis. Considering the influence of quality of life on patients’ treatment choice, radiation-therapy-induced ED prevention and treatment are major issues. In this narrative review, we briefly summarize and discuss the current state of the art on radiation-therapy-induced ED in PCa patients in terms of pathophysiology and available treatment options.

Regenerative technology to restore and preserve erectile function in men following prostate cancer treatment: evidence for penile rehabilitation in the context of prostate cancer survivorship

Introduction

Erectile dysfunction (ED) following prostate cancer treatment is not uncommon and penile rehabilitation is considered the standard of care in prostate cancer survivorship (PCS), where both patient and his partner desire to maintain and/or recover pre-treatment erectile function (EF). There is a clinical interest in the role of regenerative therapy to restore EF, since existing ED treatments do not always achieve adequate results.

Aim

To review regenerative therapies for the treatment of ED in the context of PCS.

Materials and Methods

A review of the existing PubMed literature on low-intensity extracorporeal shockwave therapy (LIESWT), stem cell therapy (SCT), platelet-rich plasma (PRP), gene therapy, and nerve graft/neurorrhaphy in the treatment of ED and penile rehabilitation, was undertaken.

Results

IESWT promotes neovascularization and neuroprotection in men with ED. While several systematic reviews and meta-analyses showed positive benefits, there is limited published clinical data in men following radical prostatectomy. Cellular-based technology such as SCT and PRP promotes cellular proliferation and the secretion of various growth factors to repair damaged tissues, especially in preclinical studies. However, longer-term clinical outcomes and concerns regarding bioethical and regulatory frameworks need to be addressed. Data on gene therapy in post-prostatectomy ED men are lacking; further clinical studies are required to investigate the optimal use of growth factors and the safest vector delivery system. Conceptually interpositional cavernous nerve grafting and penile re-innervation technique using a somatic-to-autonomic neurorrhaphy are attractive, but issues relating to surgical technique and potential for neural 'regeneration' are questionable.

Conclusion

In contrast to the existing treatment regime, regenerative ED technology aspires to promote endothelial revascularization and neuro-regeneration. Nevertheless, there remain considerable issues related to these regenerative technologies and techniques, with limited data on longer-term efficacy and safety records. Further research is necessary to define the role of these alternative therapies in the treatment of ED in the context of penile rehabilitation and PCS.

Adipose-derived stem cells modified by BDNF gene rescue erectile dysfunction after cavernous nerve injury

Cavernous nerve injury is the main cause of erectile dysfunction following radical prostatectomy. The recovery of erectile function following radical prostatectomy remains challenging. Our previous studies found that injecting adipose-derived stem cells (ADSCs) into the cavernosa could repair the damaged cavernous nerves, but the erectile function of the treated rats could not be restored to a normal level. We evaluated the efficacy of ADSCs infected with a lentiviral vector encoding rat brain-derived neurotrophic factor (lenti-rBDNF) in a rat model of cavernous nerve injury. The rats were equally and randomly divided into four groups. In the control group, bilateral cavernous nerves were isolated but not injured. In the bilateral cavernous nerve injury group, bilateral cavernous nerves were isolated and injured with a hemostat clamp for 2 minutes. In the ADSC_GFP and ADSC_rBDNF groups, after injury with a hemostat clamp for 2 minutes, rats were injected with ADSCs infected with lenti-GFP (1 × 10⁶ in 20 μL) and lenti-rBDNF (1 × 10⁶ in 20 μL), respectively. Erectile function was assessed 4 weeks after injury by measuring intracavernosal pressures. Then, penile tissues were collected for histological detection and western blot assay. Results demonstrated that compared with the bilateral cavernous nerve injury group, erectile function was significantly recovered in the ADSC_GFP and ADSC_rBDNF groups, and to a greater degree in the ADSC_rBDNF group. Neuronal nitric oxide synthase content in the dorsal nerves and the ratio of smooth muscle/collagen were significantly higher in the ADSC_rBDNF and ADSC_GFP groups than in the bilateral cavernous nerve injury group. Neuronal nitric oxide synthase expression was obviously higher in the ADSC_rBDNF group than in the ADSC_GFP group. These findings confirm that intracavernous injection with ADSCs infected with lenti-rBDNF can effectively improve erectile dysfunction caused by cavernous nerve injury. This study was approved by the Medical Animal Care and Welfare Committee of Wuhan University, China (approval No. 2017-1638) on June 20, 2017.

Erectile Dysfunction and Ischaemic Heart Disease

Erectile dysfunction (ED) is a common disorder that affects the quality of life of many patients. It is prevalent in more than half of males aged over 60 years. Increasing evidence suggests that ED is predominantly a vascular disorder. Endothelial dysfunction seems to be the common pathological process causing ED. Many common risk factors for atherosclerosis such as diabetes, hypertension, smoking, obesity and hyperlipidaemia are prevalent in patients with ED and so management of these common cardiovascular risk factors can potentially prevent ED. Phosphodiesterase type 5 inhibitors provide short-term change of haemodynamic factors to help initiate and maintain penile erection. They have been shown to be an effective and safe treatment strategy for ED in patients with heart disease, including those with ischaemic heart disease and hypertension.

Neuroprotective and Nerve Regenerative Approaches for Treatment of Erectile Dysfunction after Cavernous Nerve Injury

Erectile dysfunction (ED) is a significant cause of reduced quality of life in men and their partners. Cavernous nerve injury (CNI) during pelvic surgery results in ED in greater than 50% of patients, regardless of additional patient factors. ED related to CNI is difficult to treat and typically poorly responsive to first- and second-line therapeutic options. Recently, a significant amount of research has been devoted to exploring neuroprotective and neuroregenerative approaches to salvage erectile function in patients with CNI. In addition, therapeutic options such as neuregulins, immunophilin ligands, gene therapy, stem cell therapy and novel surgical strategies, have shown benefit in pre-clinical, and limited clinical studies. In the era of personalized medicine, these new therapeutic technologies will be the future of ED treatment and are described in this review.

Flk-1⁺Sca-1⁻ mesenchymal stem cells: functional characteristics in vitro and regenerative capacity in vivo

OBJECTIVES

Mesenchymal stem cells (MSCs) represent a powerful tool in regenerative medicine because of their differentiation and migration capacities. We aimed to investigate the possibility of Flk-1(+)Sca-1(-) mesenchymal stem cells (Flk-1(+)Sca-1(-) MSCs) transplantation to repair erectile function in patients suffering from diabetes mellitus (DM)-associated erectile dysfunction (ED).

METHODS

In this study, we isolated Flk-1(+)Sca-1(-) MSCs from bone marrow (bMSCs). Then, newborn male rats were intraperitoneally injected with 5-ethynyl-2-deoxyuridine for the purpose of tracking endogenous Flk-1(+)Sca-1(-) MSCs. Eight weeks later, 8 of these rats were randomly chosen to serve as normal control (N group). The remaining rats were injected intraperitoneally with 60 mg/kg of streptozotocin (STZ) to induce DM. Eight of these rats were randomly chosen to serve as DM control (DM group) while another 8 rats were subject to Flk-1(+)Sca-1(-) MSCs treatment (DM+MSC group). All rats were evaluated for erectile function by intracavernous pressure (ICP) measurement. Afterward, their penile tissues were examined by histology.

RESULTS

Flk-1(+)Sca-1(-) MSCs could differentiate into skeletal muscle cells and endothelial cells in vivo and in vitro. Engrafted Flk-1(+)Sca-1(-) MSCs were shown to home to injured muscle, participate in myofibers repair and could partially reconstitute the sarcolemmal expression of myocardin and ameliorate the level of related specific pathological markers.

CONCLUSION

Flk-1(+)Sca-1(-) MSCs could be used in the treatment erectile function in diabetes mellitus associated erectile dysfunction by promoting regeneration of nNOS-positive nerves, endothelium, and smooth muscle in the penis.

Optimizing in vivo gene transfer into mouse corpus cavernosum by use of surface electroporation

Purpose

Electroporation is known to enhance the efficiency of gene transfer through a transient increase in cell membrane permeability. The aim of this study was to determine the optimal conditions for in vivo electroporation-mediated gene delivery into mouse corpus cavernosum.

Materials and Methods

Diabetes was induced in C57BL/6 mice by intraperitoneal injections of streptozotocin. After intracavernous injection of pCMV-Luc (100 µg/40 µL), different electroporation settings (5-50 V, 8-16 pulses with a duration of 40-100 ms) were applied to the penis to establish the optimal conditions for electroporation. Gene expression was evaluated by luciferase assay. We also assessed the undesired consequences of electroporation by visual inspection and hematoxylin-eosin staining of penile tissue.

Results

Electroporation profoundly induced gene expression in the corpus cavernosum tissue of normal mice in a voltage-dependent manner. We observed electrical burn scars in the penis of normal mice who received electroporation with eight 40-ms pulses at a voltage of 50 V and sixteen 40-ms pulses, eight 100-ms pulses, and sixteen 100-ms pulses at a voltage of 30 V. No detectable burn scars were noted in normal mice stimulated with eight 40-ms pulses at a voltage of 30 V. Electroporation also significantly induced gene expression in diabetic mice stimulated with 40-ms pulse at a voltage of 30 V without injury to the penis.

Conclusions

We have established the optimal electroporation conditions for maximizing gene transfer into the corpus cavernosum of mice while avoiding damage to the erectile tissue. The electroporation-mediated gene delivery technique will be a valuable tool for gene therapy in the field of erectile dysfunction.

Effects of Icariside II on corpus cavernosum and major pelvic ganglion neuropathy in streptozotocin-induced diabetic rats

Diabetic erectile dysfunction is associated with penile dorsal nerve bundle neuropathy in the corpus cavernosum and the mechanism is not well understood. We investigated the neuropathy changes in the corpus cavernosum of rats with streptozotocin-induced diabetes and the effects of Icariside II (ICA II) on improving neuropathy. Thirty-six 8-week-old Sprague-Dawley rats were randomly distributed into normal control group, diabetic group and ICA-II treated group. Diabetes was induced by a one-time intraperitoneal injection of streptozotocin (60 mg/kg). Three days later, the diabetic rats were randomly divided into 2 groups including a saline treated placebo group and an ICA II-treated group (5 mg/kg/day, by intragastric administration daily). Twelve weeks later, erectile function was measured by cavernous nerve electrostimulation with real time intracorporal pressure assessment. The penis was harvested for the histological examination (immunofluorescence and immunohistochemical staining) and transmission electron microscopy detecting. Diabetic animals exhibited a decreased density of dorsal nerve bundle in penis. The neurofilament of the dorsal nerve bundle was fragmented in the diabetic rats. There was a decreased expression of nNOS and NGF in the diabetic group. The ICA II group had higher density of dorsal nerve bundle, higher expression of NGF and nNOS in the penis. The pathological change of major pelvic nerve ganglion (including the microstructure by transmission electron microscope and the neurite outgrowth length of major pelvic nerve ganglion tissue cultured in vitro) was greatly attenuated in the ICA II-treated group (p < 0.01). ICA II treatment attenuates the diabetes-related impairment of corpus cavernosum and major pelvic ganglion neuropathy in rats with Streptozotocin-Induced Diabetes.

Effect of mesenchymal stem cells associated to matrixen on the erectile function in the rat model with bilateral cavernous nerve crushing injury

OBJECTIVES

To evaluate the effect of mesenchymal stem cells (MSCs) and MSCs mixed with Matrixen as a cell carrier on the erectile dysfunction caused by bilateral cavernous nerve crushing injury.

MATERIALS AND METHODS

White male Sprague-Dawley rats were divided into 4 groups: sham-operated control group (n = 5), bilateral cavernous nerve crushing group (BCNC group, n = 10), BCNC administered with MSCs group (n = 10,1x106 in 20 µL), BCNC administered with Matrixen group (n = 10.1x106 in 20 µL), BCNC administered with MSCs/Matrixen group (n = 10.1x106 in 20 µL). After functional assessment at 4 weeks, major pelvic ganglion (MPG) and penile tissue were collected. Immunofluorescent staining of MPG was performed with PKH26 and Tuj1. Western blot analysis of endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) were done in corpus cavernosum.

RESULTS

ICP/MAP ratios of BCNC with MSCs and MSCs/Matrixen groups were significantly increased compared with BCNC and BCNC with Matrixen group. Moreover, ICP/MAP ratios of MSCs/Matrixen group were significantly increased compared with BCNC with MSCs group. In MPG, the more implantation of MSCs and increased expression of nerve cells were observed in MSCs/Matrixen group compared with BCNC with MSCs group. Significant increase expression of eNOS and nNOS was also noted in BCNC with MSCs/Matrixen group.

CONCLUSION

The erectile function was more preserved in MSCs/Matrixen group compared with the administration of MSCs alone in the rats with bilateral cavernous nerve crushing injury. Therefore, we consider that the use of transplant cell carrier such as Matrixen may help the implantation of MSCs and improve the therapeutic effect of MSCs.

Synergistic effect of mesenchymal stem cells infected with recombinant adenovirus expressing human BDNF on erectile function in a rat model of cavernous nerve injury

Purpose

To evaluate the combined role of mescenchymal stem cells (MSCs) infected with recombinant adenoviruses expressing human BDNF (rAd/hBDNF) on the erectile dysfunction in rat with cavernous nerve injury.

Materials and Methods

Rats divided into 4 groups: control group, bilateral cavernous nerve crushing group (BCNC group), BCNC with MSCs group and BCNC with MSCs infected with rAd/hBDNF group. After 4-week, functional assessment was done. PKH26 and BDNF staining of major pelvic ganglion and masson's trichrome staining of corpus cavernosum were performed. Western blot analysis of endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) was done in corpus cavernosum.

Results

After 4 weeks, BCNC with MSCs and MSCs infected with rAd/hBDNF groups showed significantly well-preserved erectile function compared with BCNC group. Moreover, the erectile function of MSCs infected with rAd/hBDNF group was significantly well-preserved than BCNC with MSCs group. The smooth muscle of corpus cavernosum was significantly preserved in BCNC with MSCs and MSCs infected with rAd/hBDNF groups compared with BCNC group. More preservation of smooth muscle was observed in rats with MSCs infected with rAd/hBDNF than with MSCs alone. Significant increase expression of eNOS and nNOS was noted in rats with MSCs infected with rAd/hBDNF than with MSCs alone.

Conclusions

The erectile function was more preserved after injection with MSCs infected with rAd/hBDNF in rat with ED caused by cavernous nerve injury. Therefore, the use of MSC infected with rAd/hBDNF may have a better treatment effect on ED cause by cavernous nerve injury.

Therapeutic angiogenesis as a potential future treatment strategy for erectile dysfunction

The cavernous endothelium plays a crucial role in regulating the tone of the underlying smooth muscle and physiologic penile erection. Recently, the link between erectile dysfunction (ED) and cardiovascular disease was unveiled, and the main etiology of ED was found to be vasculogenic. Although oral phosphodiesterase-5 inhibitors are generally effective for men with ED, such therapies do not cure underlying vasculopathy in the corpus cavernosum tissue. This review addresses current preclinical protein, gene, and cell or stem cell therapies for enhancing cavernous endothelial regeneration and restoring erectile function.

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.

Scaffoldless tissue engineering of stem cell derived cavernous tissue for treatment of erectile function

INTRODUCTION

As one-third of erectile dysfunction (ED) patients do not respond to phosphodiesterase-5 inhibitors, there is great demand for new therapeutic options. Adipose tissue-derived stem cells (ADSCs) represent an ideal source for new ED treatment.

AIM

To test if ADSCs can be differentiated into smooth muscle cells (SMCs) and endothelial cells (ECs), if these differentiated cells can be used to engineer cavernous tissue, and if this engineered tissue will remain for long time after implantation and integrate into corporal tissue.

METHOD

Rat ADSCs were isolated and differentiated into SMC and ECs. The differentiated cells were labeled with 5-ethynyl-2-deoxyuridine (EdU) and used to construct cavernous tissue. This engineered tissue was implanted in penises of normal rats. The rats were sacrificed after 1 and 2 months; penis and bone marrow were collected to assess cell survival and inclusion in the penile tissues.

MAIN OUTCOME MEASURES

The phenotype conversion was checked using morphology, immunocytochemistry (immunohistochemistry [IHC]), and Western blot for SMC and EC markers. The cavernous tissue formation was assessed using rat EC antibody (RECA), calponin, and collagen. The implanted cell survival and incorporation into penis were evaluated with hematoxylin and eosin, Masson's trichrome, and IHC (RECA, calponin, and EdU).

RESULTS

The phenotype conversion was confirmed with positive staining for SMC and EC markers and Western blot. The formed tissue exhibited architecture comparable to penile cavernous tissue with SMC and ECs and extracellular matrix formation. The implanted cells survived in significant numbers in the penis after 1 and 2 months. They showed proof of SMC and EC differentiation and incorporation into penile tissue.

CONCLUSIONS

The results showed the ability of ADSCs to differentiate into SMC and ECs and form cavernous tissue. The implanted tissue can survive and integrate into the penile tissues. The cavernous tissue made of ADSCs forms new technology for improvement of in vivo stem cell survival and ED treatment.

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α₁-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E₁. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.

Gene therapy as future treatment of erectile dysfunction

IMPORTANCE OF THE FIELD

Erectile dysfunction (ED) is a major men's health problem. Although the high success rate of treating ED by phosphodiesterase 5 (PDE5) inhibitors has been reported, there are a significant number of ED patients who do not respond to currently available treatment modalities.

AREAS COVERED IN THIS REVIEW

To elucidate the current status of gene therapy applications for ED, gene therapy approaches for ED treatment are reviewed.

WHAT THE READER WILL GAIN

Gene therapy strategies that can enhance nitric oxide (NO) production or NO-mediated signaling pathways, growth factor-mediated nerve regeneration or K(+) channel activity in the smooth muscle could be promising approaches for the treatment of ED. Although the majority of gene therapy studies are still in the preclinical phase, the first clinical trial using non-viral gene transfer of Ca(2+)-activated, large-conductance K(+) channels into the corpus cavernosum of ED patients showed positive results.

TAKE HOME MESSAGE

Gene therapy represents an exciting future treatment option for ED, especially for people with severe ED unresponsive to current first-line therapies such as PDE5 inhibitors although the long-term safety of both viral and non-viral gene therapies should be established.

Tissue engineering and stem cells: basic principles and applications in urology

To overcome problems of damaged urinary tract tissues and complications of current procedures, tissue engineering (TE) techniques and stem cell (SC) research have achieved great progress. Although diversity of techniques is used, urologists should know the basics. We carried out a literature review regarding the basic principles and applications of TE and SC technologies in the genitourinary tract. We carried out MEDLINE/PubMed searches for English articles until March 2010 using a combination of the following keywords: bladder, erectile dysfunction, kidney, prostate, Peyronie's disease, stem cells, stress urinary incontinence, testis, tissue engineering, ureter, urethra and urinary tract. Retrieved abstracts were checked, and full versions of relevant articles were obtained. Scientists have achieved great advances in basic science research. This is obvious by the tremendous increase in the number of publications. We divided this review in two topics; the first discusses basic science principles of TE and SC, whereas the second part delineates current clinical applications and advances in urological literature. TE and SC applications represent an alternative resource for treating complicated urological diseases. Despite the paucity of clinical trials, the promising results of animal models and continuous work represents the hope of treating various urological disorders with this technology.