Intracavernosal Injection of Autologous Adipose-Derived Mesenchymal Stem Cells as an Efficient Alternative Treatment for Patients with Erectile Dysfunction

Introduction

The inability to sustain a sufficient erection of the penis for successful penetration is called erectile dysfunction (ED) (1). The underlying cause of ED may be organic and/or psychogenic. Organic ED may be developed by various causes, including neurogenic, hormonal, or vasculogenic causes (2, 3). It has been reported that organic etiologies of ED are responsible for more than 80% of ED causes, among which the most common etiology is vasculogenic disorders. Vasculogenic disorders can lead to arterial blood flow and venous outflow abnormalities of the corpus cavernosum (4). The incidence of ED was estimated to be 25.9 cases per 1,000 man-years, based on the results of a longitudinal study. Moreover, there is a higher risk of developing ED in men with diabetes mellitus, lower education, coronary artery disease, hypertension, and pelvic injuries (5-8). An erection happens when nitric oxide (NO) is released. NO is released from the terminals of parasympathetic nerves. As a result, it leads to the relaxation of smooth muscles of the corpus cavernosum, resulting in an increased blood flow and, thus, erection (9, 10). A defect in NO synthesis is associated with endothelial dysfunction, which can lead to ED. Currently, there are multiple management options for ED, including phosphodiesterase type 5 inhibitors, vasoactive intracavernosal injections (ICIs), prostaglandin urethral suppositories, vacuum erection devices and penile implants (2, 11-13). In addition, the ICIs of platelet-rich plasma (PRP) have been used as a potential treatment option for ED with increasing demand (14). Regarding the treatment of ED patients, stem cell therapy has attracted the attention of researchers. Mesenchymal stem cells (MSCs) are a type of stem cells that can differentiate into multiple tissues, including bone, fat, cartilage, and muscle (15). Mesenchyme is a mesoderm-derived embryonic connective tissue that can be obtained from tissues that it generates. The main benefit of MSCs is not their capability of differentiation into other organs or target tissues. In fact, the efficacy of MSCs is mostly based on the paracrine effect, whereby releasing of growth factors and cytokines which promote healing and decrease inflammation (16-18). In the present study, we used autologous adipose-derived MSCs to treat ED in non-end-stage patients who have been under other treatment options, such as phosphodiesterase type 5 inhibitors, with some complications, including adverse effects of the drug or drug interactions. Autologous adipose-derived MSCs can be an alternative treatment modality.

Methods

Study design

This clinical trial was performed in an institutional center (Tehran University). The Ethics Committee of Tehran University of Medical Ssciences approved this study (code: IR.TUMS.MEDICINE.REC.1399.438). The ethical committee of Tehran University of Medical Sciences approved this study and sampling was started after receiving the Iranian Registry of Clinical Trials (IRCT20190624043991N11) on 27/11/2020. This study is adhered to CONSORT guidelines and include a completed CONSORT checklist.

Eligibility criteria

A total of 14 ED patients referred to ED clinic at Sina Hospital from 2020 to 2022 were enrolled in this study. Iinclusion criteria were ED patients aged 18-65 years with a healthy mental status, no history of malignancies, and no prior use of psychiatric medications. The enrolled patients had reversible ED and were unsatisfied with their current treatment or experienced side effects.

Isolation of autologous adipose-derived MSCs

To obtain autologous adipose-derived MSCs, the fat grafts obtained from the patients’ abdomens by a surgeon with traditional liposuction were harvested. In this regard, a solution containing 1200,000 of epinephrine with 0.5% lidocaine in Ringer lactate solution was infiltrated into the abdomen using a small incision. Then, an aspiration cannula was used to harvest adipose particles by connecting to the liposuction machine with a negative pressure of less than 20 cmH₂O. The adipose particles were transferred to the laboratory and centrifuged at 500 rpm for 10 minutes to separate the adipose tissue from soluble liquid and oil. The middle layer of the adipose particles was taken for further evaluation. Specimens were then washed with phosphate-buffered saline (PBS), mixed with type 1 collagenase, and incubated for 1 hour. For the assessment of cellular functions, the glycerol-3-phosphate dehydrogenase assay was used. In addition, the hematoxylin and eosin staining was used for histologic evaluation of the specimens to confirm the adipose-derived MSCs. The final products were injected into the patients 2 to 3 weeks after the initial preparation of the adipose-derived MSCs.

Study protocol

A solution containing 5 million autologous adipose-derived MSCs in 10 mL of normal saline was injected via ICI. To improve the treatment effects and prevent migration of the autologous adipose-derived MSCs to other organs by the blood flow, an erection was induced in the penis. To achieve a rigid erection, ICI of papaverine (20mg) was used. Papaverine is best known as a potent direct-acting smooth muscle relaxant and a vasodilator. The erection was maintained at least 30 minutes after the end of stem cell injection; in the case of early relaxation of the penis, the erection duration was extended using ICI of papaverine (5mg). The maximum duration of the erection was considered 45 minutes from the initial injection. The erection was then ended using epinephrine 110000 in normal saline if no relaxation occurred after 90 minutes from the first dose of papaverine. All patients were monitored for 3 hours after the initial injection and then were discharged.

Clinical assessment

The International Index of Erectile Function (IIEF) and the Erection Hardness Score (EHS) were used for the therapeutic assessment of the patients. IIEF is widely used to evaluate male sexual function (19, 20). This index consists of 5 domains, including erectile function, orgasmic function, intercourse satisfaction, sexual desire, and overall satisfaction. The maximum score of IIEF is 75. Further, EHS has 4 domains regarding the hardness of the penis during penetration. The maximum score of EHS is 4. IIEF and EHS were measured before and 3 months after the injection of stem cells. The follow-up visit was performed 3 months after the injection of stem cells.

Statistical analysis

A paired-sample t test was used to compare the EHS and IIEF scores before and after the injection of stem cells. All statistical analyses were performed using SPSS version 26 (IBM SPSS Inc., Chicago, IL, USA). P-values less than 0.05 were considered statistically significant.

Results

The mean age of the participants was 46.42 ± 10.62 years (29 to 75 years). Ten patients had a history of treatment with PRP for ED. Among those, 6 patients had temporary improvements in their erections, and 4 were unsatisfied regarding the results of the PRP treatment. Three patients had drug interactions, 4 were unsatisfied with their routine treatment for ED, 2 experienced side effects, and 5 had no improvement in their erections after consumption of their medications. The baseline characteristics of the participants are presented in Table 1.

Table 1. Baseline characteristics of the participants

Abbreviation: PRP, platelet-rich plasma.

The IIEF scores of the patients were significantly higher 3 months after the injection of autologous adipose-derived MSCs compared to the pre-treatment period (P-value=0.000). In addition, the EHS scores of the participants were significantly higher 3 months after the injection compared to the pre-treatment period (P-value=0.001; Tables 2 and 3). Only 3 patients had minor ecchymosis on their penises.

Table 2. The IIEF and EHS scores of the patients before and after the injection of stem cells

* IIEF, International Index of Erectile Function ; EHS, Erection Hardness Score

Table 3. Comparison of the EHS scores of the patients before and after the injection of stem cells

* EHS, Erection Hardness Score.

Discussion

Stem cell therapy has attracted the attention of researchers in various fields, though its exact mechanism is still unclear. To date, stem cells have been used for many medical goals, including urological disorders and ED (21). MSCs are a type of stem cells that are capable of differentiation into several tissues and self-renewal. Moreover, MSCs can be isolated from the adult organs which they form, including adipose tissue. The major hypothesis of this study is that MSCs are able to enhance the vascular system and the abnormal function of penile smooth muscle cells via a paracrine release of various cytokines and growth factors. An important concern regarding the treatment with stem cells is the migration of injected cells through the blood flow to other proximal or distal organs, such as the lungs. According to several studies, fatal pulmonary embolism may occur due to the intravenous injection of stem cells (22, 23). The corpus cavernosum structure, which is spongy, has many vessels (24). Therefore, ICI is similar to intravenous injection. Although this concern has not been answered clearly in the literature, some strategies have been performed regarding this concern. Lin et al., (25) used magnetic-forced cell retention using magnetized stem cells to achieve a therapeutic benefit in the penis. However, the major limitations of this strategy are the damage caused by the implantation and removal of magnetic rods, as well as the cytotoxicity of nanoparticles. Another method mentioned in some studies (26, 27) is the use of large-size microcarriers to trap stem cells within the corpus cavernosum. In the study by Koga and Horiguchi (28), the exfoliated deciduous dental pulp stem cells were injected into the corpus cavernosum using a small hairband attached to the base of the penis for 6 hours to ensure the treatment efficacy. In the study by Bahk et al., (29), the penile root was clamped for 30 minutes to increase the residence time of injected cells. It retained more cells within the corpus cavernosum; however, many cells still can escape from the corpus cavernosum, mainly due to the short time of penile clamping. Haahr et al., (30) conducted a clinical trial on 17 men with ED after radical prostatectomy and injected autologous adipose-derived regenerative cells via an intracavernosal injection. The therapeutic effect of stem cells was absent in patients with urinary incontinence, mainly due to disruption of the neurovascular bundle. In the present study, we used autologous adipose-derived MSCs to treat ED patients. We injected 5 million autologous adipose-derived MSCs using an intracavernosal injection. With the aim of increasing the efficacy of our treatment, we are the first to use papaverine to induce a temporary blood flow stasis following a penile erection. This allows stem cells to function in the target organ, which is cavernosal tissue. In addition, we conducted our random patient selection from the patients with ED, which was not secondary to end-stage urologic diseases, such as post-operative ED following radical prostatectomy in prostate cancer. The underlying reason for our patient selection is the important fact that the therapeutic effects of stem cells can improve the function of damaged––but not destroyed––tissues and organs. Most of our patients had DM, dyslipidemia, or hypertension leading to vascular damage. Our results showed a promising efficacy regarding the ICI of autologous adipose-derived MSCs in ED patients who have difficulties with their current treatment options, including side effects, drug interactions, and high cost of medications. While our study reports positive results regarding safety and functional recovery, future studies should explore the impact of additional injections, mid and long-term results.

Conclusion

This is the first report of the treatment of ED with autologous adipose-derived MSCs using papaverine as a method to inhibit the migration of injected stem cells from the target organ. The main goal of this treatment was to repair the damaged tissues or the vascular system of the corpus cavernosum to improve the erectile function of the patients.

Authors contributions

SAM and RAB wrote the manuscript. PDF analysed the data. LOR edited the manuscript. ES and RR and VAY found the sources.

Acknowledgments

Thanks to the Urology Research Center, Tehran University of Medical Sciences, Tehran, Iran.

Ethics statement

The Ethics Committee of Tehran University of Medical Ssciences approved this study (code: IR.TUMS.MEDICINE.REC.1399.438).

Conflict of interest

All authors declare there is not any conflict of interest for this publication.

Funding

No funding.

Data Availability

All data generated and analysed during this study are included in this article.

Abbreviations

ED        Erectile dysfunction

EHS      Erection Hardness Score

IIEF      Index of Erectile Function

MSCs   Mesenchymal stem cells

PRP      Platelet-rich plasma