Intracavernosal platelet-rich plasma therapy for erectile dysfunction: Current evidence and future directions

Abstract

Erectile dysfunction (ED) is the inability to achieve or maintain an erection sufficient for satisfactory sexual performance, affecting over 50% of men aged 50 and older. ED is often linked to lifestyle factors and comorbidities, such as diabetes and cardiovascular disease. Although conventional treatments such as phosphodiesterase type 5 inhibitors (PDE5is) and penile prostheses are commonly used, there is increasing interest in regenerative therapies, including platelet-rich plasma (PRP), which may address the underlying causes of ED. This narrative review examines ongoing trials on intracavernosal PRP for ED to better understand its potential as a treatment and offers recommendations for future research to improve the quality of evidence supporting its use. A literature search was conducted in December 2024 across PubMed, ScienceDirect, and Scopus for articles evaluating PRP for ED. The keywords used for search were PRP, ED, and randomized controlled trial. The review focused on relevant studies, with titles, abstracts, and full texts examined for key details. Five randomized clinical trials, two meta-analyses, and a systematic review were identified, revealing significant variability in PRP preparation, dosage, and follow-up protocols, which hindered definitive conclusions about its efficacy. Although the available evidence suggests promising potential for PRP in ED treatment, methodological inconsistencies highlight the need for further research. Standardization of PRP preparation and administration protocols, along with larger and longer-term trials, is essential to establish its clinical benefits for ED treatment.

Graphical abstract

Keywords

clinical trials / erectile dysfunction / platelet-rich plasma / regenerative therapy

1 INTRODUCTION

1.1 Incidence and etiology of ED

Erectile dysfunction (ED) is broadly defined as the inability to achieve or maintain an erection sufficient for satisfactory sexual performance[1]. A well-established pattern, often referred to as the “rule of 50 over 50,” indicates that more than 50% of males over the age of 50 experience some degree of ED[2]. This condition is on the rise globally, with projections suggesting that over 300 million men will be affected by next year[3].

While ED has traditionally been associated with older age groups, recent studies have demonstrated an alarming increase in its incidence among men younger than 40. This rise may be underreported due to the reluctance of younger men to seek medical advice for the condition[4]. Regardless of age, ED can significantly impact the quality of life for both men and their partners, affecting emotional well-being and intimacy in relationships[5].

ED arises from a variety of risk factors, including lifestyle choices and medical conditions. Organic risk factors such as obesity, smoking, excessive alcohol consumption, diabetes and prostate-related issues, as well as psychogenic risk factors such as depression and anxiety all contribute to the development of ED[6]. These factors not only impact overall health but also interfere with the complex mechanisms involved in achieving and maintaining an erection.

However, at the core of ED is impaired endothelial function in the blood vessels of the penis. The endothelium plays a critical role in vascular health, and when its function is compromised, the release of nitric oxide is significantly reduced. Nitric oxide is essential for vasodilation, the process that allows blood vessels to relax and increase blood flow. Inadequate vasodilation limits blood flow to the penile tissues, making it difficult to achieve a firm erection[7]. This vascular dysfunction serves as the primary mechanism underlying most cases of ED, irrespective of the contributing external factors.

1.2 Medical treatment of ED

1.2.1 Treatment of ED in the post-PDE5i era

Over the years, various approaches have been employed to treat ED, ranging from less invasive methods like behavioral therapy and pharmacological options, such as phosphodiesterase type 5 inhibitors (PDE5is), to more invasive treatments, including intracavernous injection (ICI) therapy and, ultimately, penile prosthesis implantation surgery as the final resort. While PDE5is have proven effective for many, they come with notable limitations. These medications may not be universally effective, often require premeditation that disrupts spontaneity, and, crucially, do not offer a permanent solution to the underlying causes of ED[8].

This is particularly problematic given the increasing prevalence of ED among younger men, who naturally tend to demand a higher frequency of sexual activity. The transient nature of pharmacotherapy, combined with the evolving expectations of these younger patients, has sparked growing interest in developing more durable, permanent treatment options[9]. These emerging therapies, often referred to as “regenerative” or “restorative” treatments, include shock wave therapy, intracavernous stem cell therapy, and platelet-rich plasma (PRP), which is the focus of this review.

PRP therapy, together with the other regenerative approaches, aims to stimulate the body's inherent ability to repair and regenerate tissues, with the ultimate goal of restoring normal erectile function. Unlike traditional treatments that rely on external substances to manage symptoms, regenerative therapies seek to address the root cause of ED by promoting the restoration of healthy penile tissue and vascular function[9].

1.2.2 What led to the Priapus Shot or the P-Shot?

The P-Shot, short for Priapus Shot, refers to an ICI injection of PRP. The concept behind the use of the P-Shot in treating ED originated several decades ago. In the 1970s, hematologists first utilized PRP, which is plasma with a platelet concentration higher than that found in whole blood, to treat patients suffering from thrombocytopenia[10]. This early application demonstrated the potential of PRP to enhance healing and tissue regeneration.

By the 1980s, PRP had caught the attention of maxillofacial surgeons, who began using it to promote healing in their patients[11]. Over the years, PRP has grown in popularity across a wide range of medical fields, thanks to its regenerative properties. It has shown the highest levels of evidence in areas such as hair regrowth, wound healing, and sports rehabilitation medicine[12]. More recently, PRP has made inroads into urology, where it has been used as a urethral injection for the treatment of stress incontinence[13]. In the context of ED, PRP has emerged as a promising treatment option, represented by the development of the P-Shot, which aims to employ the body's own regenerative capabilities to improve erectile function.

2 HOW PRP WORKS: MECHANISM OF ACTION

Platelets are often regarded as multitalented cells, playing a critical role in tissue repair, vascular remodeling, and the regulation of inflammatory and immune responses (Figure 1). Their ability to facilitate these processes is primarily driven by the release of a wide array of growth factors, which promote angiogenesis, cell proliferation, differentiation, and wound healing. These actions contribute to the restoration of organ function in injured tissues[14].

One of the most appealing aspects of PRP therapy is its autologous nature, meaning it is derived from the patient and administered back to the same patient. This not only lowers costs but also eliminates the need for immunosuppressive drugs or the risk of rejection. PRP delivers concentrated doses of growth factors (GFs) directly to the site of injury, intensifying the body's natural healing mechanisms[15].

Platelets serve as an exceptional reservoir of GFs, such as vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), fibroblast growth factor (FGF), transforming growth factor-beta (TGF-β), platelet-derived growth factor (PDGF), and insulin-like growth factor (IGF). Each of these GFs plays a pivotal role in regenerative medicine by promoting key processes such as angiogenesis, fibroblast proliferation, and extracellular matrix development[16]. When platelets are activated by tissue injury and triggered by exposure to substances such as thrombin or tissue collagen, they release these GFs, which initiate and enhance the process of natural tissue recovery[17].

In addition to the previously mentioned GF-mediated regenerative and angiogenic properties of PRP, its mechanism of action in ED also includes the enhancement of nitric oxide production. This, in turn, improves endothelial function and increases blood flow, thereby restoring erectile function. The combination of tissue repair, improved vascularization, and enhanced endothelial function makes PRP a promising regenerative therapy for ED[18].

PRP therapy has gained widespread popularity across various medical fields due to its biological properties. However, despite its increasing use, there remains some controversy surrounding whether the theoretical potential of PRP to promote host tissue regeneration consistently translates into clinical benefits[19]. The debate continues as researchers work to determine the precise mechanisms and effectiveness of PRP in different applications.

3 PRP PREPARATION

Studies have indicated that achieving a platelet concentration exceeding 1 million platelets/μL is optimal for promoting enhanced healing of soft tissues[20,21]. To reach this concentration, whole blood is first collected into syringes containing an anticoagulant, typically sodium citrate, at a volume ratio of 10:1. This anticoagulant helps maintain platelet viability during the preparation process. The blood is then subjected to centrifugation, which separates it into three distinct components: red blood cells, platelet-poor plasma, and PRP, with the latter containing approximately five times the platelet concentration of whole blood (Figure 2).

Before PRP is applied, platelet activators such as calcium chloride (CaCl₂) are added to stimulate platelet aggregation, forming a structure known as the platelet-rich fibrin matrix (PRFM). This matrix is crucial because it prevents the extravasation of PRP from the injection site, addressing concerns about the early washout of PRP from the target tissue. The PRFM allows for the sustained release of PDGFs over a prolonged period, thereby enhancing and extending the therapeutic effects of PRP[22].

4 PRECLINICAL STUDIES

What do the data reveal about the effects of PRP in preclinical settings? Research dating back to 2009 demonstrated that PRP positively influenced nerve regeneration in models of crushed cavernous nerves (CNs) in rats[23]. Subsequent studies have documented notable increases in axonal myelination, indicating potential neurotrophic effects on the CNs. These investigations observed neuroprotective benefits, such as the preservation of nerve axons in injured CNs following PRP injections into the corpus cavernosum[24,25].

Moreover, studies involving diabetic rats with ED have shown that ICI of PRP not only reversed nerve damage but also restored damaged corpus cavernosum tissue. This suggests that PRP may play a dual role: it not only expedites nerve regeneration but also inhibits the atrophy of corporal smooth muscle[26]. These findings collectively underscore the therapeutic potential of PRP in promoting nerve repair and enhancing erectile function, particularly in the context of ED associated with nerve injuries.

The first clinical trial examining the effects of PRP on ED was published in 2015 in Russian literature, reporting significantly positive outcomes on the Sexual Encounter Profile (SEP), the Shim score, and peak systolic velocity measurements[27]. In a subsequent study, the use of a PRFM instead of PRP also resulted in an increase in the Shim score, further highlighting the potential benefits of platelet-based therapies for ED[28].

Moreover, various combinations of PRP with other therapeutic modalities, such as PDE5is, vacuum devices, or shock wave therapy, have been proposed to enhance erectile function[29–33]. Notably, an Italian research group demonstrated that combining PRP with shock wave therapy extended the positive effects on ED, suggesting a synergistic benefit[30]. Additionally, a recent study found that PDE5i non-responders transformed into responders when treated with PRP in conjunction with daily tadalafil and on-demand vardenafil, resulting in significant improvements in the Shim score, Erection Hardness Score, and penile duplex readings[34]. A Turkish study conducted in 2021 reported that 61.29% of participants experienced improvements in erectile function, along with significant enhancements in the International Index of Erectile Function (IIEF) scores and both sexual and general satisfaction, even after excluding the use of PDE5is[35].

Despite these promising results, early clinical studies were limited by several factors, including the absence of placebo groups, small sample sizes, and a lack of long-term follow-up. These limitations highlighted the need for properly conducted randomized controlled trials (RCTs) to further evaluate the efficacy and safety of PRP for the treatment of ED.

5 RANDOMIZED CONTROLLED STUDIES

To date, there have been five RCTs evaluating the effectiveness of PRP for treating ED, which are summarized in Table 1. The first of these trials, conducted by Poulios et al., was a double-blind, randomized, placebo-controlled study. This trial reported no significant adverse events related to the treatment and found substantial improvements in both the IIEF and SEP scores at all follow-up time points. Notably, they observed a significantly higher minimal clinically important difference (MCID) in treated patients at 1 month, 3 months, and 6 months post-PRP injection compared to the placebo group[36].

Last year, Shaher and his team published the largest trial to date, which uniquely recorded objective improvements across all parameters of penile duplex ultrasound. This included measurements of cavernosal artery diameter, peaksystolic velocity, and end diastolic velocity, assessed at both 1 month and 6 months following PRP treatment[37]. However, 1 month later, the US study group failed to replicate the positive outcomes observed in earlier trials. Although they noted an increase in MCID after PRP treatment, this improvement did not differ significantly between the PRP and placebo groups at any follow-up time point[38]. Similarly, a recent study by Ragheb et al. found no significant difference in IIEF scores between the PRP-treated group and the placebo group after a 6-month follow-up period[39]. Nevertheless, a group from the urology department at Cairo University found PRP to be effective after 2 years in 25 men treated with PRP versus their control group. These men showed a significantly higher level of satisfaction. At both 3 months and 24 months, there was a statistically significant difference between the mild ED subgroup and the placebo group in terms of changes from baseline in the IIEF score, within each subgroup[40].

Although a recent systematic review and meta-analysis suggested that PRP is an effective and safe alternative treatment for mild-to-moderate ED, it included only three of the five current RCTs (Table 1). Furthermore, the authors excluded the study conducted by the US group due to the heterogeneity observed in the pooled results for the MCID, as identified in their sensitivity analysis[41].

Another meta-analysis of controlled and single-armed trials aimed to study the effectivesness of PRP for ED. Twelve controlled trials including 991 men combined revealed improved IIEF scores and MCID in the PRP treated groups versus the controls. Also a significant improvement after PRP treatment was recorded in the single-arm trials[42].

Despite these conflicting results among the studies, it is noteworthy that none of the trials reported any major adverse events associated with PRP treatment. These findings highlight the need for further research, with a focus on addressing the methodological flaws of previous RCTs, to better evaluate the efficacy and safety of PRP in treating ED.

6 CONTEMPORARY RCT LIMITATIONS

Before drawing any conclusions from the current RCTs on PRP for ED, it is crucial to critically analyze the studies and acknowledge the evident heterogeneity in their protocols. As shown in Table 1, significant variability is evident across methods ranging from patient selection to PRP collection and dosing regimens and, finally, follow-up procedures.

Currently, there is a pressing need for consensus on the optimal PRP preparation method, as differences in techniques can significantly influence the characteristics and effectiveness of the final product. Additionally, establishing standardized criteria for the quality and quantity of PRP produced, particularly regarding the concentration of GFs, is essential for ensuring consistency across studies.

Furthermore, there is no uniformity in the administration protocols for PRP treatment, including the number of injections, dosage, and specific injection sites. These discrepancies can lead to variability in clinical outcomes and make it challenging to draw meaningful comparisons between studies.

Finally, defining the ideal patient profile for whom PRP treatment would be most beneficial remains an unresolved issue. Identifying the characteristics of patients who are likely to experience optimal results from this modality is essential for tailoring treatments and improving overall efficacy. Addressing these limitations is crucial for advancing the understanding and application of PRP in treating ED.

7 FUTURE DIRECTIONS AND RESEARCH RECOMMENDATIONS

To advance our understanding and improve treatment outcomes, it is essential to focus on several key areas of standardization. First, standardization in PRP preparation methods is crucial to ensure consistency in the quality and efficacy of the product. This includes establishing protocols for PRP system calibration and administration. Second, conducting studies with larger sample sizes will enhance the statistical power and reliability of findings. Additionally, extending the duration of follow-up periods will provide better insights into the long-term effects and sustainability of PRP treatment. Lastly, incorporating more comparison arms in future studies, specifically by combining PRP with other conservative treatment modalities, will help clarify the synergistic effects of these approaches and identify the most effective strategies for managing ED.

By addressing these areas, we can establish a solid foundation for more robust evidence, allowing for a critical evaluation of the therapeutic potential of PRP in the treatment of ED.

8 CONCLUSION

In conclusion, while significant knowledge gaps remain regarding the use of PRP for the treatment of ED, the encouraging results from existing studies highlight its potential as a promising therapeutic option. Current evidence suggests that PRP may offer benefits in improving erectile function, with minimal reported adverse effects. However, to establish its efficacy, safety, optimal preparation protocols, and long-term outcomes, further high-quality, multicenter, well-designed RCTs with standardized methodologies and larger sample sizes are essential.

References

[1] Culley CC, Roger Kirby, Goldstein I, Wyllie M. Textbook of Erectile Dysfunction, Second Edition - Google Books. 2020.

[2] Carson CC, Dean JD. Management of erectile dysfunction in clinical practice. In: Management of Erectile Dysfunction in Clinical Practice. London: Springer; 2007. p. 1–94.

[3] Mulhall J, King R, Glina S, Hvidsten K. Importance of and satisfaction with sex among men and women worldwide: results of the global better sex survey. J Sex Med. 2008;5:788–795.

[4] Shamloul R, Ghanem H. Erectile dysfunction. Lancet. 2013;381:153–165.

[5] Allen MS, Wood AM, Sheffield D. The psychology of erectile dysfunction. Curr Dir Psychol Sci. 2023;32:487–493.

[6] Nguyen HMT, Gabrielson AT, Hellstrom WJG. Erectile dysfunction in young men—a review of the prevalence and risk factors. Sex Med Rev. 2017;5:508–520.

[7] Yafi FA, Jenkins L, Albersen M, Corona G, Isidori AM, Goldfarb S, et al. Erectile dysfunction. Nat Rev Dis Primers. 2016;2:16003.

[8] Salonia A, Bettocchi C, Boeri L, Capogrosso P, Carvalho J, Cilesiz NC, et al. European Association of Urology Guidelines on Sexual and Reproductive Health-2021 update: male sexual dysfunction. Eur Urol. 2021;80:333–357.

[9] Campbell JD, Milenkovic U, Usta MF, Albersen M, Bivalacqua TJ. The good, bad, and the ugly of regenerative therapies for erectile dysfunction. Transl Androl Urol. 2020;9:S252–S261.

[10] Foster TE, Puskas BL, Mandelbaum BR, Gerhardt MB, Rodeo SA. Platelet-rich plasma: from basic science to clinical applications. Am J Sports Med. 2009;37:2259–2272.

[11] Marx RE, Carlson ER, Eichstaedt RM, Schimmele SR, Strauss JE, Georgeff KR. Platelet-rich plasma. Oral Surg Oral Med Oral Pathol Oral Radiol Endodontol. 1998;85:638–646.

[12] Buontempo M, Alhanshali L, Shapiro J, Sicco K, Garshick M. Platelet-rich plasma applications, the past 5 years: a review article. EMJ Dermatol. 2023.

[13] Gupta S, Paliczak A, Delgado D. Evidence-based indications of platelet-rich plasma therapy. Expert Rev Hematol. 2021;14:97–108.

[14] Puricelli C, Boggio E, Gigliotti CL, Stoppa I, Sutti S, Giordano M, et al. Platelets, protean cells with all-around functions and multifaceted pharmacological applications. Int J Mol Sci. 2023;24:4565.

[15] Le ADK, Enweze L, DeBaun MR, Dragoo JL. Current clinical recommendations for use of platelet-rich plasma. Curr Rev Musculoskelet Med. 2018;11:624–634.

[16] Popescu MN, Iliescu MG, Beiu C, Popa LG, Mihai MM, Berteanu M, et al. Autologous platelet-rich plasma efficacy in the field of regenerative medicine: product and quality control. BioMed Res Int. 2021;2021:4672959.

[17] Eisinger F, Patzelt J, Langer HF. The platelet response to tissue injury. Front Med (Lausanne). 2018;5:317.

[18] Epifanova MV, Gvasalia BR, Durashov MA, Artemenko SA. Platelet-rich plasma therapy for male sexual dysfunction: myth or reality? Sex Med Rev. 2020;8:106–113.

[19] Cruciani M, Franchini M, Mengoli C, Marano G, Pati I, Masiello F, et al. Platelet-rich plasma for sports-related muscle, tendon and ligament injuries: an umbrella review. Blood Transfus. 2019;17:465–478.

[20] Dohan Ehrenfest DM, Rasmusson L, Albrektsson T. Classification of platelet concentrates: from pure platelet-rich plasma (P-PRP) to leucocyte- and platelet-rich fibrin (L-PRF). Trends Biotechnol. 2009;27:158–167.

[21] Marx RE. Platelet-rich plasma (PRP): what is PRP and what is not PRP? Implant Dent. 2001;10:225–228.

[22] Gigante A, Del Torto M, Manzotti S, Cianforlini M, Busilacchi A, Davidson PA, et al. Platelet rich fibrin matrix effects on skeletal muscle lesions: an experimental stud. J Biol Regul Homeost Agents. 2012;26:475–484.

[23] Ding XG, Li SW, Zheng XM, Hu LQ, Hu WL, Luo Y. The effect of platelet-rich plasma on cavernous nerve regeneration in a rat model. Asian J Androl. 2009;11:215–221.

[24] Liao C, Wu YCH. MP43-09 effects of platelet rich plasma on improving erectile dysfunction in streptozotocin-induced diabetic rats. J Urol. 2018;199:e582–e583.

[25] Wu CC, Wu YN, Ho HO, Chen KC, Sheu MT, Chiang HS. The neuroprotective effect of platelet-rich plasma on erectile function in bilateral cavernous nerve injury rat model. J Sex Med. 2012;9:2838–2848.

[26] Liao CH, Lee KH, Chung SD, Chen KC, Praveen Rajneesh C, Chen BH, et al. Intracavernous injection of platelet-rich plasma therapy enhances erectile function and decreases the mortality rate in streptozotocin-induced diabetic rats. Int J Mol Sci. 2022;23:3017.

[27] Chalyj ME, Grigorjan VA, Epifanova MVKA. The effectiveness of intracavernous autologous platelet-rich plasma in the treatment of erectile dysfunction. Urologiia. 2015;4:76–79.

[28] Matz EL, Pearlman AM, Terlecki RP. Safety and feasibility of platelet rich fibrin matrix injections for treatment of common urologic conditions. Investig Clin Urol. 2018;59:61–65

[29] Banno JJ, Kinnick TR, Roy L, Perito P, Antonini G, Banno D. 146 the efficacy of platelet-rich plasma (PRP) as a supplemental therapy for the treatment of erectile dysfunction (ED): initial outcomes. J Sex Med. 2017;14:e59–e60.

[30] Ruffo A, Franco M, Illiano E, Stanojevic N. Effectiveness and safety of platelet rich plasma (PrP) cavernosal injections plus external shock wave treatment for penile erectile dysfunction: first results from a prospective, randomized, controlled, interventional study. Eur Urol Suppl. 2019;18:e1622–e1623.

[31] Geyik S. Comparison of the efficacy of low-intensity shock wave therapy and its combination with platelet-rich plasma in patients with erectile dysfunction. Andrologia. 2021;53:e14197.

[32] Zasieda Y. HP-3-1 platelet rich plasma and low-intensity pulsed ultrasound combination in erectile dysfunction treatment. J Sex Med. 2020;17:S158.

[33] Epifanova M, Gvasalia BCM. Combined therapy for treating erectile dysfunction: first results on the use of low-intensity extracorporeal shock wave therapy and platelet-rich plasma. BJU Int. 2019;123:25.

[34] Zaghloul AS, El-Nashaar AM, Said SZ, Osman IA, Mostafa T. Assessment of the intracavernosal injection platelet-rich plasma in addition to daily oral tadalafil intake in diabetic patients with erectile dysfunction non-responding to on-demand oral PDE5 inhibitors. Andrologia. 2022;54(6):e14421.

[35] Taş T, Çakıroğlu B, Arda E, Onuk Ö, Nuhoğlu B. Early clinical results of the tolerability, safety, and efficacy of autologous platelet-rich plasma administration in erectile dysfunction. Sex Med. 2021;9:100313.

[36] Poulios E, Mykoniatis I, Pyrgidis N, Zilotis F, Kapoteli P, Kotsiris D, et al. Platelet-rich plasma (PRP) improves erectile function: a double-blind, randomized, placebo-controlled clinical trial. J Sex Med. 2021;18:926–935.

[37] Shaher H, Fathi A, Elbashir S, Abdelbaki SA, Soliman T. Is platelet rich plasma safe and effective in treatment of erectile dysfunction? Randomized controlled study. Urology. 2023;175:114–119.

[38] Masterson TA, Molina M, Ledesma B, Zucker I, Saltzman R, Ibrahim E, et al. Platelet-rich plasma for the treatment of erectile dysfunction: a prospective, randomized, double-blind, placebo-controlled clinical trial. J Urol. 2023;210:154–161.

[39] Ragheb AM, Lotfy AM, Fahmy M, Elmarakbi AA. Safety and efficacy of platelet-rich plasma injection for treatment of erectile dysfunction: a prospective randomized controlled study. Basic Clin Androl. 2024;34:1–10.

[40] Abdel-Rassoul MA, Ragab AAM, Ibrahim AM, Abdelwahab M, Hammoud KM, El Shorbagy GM. Safety and efficacy evaluation of intracavernosal injection of platelets rich plasma in treatment of vasculogenic erectile dysfunction. Arab J Urol. 2024:1–7.

[41] Deabes M, Deameh MG, Bani Irshid BA, Al Darraji AH, Serag I, Almosilhy NA, et al. Evaluating the efficacy and safety of platelet-rich plasma injection for erectile dysfunction: a systematic review and meta-analysis of randomized controlled trials. Sex Med Rev. 2024;12:739–746.

[42] Du S, Sun S, Guo F, Liu H. Efficacy of platelet-rich plasma in the treatment of erectile dysfunction: A meta-analysis of controlled and single-arm trials. PLoS One. 2024;19:e0313074.

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