Erectile dysfunction (ED) is defined as a consistent or recurrent inability to attain and/or maintain sufficient penile erections for sexual satisfaction [1] [2] . ED is a common condition and studies predict that it will become more prevalent in the future [3] . Increasing evidence suggests that it is predominantly a vascular disease, and may be a marker of occult cardiovascular disease [1] . The prevalence of ED is estimated to be approximately 40% in men aged more than 40 years [2] . The frequency of ED increases with age and is estimated to affect 15% of men aged 40 - 50 years, 45% of men in their 60s, and 70% of men aged than 70 [2] . ED can result from a disease or treatment that causes hormonal deficiency, neurological impairment, penile blood flow problems, disorders of tissue mechanics, psychological factors, or a combination of these [4] .

Several factors are associated with ED, including age, diabetes, obesity, lack of exercise, cardiovascular disease/hypertension, smoking, and low testosterone levels [5] - [7] . Some of these factors are common, and can be adjusted accordingly; for example, lifestyle changes can help manage obesity, a lack of exercise, and smoking. However, other factors such as aging and low testosterone levels are not modifiable; in particular, andropause (i.e., male menopause) is characterized by low testosterone levels [8] . Decreased testosterone levels can lead to various symptoms, including ED, fatigue, mood changes, and reduced sexual desire [8] .

The main treatment for ED is Phosphodiesterase-5 (PDE5) inhibitors, which increase the concentration of cyclic guanosine monophosphate (cGMP) in smooth muscle cells of the corpora cavernosa, leading to relaxation of the penile corpora cavernosa smooth muscle and erection promotion [9] [10] . However, the observed side effects range from mild symptoms (e.g., headaches, flushing, indigestion, and nasal congestion) to severe conditions, including nonarteritic anterior ischemic optic neuropathy and sudden hearing loss [11] [12] [13] .

Human stem cell conditioned medium (HSCM) contains endothelial growth factors that have the potential to ameliorate conditions (e.g., ED and andropause) by enhancing endothelial function [14] [15] . This study aims to report the efficacy of a cream formulated with HSCM (referred to henceforth as “the cream”) based on its clinical application and outcomes.

This pilot study included ten male patients with ED patients treated at an eHealth Clinic in Shinjuku, Tokyo, Japan. None of the patients had any underlying medical conditions that could explain their ED. The cream, which was formulated with human stem cell supernatant, was administered twice daily to the groin and scrotum. Prior to application and after 30 days of usage, patients were assessed using the Erectile Hardness Score (EHS) scale, International Index of Erectile Function-5 (IEF-5), and Aging Male Symptoms (AMS) scale, and the findings were analyzed. Qualitative interviews were conducted to obtain post-use opinions. All the patients provided written informed consent before participating in the study. Patients treated with other medications (e.g., PDE5 inhibitors for ED or testosterone replacement therapy for late-onset hypogonadism) were excluded from the study. The following data were collected from each patient: age, medical history, physical examination, laboratory testing (before cream use), aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine (Cr), estimated glomerular filtration rate (eGFR), and hemoglobin (Hb) levels.

This study investigated the efficacy of a human stem cell-conditioned medium cream for treating ED, specifically in men suspected of experiencing andropathy. The use of cream led to significant improvements in the EHS, IIEF-5, and AMS scores in men with ED without any prior medical history. Although these findings suggest potential benefits, further analyses are required to draw definitive conclusions.

Accumulating evidence indicates the promising efficacy of treating ED using human stem cell culture supernatants. A pilot study involving the direct injection of human stem cell culture supernatant into the penises of 38 patients with ED who visited a medical clinic in Japan demonstrated the efficacy of ED treatment using human stem cell culture supernatants. [20] . Moreover, another review indicated that stem cell therapy has the potential for ED treatment [21] .

Endothelial cells line the inner walls of blood vessels and play a crucial role in maintaining vascular health. These cells produce and release various physiologically active substances, including nitric oxide (NO), which contribute to vasodilation, blood flow regulation, and the suppression of inflammation. During erection, NO is released from the vascular endothelium of the corpus cavernosum in the penis, triggering the production of cyclic GMP, which dilates the blood vessels. However, when endothelial cells are damaged, NO production from the injured cells decreases. We hypothesized that our cream might restore vasodilation of the corpus cavernosum by repairing damaged vascular endothelial cells, thereby increasing NO production in the endothelium [22] . Furthermore, stem cell supernatants may contribute to ED treatment through processes other than endothelial cell modifications. Specifically, they promote angiogenesis, which increases blood flow to the penile corpus cavernosum and may improve erectile function; enhance neurogenesis by restoring the neural function of the penis, which can improve erectile sensation; exert anti-inflammatory effects; reduce inflammation in the penile corpus cavernosum, which can promote tissue repair; and stimulate cell proliferation by activating aged or damaged cells in the penile corpus cavernosum [23] [24] .

Our study observed significant improvements not only in EHS, IIEF-5 scores, but also in AMS, which is an indicator of male menopausal symptoms. Qualitative feedback further supported these findings, with participants experiencing reduced fatigue after exercise and work, particularly while working overtime, and increased motivation in both professional and personal spheres. These observations suggest the potential of the cream to alleviate male menopausal symptoms beyond its efficacy in managing ED. Despite these encouraging results, we did not measure the testosterone levels or other relevant biomarkers. Therefore, future investigations aimed at elucidating the mechanism of cream application and confirming its long-term safety and efficacy, including the assessment of hormonal changes, are warranted.

Several studies have demonstrated the effectiveness of stem cell supernatant therapy in ED. However, these studies predominantly utilized invasive methods, such as direct injection of stem cell supernatants into the penis [20] [21] . The strength of our study is that it is the first to demonstrate the efficacy of stem cell supernatants in treating ED using a noninvasive approach. However, several limitations hinder definitive conclusions and require further investigation. First, the study involved only ten participants, rendering it statistically underpowered to generate generalizable results. Larger and more representative samples are required to confirm the effects observed in diverse populations. Second, the absence of a placebo or control group prevented clear attribution of improvements solely to the cream. Other factors (e.g., such as lifestyle changes or spontaneous fluctuations in ED severity) may explain the observed results. Third, the 30-day follow-up period may not have adequately captured the long-term efficacy and safety of the cream. Long-term studies are crucial to assess sustained effectiveness and potential delayed side effects. Upon re-evaluation 30 days after cream application, the potential effects on ED appeared to have persisted, indicating a promising possibility that the treatment demonstrated lasting efficacy against ED. Finally, this study assumed that the endothelial cell growth factors within the cream contributed to the improvement; however, there is a lack of concrete data to substantiate this claim. Further research is required to elucidate the precise mechanism of action.

Our research demonstrates the contribution of stem cell supernatants to the improvement of ED using noninvasive methods. Additionally, there may be potential effectiveness in treating not only ED, but also male menopausal symptoms. Future research should incorporate control groups to prospectively investigate their efficacy.

The author thanks PC Medical Inc. and all staff members for their assistance with the study.