World J Mens Health. 2024;42:e61. Forthcoming. English.
Published online May 30, 2024.
https://doi.org/10.5534/wjmh.240032
Copyright © 2024 Korean Society for Sexual Medicine and Andrology
Original Article
Saager Tilak Chawla
,1Jad Shahan,1Nolan Soutipan,1Samuel Ryan Sorkhi,1Yong Sun Choi,2Woong Jin Bae,2,3Sae Woong Kim,2,3,4Tung-Chin Hsieh,5 and Mahadevan Raj Rajasekaran1,5
Author information
Author notes
Copyright and License
- 1Department of Research Service, San Diego VA Healthcare System, San Diego, CA, USA.
- 2Department of Urology, College of Medicine, The Catholic University of Korea, Seoul, Korea.
- 3Catholic Integrative Medicine Research Institute, College of Medicine, The Catholic University of Korea, Seoul, Korea.
- 4Green Medicine Co., Ltd, Busan, Korea.
- 5Department of Urology, University of California, San Diego, CA, USA.
- 1Department of Research Service, San Diego VA Healthcare System, San Diego, CA, USA.
Correspondence to: Mahadevan Raj Rajasekaran. Department of Research Service, San Diego VA Health Care System, 3350 La Jolla Village Drive, San Diego, CA 92161, USA. Tel: +1-858-552-8585, Fax: +1-858-552-7436, Email: mrajasekaran@health.ucsd.edu
Received February 20, 2024; Revised April 01, 2024; Accepted April 07, 2024.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-
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Abstract
Purpose
Physiological aging is associated with microvascular dysfunction, including in the penis, and this may contribute to age-related erectile dysfunction (ED). Low-intensity extracorporeal shockwave therapy (Li-ESWT) is a non-invasive intervention for ED, but its effect on penile microvascular function, remains unclear. Our objectives are to (i) evaluate the effect of Li-ESWT (specifically radial type ESWT [rESWT]) on penile microvascular perfusion (PMP) in aging rats, (ii) elucidate a possible mechanism, and (iii) evaluate its impact on angiogenic and smooth muscle biomarkers in cavernosal tissue.
Materials and Methods
Male rats (n=9; 15–18 months) were anesthetized and subjected to rESWT while monitoring PMP. The nitric oxide (NO) pathway involvement was assessed by measuring the effect of rESWT on PMP following an intracavernosal injection of N(G)-nitroarginine methyl ester (L-NAME) (NO synthase inhibitor). To elucidate the cellular mechanism, another group of rats received repeated rESWT (n=4) or no treatment (n=4) three times/week for two weeks. Rats were euthanized at the end of the study and penile tissues were analyzed for angiogenic markers (vascular endothelial growth factor-A [VEGF-A], endothelial nitric oxide synthase [eNOS]) and smooth muscle content (α-actin) using immunostaining, Western blot, and quantitative polymerase chain reaction (qPCR).
Results
rESWT resulted in more than a 2-fold increase in PMP (from 68.5 arbitrary units; 163.7 AU). L-NAME injection produced a <40%–50% decrease (185.3 to 101.0 AU) in rESWT-induced PMP response. Immunostaining revealed increased α-actin, eNOS, and VEGF-A in the cavernosum and these findings were confirmed by qPCR and Western blot results.
Conclusions
rESWT improved PMP, which may be mediated via increased VEGF expression, which stimulates the NO/cyclic guanosine monophosphate pathway, resulting in sustained PMP. rESWT devices could offer a safe, non-invasive treatment for age-related ED.
Keywords
Erectile dysfunction; Extracorporeal shockwave therapy; Fibrosis; Laser speckle contrast imaging; Microcirculation; Penis
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INTRODUCTION
Erectile dysfunction (ED) is a common problem in older men that significantly impacts quality of life. Physiological aging is associated with impairments in angiogenesis and microvascular function in several organs. Age-related impaired angiogenesis is associated with diminished endothelial cell function and lower expression of vascular endothelial growth factor (VEGF) [1]. Penile microvascular function may also play a vital role in normal erectile function, and reports suggest that microvascular dysfunction and age-related increases in penile fibrosis are important contributors to ED severity [2, 3]. Our preclinical study used a novel laser speckle contrast imaging (LSCI) to show that increased penile fibrosis impairs penile microvascular perfusion (PMP) [3].
Morphological analysis of human cavernosal tissues showed a significant inverse correlation between age and smooth muscle as well as endothelial markers, which could contribute to age-related ED [4]. During physiological aging corporal smooth muscle cells (SMCs), which are critical to the expansion of the corporal sinusoids and arterial inflow, begin to atrophy [5]. Even a small decline in SMC function can lead to venous leakage [6]. In addition, corporal SMCs express inducible nitric oxide synthase (iNOS) to make nitric oxide (NO) and combat oxidative stress responsible for SMC dysfunction, thereby attenuating venous leakage [7]. Therefore, therapies that increase both smooth muscle and endothelial contents can be an ideal intervention to prevent/treat age-related ED [8].
Low-intensity extracorporeal shock wave therapy (Li-ESWT) is a widely applied non-invasive intervention using high energy acoustic waves to treat various diseases including pathologies of penile tissue [9, 10]. Previous studies have shown that shock wave therapy can improve erectile function by stimulating angiogenesis, stem cell proliferation, and nerve regeneration [11, 12]. The microtrauma produced by ESWT is a proposed mechanism of action for its beneficial effects on erectile function [13], but the ESWT’s effect on PMP remains unclear. Additionally, most previous studies employed focused ESWT (fESWT), which targets deeper organs, while the effect of radial ESWT (rESWT) is perceived to be more superficial. rESWT is commonly used for indications such as venous ulcers and plantar fasciitis with high-quality evidence to support its use [14].
fESWT uses a narrow pattern of acoustic waves to target deeper organs, while rESWT eccentrically disperses acoustic waves, via a compressed ballistic projectile repeatedly striking an endplate, nonspecifically targeting a region 0 to 3.5 cm beneath the surface of the skin [13, 15]. Radial shock waves have the highest energy at the tip of the device, making the treatment ideal for targeting superficial pathologies [16]. We hypothesize that radial shock waves may produce a similar or greater effect in superficial tissues such as the penis and may involve similar cellular mechanisms. This is supported by Wu et al’s findings [13] that radial and focused Li-ESWT produced statistically similar clinical benefits in men with a history of vasculogenic ED.
At the cellular level, ESWT is known to increase the expression NO and VEGF, mediators of angiogenesis which could stimulate increased PMP [17]. Additionally, ESWT has been shown to increase expression of VEGF and endothelial nitric oxide synthase (eNOS) mRNA and protein levels in erectile tissue [18]. While NO is a transient biomolecule, eNOS can serve as an angiogenic biomarker to detect the long-term effects of ESWT on NO levels and blood perfusion. Additionally, NOS blockers can be used to elucidate the relationship between ESWT, the NO pathway, and changes in blood perfusion. The increase in VEGF expression caused by ESWT has been shown to activate the NO/cyclic guanosine monophosphate (cGMP) signaling pathway in the corpus cavernosum [19]. Additionally, Li-ESWT treatment employed in a diabetic rat model for ED improved erectile function and produced a significant increase in both smooth muscle and endothelial contents [8]. However, these studies employed fESWT, and the biological effects of rESWT are still unclear.
Thus, our study aims are to (i) evaluate the effect of rESWT on PMP in an aging rat model; (ii) elucidate a possible mechanism of action using the NO synthase inhibitor N(G)-nitroarginine methyl ester (L-NAME); (iii) determine the changes in angiogenic markers and smooth muscle content.
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MATERIALS AND METHODS
1. Ethics statement
The study protocol was approved by the Institutional Animal Care and Use Committee (IACUC #: A19-004). All experiments were conducted in accordance with the Guide for the Care and Use of Laboratory Animals (National Institutes of Health). Seventeen aging male Sprague-Dawley rats (aged 15–18 months) were subjected to physiological studies. At the end of these studies, the animals were euthanized, and penile tissue was harvested for histological analysis.
2. Laser speckle contrast imaging for microvascular perfusion
Briefly, rats were anesthetized using a ketamine plus xylazine co*cktail (0.3 mL/100 g bodyweight). Baseline and peak PMP were assessed with LSCI (Perimed AB). This LSCI technique quantifies PMP and displays a real-time image using arbitrary units (AU) [3]. The rats were prepared by using Nair hair remover in the pelvic region and were placed in the supine position on a custom-made rat restrainer, with their penile shaft positioned under the PeriCam (Perimed AB) (Fig. 1B). An image sampling frequency and averaging frequency of 12/s was used when recording microvascular perfusion. Anesthesia dosage, hair removal, and custom-rat restrainer were optimized to limit confounding factors such as muscle movement and physical barriers on the surface of the skin. Imaging sessions were conducted until a minimum of 180 continuous seconds with no artifacts were observed. The corpus cavernosum was selected as the region of interest, and PMP was recorded at baseline, immediately after, 10 and 20 minutes post-ESWT.
Fig. 1
(A) Experimental setup showing LSCI probe, custom-made rat restrainer, and rat under anesthesia positioned under rESWT device. (B) Penile shaft positioned directly beneath radial ESWT applicator. (C) rESWT machine display of shockwave intensity, frequency, and count. LSCI: laser speckle contrast imaging, rESWT: radial extracorporeal shock wave therapy.
3. Radial Li-ESWT in male rats
Nine animals were anesthetized and restrained as previously described. ESWT applicator was positioned over the penile shaft, ensuring full contact between the applicator, contact gel, and penile tissue. A Cenowave Air radial ESWT device was used for treatment (HNT MEDICAL Co.). Preliminary tests to compare the effect of probe size and intensity were conducted (Fig. 2, 3). A level 1 intensity (L1i) (0.12 mJ/mm2) ESWT session for 500 counts at 2 Hz (Fig. 1C) with a 2 cm diameter probe was chosen as optimal settings to increase PMP for all treatment sessions in this study. ESWT sessions lasted ~4 minutes each. For PMP studies, a maximum of one session was performed within a two-week period to control for potential changes in long-term baseline PMP.
Fig. 2
PMP at baseline (A–C) and post-ESWT (D–F) visualized on a perfusion scale with AU shows a significant increase in PMP following ESWT (n=9). ESWT: extracorporeal shock wave therapy, AU: arbitrary units, PMP: penile microvascular perfusion.
Fig. 3
(A) The larger (2 cm) radial probe size produced an approximately 10% greater effect on PMP compared to the smaller (1.5 cm) probe. (B) The level 1 (0.12 mJ/mm2) shockwave intensity produced a larger effect on PMP compared to level 2 (0.24 mJ/mm2) intensity. AU: arbitrary units, PMP: penile microvascular perfusion.
4. Administration of L-NAME
To test involvement of NO pathway, an intracavernosal (IC) injection of the NO synthase inhibitor L-NAME (200 µg/kg) [20] was administered fifteen minutes prior to rESWT. PMP response was recorded immediately after and 10 minutes post-treatment.
5. Effect of repeated radial ESWT
Eight animals were distributed into 2 equal (n=4) groups: a control group (G1) and an experimental group (G2) which underwent repeated rESWT over a two-week period using the same settings as previously described. All animals were 15–18 months old to control for altered endothelial and smooth muscle content demonstrated in aging rats [1]. Baseline LSCI readings confirmed both groups had similar PMPs prior to treatment. G1 animals received no further treatment, while G2 animals were subjected to rESWT 3 times/week for 2 weeks. Rat penile tissue was harvested and processed for immunostaining, Western blot, and quantitative polymerase chain reaction (qPCR) studies.
6. Immunostaining studies
Paraffin tissue sections (6 µm) were deparaffinized, steamed for antigen retrieval, and incubated for 20 minutes with 2.5% normal horse serum containing 0.1% Triton X-100 to block non-specific binding sites. Sections were then incubated overnight at 4 ℃ with monoclonal antibodies VEGF-A and eNOS (1:200 dilution; Cell Signaling Technology). Following 3 phosphate-buffered saline washes, sections were incubated with an appropriate secondary antibody and processed. Tissue samples staining for eNOS were processed using Vectastain alkaline phosphatase system, and samples staining for VEGF were processed with Vectastain horse radish peroxidase system (Vector Laboratories). Immunofluorescence was performed to visualize cavernosal smooth muscle content using α-actin antibody as described previously [21]. Histological images were captured and subsequently analyzed using Zeiss AxioScan slide scanner (Carl Zeiss Microscopy LLC).
7. Western blot analysis
To quantify α-actin, eNOS, and VEGF-A protein levels, tissues were hom*ogenized in lysis buffer, containing 5% 2-mercaptoethanol, and heated at 60 ℃ for 5 minutes. Denatured samples (10 µg) were loaded onto 4%–12% polyacrylamide gels, along with 250-µL PageRuler Plus prestained protein ladder (PageRuler™). Samples were transferred to polyvinylidene fluoride membranes, and Western blots were probed for specific proteins. After 60 minutes in 1X TBST containing 5% ChemCruz Blotto non-fat dry milk (Santa Cruz Biotechnology), membranes were incubated overnight at 4 ℃ with primary antibodies (1:1,000) in blocking buffer. After washing, membranes were incubated for 1 hour with horseradish peroxidase-conjugated rabbit anti-mouse IgG (Cell Signaling Technology), in a 1:2,000 dilution of 5% non-fat dry milk blocking buffer. Blots were developed and protein densitometry was analyzed using the enzyme chemiluminescence method.
8. Quantitative PCR
Frozen tissues were hom*ogenized, and the samples were transferred into TRIzol with 1 mL chloroform and centrifuged to isolate the aqueous layer. Total RNA was purified using a RNeasy Micro kit (Qiagen) and RNA purity and quantity were assessed (NanoDrop One spectrophotometer; NanoDrop Technologies). High-quality RNA (optical density [OD] 260/280 nm and OD 260/230>1.9 nm) was isolated and used to synthesize cDNA using the High-Capacity cDNA Reverse Transcription Kit (Applied Biosystems). Primer sequences are provided in Table 1.
Table 1
The corresponding primers used for Qpcr
cDNA samples were diluted (12 ng/µL) and mastermix for each primer was made using the PowerTrack SYBR Green kit (Applied Biosystems). PCR plates were loaded using 22.5 µL mastermix and 2.5 µL (30 ng) cDNA in each well. Amplification was performed using the CFX Opus 96 (BioRad). Thermocycling parameters were followed according to Applied Biosystems’ SYBR Green kit: enzyme activation for 2 minutes at 95 ℃, followed by 40 cycles of denaturation (15 seconds at 95 ℃), data collection at annealing (60 seconds at 60 ℃). Dissociation curve was run after the 40 cycles to assess primer specificity.
9. Statistical analysis
Sample size was calculated by power analysis using G*Power software with a large Cohen’s d effect size, based on our previous publication, at a significance level of 0.05 [22]. Based on our calculations, this sample size should yield a power of at least 0.8. Protein densitometry was analyzed via the chemiluminescence method using the iBright FL1500 imaging system (Thermo Fisher Scientific). qPCR analysis was performed with CFX Maestro Software (BioRad) using the ΔΔCt method, normalized to the reference gene, and glyceraldehyde 3-phosphate dehydrogenase (GAPDH). When assessing the statistical significance of the results, a paired 2-tail t-test with unequal variances was used (α=0.05).
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RESULTS
1. Radial ESWT-induced changes to PMP
ESWT produced a 2-fold increase in PMP from baseline. Fig. 2A–2C shows an average baseline PMP of 68.456±9.021 AU, while Fig. 2D–2F depicts a higher PMP of 163.742±11.787 AU following ESWT (p<0.005). The 2 cm diameter ESWT probe produced a 9.14% larger effect on maximum PMP compared to the 1.5 cm diameter radial probe (Fig. 3A). Level 1 intensity (0.12 mJ/mm2) produced a notably larger increase in PMP compared to L2i (0.24 mJ/mm2; Fig. 3B).
The injection L-NAME (n=4) resulted in a <45% decrease in ESWT-induced PMP response. Fig. 4A–4D shows an average PMP of 185.293±20.604 AU in response to rESWT before L-NAME injection, compared to 101.01±13.077 AU following L-NAME injection (Fig. 4E, 4F; p<0.005). These studies demonstrated a significant increase in PMP following rESWT and a significant decrease in ESWT-induced PMP response following administration of L-NAME.
Fig. 4
The effect of ESWT on PMP (A–D) was significantly larger compared to the ESWT-induced increase in PMP following administration of L-NAME (E–H; n=4, p<0.005). ESWT: extracorporeal shock wave therapy, PMP: penile microvascular perfusion, L-NAME: N(G)-nitroarginine methyl ester, AU: arbitrary units.
2. Immunostaining studies
Fig. 5 shows localization of α-actin, eNOS, and VEGF deposits in the cavernosal tissue of aging rats. Immunolabeling of α-actin was observed in smooth muscle (Fig. 5A), while eNOS and VEGF labeling was seen in endothelial lining of the corpus cavernosum (Fig. 5B, 5C). Higher expression of angiogenic markers, eNOS and VEGF, and smooth muscle content marker, α-actin, was observed in the cavernosal tissue of rats subjected to repeated rESWT over two weeks compared to controls.
Fig. 5
Representative photomicrographs by immunostaining of rat penile tissue harvested from control and experimental rats following repeated rESWT over 2 weeks at 1×, 5×, and 10× magnification shows. (A) IF images indicating greater expression of α-actin and (B, C) IHC images indicating greater expression of eNOS (HRP: brown staining), and VEGF-A (alkaline phosphatase: red staining) in cavernosal tissue of experimental rats (n=3–5). Red and yellow arrows point to areas of visibly higher α-actin, eNOS, and VEGF-A expression in photomicrographs of experimental rats. IHC with (HRP: brown staining), and VEGF-A (Alkaline phosphatase: red staining). rESWT: radial extracorporeal shockwave therapy, IF: immunofluorescence, IHC: immunohistochemistry, eNOS: endothelial nitric oxide synthase, HRP: horseradish peroxidase; VEGF-A: vascular endothelial growth factor-A, CC: corpus cavernosum.
3. Western blot analysis
Fig. 6A shows representative images of protein levels of α-actin, eNOS, and VEGF in controls and experimental rats. Image analysis revealed a significant increase in endothelial (eNOS and VEGF) and smooth muscle (α-actin) protein levels following repeated ESWT (p<0.05, Fig. 6B).
Fig. 6
(A) Western blot results of rat penile tissue harvested from controls and experimental rats following 2 weeks of rESWT treatment, show greater protein expression of α-actin (42 kDa), eNOS (133 kDa), and VEGF-A (21 kDa) in experimental rats. (B) Densitometry analysis conducted using chemiluminescent method via the iBright FL1500 imaging system revealed that all three proteins were expressed significantly more in ESWT rats (*p<0.05). (C) qPCR results of rat penile tissue harvested from controls and experimental rats following 2 weeks of rESWT treatment, show an increase in protein expression of Actin, eNOS, and VEGF-A in ESWT in the penile tissue of ESWT rats (n=3–5). rESWT: radial extracorporeal shockwave therapy, kDa: kilodaltons, eNOS: endothelial nitric oxide synthase, VEGF-A: vascular endothelial growth factor-A, qPCR: quantitative polymerase chain reaction, GAPDH: glyceraldehyde 3-phosphate dehydrogenase.
4. qPCR analysis
Fig. 6C shows increased mRNA expression for all endothelial and smooth muscle markers after rESWT. A 9-fold increase in mRNA expression was observed for α-actin. eNOS also had a greater than a 3.5-fold increase and VEGF had a nearly a 2-fold increase in mRNA expression (normalized to GAPDH). While the trend in qPCR results was not significant (p>0.05), the general trend of higher expression of angiogenic markers and smooth muscle content in the ESWT group is consistent across immunolocalization, protein expression, and mRNA levels.
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DISCUSSION
Our study aims were to (i) evaluate the effect of rESWT on PMP in an aging rat model, (ii) elucidate a possible mechanism of action, (iii) and determine the changes in angiogenic markers and smooth muscle content in cavernosal tissue. Our studies show a significant increase in PMP following rESWT, supporting its potential as a non-invasive therapy to improve hemodynamic function in the penis. The absence of a significant PMP increase after L-NAME suggests involvement of NO pathway. Repeated rESWT produced elevated α-actin, eNOS, and VEGF penile mRNA expression, and protein levels were significantly increased.
Our results indicate that rESWT is an effective intervention to slow the development of age-related fibrosis by increasing microvascular perfusion and smooth muscle content. Li et al’s study [12] in rats showed that fESWT induces endogenous progenitor cell recruitment and Schwann cell activation resulting in angiogenesis, tissue restoration, and nerve generation including neuronal NO synthase positive nerves from the major pelvic ganglion and cavernosal nerve to the penis. This potential for tissue remodeling should reduce fibrosis-related symptoms, and even attenuate the presence of fibrotic tissue in the microvasculature. While these studies used fESWT, Wu et al [13] demonstrated that radial and focused SWs were similarly effective for treating men with vasculogenic ED. Therefore, it is reasonable to extrapolate that fESWT’s proposed mechanism of responding to ESWT-induced microtrauma, applies to rESWT as well. Our findings show an increase in VEGF and eNOS mRNA expression and protein levels, which supports the proposed mechanism that microbubbles and endothelial microtrauma caused by rESWT result in increased expression of angiogenic factors, similar to fESWT.
In addition to rESWT’s potential to exert a greater effect on small animals and superficial tissues such as the penis, radial shock wave devices are smaller, cheaper, and more portable than its focused counterpart. Furthermore, unlike focused devices which are Food and Drug Administration (FDA) class II devices that require physicians to operate the device under an IRB-approved protocol, radial devices are FDA class I devices that may be used by anyone regardless of regulatory approval or medical training [13]. rESWT therapy has already become widespread especially for treatment of venous ulcers.
While ESWT’s mechanism in cavernosal tissue is an emerging research area, in human umbilical vein endothelial cells, radial shockwaves have been shown to contribute to angiogenesis through activation of the mechanosensory complex involving VEGFR-2, VE-cadherin, and PECAM-1 which mediates eNOS phosphorylation and angiogenic gene expression [23]. Additionally, mechanotransduction by ESWT in osteoblasts activates the mitogen-activated protein kinase (MAPK) cascade [24]. The MAPK cascade mediates hypoxia inducible factor 1-alpha (HIF-1α) which binds to VEGF promoter and increases VEGF-A transcription [24].
ESWT is implicated to induce angiogenesis through both VEGF and NOS with tissue specificity determining the extent of involvement for each pathway. Our results suggest that VEGF may be a primary factor impacted by ESWT in the cavernosum. Reduced VEGF levels have been observed in the cavernosal tissue of old rats [25], and IC injections of VEGF have been shown to increases both VEGF and eNOS (and thereby NO) expression and restore erectile function in aged rats [26]. This role of VEGF increasing NO expression in endothelial cells may explain the effect of rESWT on both VEGF and NO pathways, and supports Rajasekaran et al’s proposal [1] that decreased eNOS expression in old rats is related to impaired NO synthesis and endothelial smooth muscle relaxation of the cavernosum. This proposal accounts for L-NAME blocking the effects of ESWT on PMP, despite only directly affecting the NO pathway. The increase in cavernosal VEGF expression via ESWT activates protein kinase B (Akt) and subsequently stimulates eNOS production and activity, which ultimately results in vasodilation via the NO/cGMP signaling pathway [19]. Therefore, we propose the long-term increase in cavernosal blood flow caused by repeated rESWT is primarily dependent on microtrauma-induced increased VEGF expression, which subsequently results in increased levels of eNOS, followed by higher NO levels and finally increased PMP. Higher NO levels and PMP also have the potential to reduce the oxidative stress on SMCs and improve the corporal sinusoids’ ability to retain arterial inflow without venous leakage, further improving erectile function [5].
Limitations of our present study include a small sample size, which may explain why the trends in mRNA expression were not statistically significant. However, the correlation between expression levels of mRNA and protein abundance have historically been poor, with a correlation of about 40% found in multiple studies [27]. Mammalian cells also produce mRNA at a much lower rate than protein, as transcription rates in cells can reach 100 mRNA copies/hour compared to translation rates of up to 105 proteins/mRNA/hour [28]. Extensive cellular regulation between transcript and protein product including post-transcriptional and posttranslational modifications may further complicate this relationship. In addition, α-actin serves as an indirect marker for smooth muscle content. While our studies showed a significant increase in α-actin protein levels, further studies with more comprehensive measures of SMC function are warranted.
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CONCLUSIONS
Our study revealed a 2-fold increase in PMP from baseline following rESWT and a significant decrease in ESWT-induced PMP response after L-NAME. Additionally, repeated rESWT induced elevated expression of angiogenic markers (eNOS and VEGF) and smooth muscle content marker (α-actin), as evidenced by immunolocalization and Western blot analysis. Our findings suggest that microtrauma from rESWT leads to an increase in cavernosal endothelial and smooth muscle contents, likely mediated by increased VEGF expression, which stimulates eNOS and enhances penile perfusion via the NO/cGMP signaling pathway (analogous to mechanisms proposed for fESWT). Further studies with larger sample sizes and comprehensive mechanistic studies are warranted to elucidate the full therapeutic potential and underlying mechanism of rESWT in ED treatment. Given the widespread use of radial shock wave devices and their classification as a FDA class I device, rESWT devices are significantly more convenient and user-friendly to treat aging-related ED.
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Notes
Conflict of Interest:The authors have nothing to disclose.
Funding:This work was partially supported by funding from UCSD Academic Senate and by the Starting growth Technological R&D Program (TIPS Program [No. RS-2023-00285144]) funded by the Ministry of SMEs and Startups (MSS, Korea) in 2023.
Author Contribution:
Conceptualization: MRR, SWK, WJB, TCH.
Data curation: STC, JS, NS, SRS, MRR.
Formal analysis: STC, JS, NS, MRR.
Funding acquisition: MRR, SWK, WJB.
Investigation: STC, JS, NS, MRR.
Methodology: MRR, YSC.
Resources: MRR, SWK, WJB.
Software: MRR.
Writing – original draft: STC, JS, NS.
Writing – review & editing: MRR, STC, WJB, JS, SRS, YSC, SWK, TCH.
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Acknowledgements
The authors thank HNT Medical for providing the rESWT device used in this study.
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Data Sharing Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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- UCSD Academic Senate
- Ministry of SMEs and Startups
RS-2023-00285144
