Mitochondrial transplantation—a novel therapeutic strategy for erectile dysfunction: a narrative review

Introduction

Erectile dysfunction (ED) affects an increasing proportion of men worldwide, with prevalence estimates ranging from 3% to 76.5%, and is projected to exceed 322 million cases by 2025 due to aging populations and metabolic comorbidities (1-3). Pathophysiologically, ED is a heterogeneous disorder that can be broadly classified into five major categories: vasculogenic, characterized by arterial insufficiency or veno-occlusive dysfunction; neurogenic, arising from central or peripheral nerve injury (e.g., spinal trauma, prostatectomy); endocrinologic, involving hormonal imbalances such as hypogonadism or hyperprolactinemia; psychogenic, stemming from depression, anxiety, or relationship stressors; and iatrogenic or drug-induced, associated with agents like β-blockers, selective serotonin reuptake inhibitors (SSRIs), or antipsychotics (2-4). In many aging individuals, these etiologies converge, resulting in a multifactorial ED phenotype. Beyond its impact on sexual health, ED often heralds systemic disorders such as cardiovascular disease and diabetes, underscoring the need for mechanism-based therapies.

Since the advent of phosphodiesterase-5 inhibitors (PDE5i), ED management has primarily focused on enhancing the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway to promote relaxation of corpus cavernosum smooth muscle (5). Nevertheless, approximately 30% of ED patients, particularly those with neurogenic or diabetic etiologies, remain refractory, and many experience adverse effects or contraindications that limit adherence (6,7). These limitations highlight the unmet need for novel strategies targeting upstream pathophysiological mechanisms.

Mitochondria are critical regulators of cellular bioenergetics and redox homeostasis; their dysfunction in penile tissue disrupts endothelial NO availability and promotes oxidative stress, mitophagy imbalance, and apoptosis in cavernous smooth muscle cells (8,9). Originally developed to salvage ischemia-reperfusion-injured (IRI) myocardium, mitochondrial transplantation (MT) involves the direct delivery of viable organelles to restore adenosine triphosphate (ATP) synthesis and attenuate reactive oxygen species (ROS) (10). Preliminary ED models demonstrate that intracavernosal injection of adipose-derived mesenchymal stem cell (ADMSC)-derived mitochondria significantly improves intracavernosal pressure/mean arterial pressure (ICP/MAP) ratios, reduces ROS and cleaved-caspase-3 expression, and enhances antioxidant defenses (11). Building on these findings, this review critically examines current MT methodologies, underlying mechanistic insights, immunological considerations, and the translational challenges in refractory ED. We present this article in accordance with the Narrative Review reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-531/rc).

Methods

This review employed a systematic literature search to comprehensively synthesize evidence on MT and mitochondrial dysfunction in the context of ED. Databases searched included PubMed, Embase, and Web of Science, covering publications from January 2000 to July 2025. Search strategies utilized keywords such as “mitochondrial transplantation”, “erectile dysfunction”, “mitochondrial dysfunction”, “ROS”, and “apoptosis”, combined with Boolean operators (e.g., “mitochondrial transplantation AND erectile dysfunction” or “mitochondrial dysfunction OR apoptosis AND ED”).

Inclusion criteria were: (I) peer-reviewed original research articles or review papers examining mitochondrial dysfunction or MT in ED or related preclinical/clinical models (e.g., cavernous nerve injury or diabetic models); (II) English-language publications; and (III) studies emphasizing mechanistic insights (e.g., ATP restoration, ROS attenuation), therapeutic applications, or translational challenges. Exclusion criteria encompassed: (I) non-ED-focused mitochondrial studies (e.g., cardiac-only applications without penile tissue parallels); (II) abstracts, editorials, or case reports lacking substantive mechanistic or outcome data; and (III) preclinical investigations without functional endpoints (e.g., ICP/MAP ratios or erectile hemodynamics).

The search initially identified 1,247 abstracts, from which 289 full-text articles were retrieved and evaluated for eligibility, ultimately yielding 58 key references incorporated into this review (Table 1). To minimize selection bias, preference was given to high-impact studies with quantifiable outcomes, such as ICP/MAP improvements or ATP level measurements, while critically acknowledging the field’s skew toward positive preclinical results and limited clinical data. Potential biases, including publication bias toward efficacious interventions, are addressed throughout the manuscript via discussions of study limitations and calls for broader validation.

Mitochondrial dysfunction in ED

Mitochondrial dysfunction has emerged as a central driver of ED, manifesting as impaired bioenergetics, excessive ROS production, deranged organelle dynamics and mitophagy, and activation of apoptotic pathways in corpus cavernosum smooth muscle cells (CCSMCs) and endothelial cells. These defects impair NO signaling and relaxation of corpus cavernosum smooth muscle, ultimately reducing erectile capacity (12,13) (Figure 1).

Figure 1 Mitochondrial dysfunction-mediated pathogenesis of erectile dysfunction. This schematic illustrates the central role of mitochondrial defects in ED pathogenesis within CCSMCs and endothelial cells. Key processes include: (I) bioenergetic impairment leading to ATP depletion, often reversed by stem cell therapies or pharmacological agents via pathways such as PI3K-Akt-SIRT1-PGC-1α-TFAM; (II) oxidative stress from excessive mtROS production, causing lipid peroxidation, protein oxidation, and mtDNA damage, with interventions targeting mtROS to preserve NO/cGMP signaling and endothelial function; (III) dysregulated mitochondrial dynamics and mitophagy, involving altered fission-fusion balance and AMPK-mTOR-PINK1/Parkin pathways to control organelle turnover and reduce ROS accumulation; (IV) activation of apoptotic pathways, characterized by increased Bax/Bcl-2 ratio, cleaved caspase-3, TUNEL-positive cells, mPTP opening, cytochrome c release, and loss of MMP (Δψm), contributing to cell death, fibrosis, and reduced erectile capacity. These defects collectively impair NO signaling and corpus cavernosum smooth muscle relaxation. Created with BioGDP.com (14). Akt, protein kinase B; ATP, adenosine triphosphate; Bax, Bcl-2-associated X protein; Bcl-2, B-cell lymphoma 2; CCSMCs, corpus cavernosum smooth muscle cells; cGMP, cyclic guanosine monophosphate; ED, erectile dysfunction; MMP, mitochondrial membrane potential; mPTP, mitochondrial permeability transition pore; mtROS, mitochondrial reactive oxygen species; NO, nitric oxide; Nrf2, nuclear factor erythroid 2-related factor 2; PGC-1α, proliferator-activated receptor gamma coactivator 1-alpha; PI3K, phosphoinositide 3-kinase; SIRT1, Sirtuin 1; TFAM, transcription factor A, mitochondrial; TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labeling.

Bioenergetic impairment and ATP depletion in ED

In cavernous-nerve-injury (CNI) rat models of ED, ATP levels in penile tissue are markedly reduced. However, after injection of adipose-derived stem cells (ADSCs) or human umbilical cord mesenchymal stem cells (hUC-MSCs) into CCSMCs, phosphoinositide 3-kinase (PI3K)-protein kinase B (Akt) is phosphorylated to promote Sirtuin 1 (SIRT1) expression, thereby activating peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and promoting transcription factor A, mitochondrial (TFAM) transcription, restoring mitochondrial ATP production capacity (9). Similar findings are observed in diabetic ED models, where excessive mitochondrial autophagy and respiratory chain disruption lead to ATP depletion; pharmacological intervention with icariside II enhances ATP levels by modulating mitochondrial turnover (13).

Oxidative stress and ROS overproduction in ED

Dysfunctional mitochondria in ED generate excess mitochondrial ROS (mtROS), driving lipid peroxidation, protein oxidation, and mitochondrial DNA damage in penile tissue (12,15). Activation of mitochondrial ATP-dependent K⁺ channels has been shown to attenuate ROS overproduction, preserve endothelial NO release, and protect erectile tissue against ischemic injury, highlighting mtROS as a key therapeutic target (16). In a study of rats with diabetic ED, the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant pathway was weakened, excessive ROS impaired NO/cGMP signaling, and destroyed the rats’ penile endothelial function, and these abnormal indicators were reversed after restoring the Nrf2 pathway using dimethyl fumarate (17).

Dysregulated mitochondrial dynamics and mitophagy in ED

Alterations in mitochondrial fission-fusion balance are implicated in ED: reduced expression of the fission protein FIS1 correlates with increased ED risk, and agents such as resveratrol or quercetin can modulate FIS1 to restore mitochondrial dynamics (18). In diabetes-related ED, a piezoelectric nanosystem promotes physiological mitophagy, reducing ROS accumulation and mitochondrial damage while supporting corpus cavernosum repair, underscoring the need for controlled organelle turnover (19). AMPK-mTOR signaling fine-tunes mitophagy, where AMPK activation inhibits mTOR to promote PINK1/Parkin-dependent clearance of damaged organelles, restoring dynamics in aging-related ED (20).

Apoptosis and cell-death pathways in ED

Mitochondrial injury in ED triggers intrinsic apoptotic cascades in CCSMCs and endothelial cells, characterized by an increased B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax)/Bcl-2 ratio, upregulation of cleaved caspase-3, and accumulation of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells, ultimately contributing to smooth muscle loss and fibrosis of corpus cavernosum (13,21). Overexpression of Argonaute 2 rescues mitochondrial membrane potential (MMP) and reduces apoptosis in CNI-induced ED mice, directly linking mitochondrial integrity to cell survival and erectile function (21). Besides, mitochondrial permeability transition pore (mPTP) opening exacerbates Δψm loss and cytochrome c release, amplifying caspase-3 activation; its inhibition preserves MMP and curbs apoptosis in CNI models (21,22).

Histological and functional correlation in ED

Morphologically, ED models exhibit reduced mitochondrial mass within CCSMCs, increased collagen deposition, and decreased smooth muscle content. MSC therapies, whether through direct mitochondrial transfer or mitochondria-rich microvesicles, restore mitochondrial number, ATP levels, and tissue architecture, correlating with improved ICP and erectile outcomes (9,23).

Collectively, these findings provide a comprehensive view of mitochondrial dysfunction in ED, spanning energy failure, oxidative injury, maladaptive quality control, and apoptosis—all of which compromise penile hemodynamics and smooth muscle tone. Understanding these mechanisms lays the groundwork for the development of novel mitochondria-targeted therapies in ED.

MT

MT has emerged as a versatile approach to rescue bioenergetic failure in injured tissues by delivering healthy organelles directly into the target environment. It combines the immunological safety of autologous grafts with the scalability of stem cell-derived sources, utilizing rapid bedside isolation and stringent quality control, and adapts multiple delivery vehicles, ranging from direct injections to advanced carrier systems, to optimize mitochondrial survival, uptake, and functional engraftment (Figure 2).

Figure 2 Workflow and mechanistic actions of mitochondrial transplantation in erectile dysfunction. This workflow schematic illustrates the procedural steps and downstream cellular effects of MT for ED. First, active mitochondria are isolated from autologous or allogeneic tissues or cells, and subjected to quality control analyses—JC-1 fluorescence for Δψₘ activity and high resolution respirometry (OCR) for OXPHOS activity, and subjected to quality control assays—JC-1 fluorescence for Δψₘ and high-resolution respirometry (OCR) for OXPHOS capacity. Three delivery strategies are then employed: (I) direct intracavernosal injection for immediate organelle deposition; (II) thermosensitive hydrogel encapsulation for sustained release and extracellular protection; and (III) extracellular vesicle-mediated transfer for natural vesicular uptake. Upon internalization by CCSMCs, exogenous mitochondria restore intracellular ATP production, scavenge ROS to rebalance redox homeostasis, reestablish mitochondrial dynamics and mitophagy, and inhibit intrinsic apoptotic pathways. Collectively, these actions preserve smooth muscle integrity and ultimately restore erectile function in preclinical ED models. Created with BioGDP.com (14). ATP, adenosine triphosphate; CCSMCs, corpus cavernosum smooth muscle cells; ED, erectile dysfunction; EV, extracellular vesicle; MT, mitochondrial transplantation; OCR, oxygen consumption rate; OXPHOS, oxidative phosphorylation; ROS, reactive oxygen species.

MT protocols typically harvest viable mitochondria from autologous tissues to minimize immunogenicity, but have increasingly leveraged stem cell lines, especially ADSCs and induced pluripotent stem cell-derived MSCs, due to their high expansion capacity and robust respiratory activity (24,25). MSCs are a well-characterized and prolific source of functional mitochondria. They are readily available from multiple tissues (adipose, bone marrow) and can be expanded in culture, allowing for the generation of large mitochondrial quantities from a single donor source, which is crucial for allogeneic approaches. In contrast, sourcing mitochondria from skeletal muscle is more invasive and yields lower quantities. Most recently, a “mito-condition” culture medium was developed containing nine defined components—basic fibroblast growth factor, sodium bicarbonate, lipid concentrate, insulin-transferrin-selenium, progesterone, hydrocortisone, vitamin C, heparin sodium, and human platelet lysate. When applied to MSC cultures, this medium increased mitochondrial content by 2.8-fold per cell and, through enhanced proliferation, resulted in an overall 854-fold increase in total mitochondria over 15 days. These “mito-condition” mitochondria also exhibited significantly higher ATP production, enhanced spare respiratory capacity, and activation of the AMP-activated protein kinase-transcription factor A mitochondria mitobiogenesis pathway, thereby facilitating large-scale procurement of high-quality organelles for transplantation (26).

To minimize allogeneic risks and logistical complexity, most studies utilize “same-procedure” autografts, isolating mitochondria intraoperatively and delivering them promptly. This strategy has proven safe and effective in pediatric IRI, where mitochondria were injected intracoronarily or into the epicardium, resulting in enhanced ventricular recovery without increasing the inflammatory burden (23,27). After harvest, mitochondria are isolated using rapid mechanical homogenization combined with differential centrifugation or optimized filtration, yielding high-purity, respiration-competent organelles in less than 30 minutes—essential for preserving MMP and ATP-synthesizing capacity (28,29). Yet even subtle variations in filter pore size or homogenization cycles can markedly affect mitochondrial integrity and contamination rates, highlighting the need for standardized, automated filtration systems to ensure reproducible yields (28).

Mitochondrial quality control typically involves JC-1 staining to assess inner membrane polarization, and high-resolution respirometry [oxygen consumption rate (OCR) measurements] to confirm functional oxidative phosphorylation prior to clinical or preclinical application (29,30). Once prepared, mitochondria may be administered by direct tissue injection—intracoronary or epicardial in cardiac ischemia-reperfusion (I/R) models and intracavernosal in ED models—enabling organelles to integrate into host cells, replenish ATP, and reduce oxidative stress (11,24). To further improve mitochondrial retention and protect against extracellular insults, researchers have encapsulated organelles within hydrogels, nanoparticles, or extracellular vesicles (EVs), achieving enhanced stability and uptake in neural and cardiac injury settings (31,32). Complementing these approaches, microvesicle-mediated transfer exploits natural intercellular trafficking pathways: mitochondria packaged in exosome-like vesicles can be delivered systemically and fuse with recipient cells to restore bioenergetics without direct injections (33).

Potential therapeutic effects of MT in ED

Current therapies and limitations

ED management has traditionally targeted downstream hemodynamic modulation, yet each modality carries distinct shortcomings that leave a substantial subset of patients undertreated (Table 2). In addition to the previously mentioned “nonresponders” to PDE5i (6), systemic adverse effects (headache, flushing, dyspepsia, and rare but serious events) occur in as many as 27% of users, while nitrate therapy remains an absolute contraindication; furthermore, concomitant use of nitrates remains an absolute contraindication. This further limits the applicability of the program (7).

When PDE5i therapy proves insufficient, intracavernosal injection of prostaglandin E₁ (alprostadil) can restore erectile function in about 70% of PDE5i nonresponders; however, its invasiveness and side-effect profile hinder long-term adherence. Penile pain occurs in 61% of recipients, priapism in 6.5%, and corporal fibrosis in 3.2%, leading to discontinuation rates exceeding 40% within 1 year (34). Vacuum erection devices provide a non-pharmacologic option with immediate efficacy; however, nearly half of patients discontinue use within 12 months due to discomfort, penile bruising, and the cumbersome application process (35). For the most refractory cases, inflatable penile prostheses provide reliable rigidity and spontaneity but are generally reserved as a last resort because of surgical risks and device complications. Primary implantation carries an infection risk of 2%, while revision surgeries experience mechanical failure rates up to 13.3%; other series report infection in 6% and device malfunction in 4% of primary implants, all of which contribute to patient reluctance and underutilization (36).

Although MT is still in the preclinical stage for the treatment of ED, comparisons with regenerative therapies such as stem cell therapy (SCT) and gene therapy provide context for its translational potential. SCT, particularly adipose-derived regenerative cell (ADRC) injections, has completed phase I clinical trials. Haahr et al. reported that in patients with ED after radical prostatectomy (N≈17), a single autologous ADRC injection showed good safety within 12 months of follow-up and significantly improved International Index of Erectile Function-5 (IIEF-5) scores in patients with controlled incontinence (approximately 50% of patients improved from severe to mild/moderate), suggesting that paracrine factors such as vascular endothelial growth factor (VEGF) and NO play a role (37). For example, the ongoing NCT04594850 trial (Cellgram-ED) is also exploring its efficacy and safety. In terms of gene therapy, Melman et al. reported the world’s first phase I trial of human gene therapy for ED as early as 2006. Naked plasmid DNA carrying the hMaxi-K channel gene was injected intracavernosally. The results showed that the International Index of Erectile Function-Erectile Function domain (IIEF-EF) score showed an improvement trend within 24 weeks and was well tolerated, but the expression persistence was limited (38). In contrast, MT can provide direct bioenergetic restoration and may synergize with the trophic effects of SCT. For example, MSC-derived MT can amplify ATP in SCT transplanted cells. However, both face the obstacle of immunogenicity, and the rejection rate of allogeneic SCT is approximately 10%. The advantage of MT is the rapid (<30 minutes) autologous separation, but human data are lacking; head-to-head trials are necessary in the future.

Beyond its standalone potential, MT may also act synergistically with established therapies for ED. PDE5i have been reported to protect mitochondrial function, enhance bioenergetics, and reduce oxidative stress (39), while low-intensity shockwave therapy (LI-ESWT) promotes angiogenesis, endothelial repair, and progenitor cell recruitment (40). These mechanisms are theoretically complementary to MT, as improved vascular support and reduced oxidative injury could enhance the survival, uptake, and functional integration of transplanted mitochondria. Although no studies have yet examined MT combined with PDE5i or LI-ESWT, the demonstrated benefits of combining SCT with LI-ESWT in ED models provide proof-of-concept support (41). Future preclinical studies should therefore investigate whether MT-based combination regimens can achieve more durable and robust functional recovery than single-modality treatment.

Mechanisms of MT for the treatment of ED

Conventional vasodilatory and mechanical modalities alleviate symptoms of ED but fail to correct the fundamental bioenergetic collapse in CCSMCs. At the core of ED pathophysiology lies a cascade of mitochondrial derangements—loss of MMP (Δψₘ), ATP depletion, excessive ROS accumulation, impaired mitophagy, and initiation of apoptotic signaling—which remain unaddressed by downstream hemodynamic interventions.

Yet MT may potentially and fundamentally address these upstream failures. Studies on the molecular mechanisms of mitochondrial internalization have shown that smooth muscle cells can take up exogenous mitochondria through clathrin/dynein-dependent endocytosis or macrocytosis, and that inhibiting dynein activity significantly reduces endocytic efficiency (42). In contrast, mitochondrial uptake in endothelial cells is more likely to rely on CD36-mediated lipid rafts or caveolae-related pathways (43). Restored Δψₘ drives oxidative phosphorylation and replenishes ATP stores, while dilution of damaged mitochondria and activation of endogenous antioxidant pathways normalize redox homeostasis. Furthermore, infusion of healthy mitochondria alleviates mitophagic overload and inhibits both caspase-dependent apoptosis and ferroptosis, thereby preserving smooth muscle viability and contractile function.

Preclinical evidence suggests this mechanism-driven strategy was first validated in IR cardiac injury models, where autologous mitochondrial injections at reperfusion improved myocardial performance in pigs (44), and subsequently demonstrated safety and feasibility in phase I pediatric trials of intracoronary MT during congenital heart surgery (24,32).

Preclinical proof

The therapeutic potential of MT in ED has been substantiated through pivotal preclinical studies, which provide foundational mechanistic and functional evidence.

In a landmark investigation, Zhai et al. isolated mitochondria from ADMSCs and delivered them via intracavernosal injection to rats with CNI—a widely used model of neurogenic ED. MT-treated animals demonstrated a 50% increase in the maximal intracavernosal pressure to mean arterial pressure ratio (ICPₘₐₓ/MAP), indicating substantial recovery of erectile hemodynamics. At the molecular level, mtROS production was reduced by 40%, cleaved caspase-3 expression decreased two-fold, and antioxidant defenses were markedly enhanced, as evidenced by elevated superoxide dismutase activity and increased intracellular ATP content in CCSMCs (11).

Building on these findings, Liang et al. employed a systemic delivery strategy, administering mitochondria-rich microvesicles (Mito-MVs) to CNI-ED rats. This approach similarly restored ICPₘₐₓ/MAP values to near-baseline levels, preserved structural integrity of the penile smooth muscle [as indicated by α-smooth muscle actin (α-SMA) expression], and significantly attenuated oxidative stress and ferroptosis, including reductions in lipid peroxidation and preservation of glutathione peroxidase 4 levels (23).

While efficacy is evident at 2–4 weeks post-MT (e.g., sustained 50% ICP/MAP recovery), durability data are limited (11); cardiac analogs show 8–12 weeks mitochondrial persistence (44). Tracking the fate of transplanted mitochondria over extended periods using lineage-tracing or similar technologies is an essential future study. Future ED studies should incorporate serial OCR assessments and biopsies to track long-term engraftment, particularly in chronic models. Importantly, although improvements in erectile hemodynamics, oxidative stress, and smooth muscle preservation are consistently observed, evidence regarding broader mechanisms—such as reversal of fibrosis or restoration of endothelial function—remains preliminary and is derived from a limited number of animal studies. These data, while promising, require cautious interpretation, and further work in larger cohorts and diverse ED models is essential to delineate the robustness and clinical relevance of these mechanistic effects.

Multiple ED models’ validation is needed

Currently, preclinical studies on MT for ED have focused on CNI models only, but the etiology of ED in clinical populations is diverse, encompassing metabolic, vascular, neurogenic and medical factors. To ensure a smooth translation of MT technology to the clinic, validation in multiple ED models is essential.

One of the most prevalent and challenging forms of ED occurs in the setting of diabetes mellitus, where hyperglycemia induces chronic oxidative stress, endothelial dysfunction, and progressive mitochondrial impairment within penile tissue. Recent single-cell transcriptome analyses reveal that mitochondrial dysfunction is a central feature of diabetic ED, influencing cellular heterogeneity, inflammatory responses, and ROS-mediated smooth muscle apoptosis through cytochrome C and mtDNA release into the cytoplasm (15,45). Furthermore, systemic mitochondrial defects caused by diabetes may reduce local MT efficacy through competitive uptake/ROS amplification (45), which can be alleviated by intracavernous targeted therapy and adjunctive Nrf2 activators, thereby enhancing penis-specific repair. Although direct MT studies in diabetic ED models remain limited, existing evidence indicates reduced MMP, elevated ROS, and decreased ATP levels in CCSMCs, mirroring CNI defects and suggesting MT’s potential to restore bioenergetics via intracavernosal delivery. Preclinical platforms such as streptozotocin (STZ)-induced or high-fat diet (HFD)-fed diabetic rats offer ideal testing grounds, where MT could be evaluated for efficacy in mitigating hyperglycemia-driven mitophagy overload and fibrosis.

Similarly, aging-related ED, which affects a substantial proportion of the elderly male population, is associated with age-dependent mitochondrial dysfunction, including diminished biogenesis, accumulated mtDNA mutations, and impaired mitophagy. Age-related decline in erectile performance has been linked to reduced expression of mitochondrial regulators such as PGC-1α and SIRT3, alongside compromised ATP synthesis and oxidative stress in penile smooth muscle, as evidenced by endothelial bioenergetic blunting in obesity-aging models (8,46). Although no studies have yet applied MT to aging-related ED, these molecular signatures—exacerbated by chronic ROS—provide a strong rationale for investigation, with mitochondrial-targeted antioxidants like Mito-Q showing partial reversal of age-induced deficits. HFD models simulating gradual mitochondrial decline would enable assessment of MT’s durability in restoring biogenesis pathways.

Another clinically relevant form is radiation-induced ED, which is commonly seen in patients receiving pelvic radiotherapy for prostate or colorectal cancer. Radiation causes endothelial damage, fibrosis, and mtDNA damage in penile tissue, triggering mitochondrial fission, superoxide generation, and premature senescence that culminate in obliterative endarteritis and ischemia (47,48). It has been demonstrated that transplantation of ADSCs improves radiation-induced ED in rats by promoting cavernous nerve regeneration and restoring smooth muscle content (49); however, MT could offer superior organelle-level repair by directly countering fission and mtDNA fragmentation. Further experiments in irradiated rat models are needed to validate MT’s therapeutic efficacy, particularly in preventing long-term apoptotic cascades.

These models share core mitochondrial defects—such as ROS overproduction, Δψm collapse, and apoptotic signaling—with CNI, positioning MT as a versatile, mechanism-based therapy across ED etiologies and underscoring the urgency for expanded preclinical validation.

Challenges for future development of MT in ED

Before MT can be translated into a viable treatment for ED, several critical challenges must be addressed: scalable, standardized isolation and storage of clinical-grade mitochondria; immunogenicity and safety concerns, particularly allogeneic approaches; and targeted delivery and dose optimization. Below, we outline each challenge and propose future directions to address them.

Manufacturing and standardization

Scalable, reproducible isolation of high-quality mitochondria is paramount. Recent advances in “mito-condition” culture media have boosted mitochondrial yield by more than 800-fold in MSCs, while preserving ATP production and respiratory capacity (26). Clinical MT isolation costs ~$5,000–10,000 per procedure (24), surpassing PDE5i annual expenses ($500–1,000) yet rivaling prosthesis implantation ($15,000–25,000) (35); ‘mito-condition’ media could halve costs via 800-fold yield gains (26). Autologous MT, if effective, would likely be a one-time or limited-series procedure. While currently expensive, costs could decrease with standardized kits and automation. Its economic viability would hinge on its durability. If it provides long-term cure, it could be cost-competitive with lifelong pills or prostheses. Optimized differential filtration protocols can isolate mitochondria in under 30 minutes with high purity. However, subtle variations in filter pore size or homogenization cycles can significantly impact both yield and organelle integrity. Moreover, there is currently no standardized method for long-term mitochondrial preservation; pharmaceutical formulations or lyophilized preparations must be developed to ensure stability and support clinical logistics (50).

Immunogenicity and allogeneic considerations

While autologous MT appears safe, with no significant inflammation or adverse events reported in pediatric IRI and extracorporeal membrane oxygenation (ECMO) studies (51), allogeneic MT raises concerns about immune activation, primarily through major histocompatibility complex (MHC) class I molecules expressed on mitochondrial outer membranes, which can directly elicit CD8⁺ T-cell recognition and cytotoxic responses, as observed in cardiac allograft models where mismatched mitochondria accelerate rejection (52). Concurrently, innate immune activation occurs via Toll-like receptor 9 (TLR9) sensing of unmethylated CpG motifs in mtDNA, triggering NF-κB signaling and pro-inflammatory cytokine release that amplifies adaptive immunity (53). To mitigate these, strategies include modulating donor mitochondrial fusion/fission dynamics—e.g., promoting fusion via Mfn1/2 overexpression to mask MHC epitopes and reduce T-cell infiltration, extending graft survival by 20–30% in preclinical transplants (54). EV encapsulation leverages EVs’ inherent tolerogenic properties, such as TGF-β-enriched cargo from regulatory T-cell-derived EVs, to shield mitochondria and suppress alloimmune responses in hepatic IRI models (55). While autologous MT circumvents these risks entirely, allogeneic innovations are essential for scalability in resource-limited settings.

While some EVs (specifically mitochondrial-derived vesicles) can carry mitochondrial components, MT delivers a high dose of intact, fully functional organelles. The mechanism of EV therapy is predominantly paracrine signaling via a cocktail of miRNAs, cytokines, and growth factors, with mitochondrial transfer being a minor component. In contrast, MT’s primary proposed mechanism is direct bioenergetic support and mitochondrial genome complementation. MT and EVs are complementary but distinct approaches.

Targeted delivery and dose optimization

Efficient, site-specific delivery of mitochondria remains a key bottleneck (Table 3). Transplanted mitochondria are primarily internalized by cells in a distressed state via endocytosis-like mechanisms, potentially offering some natural targeting specificity. However, off-target effects are a theoretical risk. Off-target effects include macrophage phagocytosis in inflamed tissue, risking immune flares, or ATP provision to tumor cells in comorbid patients; however, ED models indicate >70% preferential CCSMC/endothelial uptake (11). Mitochondrial tracking using mtDNA fluorescent labeling is urgently needed to investigate the selectivity of mitochondrial uptake in various cell types. There is no direct evidence of mitochondria being taken up by immune cells or tumor cells in the context of MT therapy. The possibility of fueling tumor growth is a serious consideration. MT should be contraindicated in patients with active malignancy in or near the treatment area until more safety data are available.

Thermogelling, erodible hydrogels (composed of methylcellulose and hyaluronic acid) facilitate the localized, sustained release of viable mitochondria in vivo, preserving organelle bioenergetics and improving retention (56).

Nanoparticle- and hydrogel-assisted approaches further enhanced mitochondrial delivery in large-animal stroke models, demonstrating proof-of-principle for advanced carriers (57). Both dose and internalization kinetics are critical. Likewise, mitochondria-targeting drug delivery systems (e.g., MITO-Porter liposomal carriers) show promise for improving cellular uptake and mitochondrial localization (50).

Besides, efficient mitochondrial dosage determination is essential to balance efficacy and safety, integrating preclinical dose-response curves from cardiac ischemia-reperfusion models (e.g., 10⁷–10⁸ mitochondria/kg body weight, yielding optimal cardioprotection without toxicity) (58) scaled to penile tissue volume (~5–10 mL in humans, approximating 5×10⁷–10⁸ total organelles per injection). Pre-injection validation via OCR assays ensures viability (>80% respiratory capacity), while post-treatment endpoints like ICP/MAP ratios guide titration. Overdosing risks mitophagic overload from excessive organelle fusion or ROS bursts via mtDNA release, potentially disrupting cellular metabolism; however, no adverse events were reported in CNI-ED models at 300 µg doses (11), and cardiac data delineate a therapeutic window of 10⁶–10⁹ mitochondria, beyond which inflammation rises. Serial biopsies and ROS biomarkers are recommended for monitoring.

Clinical application of MT requires a more complete chain of evidence

To provide more comprehensive research evidence, we have devised a five-step plan: (I) porcine large-animal studies to validate intracavernosal delivery/dosing; (II) preclinical testing in diabetic/aging/radiation models; (III) phase I safety trial in post-prostatectomy CNI patients; (IV) phase II efficacy in refractory ED cohorts; (V) multicenter randomized controlled trials (RCTs) vs. sham/PDE5i, assessing >6-month durability via ICP/OCR. These research initiatives could provide the stronger support currently lacking for MT as a treatment for ED, but that doesn’t mean they all need to be started from scratch.

Cardiac MT phase I trials (e.g., autologous intracoronary delivery in pediatric IRI, showing no inflammation and <30-min isolation) inform ED trial design: prioritize bedside autologous sourcing, escalate doses from 10⁸ mitochondria, and combine ICP/MAP efficacy endpoints with penile-specific biomarkers (e.g., ROS/troponin-like assays) for safety monitoring (24). For early-phase ED trials, we can adopt these protocols, focusing on men with ED post-radical prostatectomy (a condition with clear mitochondrial involvement, akin to the targeted patient population in cardiac surgery). Other types of research can also be referenced from previous studies.

Conclusions

MT holds potential to outperform traditional therapies by directly addressing mitochondrial dysfunction, which is a fundamental contributor to ED pathology. Preclinical studies have confirmed that MT not only restores the energy metabolism and redox balance of spongy tissues but also reverses apoptosis and fibrosis, providing a mechanistic breakthrough in ED treatment. Nevertheless, several challenges remain for clinical translation: the need to standardize mitochondrial preparation to ensure consistent quality; to optimize delivery methods for improved targeting and retention; and to establish the long-term safety and immunocompatibility of allogeneic grafts. Future studies should focus on large animal model validation, efficacy assessment of multi-causal EDs (e.g., diabetes and aging-related), and designing early-phase clinical trials. If these challenges are successfully addressed, MT is expected to be a revolutionary therapeutic option for refractory ED and offer valuable insights for the treatment of other mitochondria-related diseases.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-531/rc

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-531/prf

Funding: This study was supported by National Natural Science Foundation of China (No. 82474522, to J.C.).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-531/coif). J.C. receives funding from National Natural Science Foundation of China (No. 82474522). The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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