The role of exosomes as oligonucleotide delivery system for managing α-synuclein in Parkinson’s disease: A systematic review of in vivo studies

Abstract

Although Parkinson’s disease (PD) is primarily idiopathic, genetic mutations—accounting for approximately 5%–15% of cases with regional variability—have prompted the development of gene expression modulators, such as oligonucleotides, to target and reduce alpha-synuclein (α-syn) accumulation. However, challenges in delivering these agents to the brain have limited their therapeutic potential. This study systematically reviews the use of exosomes as delivery systems for oligonucleotides aimed at reducing α-syn aggregation in PD. A comprehensive literature search was conducted using Scopus, Embase, OVID, and ISI Web of Science databases up to January 2022, targeting in vivo studies relevant to the subject. Of 904 initial records, five eligible studies were selected. Three utilized transgenic mouse models and two used induced models to simulate PD. All reported a reduction in α-syn aggregation in the midbrain—particularly in the substantia nigra—following treatment with exosome-delivered oligonucleotides. This reduction was associated with decreased neuronal death and improved motor function. No significant toxicity or immune response was reported. Exosome-mediated oligonucleotide delivery appears to be a promising approach to reduce α-syn aggregation, protect dopaminergic neurons, and improve motor symptoms in animal models of PD.

Graphical abstract

Exosome-mediated delivery of oligonucleotides effectively reduces α-synuclein aggregation, preserves dopaminergic neurons, and improves motor function in Parkinson’s disease models, highlighting exosomes as promising carriers for brain-targeted RNA therapeutics.

Introduction

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, characterized by motor impairments such as tremor, rigidity, and bradykinesia, as well as a wide spectrum of non-motor symptoms including cognitive decline, sleep disturbances, and autonomic dysfunction.^1,2,3 Current treatments—including levodopa, dopamine agonists, MAO-B inhibitors, and deep brain stimulation—provide symptomatic relief but fail to halt or reverse disease progression.^1,4 This underscores the urgent need for disease-modifying therapies.

The pathophysiology of PD involves the progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta, accompanied by widespread deposition of misfolded α-syn in Lewy bodies. Although other mechanisms, such as mitochondrial dysfunction, oxidative stress, and neuroinflammation, contribute to disease pathology, α-syn aggregation remains a central hallmark of PD and an important therapeutic target.^5,6,7,8

Oligonucleotide-based therapeutics, including antisense oligonucleotides (ASOs), small interfering RNAs (siRNAs), and DNA or RNA aptamers, represent an emerging class of disease-modifying strategies in PD. These molecules act by reducing α-syn synthesis at the mRNA level or by directly interfering with protein aggregation. Preclinical studies have shown that oligonucleotides can suppress α-syn expression, reduce aggregation, and improve neuronal survival.^9,10,11 However, their clinical translation is limited by poor stability in circulation, rapid degradation by nucleases, and inefficient delivery across the blood-brain barrier (BBB).^12,13 Exosomes offer a promising solution to these challenges due to their natural ability to encapsulate and protect nucleic acids, deliver them to target neurons, and minimize off-target immune responses.

Exosomes are nanosized extracellular vesicles (30–150 nm) secreted by most cell types and play a central role in intercellular communication. They contain proteins, lipids, and nucleic acids reflective of their parental cells and are enriched in membrane markers such as CD9, CD63, and CD81.¹⁴ Their biocompatibility and ability to transfer bioactive cargo have made them attractive therapeutic tools in neurological diseases.

A wide range of therapeutic cargo has been investigated in preclinical models. Beyond oligonucleotides, exosomes have successfully delivered small molecules (e.g., curcumin), proteins and enzymes (e.g., catalase), and even gene-editing systems such as CRISPR-Cas9.^15,16 To improve loading and targeting, several engineering approaches are employed, including electroporation, sonication, chemical conjugation, and surface functionalization with ligands such as rabies virus glycoprotein (RVG) peptide, which enhances neuronal uptake and BBB penetration.¹⁷

These features distinguish exosomes from synthetic carriers such as lipid nanoparticles or viral vectors by combining low immunogenicity with natural biodistribution. This unique versatility provides the foundation for their application in PD models, where effective and targeted delivery of oligonucleotides to reduce α-syn remains a therapeutic challenge.

In this systematic review, we summarize and critically evaluate preclinical in vivo studies that have used exosome-based oligonucleotide delivery to reduce α-syn burden in PD models.

Results

Study selection and PRISMA flow

A total of 904 papers were assessed based on title and abstract, with 878 articles being eliminated due to duplication and unnecessary content during this process. Twenty-one of the remaining 26 publications were rejected after full-text screening due to not loading any substances in exosomes or not investigating α-syn in Parkinson’s animal brain models. Finally, five papers met the criteria for this paper’s outcome analysis. These results were presented in Figure 1.

Figure 1.

PRISMA flow chart of selected articles in this systematic review

Characteristics of included animal models

A significant pathological constituent of PD neurons is α-syn aggregates. Therefore, trying to aggregate this protein can be used for PD model simulation. Three of these five studies used transgenic mice to express some human genes associated with inducing the natural accumulation of α-syn proteins. Human genes involved are the SNCA with a phosphomimic serine 129 under the control of the prion protein promoter (PrP-hSNCA-HAS129D)^18,19 and A53T mutation of SNCA.²⁰ In the S129D α-syn-HA model, although Cooper and Izco et al. found that α-syn aggregated throughout all the brain regions at 3 months, no abnormalities were detected in activity and motor functions at 6 months or dopamine neurons at 9 months of age.^18,19 Yang et al. demonstrated that the A53T mutation starts locomotor disorders at around 9 months due to expressing α-syn pathology at 6 months.²⁰ Comparing the results of these two models, it was concluded that α-syn pathology appeared earlier in the S129D α-syn-HA model. However, the duration of symptom onset was the same in both models (about 3 months) with completion occurring after 9 months of mouse ages.

Two other studies used normal mice and injected one of these substances 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or α-syn preformed fibril (PFF) for simulating α-syn aggregation. By intraperitoneal (i.p.) injection of 30 mg per kg of MPTP for 7 consecutive days in a classical neurotoxin model, Liu et al. demonstrated the α-syn aggregation in the substantia nigra (SN),²¹ and in another model, a final concentration of 2.5 μg/μL of mouse α-syn-PFF in PBS was stereotaxically injected into right dorsal neostriatum of wild-type mice for more than 5 min (about 20 min) with rate of 0.1 μL per min. In this way, indications of motor dysfunction began when α-syn localized to the intrastriatal region of the brain. However, during the short period of this model, obvious signs of dopaminergic neuron degeneration were not detected in mice.²² After all, because these two models only involved specific regions of the mice brain, they are suitable to address some particular issues.

Exosomal delivery of oligonucleotide for α-syn clearance

Yang et al.—i.c.v. delivery

Yang and colleagues demonstrated that repeated intracerebroventricular (i.c.v.) administration of 20 μg ASO4-loaded exosomes (three times per week for 6 weeks) significantly reduced α-syn mRNA and protein levels compared with scrambled controls. While naked ASO4 showed serum degradation and neuronal toxicity, exosome encapsulation protected oligonucleotides from degradation and improved therapeutic efficacy with reduced toxicity.²⁰

Ren et al.—i.p. aptamer delivery

Ren and colleagues administered 120 μg RVG-exosome-loaded DNA aptamer weekly via i.p. injection for 30 days. This significantly reduced pathological α-syn aggregation in the cortex and midbrain compared with controls. RVG-modified exosomes provided more efficient and safer aptamer delivery than unmodified exosomes.²²

Liu et al.—i.v. delivery, nanoparticle-enhanced exosomes

Liu et al. developed curcumin/phenylboronic acid-poly (2-(dimethylamino) ethyl acrylate) nanoparticles encapsulating siRNA against SNCA and delivered them via intravenous (i.v.) injection (every other day, 10 doses). Drug accumulation persisted for ≥48 h and co-localized with tyrosine hydroxylase-positive (TH+) neurons in the substantia nigra. RVG-modified exosomes showed enhanced brain uptake, avoided endo-lysosomal degradation, and outperformed unmodified exosomes and other controls.²¹

Izco et al.—i.v. shRNA-MC delivery

Izco et al. injected 150 μg RVG-exosome-short hairpin RNA (shRNA)-minicircles (MCs) intravenously into transgenic mice, resulting in reduced α-syn mRNA in the midbrain, cortex, and striatum and protein reductions primarily in the midbrain. Motor performance also improved, supporting that RVG exosomes deliver oligonucleotides more effectively and safely than unmodified carriers. Naked siRNA or unmodified exosomes did not produce significant effects.¹⁹

Cooper et al.—i.v. RVG-siRNA3 delivery

Systemic delivery of 150 μg RVG-exosome-siRNA3 into transgenic mice reduced α-syn mRNA and protein in the midbrain, striatum, and cortex after 1 week. RVG modification enhanced targeting specificity and delivery efficiency compared to exosomes alone.¹⁸

Comparative outcomes across studies

Overall, both i.c.v. and systemic administration reduced α-syn aggregation, though i.c.v. required lower doses and yielded more consistent molecular and functional benefits. Motor performance improvements and protection against dopaminergic neuronal degeneration were observed in most studies, with RVG-modified exosomes outperforming unmodified formulations. Table 1 summarizes these findings in detail.

Table 1.

A brief description of the paper’s parameters

Author name	Cell sources	Animals	Study groups	Dosage of drug type	Drug loading method	Route	Outcomes
Cooper et al.18	BmMDC	transgenic mice, 20–22 weeks, S129D α-syn-HA	1. control (RVG-exosome + CsiRNA) 2. treatment (RVG-exosome + siRNA3) 3. untreated	150 μg siRNA	electroporation	i.v.	α-syn aggregation↓; mRNA↓; protein↓; dopaminergic neuron loss↓
Izco et al.19	BmMDC	transgenic mice (C57BL6/C3H F1), 10–14 weeks, S129D α-syn-HA	1. RVG exosome + anti-α-syn shRNA-MCs (n = 10) 2. RVG exosome + anti-GFP shRNA-MCs (n = 5) 3. vehicle (n = 10)	150 μg RVG-exosomes +150 μg shRNA-MCs	electroporation	i.v.	α-syn aggregation↓; mRNA↓ protein↓; motor performance↑ dopaminergic neuron degeneration ↓
Yang et al.20	BmMSC	transgenic male mice, 24 weeks, α-syn A53T	1. exosome + scrambled ASO4 (n = 12, control) 2. exosome + ASO4 (n = 12, treatment)	20 μg ASO4	electroporation	i.c.v.	α-syn aggregation↓; mRNA↓; protein↓; motor performance↑; degeneration of dopaminergic neurons↓
Liu et al.21	BmMiDC	normal mice (C57BL/6), 6–8 weeks, no α-syn transgene	1. normal 2. 5% glucose 3. C/ANP/S 4. EXO-C/ANP/S 5. REXO-C/ANP/S	1 mg/kg siRNA	ultrasound	i.v.	α-syn aggregation↓; mRNA: not reported; α-syn protein: not reported; synaptic protein loss ↓; motor performance↑ neuronal death↓
Ren et al.22	HEKCL	normal female mice (C57BL/6J), 8–12 weeks, PFF-induced α-syn pathology	1. PBS (n = 12) 2. PFF + PBS (n = 12) 3. PFF + random DNA (n = 12) 4. PFF + aptamer (n = 12)	120 μg RVG exosomes with DNA aptamer F5R2	passive incubation (37°C)	i.p.	α-syn aggregation↓; mRNA: not reported; α-syn protein: not reported; synaptic protein loss ↓; motor performance↑ neuronal death↓

BmMSC, bone marrow mesenchymal stem cell; BmMDC, bone marrow murine dendrite cell; BmMiDC, bone marrow murine immature dendrite cell; HEKCL, human embryonic kidney cell line; MCs, minicircles; RVG, rabies viral glycoprotein; outcomes improved ↑; a decrease in outcomes ↓.

α-syn accumulation is closely linked to neuronal dysfunction and degeneration, making it a primary therapeutic target in PD through reduction of its aggregates. Accordingly, several studies have examined the role of exosomes in delivering therapeutic oligonucleotides into neurons to lower α-syn aggregation. While ASO4s alone are prone to serum degradation and toxicity, exosome encapsulation prevents these issues, enabling safer and more effective delivery. In 2021, Yang et al. demonstrated that i.c.v. injection of 20 μg exosome-ASO4, administered three times per week for 6 weeks, significantly reduced α-syn mRNA and protein levels compared with an exosome-scrambled ASO control group. They also reported that these nucleotide sequences could therefore be protected from degradation when loaded into exosomes and be more effective with less toxicity.²⁰

According to four other papers, RVG exosomes were tested as a targeting carrier that can adequately transfer the therapeutic oligonucleotides to the brain than unmodified exosomes.^18,19,21,22

Liu et al. created a device containing curcumin/phenylboronic acid-poly (2-(dimethylamino) ethyl acrylate) nanoparticle/siRNA targeting SNCA. Treatment plans included i.v. injection of five mice per group every other day for ten cycles. The authors also stated that drug accumulation lasted at 48 h and co-localized with TH+ neurons in the SN. They ultimately found that drug uptake enhancement caused the exosome and RVG-exosome groups to be significantly more effective than other controls (glucose-injected mice or C/ANP/S). The RVG-exosome group was also found to better avoid drug loss from endosome-lysosome pathways than the exosome group.²¹ Ren et al. declared that pathological α-syn aggregation decreased after 30 days compared to the control group when 120 μg RVG exosome of DNA aptamer was injected intraperitoneally every week. This reduction was observed in the cortex and midbrain. According to this study, RVG exosomes are more effective and safer at delivering aptamer to the brain neurons than unmodified exosomes.²² In a separate study, Cooper et al. reported that i.v. administration of 150 μg siRNA3 RVG exosomes for 1 week in transgenic mice significantly reduced α-syn mRNA and protein levels in the midbrain, striatum, and cortex compared with untreated controls. They also stated that adding RVG peptide to the exosome surface could target the brain more specifically.¹⁸ Another study reported that i.v. injection of 150 μg anti-α-syn shRNA-MCs, which provide longer lasting effects than siRNA3—a synthetic sequence targeting α-syn mRNA—into ten transgenic mice resulted in significantly reduced α-syn mRNA and protein levels after 45 days compared with controls. α-syn mRNA levels were significantly reduced in the midbrain, cortex, and striatum, while protein reductions were limited to the midbrain. Moreover, the researchers also proved that i.v. injection of RVG exosomes could safely and specifically transfer oligonucleotide to the central nervous system (CNS) than un-targeted exosomes. It was also noted that siRNA injected alone or into exosomes did not significantly alter the levels of mRNA or protein in the brain when administered intravenously.¹⁹ All these results are summarized in Table 1.

Dose-response and route of administration considerations

The reviewed studies varied considerably in both dosage and delivery route, which influenced their reported outcomes. Ren et al.²² and Liu et al.,²¹ which employed systemic administration (i.v. or i.p.), required relatively higher cumulative doses (≥1 mg/kg or 120 μg, respectively) to achieve measurable reductions in α-syn aggregation and improvements in motor function. By contrast, Yang et al.,²⁰ using direct i.c.v. injection of 20 μg ASO-loaded exosomes, achieved marked reductions in α-syn mRNA and protein at lower doses, likely reflecting the bypassing of peripheral clearance and direct CNS exposure.

Notably, none of the included studies provided comprehensive quantitative pharmacokinetic measurements of exosome or oligonucleotide biodistribution in brain tissue. Instead, therapeutic efficacy was inferred from staining results, behavioral assays, and molecular endpoints. This gap highlights the need for future investigations to incorporate sensitive drug quantification approaches, such as labeled oligonucleotides or advanced imaging, to correlate brain exposure with outcomes. Importantly, higher dose systemic studies (Cooper et al.¹⁸; Izco et al.¹⁹) did not consistently outperform i.c.v.-based delivery in terms of α-syn clearance, underscoring that the route of administration may be more critical than absolute dose.

Taken together, oligonucleotide therapy could significantly eliminate the aggregation of α-syn by reducing protein and mRNA levels mostly in the midbrain where SN is located. However, oligonucleotides injected locally lose their effectiveness due to nuclease degradation or cause unwanted effects on surrounding neurons. In addition, RVG peptides to the exosome surface enhanced CNS delivery compared with unmodified exosomes. Thus, exosomes are capable of transferring oligonucleotides to action sites with minimal drug clearance and toxicity, but while RVG peptide is incorporated onto their surfaces, they can deliver medications more precisely and specifically to brain regions where they are needed.

Pathology of dopaminergic neurons in PD

The α-syn has an important role in the pathogenesis of synucleinopathy like PD and multiple system atrophy, as well as the death of dopaminergic neurons caused by its aggregation. A pathological aspect of treatment in PD is the clearance of α-syn from dopaminergic neurons, which can be detected by the presence of the TH+ neurons in immunohistochemistry. In each treatment approach, therapeutic effects were more pronounced when dopaminergic neurons loss was reduced. To investigate the influence of exosomes on the reduction of neuronal loss and target therapy, all five studies investigated the presence of α-syn in neurons by using the TH+ staining of different sections of mice brains. According to findings in pathology sections, the reduced levels of markers of α-syn in staining dopaminergic cells reflected a decrease in neuronal death, potentially due to changes in the levels of α-syn protein or RNA.^{18,19,20,21,22}

Animal motor performance

In PD, motor symptoms such as bradykinesia, rigidity, and resting tremors occur when dopaminergic neurons of the SN in the midbrain degenerate due to enhanced α-syn aggregation. Therefore, wire hanging, rotarod, negative geotaxis, and pole tests were performed in four of five papers to evaluate the efficacy of exosomal oligonucleotide therapy on animal motor function. Improvement in motor outcomes appeared more pronounced in i.c.v. studies despite lower doses, whereas systemic delivery required higher doses without proportionally greater functional gains. According to the results of three studies,^19,20,21 the exosomal oligonucleotide therapy could improve the motor functions of these animals since this therapy could reduce α-syn aggregation in the midbrain and protect dopaminergic neurons from cytotoxicity of these masses in the nigrostriatal pathway. Ren et al. observed motor improvement even in the absence of clear dopaminergic degeneration, suggesting that functional benefits may precede histological protection.²² These symptoms were not observed because α-syn-PFF was injected into the striatum, so motor impairment was detected sooner than dopaminergic terminal degeneration. Therefore, the results of this study only proved that by reducing aggregation of α-syn, the motor function was significantly improved without any observation on dopaminergic neuron degeneration.

Immune and safety

Different immunological pathways and inflammatory factors such as tumor necrosis factor alpha, interferon-γ, interleukin (IL)-4, IL-5, IL-6, and IL-12P70 were discussed when using exosomes and RVG exosomes, and no risks were found by any of the studies. One study by Liu et al. also reported that neuroprotective factors including transforming growth factor β, P3, and CD4⁺ in the RVG exosomal group were higher than non-exosomal ones.²¹ The results of cell viability tests also proved that no toxicity was observed in cell health physically and physiologically when using these carriers. In addition, hematoxylin-eosin staining of the hearts, livers, spleens, lungs, and kidneys did not show any toxicity after systematic administration.²¹

Discussion

The therapeutic potential of exosome-mediated oligonucleotide delivery

The therapeutic potential of oligonucleotides targeting α-syn expression in PD is increasingly evident. However, clinical translation remains hampered by challenges in delivery efficiency, systemic stability, and BBB penetration.²³ This systematic review highlights the emerging role of exosome-based delivery systems in addressing these limitations.

Exosomes loaded with therapeutic nucleic acids have consistently demonstrated efficacy in reducing α-syn levels across various PD animal models, with associated improvements in motor behavior and dopaminergic neuron preservation. Notably, surface modification strategies—particularly the use of RVG-conjugated exosomes—have enhanced neuronal targeting and CNS penetration, reinforcing the promise of engineered vesicles in overcoming BBB-associated drug delivery barriers.

The reviewed studies employed a diverse array of PD models, including transgenic mice, neurotoxin-induced models (e.g., MPTP), and α-syn PFF seeding models. Each model provides distinct insights into α-syn pathophysiology: PFF models capture prion-like propagation and non-motor symptomatology; MPTP replicates dopaminergic neurodegeneration and symptomatic responses; and transgenic models enable the exploration of disease-modifying strategies with strong construct validity.²⁴ Nevertheless, the heterogeneity of these models—and the variation in delivery routes—highlights the need for standardized preclinical protocols to enhance cross-study comparability and accelerate clinical translation.²⁵

Comparative advantages of exosomal delivery systems

Beyond oligonucleotide delivery, exosomes derived from mesenchymal stem cells (MSCs) have shown intrinsic therapeutic properties owing to their anti-inflammatory, pro-angiogenic, and anti-apoptotic capabilities.^26,27 For instance, in a phase 1 clinical study of patients with refractory perianal fistulas, MSC-derived exosomes achieved ∼70% clinical improvement within 6 months without adverse effects,²⁸ illustrating their safety and therapeutic utility.

In PD models, MSC-derived exosomes—particularly those enriched with miR-188-3p—have demonstrated neuroprotective effects through the downregulation of CDK5 and NLRP3 signaling, reduction of autophagy and pyroptosis, and enhancement of neuronal proliferation.²⁹ These findings underscore the potential of stem cell-derived exosomes, not only as delivery vehicles but also as active therapeutic agents in their own right.

Exosome engineering strategies

Several surface and loading engineering approaches have significantly enhanced exosome delivery capabilities. For example, surface modifications such as phosphatidylcholine insertion have doubled cellular uptake in tumor models.³⁰ Electrostatic or mechanical methods like electroporation and sonication, as well as endogenous loading techniques, improve cargo incorporation.^31,32 Moreover, tissue-specific delivery of CRISPR-Cas9 using exosomes has been demonstrated successfully for liver therapy,³³ and recent reviews highlight the potential of (extracellular vesicle)-mediated CRISPR-Cas9 delivery with targeting precision.³⁴

Nucleic acid modality and delivery strategy

The therapeutic efficacy of exosome-mediated delivery is closely linked to the type of nucleic acid cargo being transported. siRNAs have been widely used for α-syn silencing due to their potent and specific mRNA knockdown; however, their rapid degradation and poor stability in circulation necessitate protective carriers such as exosomes to ensure bioavailability.³⁵ ASOs are effective in modulating RNA splicing and degradation but often require repeated dosing and may cause off-target effects. Exosome-based delivery enhances ASO stability and neuronal uptake, while off-target activity remains primarily dependent on oligonucleotide sequence and chemical modifications.³⁶ DNA aptamers, on the other hand, offer unique advantages due to their ability to bind protein aggregates with high affinity, though their relatively large size and susceptibility to nuclease degradation also benefit significantly from exosomal encapsulation.^37,38 Importantly, the choice of nucleic acid modality often dictates optimization of the delivery system, for instance, surface-modified exosomes may be more effective for delivering larger aptamers, while electroporation or sonication can maximize encapsulation efficiency for smaller siRNA molecules.^39,40 Collectively, this interplay between therapeutic nucleic acid type and exosome engineering underscores the flexibility of exosomes as precision delivery systems and highlights the importance of tailoring both cargo and vehicle to maximize therapeutic outcomes in PD.

Broader applications beyond oligonucleotides

Beyond oligonucleotide delivery, exosomes are being explored as carriers for diverse therapeutic classes. Engineered exosomes can carry proteins, CRISPR-Cas systems, and small-molecule drugs, offering biocompatibility and targeting advantages.⁴¹ Methods for effective drug and gene cargo loading—via electroporation or hybrid constructs—have been refined,^32,42 reinforcing exosomes as versatile nanocarriers.

Alternative delivery strategies and comparison with exosomes

Beyond exosome-based carriers, several alternative delivery strategies have been investigated for the transport of oligonucleotides and other therapeutic nucleic acids into the CNS. Lipid nanoparticles (LNPs) are the most clinically advanced platform, supported by their success in siRNA⁴³ and mRNA delivery.⁴⁴ However, their relatively large size, limited ability to cross the BBB, and potential for hepatic accumulation restrict their application in neurological diseases. Viral vectors, including adeno-associated viruses, have been extensively used for gene therapies due to their high transduction efficiency and stable expression. Yet, concerns over immunogenicity, insertional mutagenesis, and challenges with repeated dosing have tempered enthusiasm for their widespread use in chronic neurodegenerative conditions.^45,46 Ligand-oligonucleotide conjugates, such as GalNAc-siRNA, have demonstrated precise targeting to hepatocytes,⁴⁷ but equivalent ligands for neuronal populations remain under development and lack the same translational readiness.

Compared with these approaches, exosomes present unique advantages. Their nanoscale size and endogenous origin allow efficient biodistribution, low immunogenicity, and natural tropism toward neuronal cells, particularly when surface modifications such as RVG peptide functionalization are employed. Furthermore, exosomes are capable of crossing the BBB under both physiological and pathological conditions. Importantly, exosomes can carry diverse molecular cargos beyond oligonucleotides, including proteins, peptides, small molecules, and genome-editing tools such as CRISPR-Cas9, highlighting their versatility. On the other hand, exosomes face manufacturing and scalability hurdles, including heterogeneity in isolation methods, batch-to-batch variability, and relatively low loading efficiency compared to synthetic nanoparticles.

Overall, while alternative strategies like LNPs, viral vectors, and conjugates have paved important translational pathways, exosomes provide a biologically compatible and adaptable platform for CNS drug delivery. Continued comparative studies and standardized manufacturing protocols will be critical for defining the therapeutic niche where exosomes can surpass existing modalities in terms of safety, efficacy, and clinical applicability.

Repeated administration and translational challenges

A key limitation for clinical translation is the need for repeated administrations observed in most preclinical studies. Multiple i.v. or i.c.v. injections were required to sustain reductions in α-syn aggregation, which raises concerns about patient safety, compliance, and feasibility in chronic neurodegenerative conditions. Invasive intracerebral delivery is particularly problematic due to surgical risks, while frequent systemic injections may trigger immune recognition of exosomes or dosing fatigue in patients.⁴⁸

To address these hurdles, innovative approaches are being investigated, including exosome engineering to extend circulation time and improve BBB penetration, as well as biomaterial-based sustained-release systems that could reduce dosing frequency. Continued advances in exosome modification and formulation will be critical to transform promising preclinical findings into practical therapeutic options for long-term management of PD.^49,50,51

Exosomes in other neurological disorders

Beyond PD, exosome-based delivery systems have been actively explored in other neurodegenerative and neurological conditions. In Alzheimer’s disease, exosome-encapsulated siRNAs and miRNAs have shown potential to reduce β-amyloid and tau pathology, improving cognitive outcomes in preclinical models.⁵² In amyotrophic lateral sclerosis, exosomes have been investigated as carriers for antioxidant enzymes and neuroprotective RNAs, with reports of delayed motor decline and extended survival in mouse models.⁵³ Exosome-mediated delivery of neuroprotective cargos has also demonstrated benefits in traumatic brain injury and ischemic stroke, promoting neuronal survival and functional recovery.⁵⁴ Importantly, these studies highlight that exosomes are capable of transporting diverse therapeutic agents—ranging from oligonucleotides and proteins to small molecules—across the BBB, underscoring their versatility as delivery platforms. Integrating insights from these related fields may accelerate the translation of exosome therapeutics for PD and strengthen the evidence base for their application across neurological disorders.⁵⁵

Limitation of current PD evidence

Looking forward, several challenges must be addressed to advance exosome-based oligonucleotide therapy for PD. These include the development of Good Manufacturing Practice-grade, scalable exosome production platforms; implementation of real-time bio distribution tracking; and optimization of co-delivery strategies that combine oligonucleotides with neuroprotective or anti-inflammatory agents. Ultimately, exosome-mediated delivery represents a versatile, biocompatible, and clinically translatable approach to modulate pathogenic gene expression in PD and other neurodegenerative disorders.

Materials and methods

The systemic review was conducted according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses).⁵⁶

Literature search

Papers with keywords of “Exosome” AND “Drug Delivery” AND “Synuclein” were selected from databases such as Scopus, Embase, OVID, and Web of Sciences for in vivo models of PD until January 2022. Additionally, the PubMed database was compiled with the following items: “Exosomes” [Mesh] AND “Drug Delivery Systems” [Mesh] AND “alpha-Synuclein” [Mesh]. Each title and abstract was reviewed by three investigators, separately. Inclusion and exclusion criteria were applied by two investigators to the complete texts of potentially eligible studies. By reviewing the reference lists found in all included articles, the same three investigators were able to identify further relevant studies.

Eligibility criteria

Exosome carrier; animal research, Parkinson’s animal models; loading agents or medicines; analysis modification of α-syn; and original articles were the inclusion criteria for eligible publications. Human studies; studies performed in vitro and situ; α-syn was not induced; models without Parkinson’s; reviews, conference abstracts, letters, notes, editorials, and abstracts; full-text not in English or Persian; the study of extracellular vesicles without exosomes such as microparticles or liposomes; and exosomes are not loaded with any agents, prodrugs, or medicines were all excluded.

Data extraction

The data that we collected included the author, publication year, source of the exosome, type of animal (species, strain, sexes, age), study groups, drug loading method, the treatments used (dose and delivery route), and outcome. Several categories of outcomes were investigated: PD model, α-syn clearance, animal behavior performance, pathology of dopaminergic neurons in PD, and immune and safety. Statistical significance was considered at p < 0.05.

Data and code availability

The sources of these findings can be obtained from the corresponding authors for appropriate reasons.

Acknowledgments

We are very thankful to Dr. Ali Karamoozian, Modeling in Health Research Center, Institute for Futures Studies in Health, Kerman University of Medical Sciences, Kerman, Iran, for his assistance and support, as well as Dr. Mehran Nakhaeizadeh, Department of Biostatistics and Epidemiology in Kerman University of Medical Sciences, for his work on this project.

Author contributions

S.S. contributed to the conceptual design of the study and participated in the systematic literature search and data interpretation. F.D. was responsible for methodological quality assessment, data extraction, and drafting the manuscript. A.S. contributed to the analysis of experimental models and critically reviewed the manuscript for intellectual content. S.H. conceived the study, coordinated the research activities, and finalized the manuscript. She also served as the corresponding author and is responsible for all communication during the submission and review process. All authors read and approved the final version of the manuscript.

Declaration of interests

The authors declare no competing interests.