Exosomes and Exosome-Mimetics for Atopic Dermatitis Therapy

Abstract

Background:

Exosomes and exosome mimetics are used as alternatives to cell therapy. They have shown potential in treating skin disorders by fortifying the skin barrier, mediating angiogenesis, and regulating the immune response while minimizing side effects. Currently, numerous studies have applied exosome therapy to treat atopic dermatitis (AD) caused by a weakened skin barrier and chronic inflammation. Research on exosomes and exosome mimetics represents a promising avenue for tissue regeneration, potentially paving the way for new therapeutic options. However, the efficacy of the therapy remains poorly understood. Also, the potential of exosome mimetics as alternatives to exosomes in skin therapy remains underexplored.

Methods:

Here, we reviewed the pathological features and current therapies of AD. Next, we reviewed the application of exosomes and exosome mimetics in regenerative medicine. Finally, we highlighted the therapeutic effects of exosomes based on their cell source and assessed whether exosome mimetics are viable alternatives.

Results and conclusion:

Exosome therapy may treat AD due to its skin regenerative properties, and exosome mimetics may offer an equally effective yet more efficient alternative. Research on exosomes and exosome mimetics represents a promising avenue for tissue regeneration, potentially paving the way for new therapeutic options.

Introduction

Atopic dermatitis (AD) is a prevalent chronic inflammatory skin disease affecting people worldwide, characterized by pruritus, xeroderma, and eczematous lesions [1]. Although the precise etiology remains unclear, it is widely accepted that AD is caused by a complex interplay between environmental and genetic factors that activates innate immune responses, resulting in abnormalities of the skin's protective barrier [2]. Current standard treatments, such as corticosteroids, calcineurin inhibitors, and Janus kinase (JAK) inhibitors, have been demonstrated to provide symptomatic relief by immunoregulation [3, 4]. However, cessation of treatment may lead to a recurrence of the underlying disease process, highlighting the necessity for a comprehensive, definitive approach to managing AD [5].

Recent advances in tissue engineering and regenerative medicine have accelerated the application of cell therapy for repairing human skin disorders [6]. For example, stem cell transplantation has the potential to repair damaged skin cells via secretion of anti-inflammatory and regenerative paracrine factors [7]. Since the therapeutic mechanism may vary depending on the cell type, the selection of an appropriate cell type, as well as cellular engineering to improve the engraftment rate and therapeutic efficiency is important for successful transplantation [8, 9]. Nevertheless, safety concerns inevitably arise due to the unpredictable nature of the transplanted cells and the time required for preparation [10]. Consequently, the use of secretomes as an alternative to cell therapy has recently emerged as a promising option [11].

Exosomes are a subtype of small extracellular vesicles (EVs) in a size range of 30–150 nm, secreted by all cell types, mediating intercellular communication with target cells over various distances, from nearby to distant [12]. Exosomes consist of a phospholipid bilayer derived from the parent cell membrane, primarily encapsulating proteins and genetic materials that serve as their modes of action [13]. They are emerging as a new platform for cell therapy, addressing safety concerns associated with their non-living nature while retaining therapeutic potential by encapsulating biomolecules inherited from the parent cell [14]. The cell membrane-derived phospholipid bilayer not only enhances cargo stability but also provides a tissue-targeting moiety depending on its transmembrane protein composition [15]. Nevertheless, the low productivity of exosomes remains a significant obstacle to their clinical translation, primarily due to their high cost and low homogeneity [16]. Recent advances in exosome engineering have led to the development of synthetic exosomes, created by physically disrupting live cells, followed by their spontaneous reassembly into exosome-mimetic structures containing membrane and internal components [17]. Serial extrusion through microporous membranes is a commonly employed technique that increases productivity by 100–250 times compared to naturally secreted exosomes [18]. In addition to the massive and simple producibility, exosome mimetics could provide enhanced therapeutical effects through surface modification or drug loading. For example, vascular endothelial growth factor (VEGF) encapsulated exosome mimetics promoted proliferation of vascular endothelium, indicating wound repair, with minimal loss of VEGF [19]. Overall, the application of such exosome mimetics is a promising alternative for treating skin disorders.

This review examined the potential of exosomes and exosome mimetics for treating AD. We began by summarizing the pathological characteristics of AD and the current therapeutic strategies. We then presented a detailed account of the characteristics of exosomes and exosome mimetics, focusing on their typical applications in tissue regeneration. Finally, we discussed the role of exosomes and exosome mimetics derived from various cell types in skin barrier repair and immunoregulation, focusing on their potential use in AD therapy.

Pathological characteristics and current therapies of atopic dermatitis

Pathological characteristics of atopic dermatitis

The development of a novel treatment for AD is important due to its incurable and chronic nature, which causes a disease progression through a self-perpetuating cycle [20]. AD is generally believed to arise from genetic factors such as a deficiency in filaggrin genes (FLG) leading to skin barrier disorders, and environmental factors such as an increase in environmental allergens, which both induce a dysfunctional immune system. Symptoms typically include itching, dry skin, and the development of eczema, which contribute to the itch-scratch cycle [21]. The act of scratching compromise the integrity of the impaired barrier, facilitating further allergen penetration, microbial colonization, and inflammation, thus perpetuating disease progression (Fig. 1) [22].

Fig. 1.

Pathophysiologic characteristics of AD. AD is a chronic inflammatory skin disorder marked by impaired barrier function, driven by reduced filaggrin expression, and persistent immune dysregulation. TSLP from epithelial cells stimulated by genetic or external factors activates dendritic cells, initiating a Th2-dominant response. Th2 cytokines (IL-4, IL-13, IL-31) promote IgE production, amplify the itch-scratch cycle, and disrupt barrier repair. Th17 and Th22 cells further contribute by releasing IL-17 and IL-22, which impair keratinocyte function, promote neutrophil recruitment, and intensify local inflammation. This multifactorial immune activation perpetuates skin barrier dysfunction and chronic inflammation in AD

The pathogenesis of AD involves an interplay between skin barrier dysfunction and immune system dysregulation. Due to the activation of helper T (Th) cells [23]. The disruption of the skin barrier activates keratinocytes in the epidermal layer, which release thymic stromal lymphopoietins (TSLP) in response to cytokines, microbial stimuli, or barrier damage [24]. Local dendritic cells are key targets of TSLP, driving a Th2-mediated immune response [25]. Th2 cytokines, especially interleukin-4 (IL-4) and IL-13, which impairs the barrier by down-regulating FLG [26] and promoting Immunoglobulin-E (IgE) production which is a hallmark of allergic sensitization [27]. Another Th2 cytokine, IL-31, intensifies pruritus, perpetuating the itch-scratch cycle [28, 29]. Th17 and 22 also involve in AD pathogenesis, especially in chronic lesions. They are highly expressed in atopic lesions, secreting IL-17 and IL-22, respectively, to exacerbate inflammation and skin barrier dysfunction [30]. IL-17 promotes neutrophil recruitment and pro-inflammatory cytokine production, while IL-22 inhibits keratinocyte differentiation and induce epidermal hyperplasia which further amplifies local inflammation [30]. This multifaceted interplay between the barrier dysfunction and immune activation underscores the necessity of a novel therapeutic that targets both aspects in treatment.

Current therapeutic strategies for atopic dermatitis

Topical treatment

Topical corticosteroids (TCS) are among the most common medications used to treat AD (Table 1). TCS treatment alleviates AD symptoms through its anti-inflammatory, vasoconstrictive, immunosuppressive, and antiproliferative properties. TCS bind and activate glucocorticoid receptors that are expressed on skin cells including fibroblasts, epidermal cells, and lymphocytes. Activated glucocorticoid receptors then inhibit NF-κB and AP-1 signaling pathway, suppressing transcription of pro-inflammatory genes [31]. Also, TCS exerts its anti-inflammatory effects by reducing the secretion of phospholipase A2 and transcription factors involved in the inflammatory response, while simultaneously increasing the synthesis of lipocortin, which inhibits phospholipase A2. The vasoconstrictive action of TCS reduced skin redness and decreased the migration of inflammatory mediators, supporting its anti-inflammatory effects. TCS inhibits the activation of immune cells, such as mast cells, leukocytes, and macrophages. It suppresses T-cell proliferation by inhibiting IL-2 and induces apoptosis. In addition, TCS directly influences DNA, upregulating anti-inflammatory genes and modulating keratinocyte activity [32–34].

Table 1.

Conventional treatments and their therapeutic effects in AD

Types of treatment	Drugs	Therapeutical effects	References
Topical treatment	Topical corticosteroid	Reduce phospholipase A2 secretion and immune cell activation	[32–34]
	Topical calcineurin inhibitor	Block calcium-calmodulin-calcineurin signaling pathway, reducing inflammatory cytokine synthesis	[35, 36]
	JAK inhibitor	Block JAK-STAT signaling pathway, mitigating inflammation	[37, 38]
Systemic treatment	Systemic corticosteroid	Short-term administered, present anti-inflammatory effect	[39]
	Cyclosporine	Suppress T-cell activity attenuating severe inflammation	[40]
	Azathioprine	Inhibit purine synthesis suppressing immune response	[41, 42]
	Mycophenolate mofetil	Inhibit purine synthesis suppressing immune response	[43]
Antimicrobials	Cephalosporin	Contain β-lactam ring, inhibiting S. aureus cell wall synthesis	[47–49]
	Erythromycin	Bind to 50S ribosomal subunit impairing S. aureus function	[50, 51]
	Topical mupirocin	Inhibit protein and RNA synthesis of S. aureus	[52, 53]

Topical calcineurin inhibitors are viable alternatives due to their relatively low risk of side effects, even with long-term use to prevent lesion recurrence. These inhibitors target the calcium-calmodulin-calcineurin signaling pathway, which is activated when antigens bind to T-cell receptors [35]. By binding to FK-506 binding protein in the cytoplasm, topical calcineurin inhibitors suppress calcineurin activity, effectively blocking the production of inflammatory cytokines [36].

JAK inhibitors represent a novel class of drugs for treating AD. The JAK-STAT pathway plays a critical role in the intracellular signaling of inflammatory cytokines, including IL-4, IL-13, IL-31, IL-22, IL-5, and TSLP. Activation of this pathway drives Th2 differentiation, suppresses regulatory T cells (Tregs), promotes B cell maturation, and activates eosinophils. By blocking this signaling cascade, JAK inhibitors effectively mitigate inflammation, making them valuable in treating AD [37, 38].

Systemic treatment

Systemic immunomodulators are considered when topical treatments fail to provide sufficient relief [39]. Systemic corticosteroids administered throughout the body exert anti-inflammatory effects but are typically reserved for short-term use due to potential side effects. Cyclosporine, a calcineurin inhibitor, suppresses T-cell activity by blocking IL-2 secretion, making it effective for controlling severe inflammation [40]. Immunosuppressants such as azathioprine [41, 42] and mycophenolate mofetil [43] work by inhibiting purine synthesis, thereby reducing immune cell proliferation. While antihistamines are generally ineffective in directly treating AD, they can be used to alleviate itching, providing symptomatic relief in some cases [44].

Antimicrobials

Staphylococcus aureus (S. aureus) colonization is a hallmark feature in patients with AD, with up to 90% of lesions showing evidence of colonization [45]. This colonization not only contributes to disease severity but also perpetuates inflammation through the release of exotoxins, such as superantigens, which exacerbate the inflammatory response and impair skin barrier function [46]. Consequently, the use of antibiotics to target S. aureus has emerged as a supplementary strategy in the management of AD.

The most commonly used antibiotics include oral cephalosporins, erythromycin, and topical mupirocin, each of which employs a distinct mechanism to combat bacterial growth. Cephalosporins, which contain a β-lactam ring, inhibit bacterial cell wall synthesis by targeting penicillin-binding proteins, ultimately leading to bacterial lysis [47–49]. Erythromycin, a macrolide antibiotic, impairs bacterial protein synthesis by binding to the 50S ribosomal subunit, thereby inhibiting essential cellular functions [50, 51]. Topically applied mupirocin inhibits isoleucyl-tRNA synthetase, thereby blocking protein and RNA synthesis and ultimately leading to bacterial cell death [52, 53].asdasd.

Despite their efficacy, the routine use of antibiotics in AD is controversial due to the potential for antimicrobial resistance and disruption of the skin microbiome. Therefore, antibiotic therapy is typically reserved for cases of overt infection or heavy colonization contributing to acute flares. Emerging strategies, such as probiotics [54], bacteriophage therapy [55], and targeted anti-S. aureus approaches [56], are under investigation as adjuncts or alternatives to conventional antibiotics.

Exosomes in regenerative medicine

Characteristics of exosomes

Exosomes are a subtype of small EVs, typically 30–150 nm in diameter, released by most cell types. They originate from the multivesicular bodies that fuse with the plasma membrane to release the exosomes inside [57]. While exosomes were first recognized as vehicles for cellular waste elimination [58], recent studies have identified them as critical mediators of intercellular communication. Acting as messengers, exosomes deliver bioactive molecules within the cargo or the membrane such as proteins, lipids, and nucleic acids to target cells, thereby modulating physiological or pathological processes [59].

Production of the EVs for clinical usage is performed by culturing their parent cells in a high confluency. Exosomes are sequentially isolated them from the conditioned media, which contains various EV components secreted from the cultured cells. Body fluids such as blood or urine are also promising sources of therapeutic exosomes, but they contain a mixture of exosomes derived from different cell types, making purification challenging and resulting in high batch-to-batch heterogeneity. Multiple methods have been considered to isolate exosomes from such conditioned media or body fluids in a highly productive manner and to purify them from undesired components including cells, apoptotic bodies, debris, or smaller molecules. Differential ultracentrifugation method is one of the current standards that separate exosomes based on density differences [60]. Alternative size-based approaches include filtration such as tangential flow filtration or size-exclusion chromatography [61, 62]. Exosome precipitation [63] and exosome affinity-based capture [64] methods isolate exosome according to their biochemical properties. Technological advancements in isolation techniques, such as standardized fractionation, address the inherent heterogeneity of exosomes by ensuring consistency in vesicle size.

The role of exosomes in intercellular communication has been emphasized for their therapeutic functions, inherited from their parent cells [65, 66]. Recipient cells uptake exosomes through receptor binding and membrane fusion mechanisms, where the transmembrane proteins on the exosomes bind to the receptor of the target cells to undergo endocytosis [67, 68]. The mode of action of exosomes are still under investigation, while proteins, genetic molecules such as DNA, mRNA and non-coding RNA, metabolites, or mitochondrial components are the candidates of interest, which are the cargo released after cellular uptake [68, 69]. Among them, miRNAs highly attracted the current research since they are reported to be particularly abundant and play specific roles in post-transcriptional regulation by binding to target mRNAs, thereby modulating gene expression and cellular responses [70, 71]. Despite their potential as therapeutic agents and biomarkers, exosomes exhibit significant batch-to-batch and vesicle-to-vesicle heterogeneity, underscoring the urgent need for advanced analytical technologies to enable their reliable application in precision medicine.

Exosome mimetics

Exosome mimetics, which are sometimes designated as synthetic or artificial exosomes, exhibit similar characteristics to exosomes in terms of size, structure, and biochemical properties [72–74]. These have been developed in order to address the limitations of exosomes, productivity and cost-efficiency, which have been the most significant hurdle to their clinical application [18]. The synthesis of exosome mimetics involves the destruction of live cells through physical methods, including serial extrusion, microfluidic techniques, freeze–thaw cycles, and ultrasonication. Serial extrusion is the predominant method, as it is a simple and efficient technique that provides uniform size control while preserving the structural integrity of exosomes, making it the preferred approach for the generation of exosome mimetics. Although limited studies have compared serial extrusion with alternative techniques, such as sonication or microfluidics, it remains widely used in laboratories due to its simplicity, lack of specialized equipment requirements, and avoidance of complex chemical processing. Such physical stress causes the cells to disassemble into small fractions of plasma membranes and to release the intracellular components in the solution, which then undergo spontaneous reformation of vesicle shape surrounding the intracellular components as cargo. The production yield of the exosome mimetics is reported to be 100 to 250 times higher than that of exosomes isolated from conditioned media [18].

The characteristics of exosomes and their mimetics are comparatively analyzed based on their structures, surface properties, and genomic content. Their structures properties, such as size and shape are typically assessed using techniques like nanoparticle tracking analysis (NTA), dynamic light scattering (DLS), electron microscopy (EM), or atomic force microscopy (AFM). Surface composition is analyzed through liquid chromatography-mass spectrometry (LC–MS) based proteomics or lipidomics to identify the transmembrane protein component and the lipid component that interact with external molecules. The internal content is evaluated using polymerase chain reaction (PCR), western blot, gene ontology analysis, enzyme-linked immunosorbent assay (ELISA), or other fluorescence-based techniques to identify the cargo component. Such analytic comparisons have demonstrated the similarity of exosomes and their mimetics, supported by further in vitro and in vivo studies validating their comparable therapeutic mechanisms and efficiency. In one study, exosome mimetics derived from the breast cancer cell line MDA-MB-231 were fabricated and compared to natural exosomes. The exosome mimetics had a size of 123.2 ± 1.9 nm, closely resembling that of exosomes (109.0 ± 0.8 nm). Proteomic analysis revealed that the mimetics contained 648 of the 898 total proteins identified in natural exosomes, along with a 64.7% similarity in small RNA content, demonstrating their potential as a promising alternative to natural exosomes. In another study, the anticancer effects of doxorubicin-loaded exosome mimetics derived from RAW 264.7 cells were evaluated. in vivo experiments showed that doxorubicin-loaded exosome mimetics exhibited anticancer efficacy comparable to that of doxorubicin-loaded natural exosomes, while liposomal doxorubicin showed significantly lower efficacy. These results suggest that exosome mimetics, which mimic the membrane proteins of natural exosomes, are a promising alternative for drug delivery [18, 75, 76]. However, the process of synthesizing exosome mimetics raises concerns about inflammation due to the potential membrane flip-flop during vesicle reassembly from membrane fragments. This highlights the necessity for more comprehensive assessments of toxicity and safety in accordance with regulatory guidelines to guarantee their clinical translation.

Exosome and exosome mimetic-based therapeutics for skin tissue repair

Exosomes are emerging as a promising nanocarrier for skin drug delivery due to their biocompatibility and biostability in delivering cellular components across the skin barrier. Recently, exosomes have been widely studied in skin disorders, especially to promote angiogenesis, collagen synthesis, immunoregulation, and barrier restoration (Fig. 2). Numerous studies have demonstrated the efficacy of exosomes in topical or transdermal therapies for various skin diseases, including AD [77], aging [78], melanogenesis [79], wound healing [80], scar tissue formation [81], and even hair loss [82]. The capability of exosomes to penetrate the thick epidermal layers is still controversial. A recent study has shown that human MSC-derived exosomes in topical delivery persisted in the stratum corneum and did not penetrate into the nucleated stratum granulosum [83]. However, several evidences have indicated the potential of exosomes for transdermal delivery via different mechanisms, including endocytosis, phagocytosis, micropinocytosis, lipid fusion, transfollicular route, or through the damaged epidermal lesion, due to their small size and the existence of external plasma membrane. For instance, mesenchymal stem cells (MSC)-derived exosomes [84] and broccoli-derived membrane vesicles which resemble with mammalian exosomes [85] have been investigated for their capability to penetrate the epidermis toward the dermis layer in 3D skin biopsy models. The penetration of exosomes through the skin remains a significant challenge that requires further investigation. For example, broccoli-derived membrane vesicles enriched with aquaporin proteins have been shown to enhance permeability by altering osmotic pressure. Beyond subcutaneous injection, alternative delivery routes such as intravenous and intraperitoneal injections are being explored to improve exosome delivery efficiency. In addition, chemical modifications of exosome surfaces, including functionalization with specific compounds, are being actively investigated to enhance their delivery potential.

Fig. 2.

Schematic illustration of exosome therapy for skin repair. The process involves three key steps: selecting of a suitable cell source, generating exosomes from parent cell biogenesis or synthesizing exosome mimetics through physical methods, and isolating and characterizing exosomes by their size, shape, biochemical composition including proteins and nucleic acids. The major therapeutic mechanisms for skin repair include promoting angiogenesis, enhancing collagen synthesis, immunomodulation, and barrier restoration

Angiogenesis plays a critical role during skin repair by providing oxygen and nutrients necessary for cell migration. In addition, angiogenesis facilitates collagen synthesis by promoting the timely recruitment of fibroblasts to the wound site, thereby restoring the skin barrier. The angiogenic effects of exosomes have been extensively studied, particularly in MSC-derived exosomes. Human umbilical cord MSC (hUCMSC)-derived exosomes promote angiogenesis via the Wnt/β-catenin signaling pathway [86]. Co-culture of hUCMSC-derived exosomes with human umbilical vein endothelial cells (HUVECs) enhances tube formation [87]. Absorption of hUCMSC-derived exosomes into the skin increases collagen I and elastin expression and promotes human dermal fibroblast (DF) migration [84]. Exosomes from human-induced pluripotent stem cell-derived mesenchymal stem cells (iMSCs) demonstrated the greatest wound closure and the highest vessel densities compared to control and untreated groups. in vitro data revealed that exosomes from iMSCs promote human fibroblast migration, proliferation, and the synthesis of collagen and elastin, as well as enhancing the migration, proliferation, and tube formation of HUVECs [88]. Exosome mimetics from hUCMSCs also promote the proliferation and migration of DF cells while exhibiting higher angiogenic activity [89].

The immunoregulatory properties of exosomes from specific cell types have been extensively studied, associated to mechanisms such as macrophage polarization, T-cell regulation, modulation of inflammatory cytokines, and regulation of pro-inflammatory gene expression. For example, subcutaneous injection of M2 macrophage-derived exosomes has been shown to induce the M2 polarization of M1 macrophages, angiogenesis, collagen deposition, and re-epithelialization, thereby accelerating the wound-healing process [90]. Similarly, keratinocyte-derived exosomal MALAT1 has been reported to enhance macrophage functionality by reducing apoptosis and promoting macrophage phagocytosis and polarization, ultimately accelerating wound healing [91]. In addition, miR-181c contained in hUCMSC-derived exosomes targets the 3′-UTR of TLR4 mRNA, resulting in the downregulation of TLR4 protein expression. Since TLR4 activates immune responses by recognizing pathogen-associated molecular patterns, its suppression by miR-181c attenuates the enhanced inflammatory response observed in lipopolysaccharide (LPS)-stimulated macrophages after burn injury. This includes a decrease in pro-inflammatory cytokine levels and an increase in anti-inflammatory cytokines [92]. Moreover, hUCMSC-derived exosomes have been shown to regulate T-cell responses. They inhibit the proliferation of peripheral blood mononuclear cells and promote the generation of Tregs, with exosomes pretreated with transforming growth factor-β and interferon-γ (IFN-γ) demonstrating the most potent effects [93].

Exosome therapy for atopic dermatitis

Mesenchymal stem cell-derived exosomes

MSCs are adult stem cells mainly derived from adipose tissue, umbilical cord blood, and bone marrow. They are widely used in regenerative medicine due to their intrinsic angiogenic, anti-apoptotic, anti-inflammatory, tissue-regenerative, and disease homing effects. Therefore, MSCs have emerged as a potential candidate for skin disorder therapy, while exosomes derived from various MSCs have been studied as their alternatives by reserving the therapeutic effect and enhancing the epidermal penetration efficacy.

The immunomodulatory properties of MSCs have been exploited in several studies as therapeutic strategies to alleviate AD symptoms. For example, intravenous administration of MSCs inhibited IgE synthesis by suppressing B cell maturation through cyclooxygenase-2 signaling, thereby reducing serum IgE levels and alleviating AD [94]. Subcutaneously injected MSCs also alleviated AD by inhibiting the proliferation of Th17 cells and downregulating the expression of Th17-related genes, which are prominently associated with AD lesions. In addition, MSCs reduced mast cell infiltration, epidermal thickening, serum IgE levels, and the production of AD-associated inflammatory mediators, contributing to the overall alleviation of AD symptoms [77].

Supported by the studies on AD therapy with MSCs, various MSC-derived exosomes were studied to alleviate AD symptoms in various AD models (Table 2). For example, human adipose-derived stem cell (hASC)-derived exosomes were subcutaneously and intravenously administered at doses of 0.14, 1.4, and 10 μg per mouse to NC/Nga mice, three times per week over a four-week. While Biostir®-AD cream (contains antigens from house dust mite) induced AD lesion with abnormal innate immune system, ASC-derived exosomes reduced the inflammatory level of dendritic epidermal cells, serum IgE level, and expression of inflammatory cytokines such as tumor necrosis factor-α (TNF-α), IL-4, IL-23 and IL-31 [95]. In another study, hASC-derived exosomes were subcutaneously administered to an oxazolone-induced AD model at doses of 1, 3, and 10 μg/mL per mouse three times per week for four weeks (Fig. 3). Oxazolone induces keratosis, immune cell infiltration and increase of IgE levels in mouse model. Under exosome treatment, the skin tissue exhibited enhanced barrier function with adequate hydration, reduced levels of AD-related inflammation such as IL-4, IL-13, TSLP, IgE, increased expression of ceramides and dihydroceramides, and normalized epidermal gene expression related to skin barrier, lipid metabolism, cell cycle, and immune response [96]. Another study involves artificial 3D skin model consisting of immortalized human keratinocytes (HaCaT), human DFs, and human mast cell line-1 (HMC-1), with activated immune response via polyinosinic:polycytidylic acid sodium salt and IL-1α treatment to induce TSLP release. In this study, particulate matter has been added as a contributing factor to the development of AD by down-regulating the gene expression associated with skin barrier function, FLG and loricrin (LOR). In this model, administration of hASC-derived exosomes reversed the detrimental effects of particulate matter, via immunosuppressive effects and restoration of FLG and LOR gene expression levels [97].

Table 2.

Cell-derived exosomes and exosome mimetics application in AD treatment

Exosome source	Cell type /Modification	Therapeutical effects	References
Mesenchymal stem cell	Adipose	Reduced levels of serum IgE and inflammatory cytokines in AD induced mice	[83]
		Reduced inflammation level and recovered skin barrier-related gene expression	[84]
		Restored level of filaggrin and loricrin genes, associated with skin barrier	[85]
	miR-147a transfected	Attenuated inflammatory response by modulating MEF2A-TSLP	[86, 87]
	Induced pluripotent	Declined serum IgE level, epidermal thickness, and immune cell infiltration	[90, 91]
Dermal fibroblast	–	Up-regulated skin barrier genes (filaggrin, loricrin, involucrin, and hyaluronic acid synthase 1)	[96]
	–	Reduced epidermal thickening and immune cell infiltration	[97]
Microorganism	Lactococcus lactis	Increased expression level of skin barrier genes (fibrillin, fibronectin, filaggrin) and promoted collagen synthesis	[100]
	Lactobacillus plantarum	Reduced IL-4 gene expression and epidermal thickness	[99]
	Cutibacterium acnes	Enhanced filaggrin expression	[102]
Synthetic exosome	Melatonin-loaded	Suppressed mast cell infiltration and fibrosis	[105, 106]
	P-MEL and keratinocyte membrane fabricated	Suppressed MAPK pathway, lowering pro-inflammatory cytokines	[107]

Fig. 3.

ASC-derived exosome in AD therapy. A Schematic illustration of the subcutaneous injection of exosomes, three times a week for four weeks. B Representative photographs and C H&E images showing a visual comparison of AD lesions under dose-dependent exosome treatment. D Heatmap of differential expressed gene between vehicle and ASC-derived exosomes, identified through gene ontology (GO) analysis. Reproduced with permission from [96], Copyright 2020, Shin K–O et al.

Not only naïve MSCs, but also engineered MSCs can be a good source for exosomes with enhanced therapeutic efficacy. For example, genetic transfection of ASC for higher miR-147a expression secretes exosomes with higher miR-147a component. miR-147a is an anti-inflammatory miRNA, and its expression is reduced in 1‐chloro‐2,4‐dinitrobenzene (DNCB)-induced AD mice, along with that of TSLP and VEGF-A. In this study, miR-147a encapsulated in ASC-derived exosomes was administered at a concentration of 30 μg/mL for 24 h to HaCaT cells and HUVECs activated with TNF-α and IFN-γ, representing an in vitro AD model. miR-147a enriched exosomes attenuated the inflammatory response in HaCaT cells by modulating the MEF2A-TSLP pathway and enhanced the angiogenic response in HUVECs by targeting VEGF-A, highlighting its dual therapeutic potential in AD [98, 99].

iMSCs are another good source for MSC-derived exosomes due to higher survival rate, proliferation rate, and stemness compared to adult MSCs [100]. In addition, patient-specific iMSCs have the advantage of using autologous cells as a personalized medicine. iMSC-derived exosomes fully reflect the advantages of iMSC, making them as a promising tool for the treatment of AD. Since MSCs stimulated with IFN-γ have previously been reported to exhibit enhanced efficacy in the treatment of AD [101], a study has used exosomes derived from iMSC stimulated with IFN-γ to enhance the therapeutic effect. Those exosomes were epicutaneously administered to Aspergillus fumigatus extract-induced AD mouse, at doses of 0.25, 2.5 per mouse, resulting in significant reductions in serum IgE levels, epidermal thickness, and inflammatory cell infiltration. The in vivo results were supported by in vitro studies using HaCaT treated with IL-4 and IL-13, which demonstrated the therapeutic effects of the IFN-γ-stimulated iMSC-derived exosomes as suppressing the expression of TSLP, IL-25, and IL-33, while promoting the expression of skin regenerative genes, including keratin 1, keratin 10, and ceramide synthase 3 [102]. Similar exosomes were subcutaneously administered to DNCB-induced AD mouse models at a dose of 50 or 500 μg per mouse, once a week for 5 weeks, showing reduced expression of receptors for Th2-associated cytokines, including IL-4, IL-13, and IL-31, and protein expression of CD23, FcεRI (IgE receptor), and TSLP [103].

Dermal fibroblast-derived exosomes

DFs are the main cell type in the dermis layer, which maintain the structure and function of the skin through extracellular matrix synthesis. Extensive research has been conducted to explore the role of DF in skin regeneration so far, as well as their exosomes [104, 105]. DF-derived exosomes are known to be especially enriched in miRNA-218 and ITGBL1 protein, enabling them to promote fibroblast migration, proliferation, contraction, and collagen synthesis via the transforming growth factor β1-SMAD2/3 pathway [106], as well as promoting ECM synthesis, remodeling, angiogenesis, cell migration, and proliferation by IL-6 signaling [107]. Based on such results, DF-derived exosomes have been utilized as a potential therapeutic strategy for AD.

DNCB-treated keratinocytes seeded at a density of 1 × 10⁴ cells per well were treated with human DF-derived exosomes at a concentration of 1 × 10⁴ particles/mL, up-regulating the expression of skin barrier-related genes, including hyaluronic acid synthase 1, FLG, involucrin, and LOR, while maintaining minimal cytotoxicity [108]. In another study, neonatal DF-derived exosomes were found to ameliorate DNCB-induced AD symptoms by activating peroxisome proliferator-activated receptor alpha (PPARα). in vitro experiments showed the up-regulation of skin barrier proteins such as LOR and hyaluronic acid synthase, while suppressing the increase in IgE and IL-4 levels in HaCaT cells seeded at a density of 2 × 10⁶ cells per well. 4Importantly, these protective effects were abolished by co-treatment with GW6471, a PPARα antagonist, confirming the central role of PPARα in mediating the therapeutic effects. These exosomes were intraperitoneally administered to DNCB-induced AD mice at a dose of 1 × 10⁷ articles/mL daily for two weeks, which significantly reduced epidermal thickening, immune cell infiltration and AD-related gene expression. Consistent with the in vitro findings, these effects were abolished when GW6471 was co-administered, further validating the involvement of PPARα in the therapeutic effect of neonatal DF-derived exosomes [109].

Microorganism-derived extracellular vesicles

In healthy individuals, various microorganisms interact on the skin to form a healthy skin microenvironment, while dysbiosis of common skin microbiota is strongly associated with AD. Especially, S. aureus population significantly increases in AD patients, followed by their colonization [45, 110]. In such concept, restoring this imbalance is suggested as another therapeutic strategy to treat AD. Given the challenges of specifically targeting and eliminating a single type of microorganism, recent research has shifted toward exploring the interactions among microbial species, with microbial EVs playing a key role in such intercellular communication. Compared to the skin of AD patients, the levels of Lactococcus, Leuconostoc, Lactobacillus, and Lactobacillales(o) are higher in healthy skin [111], which are the microorganisms being considered as potential EV sources for AD therapy.

The therapeutic effects of such microbial EVs were evaluated in several studies. For example, EVs derived from Lactococcus lactis subsp. lactis were obtained via filtration of the conditioned media of with a 0.2 μm membrane. They increased the expression of fibrillin (FBN1) in fibroblasts, fibronectin (FN1) and FLG in keratinocytes, and enhancing the ability of keratinocytes to produce collagen proteins [112]. Another study has orally administered Lactobacillus plantarum-derived EVs at doses of 1, 10, and 100 μg per mouse, three times per week over a four-week treatment period, to an AD mouse model treated with S. aureus-derived EV. The treatment of Lactobacillus plantarum-derived EVs reduced IL-4 levels and epidermal thickness [111]. Cutibacterium acnes is another commensal bacterium being investigated for its potential in the treatment of AD, as Cutibacterium acne treatment in MC903-induced AD mice attenuated AD symptoms [113]. The potential of EVs derived from Cutibacterium acne to be used in the treatment of AD has also been studied. The functional differences of Cutibacterium acne EVs derived from healthy individuals, AD patients, and acne patients with exacerbated conditions were analyzed by proteomic variations. EVs derived from AD patients enhanced FLG expressions when treated to keratinocytes at a dose of 10 μg/mL for 24 h [114]. Although microbial EVs show potential as AD therapeutics due to their higher cost-effectiveness and productivity compared to mammalian EVs, the field is still in its early stages, with limited understanding of their functional complexity, necessitating further extensive research for clinical application.

Synthetic exosomes

Synthetic exosomes include engineering of naturally secreted exosomes, or nanovesicles physically synthesized from living cell components. They are usually developed to improve the limitations of naturally secreted exosomes, such as low productivity, low targeting efficacy, or low therapeutic efficiency, and structural integrity. The most frequently used method to create synthetic exosome is serial extrusion of living cells using a liposome-synthesis kit consisting of microporous membranes. This leads to synthesis of exosome-like vesicles with a size range of 100–200 nm, with similar structural, physical, chemical, and biological characteristics but higher productivity by 100–250 times compared to naturally secreted exosomes [17, 18]. The extrusion method can also be used to create hybrid vesicles, by co-extrusion of a solution containing different types of cells, EVs, or other nanodrugs. These approaches are particularly advantageous when the therapeutic effect of the internal components of one exosome type is to be preserved while incorporating the bioactive properties or therapeutic functions of another exosome type. The resulting hybrid exosome mimetics exhibit dual functionality, combining the beneficial effects of both vesicle types. Additionally, this technique can be employed to impart specialized targeting abilities or improved biocompatibility through the integration of newly synthesized membrane components [115]. Furthermore, the co-extrusion of membrane vesicles with small-core materials facilitates the encapsulation of the core material within the vesicular membrane. This method is particularly suited for applications where the internal content is replaced with a core material possessing specific therapeutic or diagnostic functions, while retaining the structural and functional characteristics of the original exosome membrane [116]. Collectively, these strategies highlight the versatility of exosome engineering in creating multifunctional therapeutic platforms with enhanced precision and efficacy.

Human embryonic kidney cell-derived exosome mimetics have demonstrated therapeutic potential in diabetic wound healing. Furthermore, based on established protocols using human embryonic kidney cell-derived exosomes as miRNA delivery vehicles, a hybrid synthetic exosome encapsulating melatonin, an antioxidant and anti-inflammatory compound that has been shown to reduce AD-related cytokines in DNFB-treated NC/Nga mice, was developed. Melatonin was co-extruded with human embryonic kidney 293 cells to produce melatonin-loaded synthetic exosomes. Based on the in vitro results demonstrating the effective role of melatonin in anti-inflammation, the synthetic exosomes were topically administered to DNCB-induced AD mouse models for 16 days, resulting in the suppression of mast cell infiltration and fibrosis. In addition, serum IgE and IL-4 levels were reduced, and IFN-γ levels were increased as assessed by ELISA [117–120].

In another study, another hybrid exosome with a surface modified by P-MEL (mannosylerythritol lipids conjugated to PEG via a thiol-maleimide reaction) was fabricated by extrusion of P-MEL together with live keratinocytes. These exosomes were topically administered to a particulate matter-induced AD mouse model associated to oxidative stress, inflammation, and barrier disruption for consecutive five days a week. The results demonstrate effective inhibition of MAPK signaling pathway, resulting in the suppression of pro-inflammatory cytokine release, as well as improved skin barrier integrity and hydration [121].

Another study has developed a more complex fusion vesicles exhibiting anti-inflammatory and antioxidant effects (Fig. 4). The first vesicle consists of grapefruit-derived EV (GEV), loaded with CX5461, a rDNA-specific transcription inhibitor which down-regulates inflamed keratinocyte proliferation, as well as acting as an immunosuppressor through JAK-STAT protein downregulation. The other vesicle is created from physical extrusion of CCR6-transfected gingiva-derived MSC (GMSC), which enhances the neutralizing effect by competing with CCR6-expressing T cells. GMSC-derived nanovesicles also possess strong immunosuppressive effects and the ability to reduce reactive oxygen species (ROS). To integrate these advantages into a single vesicle, a fusion vesicle (FV@CX5461) was generated using the co-extrusion method. in vitro, FV@CX5461, encapsulating plant-derived miR159a, demonstrated significant therapeutic effects by reducing ROS levels, suppressing inflammatory cytokine expression and inhibiting the proliferation of inflamed HaCaT cells. In addition, FV@CX5461 promoted the polarization of M2 macrophages and inhibited the proliferation of human peripheral blood mononuclear cells (PBMCs). in vivo, FV@CX5461 was administered intravenously to a DNCB-induced AD mouse model on days 16, 18 and 20. Treatment alleviated AD symptoms by reducing the ratio of Th17 and Th2 cells while increasing Treg cells. This was accompanied by decreased serum levels of IgE and IL-4, along with down-regulated expression of TSLP and CCL20, a high affinity ligand for CCR6 [122].

Fig. 4.

Synthetic exosome derived from fusion of grapefruit-derived EV and CCR6 + MSC-derived NV. A Schematic illustration of the NV preparation by fusion for anti-inflammation and targeted AD therapy. B Schematic illustration of the intravenous injection of NVs three times into DNBC-induced AD model. C AD lesion-specific targeting effect of NV via CCR6 expression. D Representative photographs showing a visual comparison of AD lesions under NV treatment. E Anti-inflammatory effect of NV by down-regulating T cell-mediated immune response. Reproduced with permission from [122] Copyright 2023, John Wiley & Sons, Inc

Conclusion and future perspectives

Exosome is an emerging tool in regenerative engineering due to their biocompatibility, structural stability, ease of storage, and versatility of engineering methods. The use of exosome mimetics can be an ideal alternative of exosomes, with improved productivity, cost efficiency, and multivalency with targeting efficacy and drug loading. AD is a skin barrier disorder associated with chronic immune dysregulation that exosomes and exosome mimetics can improve through their immunomodulatory capacity, ability to improve the skin barrier, and ability to promote skin regeneration through angiogenesis and collagen synthesis. Research into exosome therapy for AD treatment is still in its early stages of development and validation, requiring the selection of appropriate parent cells based on the target cell, and the consideration of chemical and biological modifications to enhance therapeutic effects. While novel methods to maximize the productivity and purity of exosomes and exosome mimetics have advanced these research aspects, the inherent heterogeneous nature of these biogenic materials and the lack of standardized methods for synthesis and characterization still limit their use for clinical translation. Drugs for clinical use must meet rigorous standards of consistency and comparability to ensure both safety and efficacy. Therefore, for clinical applications, it is essential to minimize the variability between exosomes or exosome mimetics and to ensure that rigorous quality control measures are implemented.

Moreover, the lack of evidence for effective transdermal penetration of exosomes remains a major challenge in skin disease therapy. The stratum corneum, the outermost layer of the skin, has lipophilic composition, thereby requiring surface membrane engineering of exosomes for effective transdermal diffusion. Physical methods have been used to overcome such limitations in skin drug delivery. For example, microneedles can physically penetrate the stratum corneum to facilitate drug delivery into the dermal layer. Sonophoresis and iontophoresis increase the permeability of the skin barrier to enhance drug transport using ultrasound and electric field, respectively. In addition to physical methods, chemical modification of the exosome surface offers a promising approach to enhance transdermal delivery. For example, modification of surface membrane potential could improve their compatibility with iontophoresis. In addition, membrane functionalization with ligands targeting skin cell-specific receptors may further increase absorption efficiency after direct injection and provide a targeted and effective delivery system.

In summary, exosomes and their mimetics hold great promise for the treatment of AD by promoting tissue regeneration and immune modulation. Further research to optimize their delivery and therapeutic efficacy will advance their application and pave the way for clinical use, offering new opportunities in dermatology.

Funding

This study was financially supported by (i) the National Research Foundation of Korea (NRF) funded by the Korean Government (MSIT) (RS-2023-00213691), (ii) the Technology Innovation Program (RS-2024-00448758) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea), and (iii) the Chung-Ang University Graduate Research Scholarship in 2022.

Data availability

The datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.

Declarations

Conflict of interest

The authors have no financial conflicts of interest.

Ethical statement

No human or animal experiments were performed in this study.