(A-10) Transdermal Delivery of Immuno-modulating Biomaterials for Atopic Dermatitis Treatment

Introduction:: Atopic dermatitis (AD) is a pervasive inflammatory skin condition affecting 25% of children and 4-7% of adults. Present treatments, such as topical corticosteroids, demonstrate limited efficacy in targeting immune system imbalances and exhibit undesirable side effects. Consequently, an efficacious drug delivery platform to modulate AD patients' immunity is essential. Macrophages are instrumental in regulating inflammation levels in AD immunity, with oxidative stress from reactive oxygen species (ROS) as a central AD pathogenesis feature. Layered double hydroxides (LDHs) are anionic lamellar compounds with positively charged layers capable of encapsulating anionic biomolecules within interlayer spaces, rendering them attractive drug delivery systems. This study investigates the therapeutic potential of LDH-based drug delivery systems for AD treatment. Indole-3-acetic acid (IAA) hybridized with inorganic layered ZnAl compounds was loaded into LDHs (IAA-LDH). By topically applying IAA-LDH to skin lesions, the stable formulation can be transdermally delivered to the epidermis, and IAA is released in a sustained manner. As a result, the anti-inflammatory and anti-atopic properties of IAA-LDH were examined in an AD mouse model by analyzing cutaneous tissues, immune organs, and cells. These results suggest that this inorganic-based drug delivery platform has significant therapeutic potential as a candidate for AD treatment.


Materials and Methods:: Hybridization of IAA with inorganic layered ZnAl compounds was achieved by ion exchange and coprecipitation reactions. For comparison, IAA was dissolved in PBS by adding NaOH (1 N), followed adjusting the pH to 7.4 with HCl (1 N). Bone marrow-derived cells were collected from the medullary cavities of mouse thighbones and pelvic bones and differentiated into macrophages. We assessed macrophage polarization through flow cytometry following IAA-LDH treatment of mouse bone marrow-derived macrophages. Additionally, we analyzed IAA-LDH's ROS reduction capability by staining intracellular ROS of immune cells. Finally, the stained cells were analyzed using flow cytometry. AD-like skin lesions were induced in 7-week-old Balb/c mice using 2,4-dinitrochlorobenzene (DNCB) applied to dorsal skin for three weeks. IAA-LDH and IAA were applied six times to sensitized skin from day seven. We examined immunological organs and cutaneous tissues to assess IAA-LDH's anti-inflammatory and anti-atopic properties in an AD mouse model. After the last treatment with IAA-LDH, mice were anesthetized and sacrificed to collect the dorsal skin and spleen samples. The spleen weight was measured, and spleen weight per body weight was calculated for standardization. The resected dorsal skin tissues were fixed and embedded in paraffin. Thereafter, each paraffin block was sectioned into 5 μm-thick slices and stained with hematoxylin and eosin (H&E) and toluidine blue (TB).


Results, Conclusions, and Discussions:: To evaluate IAA-LDH's impact on macrophage polarization, bone marrow-derived macrophages were cultured with IAA-LDH. The results revealed a significant increase in arginase 1+ expression, indicating M2 subset activation, vital for cutaneous healing. IAA-LDH fostered an anti-inflammatory environment through M2 polarization promotion and M1 phenotype suppression. We assessed IAA-LDH's ROS-scavenging ability by treating immune cells with DNCB to induce ROS production. Post-IAA-LDH incubation, ROS levels, marked by cell-permeant 2,7-dichlorodihydrofluorescein diacetate, were halved compared to the normal group, suggesting LDH-enhanced intracellular IAA delivery and internalized IAA-LDH's antioxidant properties. IAA-LDH's therapeutic potential was investigated in a DNCB-induced AD mouse model. IAA-LDH application considerably reduced erythema and erosion compared to the AD model and IAA treatment groups, signifying successful inflammation mitigation through skin penetration. After DNCB sensitization and IAA or IAA-LDH treatment, mice were sacrificed for histopathological analysis. IAA-LDH treatment resulted in a significant decrease in spleen weight, indicating attenuated excessive immune activity. Epidermal thickness assessment was performed on skin tissues collected and stained with H&E. IAA-LDH treatment reduced epidermal thickness, suggesting its potential as an efficient transdermal delivery platform for AD treatment. Skin tissues were stained with TB to examine mast cell count changes. IAA-LDH treatment remarkably reduced mast cell infiltration, akin to the healthy control group. Hence, IAA-LDH could alleviate AD symptoms by modulating inflammatory factor expression. In conclusion, LDHs show promise as medication delivery mechanisms for AD treatment. IAA-LDH effectively regulated the immune system in an AD mouse model, reducing skin inflammation and restoring skin barrier function. These findings pave the way for the development of LDH-based therapeutic platforms for the treatment of AD and other autoimmune disorders.


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