Penetration of gold nanoparticles across the stratum corneum layer of thick-Skin

Background: Transdermal particulate penetration across thick-skin, such as that of palms and sole, is particularly important for drug delivery for disorders such as small fiber neuropathies. Nanoparticle-based drug delivery across skin is believed to have much translational applications, but their penetration especially through thick-skin, is not clear. Objective: This study specifically investigates the effectiveness of gold nanoparticles (AuNPs) for thick skin penetration, especially across the stratum corneum (SC) as a function of particle size. Methods: The thick-skinned hind-paw of rat was used to characterize depth and distribution of AuNPs of varying sizes, namely, 22 +/- 3, 105 +/- 11, and 186 +/- 20 nm. Epidermal penetration of AuNPs was characterized both, in harvested skin from the hind-paw using a diffusion chamber, as well as in vivo. Results: Harvested skin segments exposed to 22 nm AuNPs for only 3 h demonstrated higher penetration (p < 0.05) as compared to the 105 and 186 nm particles. In animal studies, hind-paw skin of adult rats exposed to AuNPs solution for the same time, demonstrated nanoparticles in blood on the 4th day, and histological analysis revealed AuNPs in epidermal layers just below the SC, with no apparent tissue response. Conclusion: We conclude that the thick-skin allows nanoparticle penetration and acts as a depot for release of AuNPs into circulation long after the initial exposure has ceased. (C) 2017 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.