Evaluation of ex vivo human skin as model for the investigation of nanoparticle-based drug delivery systems for anti-inflammatory topical dermatotherapy

Nanoparticles are promising drug delivery systems for the topical treatment of inflammatory skin diseases. Nevertheless, most useful results are based on penetration studies, which are frequently limited to model drugs such as fluorescent dyes. Investigation of penetration and efficacy would be of great value to detect potential benefits of drug-loaded nanoparticles. The current study focused on the development of a barrier-disrupted skin model based on ex vivo human skin to assess preclinically the extent to which nanoparticles improve penetration and efficacy of anti-inflammatory drugs in different states of barrier disruption. Different types of skin barrier disruption were induced by physical and chemical means. Comparative studies in two short-term skin cultures systems revealed that standardization of 50-times tape-stripping and 4-hour sodium lauryl sulfate pretreatment were more reliable than abrasion and 1.5-hour sodium lauryl sulfate pretreatment: Transepidermal water loss values and interleukin-6 /-8 levels were increased reproducibly. Moreover, a wide range of inflammatory mediators was affected in cultures of skin maintained in tissue media, which preserved key skin barrier parameters and viability better than medium-free cultures. Intradermal microdialysis for up to 24 hours in one experimental setup including up to nine sets enabled comparison of intact versus barrier-disrupted skin and three dexamethasone formulations (ethyl cellulose nanocarriers, nanocrystals and a conventional cream) in parallel. Physical and chemical barrier disruption affected dexamethasone penetration differently: Penetration rates in chemically treated skin were lower than in tape-stripped skin. Nanocrystals quickly penetrated intact and disrupted skin reaching significantly higher dermal drug amounts within six hours. The benefit of encapsulation in ethyl cellulose nanocarriers was more pronounced in intact skin. High cytokine levels indicated an irritative potential of nanocrystals, while the estimation of drugmediated efficacy over time was limited by cytokine release as a result of probe insertion. Skin barrier disruption resulted in increased penetration rates, but rare events of deeper penetration of nanoparticles were also identified in intact skin at sites of high focal particle aggregations by a newly implemented in situ imaging mode based on wide-field two-photon microscopy. The current study shows an effective way for the application of ex vivo human skin models in advanced drug delivery studies by maximizing the read-out obtained from each donor skin sample using specifically adjusted protocols and methods. These insights into the influence of disease-related skin barrier disruptions on the penetration and efficacy of topically applied drugs provide valuable information on the benefits of each individual nanoparticle-based drug delivery system in different types of barrier alterations. The resulting more effective drug penetration has the potential to improve the topical therapy of inflammatory skin diseases.