Distribution and quantification of polyethylenimine oligodeoxynucleotide complexes in human skin after iontophoretic delivery using confocal scanning laser microscopy.

Iontophoresis may be a potentially useful technique for the delivery of oligonucleotides into the skin. To enhance intracellular uptake during iontophoresis, we investigated the dermal delivery of oligodeoxynucleotides (ODN) as a polyelectrolyte complex with polyethylenimine (PEI). Perpendicular cross-sectioning was performed to visualize and quantify the penetration properties of double labeled PEI/ODN complexes across full thickness human skin. Due to the net positive charge of the complexes, anodal iontophoresis was expected to enhance skin delivery by electrorepulsion compared to passive diffusion. Confocal laser scanning microscopy demonstrated that non-complexed ODN could penetrate the skin after 1 h of cathodal iontophoresis but not by passive diffusion or anodal iontophoresis. However, extensive degradation occurred as documented by a dramatic decrease of fluorescence intensity within viable skin tissue after 10 h. Anodal iontophoresis of the complexes led to a deep penetration of both the TAMRA-labeled ODN and the Oregon Green-labeled PEI. A constant increase in fluorescence indicated a protective effect of the polymer against nuclease degradation. Co-localization of red and green fluorescence was noted within numerous nuclei of epidermal keratinocytes. In contrast, passive diffusion of the complexes did not lead to successful uptake into keratinocytes and was limited to the stratum corneum. Complexation of ODN by PEI, therefore, seems to be a promising method to enhance both the transport of charged complexes into the skin and to facilitate intracellular uptake, which may potentially be useful for the local treatment of skin diseases using ODN.