Penetration of topically applied nanocarriers into the hair follicles of dog and rat dorsal skin and porcine ear skin

Background - In humans, topically applied nanocarriers penetrate effectively into the hair follicles where they can be exploited for the localized and targeted treatment of skin disorders. Objective - The objective of the present study was to examine the applicability of particle-based systems for follicular drug delivery in companion animals and livestock, which have a large follicular reservoir. Animals - Skin samples from 10 beagle dogs, 14 Wistar rats and four ears from freshly slaughtered cross-bred pigs were used. Methods - Fluoresceinamine labelled poly (L-lactide-co-glycolide) nanocarriers (256 or 430 nm) were applied on the different skin samples. After penetration, skin biopsies were removed and cryohistological cross sections prepared and investigated with regard to the follicular penetration depths (in mu m +/- standard deviation) of the nanocarriers using confocal laser scanning microscopy. Results - In canine, rat and porcine hair follicles, the smaller nanoparticles were detected at mean follicular penetration depths of 630.16 +/- 135.75 mu m, 253.55 +/- 47.36 mu m and 653.40 +/- 94.71 mu m, respectively. The larger particles were observed at average follicular depths of 604.79 +/- 132.42 mu m; 262.87 +/- 55.25 mu m and 786.81 +/- 121.73 mu m, respectively, in canine, rat and porcine hair follicles. Statistically significant differences (P < 0.05) in the mean follicular penetration depths of the differently sized nanocarriers could be determined for the canine and porcine skin samples. Conclusion - The mean follicular penetration depths of the differently sized nanocarriers were mostly significantly different between the different species, which might be due to different species-specific follicular dimensions. This issue needs to be addressed specifically in further studies.