Publication Database

Follicular penetration of nano-sized particulate FA-PLGA and the dye RhBITC in dorsal dog and rat skin, and porcine ear skin as an in vitro model for the human integument (2011)

Art

Hochschulschrift

Autor

Knorr, Fanny Esther (WE 12)

Quelle

Berlin: Mensch und Buch Verlag, 2011 — V, 108 Seiten

ISBN: 978-3-86664-961-3

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/3192

Kontakt

Institut für Tierpathologie

Robert-von-Ostertag-Str. 15
14163 Berlin
+49 30 838 62450
pathologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

The skin as the outermost covering of the body provides a compliant and painless interface for topical drug administration. It is well established that pharmaceutical agents applied to its surface spread throughout the upper corneocyte layers by diffusing into the lipid matrix of the stratum corneum. Recent studies have evidenced the hair follicles to be effective shunt routes for the transportation of topically applied substances to deeper skin layers and long-term storage reservoirs for drugs in a number of laboratory animals and humans. Interest in the hair follicles as target structures is aimed at their use as depots for localized treatments of disorders including skin diseases and follicle-related disorders, as well as for systemic drug delivery by targeting of the capillary networks and immune and stem cells found in the vicinity of the skin appendages. Research is increasingly focussed on the development of nano-sized particulate drug delivery systems loaded with therapeutic agents customized to target the hair follicles. In the follicular canal, particulates are shielded from abrasion, enabling drug retention and long-term drug release. The success and efficacy of follicular penetration is largely determined by the numbers, distributions, morphometries and activities of the hair follicles found in the treated skin, as well as the skin constitution, the agent itself and the mode of application. In spite of the obvious abundance of follicular target structures and the comparatively large follicular reservoir, only very few studies have been conducted on the follicular penetration of nano-sized drug delivery systems in companion and farm animals. In the first part of this work, the penetration of topically applied, nano-sized particulates into the hair follicles of excised dog, rat and porcine skin was investigated. The formulations used consisted of FA-PLGA particles sized 256 nm and 430 nm suspended in hydrocellulose gels. Subsequent to application of the formulations to the skin samples using massage, the particles were visualized in cross-sections of the treated skin using a laser scanning microscope, and the follicular penetration depth was determined digitally. FA-PLGA particles were found to penetrate into 60 to 70% of the hair follicles of all skin samples investigated, corresponding to ‘active’ hair follicles receptive to penetration. The results indicated that the follicular penetration depths of the particulate formulations correlated positively with the sizes of the follicular orifices and the lengths of the infundibula in the examined skin samples. Studies have shown that the follicular openings are widest in porcine skin, followed by dog and rat skin, respectively. The hair follicle infundibula extend deepest into the skin of the pig, while in the dog they reach about half, and in the rat, about one- fourth the length of the infundibula found in porcine hair follicles. This is consistent with results of this study in which the particulates penetrated deepest into porcine hair follicles, and least deep into the hair follicles of the rat. While the two FA-PLGA formulations used in this study differed solely in the size of the FA-PLGA particles, no clear trends could be substantiated suggesting that the size significantly influenced follicular penetration. The hair coat, sebaceous glands, tight junctions and capillary networks of the skin samples, as well as the aggregation, degradation and marker leakage properties of the particulates were discussed as additional potential factors influencing follicular penetration of particulate FA-PLGA. The quantification of topically applied agents located in the follicular canals is crucial for questions pertaining to administration, concentrations and dosages for follicular penetration experiments. To date, no procedure exists by which follicular contents can be quantified in porcine skin commonly used as a model for the human integument. Excised porcine skin is a particularly suitable alternative to human skin, as its follicular reservoir capacity corresponds to that of living human skin. In the second part of this study, the established method of differential stripping was modified using tape stripping and an extraction technique. This enabled the selective quantification of the dye RhBITC, which was implemented as a model drug and located in the hair follicles of porcine skin subsequent to topical administration. An average of 5% of the dye applied to the skin was extracted from the follicular canals with ethanol and detected using a fluorescence spectrometer, which was in accordance with results from previous studies, substantiating the efficacy of the developed method.