The role of corneocytes in skin transport revised--a combined computational and experimental approach.

PURPOSE: To investigate mechanisms of compound-corneocyte interactions in a combined experimental and theoretical approach. MATERIALS AND METHODS: Experimental methods are presented to investigate compound-corneocyte interactions in terms of dissolution within water of hydration and protein binding and to quantify the extent of the concurrent mechanisms. Results are presented for three compounds: caffeine, flufenamic acid, and testosterone. Two compartmental stratum corneum models M1 and M2 are formulated based on experimentally determined input parameters describing the affinity to lipid, proteins and water. M1 features a homogeneous protein compartment and considers protein interactions only via intra-corneocyte water. In M2 the protein compartment is sub-divided into a cornified envelope compartment interacting with inter-cellular lipids and a keratin compartment interacting with water. RESULTS: For the non-protein binding caffeine the impact of the aqueous compartment on stratum corneum partitioning is overestimated but is successfully modeled after introducing a bound water fraction that is non-accessible for compound dissolution. For lipophilic, keratin binding compounds (flufenamic acid, testosterone) only M2 correctly predicts a concentration dependence of stratum corneum partition coefficients. CONCLUSIONS: Lipophilic and hydrophilic compounds interact with corneocytes. Interactions of lipophilic compounds are probably confined to the corneocyte surface. Interactions with intracellular keratin may be limited by their low aqueous solubility.

Development of a fast and precise method for simultaneous quantification of the PLGA monomers lactic and glycolic acid by HPLC.

Poly(lactide-co-glycolide acid) (PLGA) is an extraordinary well-described polymer and has excellent pharmaceutical properties like high biocompatibility and good biodegradability. Hence, it is one of the most used materials for drug delivery and biomedical systems, also being present in several US Food and Drug Administration-approved carrier systems and therapeutic devices. For both applications, the quantification of the polymer is inalienable. During the development of a production process, parameters like yield or loading efficacy are essential to be determined. Although PLGA is a well-defined biomaterial, it still lacks a sensitive and convenient quantification approach for PLGA-based systems. Thus, we present a novel method for the fast and precise quantification of PLGA by RP-HPLC. The polymer is hydrolyzed into its monomers, glycolic acid and lactic acid. Afterwards, the monomers are derivatized with the absorption-enhancing molecule 2,4'-dibromoacetophenone. Furthermore, the wavelength of the derivatized monomers is shifted to higher wavelengths, where the used solvents show a lower absorption, increasing the sensitivity and detectability. The developed method has a detection limit of 0.1 µg/mL, enabling the quantification of low amounts of PLGA. By quantifying both monomers separately, information about the PLGA monomer ratio can be also directly obtained, being relevant for degradation behavior. Compared to existing approaches, like gravimetric or nuclear magnetic resonance measurements, which are tedious or expensive, the developed method is fast, ideal for routine screening, and it is selective since no stabilizer or excipient is interfering. Due to the high sensitivity and rapidity of the method, it is suitable for both laboratory and industrial uses.

Permeability of the reconstructed human epidermis model Episkin in comparison to various human skin preparations.

The objective of this work was to compare the barrier function of the small diameter reconstructed human epidermis model Episkin (d=12 mm) to human skin in vitro. For that purpose a modification for the Franz diffusion cell (d=15mm) had to be developed so as to allow direct comparison with the following human skin preparations: Full thickness skin (FTS), split thickness skin (STS), heat-separated epidermis (HSE), and trypsin isolated stratum corneum (TISC). Among the tested preparations, HSE appeared to be the most preferable due to its clear morphological structure and ease of preparation. The lipid profile of HSE and Episkin was analyzed and showed significant differences in terms of cholesterol, ceramides and triglycerides contents, whereas cholesterol esters and fatty acids were not different. Permeation data with HSE and Episkin were then gathered using caffeine and testosterone. Both test compounds permeated much faster through Episkin than through HSE. Moreover, opposed to Episkin, HSE differentiated between the two test compounds. In spite of the remarkable progress in developing RHEs in the past years at this time Episkin can obviously not yet fully replace human skin for in vitro permeability experiments.

Comparison of bovine udder skin with human and porcine skin in percutaneous permeation experiments.

Rat and pig animal skin has been the most common replacement material for human skin for use in in vitro permeability experiments. Unfortunately, the permeability barrier of skin from laboratory animals is known to be relatively weak, due to significant follicular transport. Pig skin has been shown to be a suitable model for human skin. Unfortunately, it cannot be gathered from the regular slaughtering process, which makes it unsuitable for permeation experiments. We therefore studied the suitability of bovine udder skin, an untreated waste material of the butchering process, as a possible replacement material for use in in vitro permeability tests. We investigated the barrier strength of bovine udder skin against four different substances, and its histology and lipid profile, in comparison with pig skin and heat separated human epidermis. Pig and human skin were found to be equally permeable, whilst bovine udder skin seemed to exhibit a weaker, but less variable, barrier against caffeine, benzoic acid, testosterone, and flufenamic acid. The skin of all three species contained variable contents of the major lipid classes: cholesterol, ceramides, cholesterol ester, fatty acids and triglycerides. Morphological differences mainly comprised variations in the density of hair follicles. Based on these results, the amount of free fatty acids and triglycerides and the density of hair follicles seem to be important factors in the differences between the skin barriers in the three species.

Development of a fast and precise method for simultaneous quantification of the PLGA monomers lactic and glycolic acid by HPLC / 药物分析学报

Poly(lactide-co-glycolide acid) (PLGA) is an extraordinary well-described polymer and has excellent pharmaceutical properties like high biocompatibility and good biodegradability. Hence, it is one of the most used materials for drug delivery and biomedical systems, also being present in several US Food and Drug Administration-approved carrier systems and therapeutic devices. For both applications, the quantification of the polymer is inalienable. During the development of a production process, parameters like yield or loading efficacy are essential to be determined. Although PLGA is a well-defined biomaterial, it still lacks a sensitive and convenient quantification approach for PLGA-based systems. Thus, we present a novel method for the fast and precise quantification of PLGA by RP-HPLC. The polymer is hydrolyzed into its monomers, glycolic acid and lactic acid. Afterwards, the monomers are derivatized with the absorption-enhancing molecule 2,4′-dibromoacetophenone. Furthermore, the wavelength of the deri-vatized monomers is shifted to higher wavelengths, where the used solvents show a lower absorption, increasing the sensitivity and detectability. The developed method has a detection limit of 0.1 μg/mL, enabling the quantification of low amounts of PLGA. By quantifying both monomers separately, in-formation about the PLGA monomer ratio can be also directly obtained, being relevant for degradation behavior. Compared to existing approaches, like gravimetric or nuclear magnetic resonance measure-ments, which are tedious or expensive, the developed method is fast, ideal for routine screening, and it is selective since no stabilizer or excipient is interfering. Due to the high sensitivity and rapidity of the method, it is suitable for both laboratory and industrial uses.