(W1130-07-40) Effect of Receptor Medium on Skin Permeability during In Vitro Skin Permeation Test (IVPT) Experiment

Purpose: In Vitro Permeation Test (IVPT) is commonly used to evaluate skin penetration of chemicals and the performance of dermatological products. For a permeant of low aqueous solubility, when the receptor chamber concentration of the permeant becomes close to its solubility, an additive can be used in the receptor medium to improve its solubility during IVPT. Different additives have been used because of their compatibility with the permeant, its assay, and other reasons. The receptor medium is expected not to affect the skin barrier function in IVPT. Although there are reports on the effects of these additives on the barrier properties of the skin, such effects have not been evaluated in a systematic manner. The objective of the present study was to evaluate the effects of these additives in IVPT receptor medium on skin permeability.

Methods: The experiments were performed in vertical Franz diffusion cells using split-thickness human skin. Before the start of the experiment, skin integrity was checked by Transepidermal Water Loss (TEWL) measurement. Then, the effects of receptor additives at varying concentrations in phosphate-buffered saline (PBS) on skin permeability of model permeants were determined. The additives examined in this study included bovine serum albumin (BSA), 2-hydroxypropyl-beta-cyclodextrin (HPCD), ethanol, nonionic surfactant (Brij-98), and propylene glycol (PG). The receptor solution of PBS alone was the control. Steady-state permeability coefficients were determined with a model lipophilic, moderately lipophilic, and polar permeants: estradiol, corticosterone, and mannitol, respectively. To minimize skin-to-skin variability in the data analysis, the permeation experiment was divided into three phases with the same skin sample: Phase 1 was PBS as the receptor solution (P1, control), Phase 2 was PBS with the additive as the receptor solution (P2, test phase), and Phase 3 was a repeat of Phase 1 with PBS after the removal of the Phase 2 receptor solution and rinsing the diffusion chamber (P3, test of skin reversibility). In addition, a control experiment was performed using PBS in all three phases. In the data analysis, the steady-state flux and permeability coefficient of each permeant were calculated from the “cumulative amount in the receptor solution versus time” plot. The ratio of permeability coefficients from each phase to Phase 1 was calculated for each skin sample (P2:P1 and P3:P1) and the average of these ratios of the skin samples was determined. A permeability ratio significantly greater than 1.0 would indicate the influence of the additive on skin permeability.

Results: Figures 1 and 2 present the ratios of skin permeability coefficients in Phase 2 and Phase 3 compared to Phase 1 (P2:P1 and P3:P1, respectively) using estradiol and corticosterone as the model lipophilic and moderately lipophilic permeants. In the presence of the additives in the receptor medium, the results indicate statistical differences between the PBS control and 25% ethanol, and 0.2% Brij-98 solutions for corticosterone (Figure 1). The results also indicate statistical differences between the control and 5% ethanol, 25% ethanol, and 0.2% Brij-98 solutions for estradiol (Figure 2). Although the permeability coefficients of Phase 2 are statistically different from those of Phase 1 (i.e., ratio > 1.0), the effects are generally small and less than 50% (additive-induced flux enhancement of less than 1.5x) except for the 25% ethanol solution. For mannitol, due to the large data variability, the results are not conclusive that further studies are required.

Conclusion: In summary, this study demonstrated that there are statistically significant effects from some receptor solutions but only 25% ethanol solution induced greater than 1.5-times increase in skin permeability.

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Acknowledgements:This research was supported by the Undergraduate Intelligence Scholarship (UIS), Royal Thai Government, Thailand and James L. Winkle College of Pharmacy, University of Cincinnati. The authors would like to thank Dr. Gerald Kasting for his helpful discussion and Mike Murawsky, Lijing Xu, and Cheng Zhong for their help in the laboratory.