Comparison of caffeine absorption between flow-through and static diffusion cells
by Christelle Gélis, Eurofins ADME Bioanalyses, skin@eurofins.com
Static cells (manually removing of receptor fluid) or dynamic cells (mimics blood flow and automatic sampling of receptor fluid) can be used to measure the in vitro absorption of chemicals through human skin to predict in vivo absorption.
Testing was performed by Eurofins ADME Bioanalyses for 14C-Caffeine absorption in order to compare the absorption results obtained from static and dynamic cells. The design was based on the publication, Regulatory Toxicology and Pharmacology1.
The study was performed on an occlusive system on a simplest caffeine formulation at 4 mg/mL in ethanol/UHQ water (50/50, v/v) with application of 25 μL/cm² volume on a skin surface. The receptor fluid was NaCl 0.9%, and the receptor fluid was sampled at 1, 2, 4, 8 and 24-hour post-dosing. The skin surface was 2 cm² for static cell and 1 cm² for dynamic cell. Two donors and three cells per donor were used in this study. After 24 hours, the remaining formulation was washed using five cotton swabs dampened with ethanol/UHQ water (50/50, v/v) followed by one dry cotton swab.
The radioactivity was evaluated in skin excess (washing of remaining formulation and cleaning of donor compartment), strips, skin, remaining skin (corresponding to the skin non-exposed to the formulation), receptor fluid and cleaning of receptor compartment.
The caffeine absorbed corresponded to the caffeine recovered in skin and receptor fluid, including the cleaning of the receptor compartment.
The mean caffeine absorption obtained from static and dynamic cells were 19.2% ± 10.1% and 19.4% ± 8.1% respectively of the applied dose. No statistic difference was observed between the static and dynamic systems with the occlusive system. According to the data obtained in the literature, we can conclude that the dynamic and static systems were similar in terms of absorption. While both have advantages, Eurofins can offer both systems and advise their customers to choose the best one in accordance to the objective of their studies.
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1. "in vitro predictions of skin absorption of Caffeine, Testosterone and Benzoic acid: a multi-centre comparison study," JJM van de Sandt and al. Publication in Regulatory Toxicology and Pharmacology 39 (2004) 271-281.
