Artificial sebum as a vehicle for studying ex vivo percutaneous absorption of three solid and lipophilic industrial toxicants

For testing skin absorption of chemical substances, OECD Test Guideline 428 (OECD, 2004)1 provides some recommendations as to how substances should be prepared:
“The test substance preparation (e.g., neat, diluted or formulated material containing the test substance which is applied to the skin) should be the same (or a realistic surrogate) as that to which humans or other potential target species may be exposed. Any variation from the ‘in-use’ preparation must be justified.”
However, the ex vivo percutaneous absorption flux of solid lipophilic toxicants is still very often measured after solubilisation of these substances in volatile organic solvents such as acetone, hexane, or ethanol. The use of these vehicles results in the introduction of several bias in the flux experiments. In particular, it may cause delipidation of intra- and extra-cellular structures, modify the permeability of the upper layers of the skin and consequently affect the flux of the substance of interest2.
Sebum, sometimes considered to be the first layer of the skin above the stratum corneum3, is mainly composed of squalene, wax monoesters, triglycerides and fatty acids.
Artificial sebum was prepared as close as possible to human sebum. As it showed no significant modification of the skin based on the measurement of the TransEpidermal Water Loss, cellular viability (WST), overall esterase activity and activities of the enzymes responsible for phase I and II metabolism, it was used as a vehicle in ex vivo percutaneous absorption flux assays. Data were compared for dermatomed human and rat skin exposed to three solid lipophilic compounds at infinite dose, benzo[a]pyrene (BaP), bisphenol-A (BPA), methylparaben (OHBA-M) dissolved either in sebum or in acetone.
When the substances were diluted in sebum, percutaneous absorption generally reached equilibrium, making it possible to measure the ex vivo lag time and percutaneous flux at steady-state. On the contrary, for the substances in acetone, a steady-state was barely reached. Only a mean or a maximum flux could be determined in these situations.

Based on these results, sebum appears to be an appropriate solubilisation vehicle to estimate dermal exposure to industrial toxicants.


1. OECD, 2004. Guideline for the testing of chemicals. Test Guideline 428: Skin absorption: in-vitro Method. Organization for Economic and Cooperation and Development, Paris, France.
2. Sartorelli, P., Andersen, H.R., Angerer, J., Corish, J., Drexler, H., Göen, T., Griffin, P., Hotchkiss, S.A.M., Larese, F., Montomoli, L., Perkins, J., Schmelz, M., van de Sandt, J., Williams, F. Percutaneous penetration studies for risk assessment. Environmental Toxicology and Pharmacology 8, 133-152, 2000
Degim, I.T. New tools and approaches for predicting skin permeability. Drug Discovery Today 11, 517-523, 2006.