ECVAM's research and validation activities in the fields of topical toxicity and human studies

A comparison of the in vitro permeation of 3-O-ethyl-l-ascorbic acid in human skin and in a living skin equivalent (LabSkin™)

OBJECTIVES

The safety assessment of personal care products often entails determining dermal absorption of their ingredients. Such experiments are typically performed in human or animal skin in vitro; however, ethical and safety considerations are associated with obtaining these tissues. Several human skin equivalent models (HSEs) have been developed as alternatives to human tissue. The barrier function of such models however, is normally less developed than human skin. Here, we examine the permeability of the HSE LabSkin^TM to a model compound, 3-O-ethyl-l-ascorbic acid (EA) compared with human skin.

METHODS

Skin uptake and permeation of EA was investigated in vitro using heat-separated human epidermis and LabSkin^TM . Finite dose (5 μL cm^-2 ) Franz-diffusion studies were conducted using 2 % (w/w) EA in a ternary solvent mixture comprising propylene glycol (PG), propylene glycol monolaurate (PGML), and isopropyl myristate (IPM). These excipients are commonly used in cosmetic products and they have been reported to promote permeation of EA in a different model, namely porcine skin.

RESULTS

Permeation of EA through LabSkin^TM was evident from 2 h; however, EA permeation in human skin was not detected until 5 h. Similar amounts of EA permeated through the two membranes at time points 8, 10, 12 and 24 h (p > 0.05). The cumulative amounts of EA delivered through LabSkin^TM at 24 h were 41.3 ± 2.0 µg cm^-2 , corresponding to 55.1 ± 1.8 % of the applied dose. Similar amounts permeated across human skin, 49.4 ± 4.1 µg cm^-2 , accounting for 58.0 ± 4.2 % of the dose applied (p > 0.05).

CONCLUSION

The permeation of EA in LabSkin^TM compared well with results for human epidermis in terms of the permeation profiles and the cumulative amounts of EA that permeated. The data suggest that the skin barrier of the two models was similar with regard to their overall permeability to the hydrophilic active EA. The findings are promising for the use of LabSkin^TM as a surrogate for human skin in permeability testing. Future studies will focus on exploring the reproducibility and robustness of LabSkin^TM for delivery of other actives that span a range of physicochemical properties.