Influence of the lipid-phase composition on the trans-epidermal transfer of vitamin B6 from O/W emulsions
Transfer of bioactives through epidermis can be viewed as a model of bioavailability for functional cosmetics and is relevant to their efficacy. Nine equivalent O/W emulsions differing in the composition of the lipid phase were comparatively tested for their ability to release vitamin B6 through 18-days-old reconstructed human epidermis, in vitro. Formulations afforded efficient diffusion of the vitamin through the skin, although the actual flux varied considerably, with coefficient of permeability in the range 15.0 – 297.3 10-5cm/h at 34°C. Bioavailability grew in the order: sesame oil < squalane ~ raw wheat germ oil < dibutyladipate ~ polydimethylsiloxane. Addition of 5% w/w free fatty acids (stearic, lauric, caprilyc, and oleic) to lowest performing sesame oil increased the bioavailability by 1.2-fold, 6-fold, 20-fold and 10-fold respectively.
The delivery of active principles from topical pharmaceutical preparations through epidermis has been a matter of extensive investigation in the last few decades and a number of strategies to increase drugs topical bioavailability have been designed (1). These include physical methods like iontophoresis (2) and electroporation (3), and chemical enhancing (4), i.e. the inclusion in the formulation of penetration enhancers, molecules like surfactants, terpenes, fatty alcohols and others, able to modify the barrier function of the stratum corneum (SC). Interestingly, the trans-epidermal delivery of bioactive molecules from cosmetic formulations has received comparatively less attention, despite their much broader use. On the other hand, the growing market demand for, so called, functional cosmetics or “cosmeceuticals” (5), such as protective and anti-aging formulations, poses the question of whether the functional bioactive ingredients (e.g. vitamins) claimed in the composition can effectively be delivered from the formulation into and across the epidermis. As part of an on-going systematic investigation in this regard, we have recently set ...