Caffeic acid skin absorption: Delivery of microparticles to hair follicles

Caffeic acid (CA) is a polyphenol that can be found in a wide range of vegetal dietary sources. It presents a remarkable antioxidant potential, but what is more interesting from the therapeutic point of view is, that it has demonstrated in vitro antimicrobial properties. Folliculitis is a common skin condition, usually caused by a bacterial or fungal infection, in which hair follicles become inflamed. A typical challenge in dermal application when the actives diffuse passively through the skin in a quick manner, as it is the case of CA, is to provide the effective concentration of the compound at the target site for the sufficient time to finalize the treatment adequately and reduce the possibility to trigger systemic side effects. To achieve this goal, it is necessary to appropriately design the drug delivery system. In this case, we leverage the ability of microparticles to accumulate into the hair follicles to design O/W-emulsions containing CA-loaded controlled-release microparticles. Two different emulsion types containing CA were prepared, one containing free CA and the other containing microencapsulated CA. Traditional and differential tape stripping techniques were performed to investigate drug distribution within the different skin layers and into the hair follicles. The Tape stripping results demonstrated that the tapes S3-S5 and S6-S10 presented a higher total amount of CA. The strips are collected and extracted in groups to assure the extraction of quantifiable amounts of drug. Samples S11-15 and S16-20 show a decrease in the amount of quantified CA, as it was expected. Thus, it can be seen that the amount of active decreases while the stratum corneum depth increases. The retention studies demonstrated that, the microparticles tend to produce a more homogeneous distribution of CA, within the stratum corneum and a higher retention into the hair follicle, which can be attributed to their size and uniformity. Besides, MPs present an additional advantage because they guarantee a continuous release of CA in the target for a prolonged period, allowing the treatment of folliculitis with a single dose until the MPs are removed from the hair follicle by its natural regeneration process or particle depletion of CA.