Deformable liposomes as enhancer of caffeine penetration through human skin in a Franz diffusion cell test

OBJECTIVE

The permeation of hydrophilic molecules through the skin is still a challenge due to the barrier posed by stratum corneum, the outermost layer of the skin. Liposomes have frequently been used as carriers for different types of drugs and may also function as permeation enhancers. Propylene glycol has also been used as an edge activator in liposomes to increase the permeation. The aim of this work was to prepare liposomes containing an edge activator and loaded with caffeine to evaluate the potential of caffeine reaching the deeper layers in the skin.

METHODS

The formulations were prepared by a top-down process using high-pressure homogenization at 200 00 psi for 10 min. They were characterized by size, polydispersity index (PI), zeta potential (ZP), pH, caffeine content and encapsulation efficiency (EE%) on preparation (time zero) and after 30 days. Cytotoxicity of blank and loaded liposomes was assessed by MTT proliferation assay with a normal keratinocyte cell line (HaCaT). In vitro permeation tests were performed with human skin in Franz cells over 24 h, and caffeine concentration was determined in the skin surface, stratum corneum, dermo-epidermal fraction and receptor medium by HPLC.

RESULTS

The caffeine liposomes with (DL-Caf) or without propylene glycol (CL-Caf) showed, respectively, mean size 94.5 and 95.4 nm, PI 0.48 and 0.42, ZP + 1.3 and + 18.1 mV and caffeine content of 78.57 and 80.13%. IC₅₀ values of caffeine in DL-Caf (3.59 v/v %) and CL-Caf (3.65 v/v %) were not significantly different from conventional blank liposome (3.27 v/v %). The DL-Caf formulation presented the best capability to enhance the caffeine permeation through the skin, resulting 1.94-folds higher than caffeine solution. Furthermore, the caffeine flux from DL-Caf was 1.56- and 3.05-folds higher than caffeine solution and CL-Caf, respectively. On the other hand, CL-Caf showed the lowest caffeine penetration revealing the importance of edge activator to aid hydrophilic drug penetration to all skin layers.

CONCLUSION

The DL-Caf formulation tested was able to improve the permeation of caffeine through the stratum corneum and dermo-epidermal layers, suggesting that this delivery system may be effective for deep skin delivery of hydrophilic drugs.

Topical and cutaneous delivery using nanosystems

The goal of topical and cutaneous delivery is to deliver therapeutic and other substances to a desired target site in the skin at appropriate doses to achieve a safe and efficacious outcome. Normally, however, when the stratum corneum is intact and the skin barrier is uncompromised, this is limited to molecules that are relatively lipophilic, small and uncharged, thereby excluding many potentially useful therapeutic peptides, proteins, vaccines, gene fragments or drug-carrying particles. In this review we will describe how nanosystems are being increasingly exploited for topical and cutaneous delivery, particularly for these previously difficult substances. This is also being driven by the development of novel technologies, which include minimally invasive delivery systems and more precise fabrication techniques. While there is a vast array of nanosystems under development and many undergoing advanced clinical trials, relatively few have achieved full translation to clinical practice. This slow uptake may be due, in part, to the need for a rigorous demonstration of safety in these new nanotechnologies. Some of the safety aspects associated with nanosystems will be considered in this review.