Dermal peptide delivery using enhancer molecules and colloidal carrier systems. Part III: Tetrapeptide GEKG.

Dermal application of peptides as drugs is an interesting and growing field in therapeutics. Besides therapy, they are increasingly used as cosmetic agents. Peptide delivery into the skin is highly challenging since they provide disadvantageous properties like a high molecular weight, hydrophilicity, polarity and susceptibility to enzymatic degradation. The aim of the presented study was to improve the bioavailability of a dermal administered tetrapeptide GEKG (amino acid sequence in one-letter notation). A nano-sized carrier system (microemulsion, ME) of w/o type was therefore developed since ME provide excellent penetration enhancing properties. Furthermore, enhancers were used to increase the penetration capacity of GEKG. The penetration of GEKG from the ME and enhancer-containing emulsions was compared to the penetration from a standard formulation. For this purpose ex vivo penetration studies with human skin were performed, which provide insights into dermal penetration and also localization and distribution of the active substances in each skin layer as well as the influence of vehicle variations. Experiments with three incubation times (30, 100, 300 min) and 5000 ppm GEKG in the formulations clearly show that the nano-sized carrier system is significantly better suited to transport GEKG rapidly into upper and deeper vital skin layers as well as through the skin compared to the standard cream. Studies with o/w emulsions containing 5% glyceryl caprylate/caprate 2.0× or 1.5× as enhancer and 50 ppm peptide revealed only a tendency to increased penetration into the SC and for the formulation with glyceryl caprylate/caprate 1.5× into the vital epidermis compared to the standard cream without additional enhancer. Significant better penetration rates were observed for the ME with 50 ppm GEKG. It can be concluded that liquid nano-sized systems are significantly more effective as carriers for extremely hydrophilic peptides used in cosmetics and also in therapeutics than classic cosmetic emulsions or enhancer-containing emulsions. CHEMICAL COMPOUNDS: Tetrapeptide-21 (CAS: 960608-17-7) glyceryl caprylate/caprate (CAS: 73398-61-5) sorbitan oleate (CAS: 1338-43-8) polyglyceryl-4 laurate (CAS: 75798-42-4) butylene glycol (CAS: 107-88-0) isopropyl palmitate (CAS: 142-91-6).