Influence of permeability enhancers on in vitro peptides delivery through STRAT-M® membranes

HR9 (Ac-HYWRELQYR-NH2) is an innovative and proprietary peptide designed to ameliorate skin disorders mediated by neuronal exocytosis. Its topical delivery guarantees safety and efficacy avoiding possible cholinergic side effects related to systemic administration. However, considering the hydrophilic nature and the high molecular weight of this innovative peptide, its skin permeation up to the dermis can be challenging. For this reason, the choice of the best formulation to deliver the biomolecule is a crucial aspect. In this study, the influence of different permeability enhancers for the delivery of HR9 was investigated using 3D printed in vitro Franz-type diffusion cells. Furthermore, HR9 behaviour was compared with an already commercialized peptide AHP-8 (Ac-EEMQRR-NH2). Specifically, release tests were conducted, for quality control intent, using dialysis membranes (i.e., molecoular weight cut-off 12 kDa and 6 kDa). For this purpose, the solutions of pure peptides were compared with semisolid O/W emulsions, suggesting that the release profile is dependent on the molecular weight of the peptides, and on the membrane's cut-off. Moreover, STRAT-M® membranes were employed to predict and mimic the in vitro skin diffusion rate. The effect of chemical enhancers (i.e., 30% ethanol and 5% Transcutol®) was further analysed. Results showed that the presence of the enhancers effectively improved the permeation rate of the peptides. While in the case of the semisolid emulsions, no penetration was observed at 6 h timepoint, suggesting a possible delayed delivery of the active molecules. Overall, in this study the release and permeation profile of the innovative HR9 peptide was investigated, confirming the importance of the use of permeability enhancers in topical formulations.