Transethosomal system for enhanced transdermal delivery and therapeutic effect of caryophyllene oxide

Aim: This study focuses on the design and investigation a transethosomal formulation for enhanced topical delivery and improved analgesic activity of caryophyllene oxide. In addition, this work explores new potential mechanisms of analgesic activity of the active compound including alpha-amino-3-hydroxy-5-methyl-4-isooxazole-propionic acid (AMPA) and Cyclooxygenase 2 (COX-2). Methods: The transethosomal system containing various caryophyllene concentrations was prepared. The optimum formulation was characterized for the presence of nanovesicles by atomic force microscopy (AFM) and dynamic light scattering (DLS). FTIR was conducted to examine the interaction between the nanovesicle components. The ability of the representative system to enhance the delivery of caryophyllene oxide into and through the skin compared with a coarse emulsion, was examined using porcine ear skin, Franz diffusion cells, and HPLC analysis. The in vivo analgesic efficacy of caryophyllene oxide administrated from the nanovesicular carrier was assessed using the acetic acid-induced pain mouse model compared to a conventional topical formulation. In the second part of the study, the mechanism of analgesic activity of caryophyllene oxide was investigated using AMPA and COX-2 receptors activity in vitro assays. Results: Characterization studies revealed the presence of spherical nanovesicles with an average size of 450.7 ± 55.03 nm. The transethosomal system demonstrated superior skin penetration compared to a conventional emulsion, as demonstrated by the in vitro skin penetration study, with a caryophyllene oxide permeated amount of 40.3 ± 0.881 µg/cm² via the transethosomal system compared to the emulsion which delivered only 29.5 ± 10.5 µg/cm². Moreover, a significantly greater amount of caryophyllene oxide was extracted from the skin following the application of the transethosomal formulation (251.8 ± 76.03 µg/cm²) compared to that extracted from the skin following the ointment application (13.5 ± 0.6 µg/cm²). The in vivo experiment demonstrated that the transethosomal formulation significantly reduced writhing episodes, achieving an 80.5 % Maximum Possible Effect (%MPE) compared to 24.7 % for the conventional topical formulation. In vitro mechanistic studies indicated that caryophyllene oxide exhibited a potent COX-2 selectivity and significantly modulated AMPA receptor subunit activity, highlighting a potential mechanism for pain therapy via the two investigated mechanisms. Conclusions: These findings underscore the effectiveness of the caryophyllene oxide transethosomal system in enhancing topical drug delivery and achieving adequate therapeutic efficacy, making it a promising candidate for further clinical development. The study's outcomes shed light on the possible mechanism of analgesia of caryophyllene oxide via COX and AMPAR modulation.