[Transdermal characteristics and mechanism of asiaticoside nanoemulsions and asiaticoside nanoemulsions-based gels].

To prepare the asiaticoside nanoemulsions (ASI-NEs) and asiaticoside nanoemulsions-based gels (ASI-NBGs), compare them with the commercial cream of asiaticoside (ASI-C) in terms of transdermal characteristics, and investigate the transdermal mechanism of ASI-NEs and ASI-NBGs. Their transdermal characteristics were studied by using Franz diffusion cells. The effect of topical ASI-NEs and ASI-NBGs on ultrastructure of rabbit skin was evaluated by using HE staining method. The localization and the permeation pathway of asiaticoside were visually investigated by using laser scanning confocal microscope (CLSM). The transdermal studies in vitro showed that the cumulative amount of ASI permeated from ASI-NEs and ASI-NBGs at 12 h after application were (3 504.30±180.93), (1 187.40±128.88) μg·cm⁻² respectively, 6.57, 2.23 times of that in the control group of ASI-C; the drug deposition of ASI-NEs and ASI-NBGs in skin was (159.48±7.47), (120.53±5.71) μg·cm⁻² respectively, 5.93, 4.48 times of that of ASI-C. HE staining of the rabbit skin after application of ASI-NEs and ASI-NBGs showed that the epidermis structure was basically intact; stratum corneum was loosed and the keratin fragment was increased; at the same time, the gap of prickle cell was increased and the basal cells were arranged loosely. The study of CLSM showed that significant percutaneous enhancer effect was observed for ASI-NEs after the topical application of 6 h, as the fluorescent compound was penetrated in the dermis and diffused uniformly. The fluorescence area and the integral optical density (IOD) were 28.81, 32.51 times of that in the FITC aqueous solution group, respectively. The fluorescent preparations showed strong fluorescence in the epidermis, but weak in deeper layers; with the increase of treatment time, the fluorescence in deeper layer was increased and stronger in skin appendages. The prepared ASI-NEs and ASI-NBGs have good transdermal characteristics and the transdermal mechanism is related to breaking the ultrastructure of stratum corneum and penetrating by the path of skin adnexa.