Proretinal nanoparticles: stability, release, efficacy, and irritation

Despite many potent biological activities, retinoids such as retinoic acid (RA) and retinal possess dose-related broad side effects. In this study, we show that this problem, which has been unsolvable for a long time, can be tackled through a controlled release strategy in which retinal is continuously delivered to the skin via sustained release from proretinal nanoparticles. The water dispersible proretinal nanoparticles are stable when kept in water at neutral pH and at room temperature for 8 months under light-proof conditions, and show sustained release of retinal into human synthetic sebum at a pH of 5. In the daily topical application tests performed for 4 weeks on rats' skin, the nanoparticles showed superior ability to increase epidermal thickness compared to RA and retinal, with no skin irritation observed for the proretinal particles, but severe skin irritation observed for RA and free retinal. When tested under occlusion conditions in human volunteers, insignificant skin irritation was observed for the proretinal nanoparticles. The 12-week, double-blind, split-face study on human volunteers indicates better antiaging efficacy of the particles as compared to the free RA.