Synthesis and Characterization of Highly Stable Fisetin Encapsulated in Lecithin-Chitosan-Savie Nanoparticles

Senolytic drugs, of the class of polyphenolic flavonoids, have attracted attention for a wide variety of medical applications for which they may be delivered topically, orally, and/or intravenously. However, due to their hydrophobicity and sensitivity to light and oxygen, they have been proven difficult to package and deliver. Here we report a synthesis method for encapsulated fisetin using lecithin-chitosan ionic gelation with a recently reported surfactant that is an alternative to polyethylene glycol (PEG)-containing compounds. Called "Savie" for a contraction of its components, sarcosine-Vitamin E, this surfactant allows for production of sub-100 nm nanoparticles that are bench stable for at least 10 months without aggregation. The environmentally sensitive fluorescence of fisetin allows it to be used as a tool for analysis of particle structure and stability. Absorbance, steady-state fluorescence, and fluorescence lifetime measurements alone and with quenchers indicate that a fraction of the fisetin is accessible to the surface solution and highly photooxidizable, whereas a second fraction is deeply complexed within the particle and significantly more stable. The two fractions may be distinguished from their absorbance peaks. The particles are readily taken up by cultured fibroblasts, with distinct fluorescence lifetimes occurring on the edges vs the interior of the cell. The particles show strong antioxidant activity in cells which is a combination of the effects of fisetin and Vitamin E.