Effects of Saponin and Sophorolipid on the Formation and Stability of Shikonin Lipid Nanoparticles

Shikonin is a kind of hydrophobic natural pigment with various physiological activities. In order to improve its water solubility, stability and bioavailability, a natural surfactant modified shikonin lipid nanoparticles was developed. In this study, lecithin was used as raw material to prepare shikonin lipid nanoparticles by pH-driven method. The effects of saponin or sophorolipid on the formation and stability of shikonin lipid nanoparticles were investigated. When the mass ratio of lecithin to natural surfactant was 2:1, the encapsulation rate and the loading rate of saponin modified shikonin lipid nanoparticles (Sap-SLNP) reached to 99.01% and 5.06%, respectively. For sophorolipid modified shikonin lipid nanoparticles (Sop-SLNP), the encapsulation rate and the loading rate were 98.36% and 5.16%, respectively. The environmental stability of shikonin lipid nanoparticles modified by two kinds of natural surfactants were similar. The shikonin retention rate of Sap-SLNP and Sop-SLNP after thermal treatment and light irradiation were about 2 times and 1.6 times of free shikonin, respectively. And they maintained good stability without any significant changes at pH range of 2~7 and ion concentration of 0~1000 mmol/L. After repeated freeze-thaw three times, the particle size of Sap-SLNP and Sop-SLNP showed no significant changes and the encapsulation rate was around 85%, which was nearly twice to that of unmodified lipid nanoparticles. After 4 weeks of storage, the particle size of Sap-SLNP and Sop-SLNP remained unchanged, and the encapsulation rate was about 80%, which was about 1.7 times that of the unmodified lipid nanoparticles. Moreover, the bioavailability of shikonin in Sap-SLNP and Sop-SLNP was significantly improved, which was about three times that of free shikonin.