Optimization of Conditions of Zanthoxylum Alkylamides Liposomes by Response Surface Methodology and the Absorption Characteristics of Liposomes in the Caco-2 Cell Monolayer Model

Zanthoxylum alkylamides, as a numbing substance in Zanthoxylum bungeanum has many physiological effects. However, the numbing taste and unstable properties limited its application. This study aimed to optimize the preparation process of Zanthoxylum alkylamides liposomes by response surface methodology (RSM) and to investigate the in vitro absorption characteristics of the liposomes through the Caco-2 cell monolayer model. The process parameters of liposomes were as follows: Zanthoxylum alkylamides was 15 mg, phospholipid–feedstock ratio was 6.14, phospholipid–cholesterol ratio was 8.51, sodium cholate was 33.80 mg, isopropyl myristate was 29.49 mg, and the theoretical encapsulation efficiency of the prepared liposomes could reach 90.23%. Further, the particle size of the liposomes was 155.47 ± 3.16 nm, and the ζ-potential was −34.11 ± 4.34 mV. Meanwhile, the liposomes could be preserved for 14 days under the condition that the content of Zanthoxylum alkylamides was less than 2 mg/mL and the preservation temperature was lower than 25 °C. Moreover, the uptake characteristics of the Zanthoxylum alkylamides liposomes in the Caco-2 cell monolayer model were also investigated. The results showed that the Zanthoxylum alkylamides liposomes could be taken up and absorbed by Caco-2 cells. Also, the Zanthoxylum alkylamides liposomes had a better uptake performance than the unembedded Zanthoxylum alkylamides and conformed to the passive uptake.