Characterization and In vitro Release & In vivo Behavior Study of Self-Assembled Nano-Emulsion in XiaoYao Pill for Enhanced Drug Delivery

Introduction/Background: Traditional Chinese medicine formulations often contain hydrophobic components with limited solubility and stability, leading to low oral bioavailability. Selfassembled nanoparticles (SANs) have shown promise in enhancing oral bioavailability of these components. However, whether un-decocted Chinese herbal pellets can generate SANs and the impact of SANs formed by multiple components on pharmacokinetic parameters remains unexplored. Methods: In this study, single-factor approach was employed to determine the optimal separation method of nano-emulsion phase of XiaoYao pill (N-XY). Morphological and particle size analyses confirmed the nanoscale nature of N-XY. High-performance liquid chromatography (HPLC) fingerprint analysis was conducted to compare the distribution of active ingredients among three different phases of XiaoYao pill (XY pill). In vitro release studies were performed to evaluate the release mechanism of four ingredients from N-XY. Additionally, in vivo pharmacokinetics and tissue distribution behaviors were investigated in rats. Results: N-XY exhibited uniform and stable characteristics as a water-in-oil (O/W) nano-emulsion. Fingerprint analysis identified 25 characteristic peaks and 8 key ingredients in N-XY, with the highest peak areas. In vitro release studies showed a sustained release behavior of N-XY. The pharmacokinetics study showed that the ferulic acid of N-XY had a 1.37-fold higher AUC, 1.44-fold lower Vd/F, 1.39-fold lower CL/F, and a prolonged t1/2 than A-XY, indicating enhanced bioavailability due to reduced elimination. Furthermore, the tissue distribution revealed that the levels of paeoniflorin and ferulic acid from N-XY significantly increased in liver, spleen, lungs, uterus and ovaries, exhibiting targeting characteristics. Conclusion: This study comprehensively explored the formation, characterization, and pharmacokinetics of nano-emulsion in XY pill, introducing novel perspectives and initiating preliminary research on potential SANs in un-decocted traditional Chinese medicine formulations. It also emphasized the importance of enhancing pharmacokinetics of hydrophobic components in Chinese herbal formulations and laid the foundation for future nano-formulation research for XY pill.