Preparation and characterization of tetrandrine-phospholipid complex loaded lipid nanocapsules as potential oral carriers

BACKGROUND Tetrandrine is an active constituent that is extracted from the root tuber of the Chinese herb Stephania tetrandra S. Moore. It has shown various pharmacological effects, such as antitumor activity, multidrug resistance reversal, and hepatic fibrosis resistance. In clinical applications, it has been used to treat hypertension, pneumosilicosis, and lung cancer. However, the poor water solubility of tetrandrine has limited its application. In this study, a newly emerging oral drug carrier of phospholipid complex loaded lipid nanocapsules was developed to improve the oral bioavailability of tetrandrine. METHODS The phospholipid complex was prepared with the solvent-evaporation method to enhance the liposolubility of tetrandrine. The formation of the phospholipid complex was confirmed with a solubility study, infrared spectroscopy, and a differential scanning calorimetry (DSC) analysis. The tetrandrine-phospholipid complex loaded lipid nanocapsules (TPC-LNCs) were prepared using the phase inversion method. Lyophilization was performed with mannitol (10%) as a cryoprotectant. TPC-LNCs were characterized according to their particle size, zeta potential, encapsulation efficiency, morphology by transmission electron microscopy, and crystallinity by DSC. In addition, the in vitro release of tetrandrine from TPC-LNCs was examined to potentially illustrate the in vivo release behavior. The in vivo bioavailability of TPC-LNCs was studied and compared to tetrandrine tablets in rats. RESULTS The liposolubility of tetrandrine in n-octanol improved from 8.34 μg/mL to 35.64 μg/mL in the tetrandrine-phospholipid complex. The prepared TPC-LNCs were spherical-shaped particles with a small size of 40 nm and a high encapsulation efficiency of 93.9%. DSC measurements revealed that the crystalline state was less ordered in lipid nanocapsules. The in vitro release study demonstrated a fast release of approximately 25% in the first 1 hour, which was followed by a sustained release of 70% over 12 hours. The relative bioavailability of TPC-LNCs compared to that of tablets was 208%, indicating a significant improvement in the oral absorption of tetrandrine. CONCLUSION The TPC-LNCs system developed in this study is a promising carrier that improves the oral bioavailability of tetrandrine in rats. The phospholipid complex loaded lipid nanocapsules have great potential for use as an oral drug delivery system for moderately lipophilic drugs that are encapsulated in the lipid nanocapsules.