Formulation and characterization of boanmycin-loaded liposomes prepared by pH gradient experimental design

This study reports the development of a novel liposomal formulation containing boanmycin (BAM) by the pH-gradient, spherical symmetric experimental design. DSC was used to elucidate the thermotropic transition of the soybean egg phosphatidylcholine (EPCS) bilayers. The DSC analysis showed that the incorporation of cholesterol into the EPCS bilayers caused a reduction in the cooperativity of the bilayer phase transition, leading to a dense and more stable structure. To further explore the possibility of the facilitated molecular interaction between BAM and lipids, the effective chemical shift anisotropy (Δδ) of EPCS was measured by (31)P-NMR spectroscopy in the presence and absence of BAM at 25 °C. The results revealed that the amino group of BAM interacted with the hydrophilic head group of EPCS by electrostatic attraction. Effects of the lipid concentration, pH of the outside buffer and incubation temperature on the encapsulation efficiency of the liposomes were investigated by the spherical symmetric design. Multiple nonlinear regression and second-order polynomial model were fitted to the data, and the resulting equations were used to produce the three dimensional response graphs. The actual response values were in good agreement with the predicted values calculated by the visual FoxPro software. To determine the plasma pharmacokinetics and tissue distribution characteristics of BAM, mice were i.v. injected with BAM-loaded liposomes and the commercial injection solution. The BAM-loaded liposomes exhibited significantly different t(1/2), CL and AUC in plasma and tissues. The MTT assay showed that the BAM-loaded liposomes effectively inhibited the cell proliferation by inducing apoptosis of HepG2 cells in a dose- and time-dependent manner. Compared to the control group, the BAM-loaded liposomes induced marked apoptotic morphologic alterations, including cell shrinkage and granular apoptotic bodies.