The high physiology and low toxicity of therapeutic peptides and proteins have made them a hot spot for drug development in recent years. However, their poor oral bioavailability and unstable metabolism make their clinical application difficult. The bilayer membrane of liposomes provides protection for the drug within the compartment, and their high biocompatibility makes the drug more easily absorbed by the body. However, phospholipids—which form the membranes—are subjected to various digestive enzymes and mucosal adhesion in the digestive tract and disintegrate before absorption. Improvements in the composition of liposomes or modifying their surface can enhance the stability of the liposomes in the gastrointestinal tract. This article reviews the basic strategies for liposome preparation and surface modification that promote the oral administration of therapeutic polypeptides.

10-Hydroxycamptothecin (HCPT) liposomes surface modified with stearyl glycyrrhetinate (SG) were prepared by the film dispersion method. Characterization of the liposomes, including drug release in vitro, pharmacokinetics and tissue distribution, was done. HCPT in plasma and tissues was determined by high-performance liquid chromatography (HPLC). Compared with the conventional HCPT-liposomes and commercially available hydroxycamptothecin injection (HCPT Inject), pharmacokinetic parameters indicated that SG-HCPT-liposomes had better bioavailability. Regarding tissue distribution, the concentration of HCPT loaded by SG modified liposomes in the liver was higher than other tissues and the risk to the kidney was lower than HCPT-liposomes and HCPT Inject. These results support the hypothesis that the HCPT-liposomes modified with SG show enhanced liver-targeting through the glycyrrhetinic acid (GA) receptor to be an efficient drug carrier, which may help to improve therapeutic methods for hepatic diseases in the future.