【Background】 Most of therapeutic peptide and protein drugs are administered via injection route, because they are poorly absorbed. Previously, we have investigated the role of different mucoadhesive polymers as coating materials of liposomes for enhancing oral peptide delivery. Trimethyl chitosan (TMC) is a chitosan (CS) derivative with improved permeation enhancing properties as a result of retaining its positive charge over a broad range of physiological pH values.
【Methods and results】 TMC was synthesized by reductive methylation of CS and was used for coating anionic liposomes. The efficiency of surface coating was confirmed by the inversion of surface potential and by increase in particle size. The mucoadhesive properties of TMC-coated liposomes were studied in vivo after oral administration to rats by confocal laser scanning microscopy (CLSM). The results showed comparable mucoadhesive properties of TMC-coated liposomes and CS coated liposomes. In addition, the pharmacological efficacy of calcitonin loaded liposomes was evaluated by determination of blood calcium level after oral administration. The area above blood calcium concentration-time curve (AAC) was significantly higher after oral administration of TMC-liposomes, as compared to non-coated liposomes and calcitonin solution. The obtained results showed that TMC-liposomes can contribute to the development of mucoadhesion based systems for oral peptide and protein delivery.