Chitosan-modified liposomes for delivery of membrane-active antimicrobials – exploring the role of the polymer

Abstract

Antimicrobial resistance in skin injury infections is becoming a rising problem as more conventional antimicrobials become ineffective in resistant infections. Therefore, developing novel effective antimicrobials while promoting wound healing is urgently needed. Membrane-active antimicrobials, such as antimicrobial peptides (AMPs), display promising antimicrobial activity, and could potentially solve parts of the antimicrobial resistance problems. Furthermore, the use of drug delivery systems, such as liposomes, could help overcome the challenges of AMP or other membrane-active antimicrobials, such as low stability, cytotoxicity and improve their activity. In addition, modification of liposomes with chitosan could provide appealing properties to the system, such as stability, anti-inflammatory activity, and antimicrobial activity. In this study, chlorhexidine (CHX) was used as a model compound for AMPs and incorporated in plain liposomes, chitosomes and chitosan-coated liposomes. Liposomal formulations were characterised for their size, zeta potential, entrapment efficiency and in vitro drug release. Furthermore, chitosan and CHX were assessed for their antimicrobial and anti-inflammatory activity. The majority of chitosomes and chitosan-coated liposomes with CHX had a size of 167 +/- 43 nm and 398 +/- 39 nm, respectively. The average zeta potential of the formulations was 94.4 +/- 2.2 mV for chitosomes with CHX and 83.3 +/- 3.1 mV for chitosan-coated liposomes with CHX. The percentage of entrapment efficiency of chitosomes was superior to the liposomes without chitosan. Moreover, both chitosan formulations displayed a prolonged release of CHX. The antimicrobial activities of different formulations were evaluated on S. aureus. The results demonstrated a trend of higher antimicrobial activities from vesicles with CHX compared to the other formulations. The reduction of NO-production in LPS-induced murine macrophages was used to indicate the anti-inflammatory activity of formulations. The chitosan-coated liposomes displayed an inhibitory effect on NO production independent of CHX, which confirmed the anti-inflammatory activity of chitosan. The findings suggested chitosan formulations as a potential drug delivery system for membrane-active antimicrobials in wound therapy.