Chitosan-based delivery system enhances antimicrobial activity of chlorhexidine

Infected chronic skin wounds and other skin infections are increasingly putting pressure on the health care providers and patients. The pressure is especially concerning due to the rise of antimicrobial resistance and biofilm-producing bacteria that further impair treatment success. Therefore, innovative strategies for wound healing and bacterial eradication are urgently needed; utilization of materials with inherent biological properties could offer a potential solution. Chitosan is one of the most frequently used polymers in delivery systems. This bioactive polymer is often regarded as an attractive constituent in delivery systems due to its inherent antimicrobial, anti-inflammatory, anti-oxidative, and wound healing properties. However, lipid-based vesicles and liposomes are generally considered more suitable as delivery systems for skin due to their ability to interact with the skin structure and provide prolonged release, protect the antimicrobial compound, and allow high local concentrations at the infected site. To take advantage of the beneficial attributes of the lipid-based vesicles and chitosan, these components can be combined into chitosan-containing liposomes or chitosomes and chitosan-coated liposomes. These systems have previously been investigated for use in wound therapy; however, their potential in infected wounds is not fully investigated. In this study, we aimed to investigate whether both the chitosan-containing and chitosan-coated liposomes tailored for infected wounds could improve the antimicrobial activity of the membrane-active antimicrobial chlorhexidine, while assuring both the anti-inflammatory activity and cell compatibility. Chlorhexidine was incorporated into three different vesicles, namely plain (chitosan-free), chitosan-containing and chitosan-coated liposomes that were optimized for skin wounds. Their release profile, antimicrobial activities, anti-inflammatory properties, and cell compatibility were assessed in vitro. The vesicles comprising chitosan demonstrated slower release rate of chlorhexidine and high cell compatibility. Additionally, the inflammatory responses in murine macrophages treated with these vesicles were reduced by about 60% compared to non-treated cells. Finally, liposomes containing both chitosan and chlorhexidine demonstrated the strongest antibacterial effect against Staphylococcus aureus. Both chitosan-containing and chitosan-coated liposomes comprising chlorhexidine could serve as excellent platforms for the delivery of membrane-active antimicrobials to infected wounds as confirmed by improved antimicrobial performance of chlorhexidine

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

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