Liposomal formulations for membrane active antimicrobials – Assuring safety through an optimised drug delivery system

Abstract

Skin and soft tissue infections (SSTIs) and chronic wounds are major challenges for the healthcare system worldwide. The additional rapid development of antibacterial resistance and lack of successful treatment strategies increase the chance for infected chronic wounds to be fatal for the patient. Therefore, there is a need for more efficient dermal antimicrobial therapies. A class of promising antimicrobial drug candidates that have captured attention in respect to treating resistant bacterial infections, including skin infections, is membrane active antimicrobial peptides (AMPs). Our particular interest was to develop a novel formulation that is able to deliver membrane active antimicrobials to chronic wounds, and promote wound healing. We developed a liposomes-in-hydrogel formulation and used chlorhexidine (CHX) as our model antimicrobial in this work. CHX was entrapped in liposomes with entrapment efficiency of 96 % and the size analysis indicated a mean vesicle size of 318 ± 8.6 nm. The zeta potential of CHX liposomes was measured to be 45.53 ± 1.33 mV. The vesicle formation of CHX liposomes was confirmed with transmission electron microscopy (TEM). CHX liposomes were incorporated into a 5.0 % (w/w) chitosan hydrogel comprising 10 % (w/w) glycerol and the hydrogel was characterised by a texture analyser (T.A). A novel T.A. method was developed and validated and later applied to characterise our hydrogels. The texture properties to CHX liposomes-in-hydrogels exhibited the cohesiveness of 291.3 ± 9.9 g/sec, hardness of 149.3 ± 4.5 g and adhesiveness of -327.5 ± 3.1 g/sec. The pH of the hydrogels was just below 5 and showed no significant changes upon storage for 4 weeks. In vitro evaluation of CHX release from the liposomes-in-hydrogel formulations indicated a sustained release. The investigation of the anti-inflammatory activities of empty liposomes, CHX liposomes, plain hydrogel and CHX liposomes-in-hydrogel, measured as nitric oxide production in murine macrophages, indicated that the novel drug delivery system was safe and exhibited an anti-inflammatory effect.

The results confirmed that the liposomes-in-hydrogel formulation of membrane active antimicrobials has a potential as novel antimicrobial formulation.