Bacteria-targeting liposomes for enhanced delivery of cinnamaldehyde and infection management

Drug-resistant gram-negative bacteria have emerged as a global crisis. Therefore, novel antibiotics and novel anti-infection strategies are urgently needed. Current antibiotics remain unsatisfactory due to poor targeting efficiency and poor drug penetration through the bacterial cell wall. Thus, targeted delivery of antibiotics into gram-negative bacteria should be a promising approach. Moreover, gram-negative bacteria can release lipopolysaccharide (LPS) to induce inflammatory response and septic shock, further increasing the disease burden. Hence, it is also promising to neutralize LPS while delivering antibiotics. This study aims to develop a multifunctional bacteria-targeting liposome that could enhance the delivery of antibiotics and adsorb LPS.

A polymyxin B (PMB)-modified liposomal system (P-Lipo) was developed as novel carrier of cinnamaldehyde (CA) by using a thin-film evaporation method. Liposome morphology, size, zeta potential, stability, entrapment efficiency, and in vitro release were systematically evaluated. The bacteria-targeting effect and LPS-neutralizing capacity of P-Lipo were evaluated both in vitro and in vivo. The antibacterial effect of CA-loaded P-Lipo was assessed in Escherichia coli (E. coli) O157:H7 and Pseudomonas aeruginosa (P. aeruginosa). Ultimately, the therapeutic effect of P-CA-Lipo was investigated in E. coli O157:H7-infected mice.

P-Lipo was successfully synthesized and encapsulated with CA, which was well characterized. Both in vivo and in vitro experiments demonstrated that P-Lipo could efficiently target the E. coli after modification with PMB. Compared with free CA, CA-Lipo, and P-Lipo, P-CA-Lipo exhibited a significantly enhanced inhibitory effect on E. coli and P. aeruginosa. Further analysis demonstrated that P-CA-Lipo improved the bacterial uptake of CA and enhanced its antibacterial effect. It was also confirmed that P-Lipo could neutralize the LPS to avoid the inflammatory responses and inhibit the release of proinflammatory cytokines in both macrophages and mice. Finally, P-CA-Lipo inhibited E. coli-induced skin damage and death in mice and showed good biocompatibility.

The P-Lipo could target E. coli by binding with LPS and enhancing the delivery and internalization of CA. In addition, P-Lipo could adsorb free LPS synergistically, thus promoting the infection management. We believe that this strategy can provide innovative insights into antibacterial agent delivery for the treatment of persistent and severe bacterial infections.