Liposomes in Antibacterial Drug Carriers

Introduction

Liposomes as carriers of antibacterial drugs can significantly improve the distribution of antibacterial drugs in tissues and enhance the release of drugs at the target site, thus enhancing the antibacterial effect and reducing adverse reactions. And it can also overcome the drug resistance of some bacteria. In addition, liposomes are biodegradable in vivo without the risk of residues, making them excellent carriers of antibacterial drugs.

Application

Amphotericin is the most effective polyene antibiotic for the treatment of systemic fungal diseases. However, its use is limited due to its high nephrotoxicity. Taking advantage of the high affinity of liposomes to biological cell membranes, making amphotericin into liposomes reduces drug resistance and cardiotoxicity and can significantly improve the antibacterial effect of the drug.

Gregoriadis first reported on the potential value of liposomes as carriers for antimicrobial drug delivery. He used egg lecithin, cholesterol, phosphatidic acid, dipalmitoyl lecithin, stearylamine and other components to encapsulate benzylated liposomes. The delivery system, based on potassium penicillin, successfully penetrated RES cell membranes and achieved liver and spleen targeting in an in vivo experiment in mice. Subsequently, some researchers reported that liposomes could deliver antibacterial drugs such as dihydrostreptomycin, cefotaxime, penicillin G, vancomycin and teicoplanin to achieve intracellular inhibition of a wide range of sensitive or recalcitrant bacteria. However, early researchers focused on the potential of liposomal delivery systems to release drugs at the target site and did not specifically investigate ways to improve the bacterial inhibition capacity of the delivery systems.

Subsequent studies have found that surface modification of liposome carriers can improve the therapeutic index of antibacterial drugs, including increasing the antibacterial effect of the drug, improving the stability of the liposome in circulation in vivo and reducing the toxic side effects of the drug. Conventional liposomes are readily phagocytosed by RES in vivo. Although they can exert short-term antibacterial effects in cells, their residence time in circulation is short and the sustained release of antibacterial drugs is not ideal. Modification of polyethylene glycols results in longer circulation times and increased half-lives for liposomal drugs in vivo. For example, conventional vancomycin formulations have very low concentrations in lung tissue, making it difficult to cure pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA) infection. a delivery system was prepared by Mupidi et al. using PEGylated liposomes to encapsulate vancomycin. As PEGylation greatly increased the circulation time of the delivery system in vivo, it further increased the concentration of vancomycin in organs such as the lung, liver and spleen. The concentrations in the organs and the deposition of the drug in the kidneys are reduced so that MRSA-infected pneumonia can be treated effectively and the risk of nephrotoxicity of the drug is reduced.

Liposomes can also inhibit resistance to some bacteria. Upon contact with bacteria, liposomes can fuse with the lipoproteins and lipopolysaccharides of the bacterial outer membrane through the interaction of the bilayer phospholipid membrane on the surface, and then enter the bacterial cell to release antibacterial drugs and inhibit bacterial proliferation. Thus, bacterial resistance mechanisms due to altered membrane permeability and the production of hydrolases are avoided. Rukholm et al. used liposomes formulated with dipalmitoyl phosphatidylcholine and cholesterol to deliver gentamicin and tobramycin to the site of bacterial infection. The results showed that the liposomes could fuse with the bacterial outer membrane within approximately 6 hours. The drugs were delivered to the cells of the drug-resistant bacteria and exerted their inhibitory effect.

References

1. Wang B; et al. Nanoparticle-induced surface reconstruction of phospholipid membranes. Proceedings of the National Academy of Sciences of the United States. 2008, 105(47): 18171-18175.
2. Muppidi K; et al. PEGylated liposome encapsulation increases the lung tissue concentration of vancomycin. Antimicrobial Agents and Chemotherapy. 2011, 55(10): 4537-4542.