Azithromycin-liposomes as a novel approach for localized therapy of cervicovaginal bacterial infections

Abstract

Background

Efficient localized cervicovaginal antibacterial therapy, enabling the delivery of antibiotic to the site of action at lower doses while escaping systemic drug effects and reducing the risk of developing microbial resistance, is attracting considerable attention. Liposomes have been shown to allow sustained drug release into vaginal mucosa and improve delivery of antibiotics to bacterial cells and biofilms. Azithromycin (AZI), a potent broad-spectrum macrolide antibiotic, has not yet been investigated for localized therapy of cervicovaginal infections, although it is administered orally for the treatment of sexually transmitted diseases. Encapsulation of AZI in liposomes could improve its solubility, antibacterial activity, and allow the prolonged drug release in the cervicovaginal tissue, while avoiding systemic side effects.

Purpose

The objective of this study was to develop AZI-liposomes and explore their potentials for treating cervicovaginal infections.

Methods

AZI-liposomes that differed in bilayer elasticity/rigidity and surface charge were prepared and evaluated under simulated cervicovaginal conditions to yield optimized liposomes, which were assessed for antibacterial activity against several planktonic and biofilm-forming Escherichia coli strains and intracellular Chlamydia trachomatis, ex vivo AZI vaginal deposition/penetration, and in vitro cytotoxicity toward cervical cells.

Results

Negatively charged liposomes with rigid bilayers (CL-3), propylene glycol liposomes (PGL-2) and deformable propylene glycol liposomes (DPGL-2) were efficient against planktonic E. coli ATCC 700928 and K-12. CL-3 was superior for preventing the formation of E. coli ATCC 700928 and K-12 biofilms, with IC₅₀ values (concentrations that inhibit biofilm viability by 50%) up to 8-fold lower than those of the control (free AZI). DPGL-2 was the most promising for eradication of already formed E. coli biofilms and for treating C. trachomatis infections. All AZI-liposomes were biocompatible with cervical cells and improved localization of the drug inside vaginal tissue compared with the control.

Conclusion

The performed studies confirm the potentials of AZI-liposomes for localized cervicovaginal therapy.

Keywords:

• vaginal drug delivery
• biofilm
• Escherichia coli
• Chlamydia trachomatis
• cervical cells
• biocompatibility

Acknowledgments

This research was financed by the Phospholipid Research Centre (Heidelberg, Germany). The authors are very thankful to Lipoid (Ludwigshafen, Germany) and PLIVA (Zagreb, Croatia) for the donation of phospholipids and AZI, respectively. We would also like to appreciate the contribution of the Jane & Aatos Erkko Foundation to A.F.

Abbreviation list

AZI, azithromycin; CFU, colony forming units; CLs, conventional liposomes; Ct, cycle threshold; DPGLs, deformable propylene glycol liposomes; E, degree of liposome membrane elasticity; EPC, egg phosphatidylcholine, EPG, egg phosphatidylglycerol sodium salt; IC₅₀, half-maximal inhibitory concentration; J, mass of extruded liposomes in elasticity measurements; LB, Luria-Bertani; MIC, minimum inhibitory concentration; MIC₅₀, concentration of the antibiotic that inhibited bacterial growth by 50%; MRSA, methicillin-resistant Staphylococcus aureus; PBS, phosphate-buffered saline; PCS, photon correlation spectroscopy; PDI, polydispersity index; PGLs, propylene glycol liposomes; qPCR, quantitative polymerase chain reaction; r_p, pore size of the membrane in elasticity measurements; r_v, average diameter of the liposomes after passage through a defined membrane in elasticity measurements; SLPC-80, monoacyl phosphatidylcholine from soybean; SPC-3, hydrogenated soybean phosphatidylcholine; VFS, vaginal fluid simulant.

Disclosure

Dr Adyary Fallarero is currently employed by Thermo Fisher Scientific in Vantaa, Finland. The authors report no other conflicts of interest in this work.