Eradication of mucoid Pseudomonas aeruginosa with fluid liposome-encapsulated tobramycin in an animal model of chronic pulmonary infection

Abstract

Despite controversies associated with forms and value of antibiotic therapy for cystic fibrosis patients, antibiotherapy remains a cornerstone in the management of those patients. Locally administered liposome-encapsulated antibiotics may offer advantages over free antibiotics, including sustained concentration of the antibiotic, minimal systemic absorption, reduced toxicity, and increased efficacy. We evaluated the efficacy of free and encapsulated tobramycin in fluid and rigid liposomal formulations administered to rats chronically infected with Pseudomonas aeruginosa. Chronic infection in lungs was established by intratracheal administration of 10(5) CFU of a mucoid variant of P. aeruginosa PA 508 prepared in agar beads. Antibiotic treatments were given intratracheally at time intervals of 16 h. After the last treatment, lung bacterial counts were determined and tobramycin levels in the lungs and kidneys were evaluated by high-performance liquid chromatographic analysis and microbiological assay. Two independent experiments showed that animals treated with encapsulated tobramycin in fluid liposomes had a number of CFU less than the minimal CFU number required to be statistically acceptable compared with > or = 10(6) CFU per pair of lungs for animals treated with encapsulated tobramycin in rigid liposomes, free antibiotic, or liposomes without tobramycin. Tobramycin measured in the lungs at 16 h after the last treatment following the administration of encapsulated antibiotic was still active, and its concentration was > or = 27 micrograms/mg of tissue. Low levels of tobramycin were detected in the kidneys (0.59 to 0.87 micrograms/mg of tissue) after the administration of encapsulated antibiotic, while 5.31 micrograms/mg of tissue was detected in the kidneys following the administration of free antibiotic. These results suggest that the local administration of fluid liposomes with encapsulated tobramycin could greatly improve the management of chronic pulmonary infection in cystic fibrosis patients.

Murine models of acute and chronic lung infection with cystic fibrosis pathogens

“…The mouse model of chronic infection with agar beads responds to several therapeutic interventions (e.g. anti-inflammatory, antibiotics, and vaccines) in a manner similar to that in CF patients (Pier et al, 1990;Konstan et al, 1990;Johansen et al, 1995;Beaulac et al, 1996Beaulac et al, , 1999Hoffmann et al, 2007). Indeed, the use of mouse models has made a major contribution in providing the rationale and the proof-of-concept for the validation of novel therapies before entering in clinical trial.…”

Differential Behaviour of Fluid Liposomes Toward Mammalian Epithelial Cells and Bacteria: Restriction of Fusion to Bacteria

“…The liposomes were negatively charged and had an overall low T C #378C. They were prepared by a hydration -extrusion method as previously described (Beaulac et al, 1996;Sachetelli et al, 2000). Appropriate amounts of lipid mixtures were dissolved with an organic solvent composed of methanol/chloroform (1:2).…”

“…Thus, adverse effects and toxicity associated with potent antibiotics like aminoglycosides can be reduced. Tobramycin encapsulated in the fluid liposomal formulation was used successfully to eradicate mucoid P. aeruginosa in an animal model of chronic pulmonary infection (Beaulac et al, 1996). These liposomes also showed increased bactericidal efficacy, in vitro, against other related and unrelated bacteria (Beaulac et al, 1998).…”

“…Previous spectrophotometric and light-scattering studies (US Pharmacopeia) to evaluate the size distribution of the fluid liposomes showed that 80% of the vesicles had a diameter between 200 and 400 nm as determined by a 90 Plus Particle Size Analyser s/n 11191 (Brookhaven Instruments Corporation, NY) (unpublished data). Fluid liposome-encapsulated antibiotics can be directly administered in the pulmonary tract (Beaulac et al, 1996;1999). The direct in situ administration enables delivery of an elevated dose of the drug to the site of infection while it avoids unwanted systemic exposure.…”

“…To increase the penetration of antibiotics, fluid liposomes were developed to enhance drug delivery through bacterial membranes. These negatively-charged liposomal formulations (which do not contain cholesterol) are made by combining dipalmitoyl phosphatidylcholine (DPPC) and dimiristoyl phosphatidylglycerol (DMPG) phospholipids (at a molar ratio of 5:1 to 18:1) to confer a low gel -liquid crystalline transition temperature (T C ) #378C (Beaulac et al, 1996;1997). Differential scanning calorimetry (DSC) studies performed using a 10:1 molar ratio of the DPPC/DMPG formulation showed the rise of a first peak beginning at 29.58C and a more narrow second peak rising at about 378C (Beaulac, 1995).…”