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Antimicrobial Agents and Chemotherapy, July 2005, p. 3028-3030, Vol. 49, No. 7
0066-4804/05/$08.00+0 doi:10.1128/AAC.49.7.3028-3030.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Infectious Diseases Research Laboratory, Infectious Diseases Division, Hospital Universitari Vall d'Hebron, Universitat Autònoma de Barcelona, Barcelona, Spain
Received 21 December 2004/ Returned for modification 21 January 2005/ Accepted 30 March 2005
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The efficacy of nebulized deoxycholate AMB or liposomal AMB was compared to that of conventional intravenous (i.v.) dosages of both formulations, using a murine model of invasive pulmonary aspergillosis (IPA). The potential benefits of inhalation plus i.v. administration were also explored. This experimental protocol was approved by the Ethics Committee of Vall d'Hebron Hospitals.
Female Wistar rats (180 to 200 g; Harland Iberica, Spain), fed with a low-protein diet, were immunosuppressed with 125 mg of subcutaneous cortisone acetate (Sigma Chemical Co., St. Louis, MO) per kg of body weight three times per week, from 14 days before infection to the end of the experiment (11).
On day 0, animals were intratracheally challenged with 0.3 ml of a conidial suspension prepared from a 1-week-old subculture on Sabouraud dextrose agar of a clinical isolate of A. fumigatus (AF19/68). Conidia were counted in a hemocytometer and adjusted to 8 x 106 cells/ml in sterile saline.
Intravenous treatments were administered through a central venous catheter (11). Aerosols were generated by a CR60 compressor (Medic-Aid Ltd., West Sussex, United Kingdom; flow rate, 10 liter/min) attached to a Nebulizer II Oxinova (Carburos Metálicos, Barcelona, Spain) and were led through a nose-only exposure inhalation chamber (Panlab, Spain) over a 60-min period. The total dosage of AMB administered to each animal was calculated with the following formula: the total dosage = the chamber concentration of AMB (mg/liter) x the minute volume (liter/min) x the duration of exposition (min) x the animal's weight (kg–1) (1). The minute volume is equal to the body weight0.75 (grams) x 0.00254 (6).
Animals were randomized to receive 5% dextrose i.v. (control) (n = 23), deoxycholate AMB (d-AMB) at 1 mg/kg i.v. (Fungizone; Bristol-Myers Squibb Group, Spain) (n = 25), liposomal AMB (L-AMB) at 5 mg/kg i.v. (AmBisome; Gilead Sciences, Spain) (n = 27), nebulized d-AMB (nd-AMB) at 1.13 mg/kg (n = 18), nebulized L-AMB (nL-AMB) at 2.3 mg/kg (n = 16), or nL-AMB at 2.3 mg/kg plus L-AMB at 5 mg/kg i.v. (n = 16). Treatment was administered daily, starting 24 h after infection, for a total of 10 days.
Surviving rats were sacrificed 24 h after the last dose of treatment. All animals were aseptically dissected. Lungs were weighed and homogenized in sterile distilled water, and aliquots were serially diluted and plated onto Sabouraud dextrose agar for colony counts. Lung homogenates were processed for chitin assay, as described elsewhere (9), to quantify fungal burden. In brief, homogenates were suspended in 21.4 M KOH after being washed with 0.10 M sodium dodecyl sulfate (Sigma Chemical Co., St. Louis, MO) and heated at 130°C for 1 h. After cooling, 8 ml of 75% ethanol and 0.3 ml of a Celite 545 suspension (Sigma) were added. Pellets were washed with 40% ethanol and distilled water and suspended in 0.5 ml of 0.7 M NaNO2 and 0.5 ml of 0.4 M KHSO4. Volumes of the supernatants were mixed with 1.10 M ammonium sulfamate, followed by 3-methyl-2-benzothiazolinone hydrazone hydrochloride hydrate monohydrate (Sigma) and 0.03 M FeCl3 · 6H2O. The optical density was spectrophotometrically read (UV-160A; Shimadzu Corp., Japan) at 650 nm.
Survival was analyzed using Kaplan-Meier analysis and the log rank test. Lung weight (grams), chitin content (micrograms of glucosamine/paired lungs), and numbers of CFU/gram of lung (log10 numbers of CFU/gram) were expressed as means and 95% confidence intervals of the means and compared using one-way analysis of variance and Bonferroni's test. P values of 
0.01 were considered significant.
Results obtained from animals surviving 5 days or longer with the treatment are shown in Table 1 and Fig. 1 and 2. Results were pooled, since preliminary studies revealed that pulmonary glucosamine reaches a plateau by this time in animals left untreated (J. Gavaldà, P. López, T. Martín, X. Gomis, M. Rosal, B. Almirante, C. Pigrau, and A. Pahissa, Abstr. 40th Intersci. Conf. Antimicrob. Agents Chemother., abstr. 1682, 2000).
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0.003); compared to the i.v. L-AMB group, the survival of animals receiving nL-AMB was prolonged, reaching levels close to significance (P = 0.066). Aerosolization plus i.v. administration of L-AMB produced results similar to those with nL-AMB alone compared with the control. Compared to results with i.v. d-AMB, an important reduction of glucosamine was noted (P = 0.016), although the combined administration achieved the most remarkable diminution of log10 numbers of CFU (P = 0.071, versus i.v. d-AMB results). Discrepancies between CFU counts and chitin measurements have been previously reported, due to the peculiar structure of molds (2).
Pulmonary concentrations achieved with recommended doses (up to 5 mg/kg/day) of L-AMB can be considered suprainhibitory according to in vitro data, but in vivo, they might be insufficient to eradicate the fungus. Therefore, pulmonary AMB concentrations could be increased by nebulization. Experimental animal studies have shown that aerosolization leads to measurable concentrations of AMB in lungs (1, 14, 16), and levels have been reported to be higher with lipid formulations (1, 3). Nebulization minimizes the risk of adverse events by avoiding systemic exposure to the drug (16, 18), focusing the drug activity at the site of infection.
The efficacy of aerosol AMB prophylaxis against Aspergillus infection has been extensively studied. Experimental models of IPA have shown that nebulized AMB increases survival with respect to that of controls (1, 3, 18), and it has also been described as a protective factor against Aspergillus species infection in lung transplant recipients (12, 13). In contrast, few studies have investigated the efficacy of nebulized AMB for the treatment of IPA (17, 18). Nebulized L-AMB has proved to be useful for the treatment of experimental invasive aspergillosis of neutropenic rats (17). In humans, Ruffini and coworkers (E. Ruffini, S. Baldi, D. Libertucci, P. Solidoro, P. di Marzio, A. Cavallo, and M. Mancuso, Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-1237, 2002) have reported that nL-AMB alone resolved nine episodes of colonization, and in association with L-AMB i.v., it resolved all four cases of invasive aspergillosis.
Our work shows that aerosolization of AMB is a useful approach to the treatment of experimental IPA, with a more favorable outcome achieved with nL-AMB than with nd-AMB. This may suggest that both nd-AMB and nL-AMB reached satisfactory concentrations in the lungs, although concentrations were probably slightly higher with the liposomal formulation.
Combined administration of nebulized plus i.v. L-AMB produced results similar to those with nL-AMB alone, probably because the two methods rendered little difference in pulmonary concentrations of AMB. Being outside the scope of the study, we did not investigate whether the combination prevented the risk of extrapulmonary dissemination. Since in humans dissemination is difficult to discard, administering aerosolized plus i.v. L-AMB seems prudent.
We conclude that the use of nebulized AMB, in particular L-AMB, may be a useful approach to the treatment of experimental IPA. Further studies might be warranted.
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ACKNOWLEDGMENTS |
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This work has been supported by the Spanish Fondo de Investigaciones Sanitarias (grants FIS 01/1412 and FIS G03/075 RESITRA).
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FOOTNOTES |
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, significant relative to value for i.v. d-AMB; 
, significant relative to value for nd-AMB.