Treatment of experimental salmonellosis in mice with streptomycin entrapped in liposomes

Abstract

Liposome-entrapped streptomycin (SM) was compared with free SM for therapeutic efficacy against experimental salmonellosis in mice. All of the mice infected with the virulent strain of Salmonella enteritidis 116-54 died between days 5 and 7, and a dose of 20 mg of free SM per kg administered 24 h after the bacterial inoculation did not prolong the survival. In contrast, the same dose of SM entrapped in liposomes prolonged the survival for all mice to more than 15 days. The therapeutic activity paralleled the dose in the liposomes, and a dose as low as 1. Synthetic phospholipid bilayer vesicles, called liposomes, have attracted considerable interest as potent drug carriers (6). They are nontoxic and biodegradable and can protect the entrapped drugs from enzymatic attack or immune recognition until they reach the target cells. The toxicity of a drug itself can be reduced by this shielding in the liposomes. Upon intravenous injection, liposomes, especially multiplelayer vesicles, are removed rapidly by reticuloendothelial (RE) cells and at least partly localized in lysosomes, where they are slowly degraded (7,13,15). This behavior of liposomes has some advantages for the treatment of diseases caused by intracellular parasites (5).In this study, experimental salmonellosis in mice was adopted as a model system of bacterial infection by intracellular parasites, and the therapeutic effect of streptomycin (SM) entrapped in liposomes was investigated. The results clearly indicated that the administration of liposomeentrapped SM could prolong the survival far more than the injection of free SM. Various applications of this method of selective drug delivery to RE cells were discussed. MATERIALS AND METHODSMice. Male C57BL/6 mice were obtained from the Laboratory of Experimental Animals (Institute of Medical Science, University of Tokyo, Japan). The animals were maintained on laboratory chow and acidified chlorinated water and used when 2 to 4 months old.Lipids. Egg yolk phosphatidylcholine was prepared by chromatography on alumina and silicic acid. Dipalmitoylphosphatidic acid and cholesterol were purchased from Sigma Chemical Co., St. Louis, Mo. Preparation of liposomes containing SM. Liposomes were * Corresponding author. prepared from a lipid mixture of egg yolk phosphatidylcholine (5 p.mol), cholesterol (5 ,umol), and dipalmitoylphosphatidic acid (0.5 ,umol) (negatively charged). The dried lipid film, obtained on rotary evaporation and subsequent vacuum desiccation, was dispersed in 0.5 ml of an SM solution (streptomycin sulfate, Meiji Seika Co. Ltd., Tokyo, Japan) in saline at the following concentrations: 250 mg/ml for an injection of 20 mg/kg, 125 mg/ml for 10 mg/kg, 62.5 mg/ml for 5 mg/kg, 31.2 mg/ml for 2.5 mg/kg, and 15.6 mg/ml for 1.2 mg/kg. Unencapsulated SM was removed by centrifugation at 20,000 x g for 20 min at 4°C, and the final pellet was resuspended in 5 ml of saline. Under these experimental conditions the entrapment of SM in the liposomes was equivalent to about 2 to 4% of the original solution.Measu...

Versatility of Aminoglycosides and Prospects for Their Future

“…One example is the use of aerosolized tobramycin or gentamicin solutions for inhalation as a promising addition to the traditional therapy and prophylaxis of respiratory tract infections, including those occurring in cystic fibrosis patients (59,122,201,202,238,243). Another interesting approach is the development and use of liposome-encapsulated aminoglycosides (256), used for both local applications (14,227,234,235,325) and intravenous administration (283,285). The activity of liposome-encapsulated aminoglycosides against intracellular microorganisms is of special interest (8,88,97,174,176).…”

Pharmacokinetics and in vivo activity of liposome-encapsulated gentamicin

“…Most studies of antibacterial agents have focused on the efficacy of these preparations in the treatment of facultative, intracellular bacterial infections of the reticuloendothelial system such as salmonellosis (5,19), brucellosis (6), listeriosis (1), and mycobacterial infections (4,12,21).…”

Drug delivery systems for potential treatment of intracellular bacterial infections

“…A 20 mg dose of liposome-entrapped streptomycin was shown to prolong survival of mice to at least one month. When 2 doses of 20 mg or a single dose of 80 mg were administered, the mice survived for more than 55 days (109). Moreover, the liposome entrapment of streptomycin markedly decreases its toxicity.…”