Effectiveness of nanoparticle-bound ampicillin in the treatment of Listeria monocytogenes infection in athymic nude mice

Abstract

The effectiveness of nanoparticle-bound ampicillin was tested in the treatment of experimental Listeria monocytogenes infection in congenitally athymic nude mice. Nanoparticles of polyisohexylcyanoacrylate (PIHCA) 187 13 nm in diameter were bound to ampicillin at an ampicillin/PIHCA ratio of 0.2:1. The proportion of ampicillin bound was 90% + 3%. After adsorption onto nanoparticles, the therapeutic activity of ampicillin increased dramatically over that in the free state. Thus, 2.4 mg of nanoparticle-bound ampicillin (three doses of 0.8 mg each) had a greater therapeutic effect than 48 mg of free ampicillin (three doses of 16 mg each). These results might provide an incentive for further development of intracellular targeting of antibiotics on biodegradable polymeric carriers.Infections caused by obligate or facultative intracellular microorganisms such as Listeria monocytogenes are difficult to treat, especially in immunocompromised patients (15). The need for intracellular chemotherapy of these infections has been recognized for many years (19). It was recently observed that the use of particulate carriers able to undergo endocytosis increased intracellular delivery of antibiotics (18,20). For instance, when ampicillin was entrapped in liposomes it had an enhanced therapeutic effect on listeriosis in normal mice (1). This was probably because the liposomal encapsulation of ampicillin made it more readily available to intracellular bacteria and allowed lysosomal uptake of the drug (2).Although these results are interesting, large-scale manufacture of liposomes is still difficult. The disruptive effects of human serum on liposomes may lead to some extrusion of trapped drugs (11), and the limited stability of liposomes in circulating blood has been stressed (17). For these reasons, we investigated the possibility of using biodegradable polymeric nanoparticles as an alternative carrier to enhance intracellular drug delivery (4). Owing to their polymeric nature, polyalkylcyanoacrylate nanoparticles may be more stable than liposomes in biological fluids and during storage, and they can generally entrap molecules in a stable and reproducible way (5). This is why we recently described the conditions required for the binding of ampicillin to nanoparticles of polyisohexylcyanoacrylate (PIHCA) and showed that the antimicrobial activity of the drug remained unaltered after linkage to this carrier (8). Desorption of ampicillin from PIHCA nanoparticles is only 10% of the loaded dose after 2 h of incubation in phosphate buffer at 37°C (8).In the present study of experimental murine listeriosis, we found that such nanoparticle-bound ampicillin was significantly more effective than free ampicillin. MATERIALS AND METHODSIsohexylcyanoacrylate monomer (Sopar, Saint-DarmesAvelines, Belgium) (100 ,u) was mechanically stirred at room temperature into 10 ml of an aqueous polymerization medium (1% dextran 70 [Sigma], 5% glucose, 0.001 N HCI) containing 2 mg of ampicillin trihydrate (Negma, Buc, France) per ml. After a 6-h polymerizat...

Liposome-entrapped ampicillin in the treatment of experimental murine listeriosis and salmonellosis

“…At day 19 after challenge, the same differences in the hepatic counts were observed whereas splenic counts were not significantly different between the various groups of mice. This effect was greater than that observed previously in the spleen and liver after the injection of free ampicillin (9) and was more pronounced in the spleen than that observed previously after treatment with ampicillin bound to PIHCA nanoparticles (9). Our liposomal preparation was also more effective than the preparation described by others (2), which, in the same experimental model, had no effect on bacterial counts, presumably, as stated above, because a smaller amount of liposome-entrapped ampicillin was injected into the mice (2 doses of 0.27 mg each versus 3 doses of 0.8 mg each in the present study).…”

“…We also showed with athymic nude mice that this linkage enhanced the effectiveness of ampicillin in treating chronic listeriosis (9), although Bakker-Woudenberg et al, who used liposome-entrapped ampicillin, observed no such enhancement (2). In their study, however, the dose of liposomeentrapped ampicillin injected was only 23% of the one we injected after linkage to nanoparticles (9).…”

“…Chronic listeriosis was established in 91 locally bred C57BL/Ka mice, homozygous for the nude mutation nulnu, by inoculating them with Listeria monocytogenes EGD (NCTC7973) serovar 1/2a, as previously described (9). Two, five, and eight days later, 350 ,ul of the ampicillin-loaded or nonloaded liposomes or of the liposomes that were simply mixed with ampicillin was injected into the tail vein.…”

Drug delivery systems for potential treatment of intracellular bacterial infections

“…Regarding nanoparticles, ampicillin-containing polymeric nanoparticles were also significantly more effective than free ampicillin in a chronic experimental listeriosis in athymic nude mice (114). Seven days after the treatment administration, ampicillin-bound nanoparticles completely eradicated the infection in the liver, while free ampicillin did not ensure liver sterilization during the 19 days that the experiment lasted, even with doses as high as 48 mg (this total dosage was divided into three doses of 16 mg/each).…”

Development of Indinavir Submicron Lipid Emulsions Loaded with Lipoamino Acids—In Vivo Pharmacokinetics and Brain-Specific Delivery

“…This site specific or targeted delivery using specific ligands combined with delivery at an optimal rate would not only improve the efficacy of drug but would also reduce the possible unwanted side effects of drug thus improving the therapeutic index (13).…”