Liposomes in the Treatment of Parasitic, Viral, Fungal and Bacterial Infections

Long-Circulating Sterically Stabilized Liposomes in the Treatment of Infections

The administration of antimicrobial agents encapsulated in long-circulating sterically stabilized liposomes results in a considerable enhancement of therapeutic efficacy compared with the agents in the free form. After liposomal encapsulation, the pharmacokinetics of the antimicrobial agents is significantly changed. An increase in circulation time and reduction in toxic side effects of the agents are observed. In contrast to other types of long-circulating liposomes, an important characteristic of these sterically stabilized liposomes is that their prolonged blood circulation time is, to a high degree, independent of liposome characteristics such as liposome particle size, charge and lipid composition (rigidity) of the bilayer, and lipid dose. This provides the opportunity to manipulate antibiotic release from these liposomes at the site of infection, which is important in view of the differences in pharmacodynamics of different antibiotics and can be done without compromising blood circulation time and degree of target localization of these liposomes. Depending on the liposome characteristics and the agent encapsulated, antibiotic delivery to the infected site is achieved, or the liposomes act as a micro-reservoir function for the antibiotic. In experimental models of localized or disseminated bacterial and fungal infections, the sterically stabilized liposomes have successfully been used to improve antibiotic treatment using representative agents of various classes of antibacterial agents such as the beta-lactams, the aminoglycosides, and the quinolones or the antifungal agent amphotericin B. Extensive biodistribution studies have been performed. Critical factors that contribute to liposome target localization in infected tissue have been elucidated. Liposome-related factors that were investigated were poly(ethylene glycol) density, particle size, bilayer fluidity, negative surface charge, and circulation kinetics. Host-related factors focused on the components of the inflammatory response.

Long-circulating sterically stabilized liposomes as carriers of agents for treatment of infection or for imaging infectious foci

Liposomes are considered as potential carriers for biologically active compounds. One evident drawback of 'classical' liposomes is their fast elimination by cells of the mononuclear phagocyte system (MPS), primarily by liver and spleen. An important breakthrough in this respect is the development of long-circulating liposomes among which liposomes coated with polyethyleneglycol (PEG), the so-called 'sterically stabilized' liposomes (SSL). An important characteristic of SSL is that their prolonged blood residence time and infectious target localization is relatively independent of the lipid dose, particle size or lipid composition of the bilayer. SSL are applied as carriers of antimicrobial agents to achieve infectious target localization, to reduce side effects, or to serve as a micro-reservoir in the circulation. In addition, radiolabelled SSL are used to image infectious and inflammatory foci.

Treatment of visceral leishmaniasis with sterically stabilized liposomes containing camptothecin

The efficacy of 20(S)-camptothecin (CPT), free and incorporated into sterically stabilized liposomes, has been investigated in vitro against Leishmania donovani promastigotes and in vivo in a murine model of visceral leishmaniasis. Incubation of L. donovani promastigotes with free or liposomal CPT inhibited the growth of parasites in a dose-dependent manner. Tissue distribution studies revealed that the intraperitoneal administration of liposomal CPT was efficient for the delivery of high drug levels to the liver and spleen. Treatment of infected mice with intraperitoneal injections of free and liposomal CPT significantly reduced the parasite loads in the livers by 43 and 55%, respectively, compared with the loads for untreated controls. However, both treatments caused normochromic anemia and neutropenia.

Targeted delivery of antibiotics using liposomes and nanoparticles: research and applications

This review examines current technologies for increasing the bioavailability of antibiotics by means of liposomes or nanoparticles. The main focus is on liposomes. These carriers were preferentially developed because their composition is compatible with biological constituents. Biodegradable polymers in the form of colloidal particles have also been used and show promise for future applications in antimicrobial chemotherapy. The in vivo behaviour of both types of carriers and consequently their therapeutic potential, are determined by their route of administration. Conventional carrier strategies permit the mononuclear phagocyte system to be targeted by intravenous injection of antibiotics. Stealthy strategies avoid major uptake by these cells and extend the systemic presence of these carriers. The purpose of this review is to provide background information in antibiotic targeting gathered from papers published over the last twenty years. It seems clear that such drug carriers (liposomes, nanoparticles) allow increased drug concentration at infected sites but reduce drug toxicity.

Liposomes as drug delivery system: a strategic approach for the treatment of HIV infection

As the number of individuals infected with human immunodeficiency virus (HIV) is growing dramatically throughout the world, it is important to develop strategies to improve the treatment of this deadly disease. It is now well established that macrophages play a central role in HIV pathogenesis, acting as reservoirs for dissemination of virus throughout the immune system. As liposomes are naturally taken up by cells of the mononuclear phagocytic system, liposome-based therapy represents a convenient approach to improve the delivery of anti-HIV agents into infected cells improving thereby the efficacy of drugs and reducing their adverse side-effects. A more specific targeting of HIV-infected cells could also be obtained by using liposomes bearing surface attached-antibodies. This review details the applications of liposomes as drug carriers for the treatment of AIDS. It also gives an overlook of the different strategies that could be explored to control the progression of the disease in infected individuals.