Nanoemulsões carregadas com anfotericina B para o tratamento das leishmanioses: uma nova abordagem

Abstract

The treatment of leishmaniasis includes topical and systemic approach.The conventional parenteral therapy is based on the use of pentavalent antimonials. Amphotericin B (AmB), the second drug of choice, can be used when treatment with antimonials is not indicated or in the case of therapeutic failure. The particular chemical structure of AmB makes it practically insoluble in water and in most organic solvents. The conventional formulation of AmB is a colloidal dispersion in which the drug is associated with sodium deoxycholate (AmB-D). Although effective, treatment with this formulation is often accompanied by toxicity. The commercially available lipid formulations appear as a way to overcome this drawback. It is known that such systems reduce AmB-related toxicity, but its high cost and difficulty of manufacturing impede its widespread use. Nanoemulsions (NE) are attractive carriers of AmB, since they are lipid systems, which are able to reduce the drug-related toxicity, in addition to being inexpensive and easy to manufacture. The strategy of incorporation of AmB in the NE droplets, without organic solvents, makes use of the pH-solubility profile of the drug. This work aims to develop AmB-loaded NE with and without the cationic lipid stearylamine (STE). The influence of STE on the physico-chemical and biological properties of NE was investigated. The NE were prepared by hot homogenization method using ultrasound probe. The average diameter of the droplets was lower in the presence of STE than in its absence. The zeta potential was positive and increased as a function of STE content, in contrast to the formulations without this lipid, which showed negative zeta potential. The encapsulation efficiency (EE) of AmB was high despite the presence of STE. Stability studies of AmB-loaded NE, with and without STE, indicated that both formulations are stable. Analysis of circular dichroism showed that AmB present in NE is predominantly in monomeric form, which is the least toxic to the host cells and more active against the parasite, in contrast with commercial AmB-D, in which there is a large proportion of free drug in oligomeric form. The results of in vitro cytotoxicity studies, by MTT assay in J774 macrophage lineage, indicated that the NE loaded with AmB, without STE and 0.1 % w/v STE, are less cytotoxic than the commercial formulation AmB- D. In addition, increasing concentration of cationic lipid leads to an increase in cytotoxicity. In vitro efficacy studies in J774 macrophages infected with Leishmania (Leishmania) amazonensis showed that AmB loaded-NE with 0.1% w/v STE shows efficacy comparable to AmB-D. Although AmB loaded-NE without STE had shown statistically lower efficacy than the conventional formulation, this reduction is not significant in view of the gain that such a formulation brings in terms of selectivity between cells of the host and parasite, therefore, an attractive option for the treatment of leishmaniasis.