Rigidez de membrana em leishmania amazonensis causada por lipossomas contendo miltefosina e/ou anfotericina B

Abstract

Leishmaniasis is a tropical disease, still neglected, caused by protozoa of the genus Leishmania, representing a serious public health problem in many regions of the world. In this study, liposome formulations containing the leishmanicidal drugs miltefosine (MTF) and amphotericin B (AmB) were prepared. The liposomes are intended to function as carriers for the drugs, eliminating the need for potentially toxic organic solvents and aiding in their delivery to target cells. To characterize the liposomes, Dynamic Light Scattering (DLS) analysis was performed to assess vesicle size, and Zeta potential was measured to evaluate liposome stability. Drug quantification was carried out to estimate losses during the preparation process, using HPLC for MTF-containing liposomes and absorbance for AmB-containing liposomes. Electron Paramagnetic Resonance (EPR) was employed to uncover the crucial interactions of the drugs with the liposome membrane, the stratum corneum (SC), parasites, and macrophages, paving the way for significant advancements in the understanding of their mechanism of action. The formulations were applied to the SC to evaluate the outcome of their interaction with the liposomes. EPR data revealed that formulations containing soybean phosphatidylcholine (PC) caused an increase in stratum corneum fluidity, while those containing distearoylphosphatidylglycerol (a lipid found in commercial liposomal AmB) did not cause significant changes. The increase in fluidity provided by PC is expected to facilitate the targeted delivery of the compounds to the parasites, thereby enhancing therapeutic efficacy in the topical treatment of cutaneous leishmaniasis. The drugs, when encapsulated in liposomes, also caused increased rigidity in Leishmania membranes after 24 hours of exposure, suggesting that both drugs generate oxidative stress in the parasite. However, the formulations did not cause changes in the membrane of the uninfected macrophage. On the other hand, they caused membrane rigidity in the system of Leishmania-infected macrophages at concentrations in the range of their IC50 values in promastigotes. The EPR data also indicated that the membranes of the macrophageamastigote system can also undergo oxidative processes even without treatment. This work further showed that both MTF and AmB are active drugs at the plasma membrane of the Leishmania parasite and suggest that their antileishmanial mechanisms of activity are associated with their primary effects on the cell membrane. The increase in fluidity caused by MTF or the pore formation produced by AmB are membrane alterations that can likely result in ionic leakage, leading to plasma membrane depolarization, which in turn should hyperpolarize the mitochondrial membrane and thus increase the formation of reactive oxygen species (ROS), triggering other events such as membrane rigidity, which result in the death of the parasite. These findings have the potential to significantly contribute to the development of more effective and safer therapies for the treatment of leishmaniasis. However, additional studies are needed to validate these results in clinical trials and to further improve the liposomal formulations.