Miltefosine and amphoterin B induce membrane rigidity in Leishmania amazonensis and Leishmania-infected macrophages

Miltefosine (MTF) and amphotericin B (AmB), drugs approved for leishmaniasis treatment, induce membrane rigidity in Leishmania amazonensis at concentrations that inhibit parasite growth, as demonstrated through spin-probe electron paramagnetic resonance (EPR) spectroscopy. Notably, the rigidity induced by MTF is not due to its direct interaction with the membrane, as shorter incubation periods instead increase fluidity. However, measurements taken following short-term drug exposure reflect conditions before possible oxidative stress has fully developed. AmB causes membrane rigidity, but only at concentration 100 times higher than those causing rigidity after 24 h of exposure. In contrast, oxidative stress-induced membrane rigidity was not observed in macrophages, suggesting that nitric oxide production by these cells may mitigate oxidative damage. Both drugs, however, induced significant membrane rigidity in Leishmania-infected macrophages at concentrations slightly above the IC₅₀ for amastigotes. EPR data further suggest that oxidative processes can occur within the membranes of the macrophage-amastigote system even without drug exposure. This study also suggests that the primary mechanisms underlying the antileishmanial activity of these two membrane-active drugs are associated with their effects on the cell membrane. Membrane alterations likely lead to ionic imbalances, which may, in turn, disrupt mitochondrial membrane potential and thereby enhance reactive oxygen species (ROS) formation.