Nerolidol and a zwitterionic surfactant induce membrane rigidity inLeishmania amazonensisand infected macrophages

Spin-label electron paramagnetic resonance (EPR) spectroscopy revealed that the sesquiterpene nerolidol and the ionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) induce membrane rigidity in Leishmania amazonensis after 24 h of exposure. These compounds exhibit antileishmanial activity with IC₅₀ values of ∼74 µmol L^-1 (nerolidol) and ∼10 µmol L^-1 (HPS). At concentrations near 1-3 × their IC₅₀ values, both agents caused pronounced membrane rigidity, attributed to lipid peroxidation and/or oxidation of membrane proteins driven by elevated ROS levels promoted by the compounds. Both compounds are active in the parasite's plasma membrane, causing a remarkable increase in fluidity immediately after treatment and throughout the 24h-incubation period of the antiproliferative activity assay, the effect reverts to rigidity. Notably, membrane stiffening was absent in uninfected J774A.1 macrophages, suggesting that nitric oxide production may mitigate oxidative damage. In contrast, rigidity was observed in membranes of Leishmania-infected macrophages, indicating compound-induced oxidative stress in infected host cells. These findings support a membrane-centered mechanism of action for both compounds. The early increase in membrane fluidity may promote ion leakage and depolarization of the parasite plasma membrane, leading to mitochondrial hyperpolarization and enhanced ROS generation, which triggers downstream events, including membrane oxidation and stiffening, which ultimately result in parasite death.