Electron paramagnetic resonance (EPR) spectroscopy of spin labels was used to characterize the interactions of amphotericin B (AmB), miltefosine (MIL) and nerolidol (NER) with the plasma membrane of Paracoccidioides brasiliensis. Spin-labeled analogs of stearic acid and steroid androstane distributed into the plasma membrane of the fungus treated with AmB, showed strong interactions with putative AmB/sterol complexes. The observed increase in the EPR parameter 2A// caused by AmB can be interpreted as a remarkable reduction in the spin label mobility and/or an increase in the local polarity. The 2A// parameter reduced gradually as the concentration of MIL and NER increased. The membrane-water partition coefficient (KM/W) of the three compounds under study was estimated based on the minimum concentration of the compounds that causes a change in EPR spectrum. The KM/W values indicated that the affinity of the compounds for the P. brasiliensis membrane follows the order: AmB > MIL > NER. The minimum inhibitory concentration (MIC) values were lower than the respective minimum concentrations of the compounds to cause a change in the EPR spectrum, being ∼3.5-fold lower for AmB, 3.9-fold for MIL and ∼1.4-fold for NER. Taken together, the EPR spectroscopy results suggest that the anti-proliferative effects of the three compounds studied are associated with alterations in cell membranes. One of the most likely consequences of these changes would be electrolyte leakage.Communicated by Ramaswamy H. Sarma.
Keywords: Amphotericin B; Paracoccidioides brasiliensis; electron paramagnetic resonance; miltefosine; nerolidol.