EPR spectroscopy was applied to investigate the effects of the treatment of Candida albicans cells with fluconazole (FLC) and two newly synthesized azoles (CPA18 and CPA109), in a concentration not altering yeast morphology, on the lipid organization and dynamics of the plasma membrane. Measurements were performed in the temperature range between 0°C and 40°C using 5-doxyl- (5-DSA) and 16-doxyl- (16-DSA) stearic acids as spin probes. 5-DSA spectra were typical of lipids in a highly ordered environment, whereas 16-DSA spectra consisted of two comparable components, one corresponding to a fluid bulk lipid domain in the membrane and the other to highly ordered and motionally restricted lipids interacting with integral membrane proteins. A line shape analysis allowed the relative proportion and the orientational order and dynamic parameters of the spin probes in the different environments to be determined. Smaller order parameters, corresponding to a looser lipid packing, were found for the treated samples with respect to the control one in the region close to the membrane surface probed by 5-DSA. On the other hand, data on 16-DSA indicated that azole treatments hamper the formation of ordered lipid domains hosting integral proteins and/or lead to a decrease in integral protein content in the membrane. The observed effects are mainly ascribable to the inhibition of ergosterol biosynthesis by the antifungal agents, although a direct interaction of the CPA compounds with the membrane bilayer in the region close to the lipid polar head groups cannot be excluded.
Keywords: 1-(1-(biphenyl-4-yl)-3-(4-fluorophenyl)propan-2-yl)-1H-imidazole; 1-(1-(biphenyl-4-yl)-3-(5-chlorothiophen-2-yl)propan-2-yl)-1H-imidazole; 16-DSA; 16-doxylstearic acid; 5-DSA; 5-doxylstearic acid; Antifungal azole; CPA109; CPA18; Candida albicans; Doxyl-stearic acid; EPR; Electron Paramagnetic Resonance; FLC; FS; Fluconazole; MOMD; Membrane fluidity; PA; PE; PG; PI; PL; PS; fluconazole; free sterols; microscopically ordered macroscopically disordered; phosphatidic acid; phosphatidylethanolamine; phosphatidylglycerol; phosphatidylinositol; phosphatidylserine; phospholipid.
© 2013.