Charged phospholipid effects on AAPH oxidation assay as determined using liposomes

•Anionic lipids within liposomes increase oxidation rate of a fluorescent probe.•Cationic lipids can retard oxidation rate of a fluorescent probe in lipid bilayers.•Phase state of saturated lipids has greatest effect on oxidation retardation in liposomes when anionic lipids are present. The capacity of molecules to inhibit oxidation is widely tested using liposomes as host matrices of the antioxidant molecule of interest. Spectroscopic assays are readily used for this purpose, specifically assays using 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AAPH). In this work the effect that charged lipids have on an AAPH antioxidation assay using 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid (C11-BODIPY® 581/591) as the reporter molecule was investigated. We measured the diameter, zeta potential and spectroscopic rate of decay and area-under-the-curve (AUC) associated with liposomes containing C11-BODIPY® 581/591 at varying molar percentages (0–10 mol%) of charged (cationic or anionic) lipids and compared the results. We showed that although increasing amounts of cationic or anionic lipids did change the diameter of the liposomes, size had little to no effect on the area-under-the-curve or decay rate of fluorescence. Increased (more positive) or decreased (more negative) zeta potentials did, on the other hand, affect the spectroscopic decay rates and area-under-the-curve. The results demonstrate the importance of considering the presence of charged lipids in the AAPH antioxidation assay.