Micromolar concentrations of Al 3+ induce phase separation, aggregation and dye release in phosphatidylserine-containing lipid vesicles

Abstract

The interaction of Al 3+, Cd 2+ and Mn 2+ with phosphatidylserine-containing lipid vesicles was studied. Phase separation of vesicles was investigated by monitoring fluorescence quenching of the phospholipid analogue 1-palmitoyl-2-(6-[ N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)]aminocaproyl)phosphatidylcholine (C 6-NBD-PC). Aggregation was determined by turbidimetry and leakage of vesicles content during fusion was monitored by the fluorescence of released 6-carboxyfluorescein. Al 3+ demonstrated quenching at less than 30 μmol/1 with a maximum effect at 100 μmol/1. Al 3+-induced aggregation and dye release from the lipid vesicles were observed in the same concentration range. The effect of Cd 2+ and Mn 2+ on quenching was much less pronounced and could only be demonstrated in the 0.1–1 mmol/1 range. Increasing amounts of phosphatidylcholine or phosphatidylethanolamine in the vesicles decreased both Al 3+-induced quenching and aggregation, wheras cholesterol only slightly increased aggregation without affecting quenching.