Interaction of Na2B12H11SH with dimyristoyl phosphatidylcholine liposomes.

Previous investigations have revealed that the boron cluster compound Na2B12H11SH (BSH) is very potent in causing major structural rearrangements of and leakage from phosphatidylcholine liposomes. This somewhat unexpected finding is interesting from a fundamental point of view and may also constitute the basis of future important pharmaceutical/medical applications of BSH. In order to further explore the BSH-lipid interaction, we have studied the effects caused by BSH on dimyristoyl phosphatidylcholine (DMPC) liposomes. Cryo-transmission electron microscopy showed that BSH induces aggregation, membrane rupture and increasing wall thickness of the liposomes. Differential scanning calorimetry revealed a BSH dependent shift of the gel to liquid crystalline phase transition temperature of DMPC. The zeta potential of the liposomes decreases with increasing BSH concentrations, and an apparent dissociation constant of 0.23 mM was found. BSH caused leakage of liposome-encapsulated carboxyfluorescein; leakage was higher at 23 degrees C (near the phase transition temperature) than at 15 degrees C and 37 degrees C. It induced lipid mixing only at very high concentrations.