The interaction of cortisone esters with liposomes as studied by differential scanning calorimetry

The interaction of a series of cortisone esters with dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles (MLV) has been investigated using differential scanning calorimetry (DSC). The extent of the interaction is dependent on the ester chain-length with increased interaction observed as the chain lengthens. For cortisone hexadecanoate the maximum incorporation is 11.25 mole· %. The presence of cholesterol excludes cortisone hexadecanoate from DPPC liposomes. This effect increases with increasing cholesterol concentrations.Cortisone hexadecanoate is incorporated into DPPC liposomes in such a manner that it is probable that the steroid moiety interacts strongly with the bilayer.A correlation exists between the in vitro cortisone ester release rate at 37°C from DPPC liposomes and broadening of DPPC MLV thermograms only over the range of 6–14 carbon chain-length. This indicates that the interaction of the ester chain of the steroid with the acyl chain of the lecithin are not necessarily the sole factors controlling efflux rate.