Influence of salicylic acid on the biophysical properties of dipalmitoyl phosphatidylcholine vesicles

The effect of the keratolytic drug salicylic acid (SA) on the thermotropic behaviour, and dynamics of dipalmitoyl phosphatidyl choline (DPPC)–water/buffer pH?7.4 vesicles was studied using DSC and ¹H NMR. In both systems, incorporation of SA in DPPC bilayer causes a significant depression in the transition temperature of both the pre-transition (PT) and the gel-to-liquid crystalline (CM) transition. The presence of the drug reduces the cooperativity of both the PT and CM transitions. These findings indicate that SA is bound strongly to the lipid bilayer leading to increased membrane fluidity. The DPPC vesicles incorporated with high drug concentration show phase segregation. One of the interesting findings in this study is the formation of a more ordered high temperature gel (L_β2) phase when the SA-doped DPPC dispersion is prepared at physiological pH. The effect of inclusion of cholesterol in the SA-free and SA-doped DPPC dispersion was also studied.