Effect of progesterone on DPPC membrane: Evidence for lateral phase separation and inverse action in lipid dynamics

Interactions of progesterone with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes were investigated as a function of temperature and progesterone concentration by using three non-invasive techniques namely Fourier transform infrared spectroscopy, turbidity at 440 nm, and differential scanning calorimetry. The results reveal that progesterone changes the physical properties of DPPC bilayers by decreasing the main phase-transition temperature, abolishing the pre-transition, broadening the phase-transition profile, disordering the system both in gel and liquid crystalline phase, increasing the dynamics at low concentrations whereas stabilizing the membrane at high concentrations, and inducing phase separation. Progesterone does not change the hydration of the CO groups, while it strengthens the hydrogen bonding between the PO 2 - groups of lipids and the water molecules around.