Effects of Progesterone on Neutral Model Membranes

Interactions of progesterone with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes (MLVs) were investigated as a function of temperature and progesterone concentration by using three non‐invasive techniques namely Fourier transform infrared (FTIR) spectroscopy, turbidity at 440 nm and differential scanning calorimetry (DSC). The results reveal that progesterone changes the physical properties of DPPC bilayers by decreasing the main phase transition temperature, abolishing the pretransition, broadening the phase transition profile, disordering the system both in gel and liquid crystal 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 C=O groups, whilst it strengthens the hydrogen bonding between the PO 2 − groups of lipids and the water molecules around [1]. Our results also clearly show that the effect of progesterone on membrane dynamics is dependent on progesterone concentration. Progesterone behaves differently at 1 mol% which is close to physiological level. The decrease in dynamics is more profound for 1 mol% progesterone for which a dramatic decrease in the strength of hydrogen bonding in the interfacial region of the bilayer is also observed. For higher progesterone concentrations till 12 mol%, an opposite behavior is observed in the interactions including membrane fluidity. Above 12 mol%, progesterone behaves as it almost causes no effect on DPPC membranes. (Supported by METU research fund)