Biomimetic transport of simple olive biophenol and analogues through modelbiological membranes by differential scanning calorimetry

The different interactions of p-hydroxybenzoic acid (1), a simple biophenol (BP) found in olives and their food products, and its substitute analogues , benzoic (2), anisic (3), and toluic (4) acids, with a model membrane repr esented by dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles (ML V) was studied by differential scanning calorimetry (DSC). The influence of their different lipophilic character on transfer and absorption processes through an aqueous medium into a lipid bilayer was also investigated. DSC e xperiments allowed monitoring of the interaction of BP with biomembranes by considering the effects exerted on the thermotropic behavior of DMPC multi lamellar and unilamellar vesicles at different pHs (4 and 7.4). The examine d compounds affect the transition temperature (T-m) of phospholipid vesicle s, causing a shift toward lower values, which is modulated by the molecular fraction entering into the lipid bilayer, as well as by their molecular in teraction with the lipids. Kinetic calorimetric measurements were performed on suspensions of blank liposomes immediately after being added to fixed w eighed amounts of powdered compounds and after increasing incubation period s at 37 degreesC. T-m shifts, due to molecular dissolution and transfer of the compounds into the membrane surface occurring during the incubation tim e, were compared with those determined by a fixed molar fraction of free co mpounds directly dispersed in the membrane. The results show that the kinet ic process, involved in molecular release, transfer through aqueous medium, and uptake by the model membrane surface, is influenced by lipophilicity a s well as by pH, acting on the acid solubility and membrane disorder, allow ing us to gather useful information on the BP intake process of olive deriv ed foodstuffs.