FLAVONOID-BIOMEMBRANE INTERACTIONS - A CALORIMETRIC STUDY ON DIPALMITOYLPHOSPHATIDYLCHOLINE VESICLES

Flavonoids, a group of naturally occurring benzo-gamma-derivatives, ha ve been shown to possess several biological properties, many of which may be related, partially at least, to their capacity to penetrate int o the cell membrane and so to affect membrane-dependent processes. In the present paper we report the results of an investigation by differe ntial scanning calorimetry (DSC) on the effects of three flavonoids (q uercetin, hesperetin and naringenin) upon the gel-to-liquid crystallin e phase transition of model membranes constituted by L-alpha-dipalmito ylphosphatidylcholine (DPPC) vesicles. All tested flavonoids interacte d with DPPC liposomes causing different shifts, towards lower values, of the T-m typical for DPPC multilayers; the enthalpy changes (Delta H ), related to the calorimetric peak area, remained nearly constant. Fu rthermore, their effects on DPPC thermotropic behaviour were greater f or high molar concentrations (up to a limit value different for each f lavonoid) and were affected by the time. Several hypotheses (drug mole cule aggregation into the model membrane, changes in the barrier funct ion of the lipid bilayer, different drug structural features and confo rmation, possible formation of flavonoid-phospholipid complexes) are p resented to explain the nature of the interaction between flavonoids a nd phospholipid vesicles.