Differential interaction of Sophora isoflavonoids with lipid bilayers

The mechanisms of some biological effects exerted by flavonoids (e.g. activity against lipid oxidation, multidrug resistance modulation) may involve their interactions with lipid bilayers. Due to variety of substituents attached to the flavonoid nucleus individual isoflavones significantly differ in their properties; in particular they may differently interact with membranes. For this reason we have investigated the interactions of different isoflavones with lipid bilayers. The influence of four plant isoflavones on the phase transitions of dipalmitoylphosphatidylcholine (DPPC) and on liposome aggregation was studied, using microcalorimetry and absorption measurements, respectively. We found that isoflavones substituted with one or two prenyl groups less effectively induce liposome aggregation than more polar ones, possessing no prenyl groups. For aggregation-promoting compounds, rather small differences in the influence on phosphatidylcholine, phosphatidylserine and phosphatidylinositol liposomes were recorded. On the other hand, the alteration of DPPC phase transitions by prenyl-substituted isoflavones was more pronounced than changes induced by non-prenyl ones. On the basis of observed effects we conclude that prenyl-substituted isoflavones penetrate deeper into the lipid bilayer while more polar ones act closer to the membrane surface. Comparing our results with biological tests it seems that interactions with the hydrophobic core of membranes are responsible for the activity of the studied isoflavones.