Abstract
This review is a presentation of data gathered on the interactions of several polyphenolics (i.e., phenolic acids, stilbenes, flavonoids) with lipid bilayers of different lipid compositions. These polyphenolics have been investigated through a combination of fluorescence spectroscopy, electron paramagnetic resonance spectroscopy, and differential scanning calorimetry, to detect changes in membrane fluidity. Among the investigated phenolic acids, the least polar phenolic acid, p -coumaric acid, has the greatest effect on lipid membrane structure. It appears to have a greater ability to cross membranes by passive transport than more polar phenolic acids. On the other hand, among the flavonoids that have been studied, the anthocyanins cyanidin 3-glucoside and its aglycone are inactive. All of the flavonols tested, except for epigallocatechin-3-gallate, promote small decreases in membrane fluidity. Computer simulation of electron paramagnetic resonance spectra for flavonoids indicated two or three regions in the phosphatidylcholine/ phosphatidylserine (2.4:1) membrane with different fluidity characteristics. The effects of the different flavonoids are correlated to their structural characteristics, whereby even the difference in one -OH group can be important, as can the number of H-bonds they form. The role of membrane composition and flavonoid structure in these interactions with lipid membranes are of great importance for bioavailability of these compounds and for their biological effects in an organism
Highlights
Phenolic compounds or phenolics in herbs and spices have been thoroughly studied for several years to characterize, mainly in-vitro, their diverse biological effects
We propose that the structure of a compound determines its behaviour in terms of its membrane transport, and that the polarity, number of H-bonds, and topological polar surface area (TPSA) can be used to predict how a phenolic acid or flavonoid will penetrate cell membranes
Effects of hydroxycinnamic acids on model lipid membranes in the liquid state The polarisation values of multilamellar vesicles (MLVs) and unilamellar vesicles (ULVs) composed of POPC/POPE/POPS/cholesterol (4:2:1:3.6) before addition of the phenolic acids and their styrenes were 0.2410±0.0006 and 0.3200±0.0005, respectively
Summary
Phenolic compounds or phenolics in herbs and spices have been thoroughly studied for several years to characterize, mainly in-vitro, their diverse biological effects Among these are the phenolic acids, a diverse group of aromatic secondary plant metabolites that are widely distributed throughout the plant kingdom. The hydroxycinnamic acids (C6-C3) include p-coumaric, caffeic and ferulic acids, and occur most frequently as simple esters These have various biological and pharmacological activities, including antioxidative activities, which follow the sequence: caf-. Flavonoids can interfere with the growth of microorganisms and they can act as synergists to increase the effects of preservatives They can modify the permeability of bacterial cell membranes, change the fatty-acid composition and phospholipid content of membranes, and interact with membrane proteins (Burt, 2004). The model membranes were set up as liposomes with one or more lipid bilayers and their interactions have been characterized using fluorescence spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and differential scanning calorimetry (DSC); of interest were encapsulated epigallocatechin-3-gallate (EGCG) and resveratrol
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