Effect of tea catechins on the structure of lipid membrane and beta-ray induced lipid peroxidation

Green tea extract-biomembrane interaction study: The role of its two major components, (-)-epigallocatechin gallate and (-)-epigallocatechin

The interaction of antioxidants with biological membranes is closely related with their efficacy to inhibit the lipid peroxidation, the cause of several pathologies including cancer, neurodegenerative and cardiovascular disorders. Despite being pointed as a promising antioxidant agent by some authors, the anti-lipid peroxidation of green tea extract (GTE) has not aroused consensus among the scientific community. Since the interaction of drugs with biological membranes plays a key role on their therapeutic activity, this study aims to evaluate the interaction of GTE with liposomes as in vitro biomembrane models composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine phospholipids in the absence and presence of cholesterol (CHOL) (15 mol%). The affinity of GTE and its main components (-)-epigallocatechin gallate (EGCG) and (-)-epigallocatechin (EGC) to the lipid bilayer, their membrane location as well as their effect on the membrane fluidity was investigated by diverse biophysical techniques. Derivative spectrophotometry results proved that GTE has high affinity to the membrane by establishing hydrophobic interactions with the non-polar region of phospholipids and electrostatic interactions with the polar phospholipid heads. Fluorescence and dynamic light scattering data confirm that GTE is located in both hydrophobic and hydrophilic regions of the lipid membrane, therefore affecting the structure of the biomembrane by increasing its fluidity. However, the increased stiffness and organization of the lipid bilayer caused by CHOL significantly affected the interaction of GTE with the membrane. Moreover, the obtained findings suggest a direct contribution of EGCG and EGC on the GTE-membrane interaction.

Revisiting the polar paradox theory: a critical overview

The polar paradox is a theory that illustrates the paradoxical behavior of antioxidants in different media and rationalizes the fact that polar antioxidants are more effective in less polar media, such as bulk oils, while nonpolar antioxidants are more effective in relatively more polar media, such as oil-in-water emulsions or liposomes. For 2 decades since it was proposed, the theory has been used to interpret results in antioxidant efficiency studies. However, more recently, new evidence from more comprehensive assessments has emerged that contradicts the polar paradox theory, hence necessitating its re-evaluation. More complex factors in addition to polarity must be taken into account to explain antioxidant efficacy.

Molecular binding of catechins to biomembranes: relationship to biological activity

Molecular dynamics simulations were used to study the interactions of four green tea catechin compounds with lipid bilayers. Reported studies have shown that catechins are linked to beneficial health effects, specifically those related to interactions with the cell membrane. To better understand the molecular interaction of catechins with membranes, simulations were carried out of interactions of four catechin molecules [epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG)] with a 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) lipid bilayer. The simulations show that catechins possess a strong affinity for the lipid bilayer. Some are absorbed into the bilayer. The molecular structure and aggregated condition of the catechins significantly influences their absorption, as well as their ability to form hydrogen bonds with the lipid headgroups. Insight into these molecular interactions helps to distinguish the structure-function relationship of the catechins with lipid bilayers and provides a foundation for a better understanding of the role of catechins in biological processes.