Many of the benefits from drinking tea are related to catechins, chemicals present in almost all teas. Numerous research groups have linked catechins with anti-carcinogenic, anti-cholesterol, anti-inflammatory, and antimicrobial activity, and they have a wealth of other properties. But why arecatechins such good bioactive agents?
Figure 1: Seven common catechins found in tea.
Previous work has shown that catechins operate at the cellular-molecular level by interacting with components of cell membranes. Catechins can prevent binding of enzymes, cause a change in the membrane potential, or increase the membrane's permeability to certain ions. Exactly how the various chemical structures of catechins interact with the cell membranes was unknown. To gain further insight, researchers examined the dynamics and binding of catechins through computer simulations and presented their work in an advanced article from the Journal of Agricultural and Food Chemistry.
The researchersperformed molecular dynamic simulations for seven popular catechins (Figure 1) and focused on molecular parameters like hydrogen bonding, adsorption, absorption, molecular orientation, and presence of functional groups. They used an all-atom molecular representation for the catechins,a phospholipid membrane, and water to calculate the atomic forces on each atom as they interact with one another.
Out of the seven catechins, three absorbed (C, EC, and EGCG) into the cell membrane, while the other four adsorbed onto its surface. The membrane surface catechins remained flexible and could diffuse across the surface by forming and breaking hydrogen bonds. However, the absorbed catechins had extremely limited mobility because they were trapped within the bilayer.
Figure 2: A phospholipid.
The difference between adsorption and absorption is due to the number and types of hydrogen bonds. Catechins that formed more hydrogen bonds with oxygens that are deeper in the lipid bilayer surface were able to incorporate into the membrane. The surface adsorbing catechins formed hydrogen bonds with phosphate oxygens (Figure 2). Catechins mostly preferred to be hydrogen bond donors rather than acceptors; in particular, EGCG formed the most number of hydrogen bonds with the lipid bilayer.
The results from the molecular simulations could help explain differences in catechin bioactivity. For example, two of the catechins (EGCG and ECG) that can penetrate the cell membrane showed the most promise at inhibiting carcinogenesis, while the catechin with the greatest number of hydrogen bonds, EGCG, was the most effective at disturbing bacterial membranes. Further simulations may provide a more complete picture by exploring catechin interactions with other types ofphospholipids.
Journal of Agricultural and Food Chemistry, 2008. DOI: 10.1021/jf8013298