Synthesis of oolongtheanins and their inhibitory activity on micellar cholesterol solubility in vitro

Molecular Mechanism by Which Tea Catechins Decrease the Micellar Solubility of Cholesterol

Tea polyphenols lower the levels of cholesterol in the blood by decreasing the cholesterol micellar solubility. To clarify this mechanism, the interactions between taurocholic acid and (-)-epigallocatechin gallate (EGCg) and its derivatives were investigated. ¹³C NMR studies revealed remarkable chemical-shift changes for the carbonyl carbon atom and the 1″- and 4″-positions in the galloyl moiety. Furthermore, ¹H NMR studies using (-)-EGCg derivatives showed that the number of hydroxyl groups on the B ring did not affect these interactions, whereas the carbonyl carbon atom and the aromatic ring of the galloyl moiety had remarkable effects. The configuration at the 2- and 3-positions of the catechin also influenced these interactions, with the trans-configuration resulting in stronger inhibition activity than the cis-configuration. Additionally, a 1:1 component ratio for the catechin-taurocholic acid complex was determined by electrospray ionization-mass spectrometry. These molecular mechanisms contribute to the development of cholesterol-absorption inhibitors.

Interaction between Tea Polyphenols and Bile Acid Inhibits Micellar Cholesterol Solubility

The molecular mechanism by which tea polyphenols decrease the micellar solubility of cholesterol is not completely clear. To clarify this mechanism, this study investigated the interaction between tea polyphenols (catechins and oolongtheanins) and cholesterol micelles. A nuclear magnetic resonance (NMR) study was performed on a micellar solution containing taurocholic acid and epigallocatechin gallate (EGCg), and high-performance liquid chromatography (HPLC) analysis was carried out on the precipitate and the supernatant that formed when EGCg was added to a cholesterol-micelle solution. The data indicated a regiospecific interaction of EGCg with taurocholic acid. Therefore, the ability of EGCg to lower the solubility of phosphatidylcholine (PC) and cholesterol in micellar solutions can be attributed to their elimination from the micelles due to interaction between taurocholic acids and EGCg.

Polyphenols: From Plants to a Variety of Food and Nonfood Uses

Polyphenols are major plant secondary metabolites, structurally extremely diverse, essential for a variety of functions in plants, responsible for major organoleptic and nutritional properties of plant-derived foods, and useful for numerous practical applications. During the 27th International Conference on Polyphenols and 8th Tannin Conference, held jointly in September 2014 in Nagoya, Japan (ICP2014), the latest advances in polyphenol research have been presented. These include advances in polyphenol chemistry, physicochemistry, and materials science; their biosynthesis, genetics, and metabolic engineering; and their role in plant interactions with the environment, in nutrition and health, and in natural medicine. This special issue presents a selection of research papers presented at the meeting, covering these different fields. Major recent progress and perspectives in these areas are also outlined in this introductory paper.