Green Tea and Black Tea Polyphenols Antioxidative Effects and Their Binding to LDL/vLDL

Catechins of green tea and Theaflavins of black tea are believed to be great antioxidants that can help lower the risk of cardiovascular disease. Researches on tea polyphenols have been in a dramatic increase and their antioxidative effects have been attributed to their ability of scavenging reactive oxygen and nitrogen species and chelating redox-active transition metal ions in vitro. In this experiment, it is proposed that tea polyphenols help prevent arthrosclerosis by LDL/vLDL enrichment, in which process tea polyphenols binding to LDL/vLDL thus provide protection to LDL/vLDL, when the latter penetrate the endothelium of the aorta. An ex vivo kinetic study was carried out to compare the effectiveness of tea polyphenols to inhibit Cu 2+ mediated LDL/vLDL oxidation. Green tea polyphenols presented better antioxidizing power than black tea polyphenols, ie. Theaflavins, and all tea polyphenols tested exhibited greater antioxidizing power than Vitamin E, except for methylated Catechins. The antioxidant activity of tea polyphenols in kinetic study was in the order: Epicatechin ＞ EGCG＞ EGC ＞ Catechin＞ Theaflavins ＞ Vitamin E＞4’Methyl-Catechin ＞3’Methyl-Catechin. A binding study comprised of incubation, affinity column separation and HPLC analysis was carried out to prove that tea polyphenols inhibit LDL/vLDL oxidation in exvivo by free radical scavenging mechanism, instead of cupric ion chelation. Epicatechin was found out to have the highest LDL/vLDL bound concentration, followed by EGC, EGCG, Catechin and then ECG, with Theaflavins being the poorest binding compound among the six polyphenols tested. Tea polyphenols are metabolized by human body after consumption, so more attention should be given to their phase II metabolites, which mainly are glucuronides, sulfates, and methylated polyphenols. Glucuronidation with both pig’s microsomal fractions and human supersomal fractions were tried but failed to work. However, two methylated Catechins were synthesized by Patrick Donnelly and studied in this research