Inhibition of Endothelial Cell Mediated Low-Density Lipoprotein Oxidation by Green Tea Extracts

Plant phenolics present in fruits and vegetables and that are particularly rich in tea and wine have received considerable attention because of their potential antioxidant activity. Two types of commercial green tea from Japan and two active components of green tea, catechin and epicatechin, were assessed for their relative abilities to inhibit the oxidation of low-density lipoprotein (LDL) mediated by human aortic endothelial cells (HAEC). The tea extracts, catechin and epicatechin, were incubated with HAEC and LDL for 12 h. After incubation, conjugated dienes were measured by spectrophotometry at 234 nm as an index of hydroperoxide formation, and hexanal was measured by static headspace gas chromatography as an index of hydroperoxide decomposition. On the basis of conjugated dienes and hexanal, inhibition of LDL oxidation was dose dependent for all compounds tested. LDL oxidation was inhibited 3.9−98% at concentrations ranging from 0.08 to 5 ppm of the green tea extracts. Both catechin and epicatechin inhibited oxidation by 0.5−97% at concentrations ranging from 0.08 to 5.00 μM. The pure compounds and the two tea extracts tested inhibited the formation of early lipid peroxidation products as well as the end stage lipid peroxide decomposition products. The polyphenolic components of green tea may have nutritional benefits as inhibitors of LDL oxidation. Keywords: Antioxidants; green tea; catechin; epicatechin; plant phenolics; human aortic endothelial cells; low-density lipoprotein (LDL) oxidation