INHIBITION OF ENDOTHELIAL-CELL MEDIATED LOW-DENSITY-LIPOPROTEIN OXIDATION BY GREEN TEA EXTRACTS

Plant phenolics present in fruits and vegetables and that are particul arly rich in tea and wine have received considerable attention because of their potential antioxidant activity. Two types of commercial gree n 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 e ndothelial cells (HAEC). The tea extracts, catechin and epicatechin, w ere incubated with HAEC and LDL for 12 h. After incubation, conjugated dienes were measured by spectrophotometry at 234 nm as an index of hy droperoxide formation, and hexanal was measured by static headspace ga s chromatography as an index of hydroperoxide decomposition. On the ba sis 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 e xtracts. Both catechin and epicatechin inhibited oxidation by 0.5-97% at concentrations ranging from 0.08 to 5.00 mu M. The pure compounds a nd the two tea extracts tested inhibited the formation of early lipid peroxidation products as well as the end stage lipid peroxide decompos ition products. The polyphenolic components of green tea may have nutr itional benefits as inhibitors of LDL oxidation.