Interaction between flavonoids and alpha-tocopherol in human low density lipoprotein

Oxidative modification of low density lipoprotein (LDL) may play an importa nt role in the development of atherosclerosis. alpha-Tocopherol functions a s a major antioxidant in human LDL. The present study was to test whether f our natural flavonoids (kempferol, morin, myricetin, and quercetin) would p rotect or regenerate alpha-tocopherol in human LDL. The oxidation of LDL in cubated in sodium phosphate buffer (pH 7.4, 10 mM) was initiated by additio n of either 5.0 mM CuSO4 at 37 degrees C or 1.0 mM of 2,2'-azo-bis (2-amidi nopropane) dihydrochloride (AAPH) at 40 degrees C. It was found that alpha- tocopherol was completely depleted within 1 hour. Under the same experiment al conditions, all four flavonoids demonstrated a dose-dependent protecting activity to alpha-tocopherol in LDL at the concentration ranging from 1 to 20 mu M. All flavonoids showed a varying protective activity against deple tion of alpha-tocopherol in LDL, with kempherol and morin being less effect ive than myricetin and quercetin. The addition of flavonoids to the incubat ion mixture after 5 minutes demonstrated a significant regeneration of alph a-tocopherol in human LDL. The protective activity of four flavonoids to LD L is related to the number and location of hydroxyl groups in the B ring as well as the stability in sodium phosphate buffer. (J. Nutr. Biochem, 11:14 -21, 2000) (C) Elsevier Science Inc. 2000. All rights reserved.