Antioxidant Properties of Flavone C ‐Glycosides from Atractylodes japonica Leaves in Human Low‐density Lipoprotein Oxidation

Three antioxidant flavone C ‐glucosides, isoorientin, vitexin, and isovitexin, were identified for the 1st time from Atractylodes japonica leaves by an activity‐guided fractionation with various analytical techniques including column chromatography, high‐performance liquid chromatography (HPLC), fast atom bombardment mass spectrometry (FAB‐MS), and nuclear magnetic resonance (NMR). Hydroxyl and superoxide anion radicals scavenging activities of these compounds were examined using electron spin resonance (ESR). Inhibitory activities of these compounds on human low‐density lipoprotein (LDL) oxidation were evaluated by malondialdehyde (MDA) and thiobarbituric acid‐reactive substances (TBARS), both representing intermediates of lipid peroxidation. These flavone C ‐glucosides displayed about 50% of scavenging activity against hydroxyl radicals at the concentrations below 10 μ M . The superoxide dismutase (SOD)‐equivalent activities of isoorientin, vitexin, and isovitexin at 1 m M were 31.37, 2.71, and 2.63 unit/mL, respectively. Isoorientin at 1 μ M exhibited over 60% inhibition of MDA formed during copper‐mediated human LDL oxidation. Amounts of free MDA in LDL treated with isoorientin, vitexin, isovitexin, and control were 20.06, 40.73, 34.08, and 48.03 n M /mg protein, respectively. These compounds also prolonged the lag phase time of the conjugated diene formation. There was a positive correlation between the free radical scavenging activities and the inhibitory effects on the LDL oxidation of these compounds. These results suggest that the flavone C ‐glucosides isolated from the leaves of A japonica possess beneficial antioxidant properties against free radicals as well as LDL oxidation.