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Atherosclerosis is main cause of arteriosclerosis. The pivotal role of low-density lipoprotein (LDL) oxidation in atherogenesis suggests antioxidants may help prevent cardiovascular disease. Fraxinus rhynchophylla DENCE (Oleaceae) is a traditional medicinal plant from East Asia. During the course of characterizing potential drug candidates from natural products, we isolated two major coumarins, esculetin and fraxetin and found that fraxetin has dual-antioxidative functions. Low concentrations (1-5 m mM) of fraxetin potently inhibited LDL oxidation induced by metal and free radicals. Moreover, treatment of vascular smooth muscle cells (VSMCs) with higher concentrations (above 30 m mM) of fraxetin significantly increased the protein level of heme oxygenase-1 (HO-1), a key enzyme that inhibits vascular proliferation and atherosclerosis. Subcellular fractionation and reporter gene analysis using an antioxidant response element (ARE) construct revealed that fraxetin increased the level of nuclear factor (NF)-E2-related factor 2 (Nrf2) and reporter activity, and these were associated with the induction of antioxidant enzymes, such as HO-1 and glutathione S-transferase-a a. In conclusion, fraxetin has direct protective properties against LDL oxidation at lower concentrations, and higher concentrations of fraxetin induce antioxidant enzymes via Nrf2/ARE activation. These effects suggest potential anti-atherosclerosis effects of Fraxinus rhynchophylla D.

Bioassay-guided fractionation of methanol extract of Reynoutria sachalinensis flower using DPPH assay has led to the isolation of three anthraquinones and three flavonoids. Their structures were identified as emodin (1), emodin-8-O-beta-D-glucopyranoside (2), physcion-8-O-beta-D-glucopyranoside (3), quercetin-3-O-alpha-L-arabinofuranoside (4), quercetin-3-O-beta-D-galactopyranoside (5), and quercetin-3-O-beta-D-glucuronopyranoside (6) by comparing their physicochemical and spectral data with those published in literatures. All isolated compounds were evaluated for antioxidant activities with free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging, superoxide radical scavenging and Cu2+-mediated low density lipoprotein (LDL) oxidation assay. The results demonstrated that three flavonoids, 4, 5, and 6 had remarkable antioxidant activities with the IC50 values of 64.3, 54.7, and 46.2 microM (DPPH scavenging), the IC50 values of 6.0, 6.7, and 4.4 microM (superoxide radical scavenging) and the IC50 values of 3.8, 3.2, and 5.4 microM against LDL oxidation, respectively.

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