The effect of a single oral administration of proanthocyanidins, oligomeric and polymeric polyhydroxyflavan-3-ol units, on the antioxidative potential of blood plasma was studied in rats. Proanthocyanidin-rich extract from grape seeds was administered by intragastric intubation to fasted rats at 250 mg/kg of body weight. The plasma obtained from water- or proanthocyanidin-administered rats was oxidized by incubation with copper sulfate or 2, 2'-azobis(2-amidinopropane) dihydrochloride (AAPH) at 37 degrees C, and the formation of cholesteryl ester hydroperoxides (CE-OOH) was followed. The plasma obtained from proanthocyanidin-administered rats was significantly more resistant against both copper ion-induced and AAPH-induced formation of CE-OOH than that from control rats. The lag phase in the copper ion-induced oxidation of rat plasma was remarkably increased at 15 min after administration of proanthocyanidins and reached a maximum level at 30 min. When the plasma from proanthocyanidin-administered rat was hydrolyzed by sulfatase and beta-glucuronidase following analysis by high-performance liquid chromatography with electrochemical detection, metabolites of proanthocyanidins occurred in rat plasma at 15 min after administration, three peaks of which were identified as gallic acid, (+)-catechin, and (-)-epicatechin. These results suggest that the intake of proanthocyanidins, the major polyphenols in red wine, increases the resistance of blood plasma against oxidative stress and may contribute to physiological functions of plant food including wine through their in vivo antioxidative ability.
The protective effect of a vitamin E analog, phosphatidylchromanol [1,2-diacyl-sn-glycero-3-phospho-2'-(hydroxyethyl)-2',5',7',8'-tetrameth yl-6'-hydroxychroman; PCh], against oxidative hemolysis of human erythrocytes was examined and was compared with those of vitamin E (alpha-tocopherol) and 2,2,5,7,8-pentamethyl-6-chromanol (PMC). These three compounds at 50 microM protected the erythrocytes from hemolysis, when erythrocyte suspension (10%, vol/vol) was incubated with a water-soluble radical generator, 2,2'-azobis(2-amidinopropane)-dihydrochloride (75 mM). When erythrocyte suspension was oxidized after pretreatment with these compounds (50 microM) for 30 min followed by washing, PCh protected about 54% of erythrocytes from the hemolysis, while alpha-tocopherol protected only about 16% of the cells and PMC did not show any protective effect. During preincubation, alpha-tocopherol, PMC, and PCh were incorporated into the cells at the concentration of 12.6, 3.7, and 16.3 nmol/mg protein, respectively. Moreover, PCh was found in the ghost membrane fraction at a 20% higher level than alpha-tocopherol, and no PMC was detected in this fraction. These results indicate that phosphatidyl group in PCh acts as an excellent carrier of chromanol moiety into cells as well as an anchor within membranes more efficiently than phytyl group in alpha-tocopherol. PMC seems to be slightly anchored within membranes because of the lack of hydrophobic side chain. The excellent antihemolytic activity of PCh is likely to be caused by its accumulation within erythrocyte membranes.
Natural flavor compounds, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) and 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF), were evaluated for antioxidative behaviors against lipid peroxidations. They inhibited hydroperoxidation of methyl linoleate initiated by a lipid-soluble azo compound, 2,2‘-azobis(2,4-dimethylvaleronitrile) (AMVN), in solution. The antioxidative activities of HDMF and HEMF were less than that of ascorbic acid when the emulsified methyl linoleate oxidized by a water-soluble azo compound, 2,2‘-azobis(2-amidinopropane) dihydrochloride, while they were more effective than ascorbic acid when lipid peroxidation was initiated by a lipid-soluble AMVN. These furanones were also more effective than ascorbic acid in the inhibition of the formation of cholesteryl ester hydroperoxides in plasma. HEMF suppressed the oxidation of low-density lipoprotein without any synergistic effect with α-tocopherol. In the autoxidation of rat brain homogenate, HDMF and HEMF acted as inhibitors, while ascorbic acid acted as a prooxidant. These results indicate that HDMF and HEMF are potent antioxidants so that they would be important components not only in exhibiting desirable flavor but also in inhibiting oxidative deterioration in foods. Keywords: 4-Hydroxy-2,5-dimethyl-3(2H)-furanone; 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone; antioxidant; lipid peroxidation; flavor
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