PHENOLIC CONTENT OF VARIOUS BEVERAGES DETERMINES THE EXTENT OF INHIBITION OF HUMAN SERUM AND LOW-DENSITY-LIPOPROTEIN OXIDATION IN-VITRO - IDENTIFICATION AND MECHANISM OF ACTION OF SOME CINNAMIC ACID-DERIVATIVES FROM RED WINE

1. An antioxidant effect of phenolic substances in red wine to reduce oxidizability of low-density lipoprotein has been proposed as the basi s for a relatively lower incidence of coronary disease in populations with high red wine intake. We have now investigated the possible antio xidant effects of various beverages, including red wines, white wines, beers and red grape juices (diluted 1:500), on metal ion-dependent (c opper) and -independent (aqueous peroxyl radicals) oxidation of isolat ed human low-density lipoprotein. We also tested the effects of these beverages on copper-initiated oxidation of lipoproteins in serum. 2. T he higher the polyphenolic content of a beverage, the greater was its antioxidative effect measured as change in lag time in the different o xidation systems. Upon stripping the polyphenolics from the drinks, th e lag times returned to control levels in isolated low-density lipopro tein; however, the low concentrations of phenolics remaining after str ipping had a lesser but still significant effect on oxidation of lipop roteins in serum. The inhibitory effect of these phenolics appeared to be more pronounced for metal ion (copper)-induced oxidation than for those induced by aqueous peroxyl radicals, suggesting that both copper -binding and free radical-trapping activities may be involved. A mixtu re of the carboxylic acids representative of those present in red wine exhibited no significant effect on lag time of metal ion-dependent an d -independent low-density lipoprotein oxidations. Ethanol, at concent rations of 0.1-0.5%, had no effect on either copper-induced or aqueous peroxyl radical oxidations. 3. Extracts of acid-hydrolysed red wine w ere separated by thin-layer chromatography and the most active antioxi dant fractions identified. GC-MS and HPLC analysis of these fractions resulted in the identification of several cinnamic acid derivatives, s uch as coumaric acid, caffeic acid and protocatechuic acid. Dose-respo nse studies using the pure compounds indicated that caffeic acid was t he most active antioxidant with an IC50 <1 mu mol/l for copper-initiat ed low-density lipoprotein oxidation. Caffeic acid (1 mu mol/l) signif icantly inhibited lipid hydroperoxide formation while sparing alpha-to copherol consumption. Caffeic acid at the same concentration also inhi bits aqueous peroxyl radical-induced oxidation of low-density lipoprot ein, sparing alpha-tocopherol. There was no evidence of caffeic acid p reventing the binding of copper to low-density lipoprotein. 4. We conc lude that phenolics in both alcoholic and non-alcoholic beverages can give dose-dependent protection against oxidation of low-density lipopr otein. Caffeic acid and protocatechuic acid are two compounds likely t o contribute to these effects. These findings may be relevant to the p utative cardiovascular-protective effects of high phenolic content alc oholic beverages such as red wine; however, the widespread occurrence of antioxidants such as caffeic acid in fruits and vegetables suggests that these protective principles are not limited to red wine.