Grape extract inhibits lipid peroxidation of human low density lipoprotein

Some epidemiological data have linked dietary polyphenols with lower risk of coronary heart disease. Polyphenols might impair lipoprotein oxidation which is believed to be an important step in initiating atherogenesis. The purpose of this study was to determine if grape extract known to contain polyphenolic substances can block copper-induced oxidative modification of human low density lipoprotein (LDL).LDL oxidation was monitored spectrophotometrically by measurement of change in absorbance at 234 nm. Incubation of LDL (0.05 mg protein/ml) with 1.66 microM cupric chloride produced a lag phase of 130 min before onset of the propagation phase where polyunsaturated fatty acids undergo conversion to conjugated lipid hydroperoxides. However, in the presence of grape extract at a final concentration equal to an 8000-fold dilution, the lag phase was extended to 185 min. A 4000-fold and 2000-fold dilution of grape extract produced lag phases of 250 and 465 min, respectively. LDL oxidation was essentially blocked for at least 10 h with a 1000-fold dilution of grape extract. In other experiments, incubation of LDL (0.2 mg protein/ml) with 5 microM cupric chloride for 1-4 h increased both thiobarbituric acid-reactive substances and electrophoretic mobility of LDL on agarose gel. In addition, there was loss of immunoreactivity of LDL with a murine monoclonal antibody against human apolipoprotein B-100. However, these oxidative changes to LDL by copper were prevented when diluted grape extract was present during incubation. It is concluded that grape extract contains antioxidants in the form of polyphenols with the capacity to inhibit oxidative modification of LDL.