Cranberry proanthocyanidins associate with low-density lipoprotein and inhibit in vitro Cu2+-induced oxidation

Antioxidant activity of six fractions of cranberry phenolic compounds was d etermined by inhibition of Cu2+-induced low-density lipoprotein (LDL) oxida tion. The phenolic composition of each fraction was determined by high-perf ormance liquid chromatography. The phenolic fractions were mixed with aliqu ots of modified human serum prior to LDL isolation. The serum was modified to remove very-low-density lipoprotein and chylomicrons that may bind pheno lic compounds. Only fractions 5 and 6 that contained proanthocyanidins (PAs ) significantly increased the lag time of LDL oxidation, and the lag time f or fraction 6 was significantly higher than for fraction 5. The mass distri bution of PAs in these fractions was obtained by matrix-assisted laser deso rption/ionisation time-of-flight mass spectrometry, a technique that allows rapid characterisation of the molecular weight distribution in mixtures of oligomeric compounds. Fraction 5 contained trimers through heptamers, wher eas fraction 6 contained pentamers through nonamers. In addition, fraction 6 contained PA oligomers with more doubly linked, A-type interflavan bonds. Results indicate that PAs specifically associate with LDL in modified seru m and increase the lag time of Cu2+-induced oxidation. Differences between fractions 5 and 6 in PA structure and cffects on LDL oxidation suggest that the degree of polymerisation and the nature of the interflavan bond influe nce antioxidant properties. (C) 2001 Society of Chemical Industry.