Walnut polyphenolics inhibit in vitro human plasma and LDL oxidation

Recent epidemiologic studies have associated nut consumption with a reduced incidence of cardiovascular mortality. However, little is known about the contribution of nut polyphenols to antioxidant and cardiovascular protectio n. In this investigation, polyphenol-rich extracts from English walnuts (Ju glans regia) were studied and compared with ellagic acid for their ability to inhibit in vitro plasma and LDL oxidation, as well as their effects on L DL a-tocopherol during oxidative stress. In addition, the Trolox equivalent antioxidant activity (TEAC) was determined and liquid chromatography elect rospray detection mass spectrometry (LC-ELSD/MS) analyses of the walnut ext racts were performed. 2,2'-Azobis'(2-amidino propane) hydrochloride (AAPH)- induced LDL oxidation was significantly inhibited by 87 and 38% with the hi ghest concentration (1.0 mu mol/L) of ellagic acid and walnut extract, resp ectively. In addition, copper-mediated LDL oxidation was inhibited by 14 an d 84% in the presence of ellagic acid and walnut extract, respectively, wit h a modest, significant LDL alpha -tocopherol sparing effect observed. Plas ma thiobarbituric acid reacting substance (TBARS) formation was significant ly inhibited by walnut extracts and ellagic acid in a dose-dependent manner , and the extracts exhibited a TEAC value greater than that of alpha -tocop herol. LC-ELSD/MS analysis of the walnut extracts identified ellagic acid m onomers, polymeric ellagitannins and other phenolics, principally nonflavon oid compounds. These results demonstrate that walnut polyphenolics are effe ctive inhibitors of in vitro plasma and LDL oxidation. The polyphenolic con tent of walnuts should be considered when evaluating their antiatherogenic potential.