A method to screen for the antioxidant effect of compounds on low-density lipoprotein (LDL): illustration with flavonoids.

We used a recently described anion-exchange chromatographic method (Vedie et al. J Lipid Res 1991;32:1359) to study the protective effect of potential inhibitors of low-density lipoprotein (LDL) oxidation mediated by cupric ion. By way of an example, we studied eight flavonoids (flavone, 3-hydroxyflavone, chrysin, galangin, fisetin, morin, quercetin, and myricetin) as well as three non-flavonoid antioxidants, butylated hydroxytoluene (BHT), probucol, and vitamin C, as reference compounds. Each compound was tested at various concentrations (1-100 microM). For flavonoid concentrations of 10 microM, an index was calculated as the (LDL control-flavonoid)/(LDL control-probucol) ratio, in which each term is expressed as the percentage of the most electronegative LDL fraction (fraction E). If the index is positive, the flavonoid inhibits LDL oxidation. A value > 1 (3-hydroxyflavone and galangin) means greater activity than probucol, whereas a value < 1 means lower activity (fisetin). If the index is around 0 (flavone and chrysin), the flavonoid is inactive. Finally, a negative value reflects possible prooxidant activity (morin, quercetin, and myricetin). Our results show that this chromatographic method can be applied to screening new pharmacological agents for activity against LDL oxidation.