Inhibitory activity of minor polyphenolic and nonpolyphenolic constituents of olive oil against in vitro low-density lipoprotein oxidation.

The minor polyphenolic and nonpolyphenolic constituents of olive oil were examined, in various doses, against copper ion-induced low-density lipoprotein (LDL) oxidation and were found, in optimal doses (final concentration, 10 microM or 20 microM), to have remarkable biological activity, contributing to that previously reported for the major phenolic compounds. The main phytosterols, beta-sitosterol, campesterol, and stigmasterol, were found to have 43.8%, 37.3%, and 33.4% LDL mean protection (MP) activity, respectively, while free cholesterol exhibited 43.2% MP. The triterpenoid derivative compounds, ursolic acid, uvaol, and oleanolic acid, had similar MP activities of 50.5%, 46.8%, and 46.0%, respectively. Tocopherol (Toc) isomers exhibited an increasing effect in the following order: alpha-Toc (33.6%) < beta-Toc (36.1%) < gamma-Toc (42.9%) < delta-Toc (46.0%). The flavonoid polyphenols, quercetin, luteolin, and rutin, exhibited the highest activities--46.8%, 49.5%, and 53.7% MP, respectively, comparable to the 49.0% MP activity found for oleuropein. These findings indicate the relative independence of LDL protection activity in regard to structural differences among the involved compounds. A relation to the Mediterranean diet is also demonstrated.