Effect of phytosterols on copper lipid peroxidation of human low-density lipoproteins

Objective: Phytosterols and stanols have received much attention in the past several years because of their cholesterol-lowering properties, and several studies have shown a protective effect against cardiovascular disease and colon and breast cancer development. A significant decrease of plasma low-density lipoprotein (LDL) cholesterol and apolipoprotein B has been demonstrated in subjects whose diet was supplemented with 2 g/d of plant sterols. Changes in plasma lipoprotein levels were associated with a decrease of oxidized LDL, suggesting that plant sterols could exert an antioxidant effect. The aim of the present study was to further investigate the interaction between the major dietary phytosterols and plasma lipoproteins. Moreover, their antioxidant effect against in vitro induced lipid peroxidation of human LDL was investigated. Methods: Susceptibility to copper-induced lipid peroxidation was investigated in LDLs isolated from plasma of normolipemic subjects. Concentrations of beta-sitosterol, campesterol, and stigmasterol ranging from 5 to 50 mu M were studied. Analyses of the emission fluorescence spectra of tryptophan and of the probe 6-dodecanoyl-2-dimethyl-aminoaphthalene were used to investigate the effect of phytosterols on apoprotein structure and physicochemical properties of LDL. Results: Our results demonstrated that phytosterols exert an inhibitory effect against copper-induced lipid peroxidation of LDLs, as shown by the lowered levels of conjugated dienes in oxidized lipoproteins incubated with different concentrations of plant sterols (5-50 mu M). Moreover, analysis of fluorescence emission spectra of tryptophan and 6-dodecanoyl-2-dimethyl-aminoaphthalene demonstrated that phytosterols prevent the alterations of apoprotein structure and physicochemical properties associated with copper-triggered lipid peroxidation of lipoproteins. Conclusion: We suggest that the effect exerted by beta-sitosterol, stigmasterol, and campesterol against lipid peroxidation of LDL possibly related to phytosterol lipoprotein interactions could be of physiologic relevance. (C) 2010 Elsevier Inc. All rights reserved.