The Effects of Lipophilic Antioxidants on the Affinity of LDL to Its Receptor: A Model for Prevention of Atherogenesis

The affinity of low density lipoprotein (LDL) to its receptor is very important, because most of LDL-uptake pathway is done by the LDL receptor and the change in size of LDL particle and the modification in its components may affects the LDL affinity for its receptor. In this study, the effects of lipophilic agents such as vitamin E and seven volatile oils: anethol, eugenol, geraniol, limonene, linalool, pulegone and thymol have been investigated on the affinity of LDL to its receptor. LDL receptor was purified of bovine adrenal tissue. LDL was isolated by sequential density ultracentrifugation from normolipidemic human plasma. Then, LDL was labeled with fluoresein isothiocyanate (FITC) at 4°C for 24 h. Native LDL was incubated with various concentrations of each of the volatile oils and vitamin E for 2 h. Finally, the native LDL treated with volatile oils and vitamin E was incubatd with the LDL receptor in the presence of labeled-LDL at 37°C for 30 min. After incubation, the medium was centrifuged at 4000 ×g for 20 min and the fluorescence intensity (FI) of supernatant from each sample was determined at excitation 495 nm and emission 515 nm. The elevation of FI in each fraction demonstrates increasing the affinity of non-labeled-LDL to its receptor. We showed that vitamin E and volatile oils increased the affinity of LDL to its receptor, and among these compounds, vitamin E and thymol are the best agents that increase the affinity of native LDL to its receptor. The effects of these compounds are as follows: vitamin E > thymol > eugenol > anethol > geraniol > linalool > limonene > pulegone. These findings raise the possibility that vitamin E and some of the volatile oils may decrease the effect of LDL in formation of atherosclerotic lesions.