The Effect of α-Tocopherol on Copper Binding to Low Density Lipoprotein

The oxidative modification of low density lipoprotein (LDL) may play an important role in atherogenesis. Antioxidants that can prevent LDL oxidation may act as antiatherogens. Our understanding of the mechanism of LDL oxidation and factors that determine its susceptibility to oxidation is still incomplete. Copper is a candidate for oxidizing LDL in atherosclerotic lesions. The binding of copper ions to LDL is usually thought to be a prerequisite for LDL oxidation by copper. Therefore we investigated the effect of α-tocopherol (as a major fat soluble antioxidant) on copper bound to LDL and furthermore effect of this binding on the susceptibility of LDL to oxidative modification.

In this study LDL was isolated from EDTA-plasma (1 mg EDTA/ml blood) by ultracentrifugation using a single-step discontinuous gradient. Then α-tocopherol was added to LDL and incubated for 1 h at 37° C. The oxidation rate of LDL was estimated by thiobarbitoric acid reactive substances (TBARS) after CuSO₄ addition. Finally, the effect of α-tocopherol on formation of LDL-copper complex by gel filtration was studied.

Our results showed that α-tocopherol (dose dependently) suppressed the formation of TBARS and LDL-copper complex. The α-tocopherol with concentrations of 10, 50 and 100 µM reduced susceptibility of LDL to oxidative modification approximately by 2, 13 and 21 percent, respectively. Furthermore, addition of α-tocopherol to the LDL and CuSO₄ mixture containing before hand prevented the formation of LDL-copper complex, approximately by 30 percent.

In conclusion we found that α-tocopherol with inhibition of copper binding to LDL may decrease the susceptibility of LDL oxidation to this ion and thus could play a role in prevention of atherosclerosis.