Effect of Curcumin on LDL Oxidation in Vitro, and Lipid Peroxidation and Antioxidant Enzymes in Cholesterol Fed Rabbits

In this study we examined the antioxidant effect of curcumin on lipid oxidation in vitro and in vivo. In vitro, curcumin at 5 microgM concentration completely prevented low-density lipoprotein (LDL) oxidation by CuS0₄, indicating that curcumin is an effective antioxidant in vitro. In vivo, feeding a pure cholesterol (PC)-rich diet to rabbits significantly increased the plasma and liver lipids as well as thiobarbituric acid reactive substances (TBARS) levels. Addition of curcumin to the PC diet did not show any effect on either plasma lipid and TBARS or liver lipids. Liver TBARS tended to decrease but that decrease was not significant. Erythrocyte glutathione peroxidase (GSH-Px) activity was significantly decreased while catalase activity was significantly increased in rabbits fed a PC diet. The addition of curcumin to a PC diet did not show any significant effect on erythrocyte enzyme activities compared to the rabbits fed a PC diet. The liver GSH-Px and catalase activities were significantly decreased in rabbits fed a PC diet, but the addition of curcumin to the PC diet enhanced the liver GSH-Px activity, which became nonsignificantly different from the control group. These results were discussed considering that curcumin may not be well absorbed and it did not reach a level high enough in vivo to overcome the severe hypercholesterolemia and oxidative stress produced by the PC-rich diet.