Protective effects of curcumin and alpha-tocopherol on hemin induced LDL oxidation

Abstract

Oxidative modification of low-density lipoprotein (LDL) plays a major role in the pathogenesis of atherosclerosis. Hemin, a degradation product of hemoglobin, is one of oxidative mediator that found to be elevated in pathological cases like severe hemoglobinopathies, sickle cell anemia and thalassemia. This study was interested in oxidative modification of LDL induced by hemin and focusing on the change of lipid composition. The study was also investigated the protective effect of alpha-tocopherol and curcumin on hemin induced LDL oxidation. This in vitro LDL oxidation study was performed by incubation of LDL with hemin (25 uM/350 ug protein) for 24 hours. The protective effect of antioxidants was also performed by preincubation LDL with curcumin or a-tocopherol and then incubation with hemin for 9 hours. Hemin induced LDL oxidation was shown by the alteration of lipid composition in LDL, the depletion of a-tocopherol and the increasing of thiobarbituric acid reactive substances (TBARs) level. There is an inverse correlation between TBARs level and alpha-tocopherol (r = -0.734, p<0.001). Cholesteryl arachidonate (CA) and cholesteryl linoleate (CL) were decreased 48.2% and 32.3% respectively while other cholesteryl esters were not affected including cholesteryl oleate (CO). In addition, the percent decreasing of CA and CL were good correlation with TBARs level (r = 0.837 and 0.824 respectively; p<0.001). The CL/CO ratio which is a direct oxidative marker in lipoprotein was also decreased. The CL/CO ratio was an inverse correlation with TBARs level (r = -0.706, p<0.001). Both curcumin and alpha-tocopherol showed the protective effect on lipid peroxidation. However, curcumin can inhibit TBARs level more potent than alpha-tocopherol at the dosing of 25 um/350 ug protein. Curcumin was able to inhibit TBARs level more than 80% at 9 hours incubation while alpha-tocopherol inhibited only 23%. Curcumin also protects the decreasing of CL and CA, as well as CL/CO approximately 2-3 times more than alpha-tocopherol. We concluded that lipid composition of LDL was changed by hemin. CA and CL were susceptible to oxidation in hemin induced LDL oxidation. The protective effect of curcumin against hemin induced LDL oxidation was more potent than alpha-tocopherol.