Effects of different dietary fatty acid supplements upon lipoprotein metabolism and lipid peroxides production in hyperlipidemic rats.

It has been well documented that hypercholesterolemia represents both a common and a dominant, although non-obligatory, risk factor in the progression of atherosclerosis. Research was conducted upon experimentally induced hyperlipidemic animals by means of a custom-tailored atherogenic diet. Cell susceptibility to nonenzyme-induced oxidative stress appears to be influenced by membrane fatty acid composition. This study was undertaken to determine whether differences in lipid peroxidation in steady-state and induced lipid peroxidation is a result of a different fatty acid supplementation. Adult Wistar strain rats of male gender were exposed to an atherogenic diet for a period of 160 days, before randomization into 6 dietary groups with different intragastral oil supplementation. Lipid peroxidation products were measured in 2.5% (w/v) of fresh liver homogenates (Tris-HCl, pH 7.4), by the assay of a thiobarbituric acid reactive substances (TBARS) formation using the procedures described by Okhawa (1979), including modifications (1989) in three different experimental conditions: steady-state (which corresponds to concentration of lipid peroxides in vivo ), spontaneous and metal-stimulated lipid peroxidation. Results were expressed as nmol TBARS per g of liver homogenate, calculated from the absorbency at 532 nm, using TEP as an external standard. This study shows that prolonged atherogenic dietary treatment causes moderate hypercholesterolemia and enhanced hypertriglyceridemia (+34.1% and +114.8, p < 0.001, respectively). Despite the lowering effects of the lipoprotein profiles, resulting from a fatty acid supplementation, at the end of each supplementation period, omega-6 fatty acids (soybean and corn oil) revealed an enhancement in the production of lipid peroxides (TBARS formation) measured in steady-state levels (+22.9%, p < 0.05 and +22.6%, p < 0.05, respectively). When liver homogenates were exposed to Fe2+ and ascorbic acid-induced oxidative stress, lipid peroxidation (LPO) was enhanced in the group treated with soybean oil (omega-6) and fish oil (omega-3; +48.4 %, p < 0.001 and +44.1%, p < 0.001, respectively), but not in the group receiving corn oil. The achieved results support the hypothesis that the process of lipid peroxidation is not always in correlation with the number of double bonds in fatty acids esterified in phospholipid molecules. Consequently, it can be concluded that supplementation of unsaturated fatty acids, in the therapy of cardiovascular diseases, should include the administration of antioxidants, in order to prevent fatty acid decomposition in the case of oxidative insult.