Oxidatively modified LDL and atherosclerosis: an evolving plausible scenario

Principales métodos para la determinación de la oxidación lipídica Main methods used in lipid oxidation determination

Main spectrophotometric and chromatographic methods for determination of lipid oxidation in foods and biological systems are reviewed. A new classification, according to the compounds produced in the oxidation phases, is suggested as follows: measurement of oxygen absorption, conjugated dienes, peroxide values, and decomposition of lipid peroxides. Both conjugated dienes (propagation phase) and thiobarbituric acid (termination phase) methods are the most used, despite their interferences; however, chromatographic methods are more precise and selective. Determination of bioavailability and metabolic pathway of the antioxidants in the human body are problems to be solved in the devel opment of new biological antioxidants.

LDL biochemical modifications: a link between atherosclerosis and aging

Atherosclerosis is an aging disease in which increasing age is a risk factor. Modified low-density lipoprotein (LDL) is a well-known risk marker for cardiovascular disease. High-plasma LDL concentrations and modifications, such as oxidation, glycosylation, carbamylation and glycoxidation, have been shown to be proatherogenic experimentally in vitro and in vivo. Atherosclerosis results from alterations to LDL in the arterial wall by reactive oxygen species (ROS). Evidence suggests that common risk factors for atherosclerosis raise the likelihood that free ROS are produced from endothelial cells and other cells. Furthermore, oxidative stress is an important factor in the induction of endothelial senescence. Thus, endothelial damage and cellular senescence are well-established markers for atherosclerosis. This review examines LDL modifications and discusses the mechanisms of the pathology of atherosclerosis due to aging, including endothelial damage and oxidative stress, and the link between aging and atherosclerosis.

Effect of vitamin C supplementation on concentrations of vitamins C and E in fasting plasma

Vitamin C may 'spare' vitamin E, but this has not to date been confirmed as occurring in vivo. The aim of this study was to test the effect of dietary supplementation with vitamin C on total and lipid standardised vitamin E concentrations in fasting plasma, the hypothesis being that increased vitamin C intake leads to improved vitamin E levels. In this single-blinded study, 12 apparently healthy adults (seven men, five women) took 1 g/day vitamin C for 28 days, with a 28-day placebo-controlled run-in cycle and a 28-day placebo-controlled washout cycle. Concentrations of ascorbic acid, total vitamin E (as total tocopherols) and lipid standardised vitamin E (Vit ELS, expressed as mol vitamin E/mmol total cholesterol plus triglycerides) were measured in fasting plasma after each cycle. Results showed that vitamin C supplementation led to significant increases in ascorbic acid, total vitamin E and Vit ELS. These findings indicate that, by a combination of a vitamin E 'sparing' effect perhaps via improved redox recycling of vitamin E in vivo and a lipid lowering effect, increased intake of vitamin C could increase plasma vitamin E levels, and possibly vitamin E status. Further study of possible in vivo interrelationships between vitamins C and E, and the role of vitamin C in lipid metabolism, is needed.

Chronic uremia stimulates LDL carbamylation and atherosclerosis

Carbamylated LDL (cLDL) is a potential atherogenic factor in chronic kidney disease (CKD). However, whether elevated plasma cLDL associates with atherosclerosis in vivo is unknown. Here, we induced CKD surgically in apolipoprotein E-deficient (ApoE(-/-)) mice fed a high-fat diet to promote the development of atherosclerosis. These mice had two- to threefold higher plasma levels of both oxidized LDL (oxLDL) and cLDL compared with control mice. Oral administration of urea increased cLDL approximately eightfold in ApoE(-/-) mice subjected to unilateral nephrectomy and a high-fat diet, but oxLDL did not rise. Regardless of the model, the uremic mice with high plasma cLDL had more severe atherosclerosis as measured by intravital ultrasound echography and en face aortic staining of lipid deposits. Furthermore, cLDL accumulated in the aortic wall and colocalized with ICAM-1 and macrophage infiltration. In summary, these data demonstrate that elevated plasma cLDL may represent an independent risk factor for uremia-induced atherosclerosis.

Oxidative modification and nitration of human low-density lipoproteins by the reaction of hypochlorous acid with nitrite

Hypochlorous acid (HOCl) reacts with nitrite (NO2-) at a molar ratio of 1:1 yielding an equimolar amount of nitrate. The rate of this reaction follows the dissociation of hypochlorous acid and decreases with the increasing of pH from 4 to 10 as assayed by stopped-flow analysis, suggesting that HOCl, not hypochlorite, is the reactant. The second-order rate constant at pH 7.2, 25 degrees C, was estimated as (7.4 +/- 1.3) x 10(3) M(-1) s(-1), a rate considerably higher than that of the Fenton reaction (42 M(-1) s(-1)). In human low-density lipoproteins (LDL) the reaction led to a loss of beta-carotene and alpha-tocopherol. The NO2-/HOCl mixture initiated lipid peroxidation in LDL, whereas NO2- or HOCl alone had only little effect. When LDL was added immediately after mixing of NO2- with HOCl, no loss of antioxidants or accumulation of lipid peroxidation products was observed, suggesting that a short-lived reactive intermediate, previously postulated as nitryl chloride, is the reactive species. The mixture NO2-/HOCl as well as peroxynitrite led to the formation of 3-nitrotyrosine in LDL as assayed using a monoclonal anti-nitrotyrosine antibody. Furthermore, incubation of J774.2 macrophage-like cells with LDL, pretreated with the NO2-/HOCl mixture, led to increased cellular accumulation of cholesterol. Thus modification of LDL caused by the reaction of nitrite with HOCl contributes to the formation of cholesterol-rich cells, a key feature of the early atherosclerotic lesion.