Oxidative susceptibility of low density lipoprotein subfractions is related to their ubiquinol-10 and alpha-tocopherol content.

Abstract

The conjugated polyene fatty acid parinaric acid (PnA) undergoes a stoichiometric loss in fluorescence upon oxidation and can be used to directly monitor peroxidative stress within lipid environments. We evaluated the course of potentially atherogenic oxidative changes in low density lipoproteins (LDL) by monitoring the oxidation of PnA following its incorporation into buoyant (p = 1.026-1.032 g/ml) and dense (p = 1.040-1.054 g/ml) LDL subfractions. Copperinduced oxidation of LDL-associated PnA exhibited an initial lag phase followed by an increased rate of loss until depletion. Increased PnA oxidation occurred immediately after the antioxidants ubiquinol-10 and a-tocopherol were consumed but before there were marked elevations in conjugated dienes. Despite differences in sensitivity to early oxidation events, PnA oxidation and conjugated diene lag times were correlated (r = 0.582; P = 0.03), and both indicated a greater susceptibility of dense than buoyant LDL in accordance with previous reports. The greater susceptibility of PnA in dense LDL was attributed to reduced levels of ubiquinol-10 and a-tocopherol, which were =50% lower than in buoyant LDL (mol of antioxidant/mol of LDL) and together accounted for 80% of the variation in PnA oxidation lag times. These results suggest that PnA is a useful probe of LDL oxidative susceptibility and may be superior to conjugated dienes for monitoring the initial stages of LDL lipid peroxidation. Differences in oxidative susceptibility among LDL density subfractions are detected by the PnA assay and are due in large part to differences in their antioxidant content.Free-radical-mediated oxidation induces potentially atherogenic changes in low density lipoproteins (LDL) (1). Chief among these is an ability to stimulate cholesterol engorgement by macrophages (2, 3), which are progenitors of lipidladen foam cells found in early atherosclerotic lesions. In addition, oxidized-LDL influences the chemotactic behavior of monocytes and monocyte-derived macrophages (4, 5), promotes endothelial cell damage (6, 7), and induces potent mediators of cell proliferation, monocyte adherence, and platelet aggregation (8-12), all of which may contribute to lesion formation and growth.LDL oxidation is believed to proceed through initial oxidation of the fatty acyl components. The resulting lipidderived radicals are intercepted by radical scavenging antioxidants including ubiquinol-10 and a-tocopherol. However, if the oxidant stress is sufficiently great or prolonged, these antioxidants are depleted (13)(14)(15)(16) and injury is propagated among LDL lipids with spread to the protein component through reactive lipid breakdown products (6,17). The atherogenic properties of oxidized-LDL are attributed to this extensively altered particle (1)(2)(3)(4)(5)(6)(7)17), although minimal modifications associated with the initial stages of injury also may be important (10-12).As evidence has accumulated in support of a role for LDL oxidation in atherogenesis, assays of oxidative susceptibility hav...

Superoxide Activates Uncoupling Proteins by Generating Carbon-centered Radicals and Initiating Lipid Peroxidation

“…Lipid peroxidation in beef heart mitochondrial membranes was measured as the loss of fluorescence of cPA, a polyunsaturated fatty acid that partitions into phospholipid bilayers and loses its fluorophore on oxidation, so it can be used as a convenient marker of phospholipid peroxidation in membranes (33). AAPH led to a loss of cPA fluorescence that was prevented by MitoPBN (Fig.…”

“…PBS, phosphatebuffered saline. 37°C with constant stirring (33). Beef heart mitochondrial membranes, prepared as described (34), were incubated in 50 mM KP i buffer, pH 8.0, and after 40 s, cis-parinaric acid (0.5 M) was added, and its oxidation was monitored.…”

The Importance of Lipid and Lipoprote in Ratios in Interpretetions of Hyperlipidaemia of Pregnancy

“…Finally, their uptake into macrophages to create form cells, and initiate atherogenesis, is facilitated [84]. This may explain their identification as an independent risk factor for coronary heart disease [82][83][84].…”

“…These lipoproteins contain subfractions of various sizes, densities and compositions, which differ in their ability to initiate atherogenesis [81]. One of the subfractions of LDL (LDL-3) is small, dense LDL particles which do not bind readily to the LDL receptors and therefore remain in the circulation for longer time, penetrate the arterial intima better than do larger ones [82] and are more readily oxidized, probably because they contain less vitamin E and other antioxidants [83]. Finally, their uptake into macrophages to create form cells, and initiate atherogenesis, is facilitated [84].…”

Metabolic and genetic aspects of familial combined hyperlipidaemia with emphasis on low‐density lipoprotein heterogeneity

“…Recently, in subjects with FCH, total LDL was found to be more prone to in vitro oxidation owing to the predominance of dense LDL particles. In addition, it was suggested that the decreased redox status of coenzyme Q10 in LDL from subjects with a dense LDL subfraction profile reflected the presence of already in vivo modified LDL owing to lipid peroxidation in the circulation [125,126].…”