Seasonal Variation in Low Density Lipoprotein Oxidation and Antioxidant Status

Accumulating evidence indicates that oxidative modification of low-density lipoproteins is atherogenic and that antioxidants may play a role in protection of LDL against oxidation. Several studies have reported a seasonal fluctuation in antioxidant levels, but to date nothing is known about seasonal fluctuations in parameters of oxidizability. We collected blood from 10 volunteers at four different periods over one year (February, May, September and December), and measured the amount of plasma lip ids, plasma antioxidants, lipid and fatty acid composition of the LDL particle, LDL antioxidant content, LDL particle size and oxidation parameters (lag time and propagation rate). No seasonal fluctuation for lag time and propagation rate of copper ion-induced LDL oxidation was found. Small seasonal fluctuations were observed for some determinants of LDL oxidation, e.g. plasma and LDL vitamin E and LDL particle size, and for plasma lipids, plasma and LDL lutein and LDL p-carotene. Fatty acid composition of LDL did not change during the year. The main determinant of oxidation susceptibility was the fatty acid composition of LDL. We conclude that LDL oxidation parameters do not change over the year.     

Solid monounsaturated diet lowers LDL unsaturation trait and oxidisability in hypercholesterolemic (type IIb) patients

Lowering high cholesterol concentration decreases the probability of atherosclerotic-related pathology onset. MUFA and PUFA decrease total plasma and LDL cholesterol but PUFA may increase the susceptibility of LDL to undergo oxidative modifications thus becoming more atherogenetic. Olive oil, the predominant fat source in Mediterranean diet, may combine the advantages of both lowering cholesterol level and decreasing LDL susceptibility to oxidation. We studied the effects of feeding MUFA vs PUFA enriched diet on LDL composition and feature in hypercholesterolemic (IIb) patients. Antioxidant values remained constant during the study while LDL fatty acids composition reflected the dietary intake: MUFA concentration increased 11% whereas PUFA decreased 10% after olive oil diet (p < 0.05). PUFA/MUFA ratio and the unsaturation index were lower at the end of MUFA-enriched diet. The challenge, in vitro, of oleate-enriched LDL with Cu2- yielded to lower lag-phase (p < 0.05) in diene conjugated production; the same LDL gave lower lipid hydroperoxide contents after exposition to AAPH. We conclude that oleate-enriched LDL and with lower PUFA content were more resistant to oxidative modifications, as measured by different peroxidation indexes. This feature acquired with the diet may be an useful tool for lowering LDL oxidation and indirectly their atherogenicity.     

Dark chocolate consumption increases HDL cholesterol concentration and chocolate fatty acids may inhibit lipid peroxidation in healthy humans

Cocoa powder is rich in polyphenols and, thus, may contribute to the reduction of lipid peroxidation. Our aim was to study the effects of long-term ingestion of chocolate, with differing amounts of polyphenols, on serum lipids and lipid peroxidation ex vivo and in vivo. We conducted a 3 week clinical supplementation trial of 45 nonsmoking, healthy volunteers. Participants consumed 75 g daily of either white chocolate (white chocolate, WC group), dark chocolate (dark chocolate, DC group), or dark chocolate enriched with cocoa polyphenols (high-polyphenol chocolate, HPC group). In the DC and HPC groups, an increase in serum HDL cholesterol was observed (11.4% and 13.7%, respectively), whereas in the WC group there was a small decrease (-2.9%, p < 0.001). The concentration of serum LDL diene conjugates, a marker of lipid peroxidation in vivo, decreased 11.9% in all three study groups. No changes were seen in the total antioxidant capacity of plasma, in the oxidation susceptibility of serum lipids or VLDL + LDL, or in the concentration of plasma F2-isoprostanes or hydroxy fatty acids. Cocoa polyphenols may increase the concentration of HDL cholesterol, whereas chocolate fatty acids may modify the fatty acid composition of LDL and make it more resistant to oxidative damage.     

Postprandial oxidative stress

Consumption of a meal containing oxidized and oxidizable lipids gives rise to an increased plasma concentration of lipid hydroperoxides, detectable by a sensitive chemiluminescence procedure. This is associated with increased susceptibility of LDL to oxidation, apparently due a structural perturbation at the particle surface brought about by lipid oxidation products. The postprandial modification of LDL is at least partially accounted for by an increase of LDL-, a subfraction containing lipid oxidation products where apoprotein-B-100 (apoB-100) is denatured. Consuming the meal with a suitable source of antioxidants, such as those found in red wine, minimizes this postprandial oxidative stress. The inhibition of peroxidation of lipids present in the meal during digestion is a possible mechanism for the observed protection of LDL. The in vivo oxidatively modified LDL- has numerous features that correspond to the atherogenic minimally modified LDL produced in vitro. These modified particles could account for a relevant link between nutrition and early biological processes that foster the development of atherosclerosis.     

Kinetic analysis of copper-induced peroxidation of HDL, autoaccelerated and tocopherol-mediated peroxidation

Comparison of the kinetic profiles of copper-induced peroxidation of HDL and LDL at different copper concentrations reveals that under all the studied experimental conditions HDL is more susceptible to oxidation than LDL. The mechanism responsible for HDL oxidation is a complex function of the copper/HDL ratio and of the tocopherol content of the HDL. At high copper concentrations, the kinetic profiles were similar to those observed for LDL oxidation, namely, relatively rapid accumulation of oxidation products, via an autoaccelerated, noninhibited mechanism, was preceded by an initial "lag phase." Under these conditions, the maximal peroxidation rate (V(max)) of HDL and LDL depended similarly on the molar ratio of bound copper/lipoprotein. Analysis of this dependency in terms of the binding characteristics of copper to lipoprotein, yielded similar dissociation constant (K = 10(-6) M) but different maximal binding capacities for the two lipoproteins (8 Cu(+2)/HDL as compared to 17 Cu(+2)/LDL). Given the size difference between HDL and LDL, these results imply that the maximal surface density of bound copper is at least 2-fold higher for HDL than for LDL. This difference may be responsible for the higher susceptibility of HDL to copper-induced oxidation in the presence of high copper concentrations. At relatively low copper concentrations, the kinetic profile of HDL oxidation was biphasic, similar to but more pronounced than the biphasic kinetics observed for the oxidation of LDL lipids at the same concentration of copper. Our results are consistent with the hypothesis that the first phase of rapid oxidation occurs via a tocopherol-mediated-peroxidation (TMP) mechanism. Accordingly, enrichment of HDL with tocopherol resulted in enhanced accumulation of hydroperoxides during the first phase of copper-induced oxidation. Notably, the maximal accumulation during the first phase decreased upon increasing the ratio of bound copper/HDL. This behavior can be predicted theoretically for peroxidation via a TMP mechanism, in opposition to autoaccelerated peroxidation. The possible pathophysiological significance of these findings is discussed.     

Antioxidants and resistance against oxidation of porcine LDL subfractions

The objective of this study was to determine the level of antioxidants, the content of fatty acids and peroxidation products, and the resistance against oxidation of native porcine LDL1 and LDL2. There were no significant differences in the fatty acid distribution of both native low density lipoprotein (LDL) subfractions, which was similar to that of human LDL. The total amount of alpha- and gamma-tocopherol of pig LDL was significantly lower than in human LDL, and beta-carotene, lycopene, and retinyl esters were totally absent. Levels of thiobarbituric acid-reacting substances (TBARS) and lipid peroxides in freshly isolated pig LDL subfractions were below or only slightly above the detection limit. The susceptibility to oxidation of both LDL subfractions was investigated by addition of Cu2+ as prooxidant. The results show that pig LDL subfractions are much more susceptible to oxidation as measured by the duration of the lag phase preceding the onset of rapid lipid peroxidation. From the low content of vitamin E one would expect even much shorter lag phases. The possibility therefore exists that pig LDL contains additional, and as yet unidentified, antioxidants.     

Copper supplementation in humans does not affect the susceptibility of low density lipoprotein to in vitro induced oxidation (FOODCUE project)

The oxidative modification of low-density lipoprotein cholesterol (LDL) has been implicated in the pathogenesis of atherosclerosis. Copper (Cu) is essential for antioxidant enzymes in vivo and animal studies show that Cu deficiency is accompanied by increased atherogenesis and LDL susceptibility to oxidation. Nevertheless, Cu has been proposed as a pro-oxidant in vivo and is routinely used to induce lipid peroxidation in vitro. Given the dual role of Cu as an in vivo antioxidant and an in vitro pro-oxidant, a multicenter European study (FOODCUE) was instigated to provide data on the biological effects of increased dietary Cu. Four centers, Northern Ireland (coordinator), England, Denmark, and France, using different experimental protocols, examined the effect of Cu supplementation (3 or 6 mg/d) on top of normal Cu dietary intakes or Cu-controlled diets (0.7/1.6/6.0 mg/d), on Cu-mediated and peroxynitrite-initiated LDL oxidation in apparently healthy volunteers. Each center coordinated its own supplementation regimen and all samples were subsequently transported to Northern Ireland where lipid peroxidation analysis was completed. The results from all centers showed that dietary Cu supplementation had no effect on Cu- or peroxynitrite-induced LDL susceptibility to oxidation. These data show that high intakes (up to 6 mg Cu) for extended periods do not promote LDL susceptibility to in vitro-induced oxidation.     

Comparison of the effect of alpha-lipoic acid and alpha-tocopherol supplementation on measures of oxidative stress

In vitro studies have shown that alpha-lipoic acid (LA) is an antioxidant. There is a paucity of studies on LA supplementation in humans. Therefore, the aim of this study was to assess the effect of oral supplementation with LA alone and in combination with alpha-tocopherol (AT) on measures of oxidative stress. A total of 31 healthy adults were supplemented for 2 months either with LA (600 mg/d, n = 16), or with AT (400 IU/d, n = 15) alone, and then with the combination of both for 2 additional months. At baseline, after 2 and 4 months of supplementation, urine for F2-isoprostanes, plasma for protein carbonyl measurement and low-density lipoprotein (LDL) oxidative susceptibility was collected. Plasma oxidizability was assessed after incubation with 100 mM 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH) for 4 h at 37 degrees C. LDL was subjected to copper- and AAPH-catalyzed oxidation at 37 degrees C over 5 h and the lag time was computed. LA significantly increased the lag time of LDL lipid peroxide formation for both copper-catalyzed and AAPH-induced LDL oxidalion (p < .05), decreased urinary F2-isoprostanes levels (p < .05), and plasma carbonyl levels after AAPH oxidation (p < .001). AT prolonged LDL lag time of lipid peroxide formation (p < .01 ) and conjugated dienes (p < .01) after copper-catalyzed LDL oxidation, decreased urinary F2-isoprostanes (p < .001), but had no effect on plasma carbonyls. The addition of LA to AT did not produce an additional significant improvement in the measures of oxidative stress. In conclusion, LA supplementation functions as an antioxidant, because it decreases plasma- and LDL-oxidation and urinary isoprostanes.     

人血浆低密度脂蛋白亚组分氧化反应敏感性的比较

本文对３种ＬＤＬ亚组分在体外对Ｃｕ＾２＋催化氧化反应敏感性进行了比较。结果表明,随氧化时间延长,各ＬＤＬ亚组分的电泳迁移率均增加。测定脂质过氧化物的含量以及用结合二烯法测定氧化反应的潜伏期,发现较高密度的ＬＤＬ亚组分更易氧化。荧光免疫测定结果显示,较高密度ＬＤＬ中载脂蛋白Ｂ上新生的４－羟壬烯醛抗原决定簇的表达高于较低密度的ＬＤＬ,从而证明较高密度的ＬＤＬ亚组分对氧化反应的敏感性高于较低密度的亚组分     

Paradoxical protective effect of aminoguanidine toward low-density lipoprotein oxidation: inhibition of apolipoprotein B fragmentation without preventing its carbonylation. Mechanism of action of aminoguanidine

Oxidative modification of low-density lipoproteins (LDLs) is an important feature in the initiation and progression of atherosclerosis. Aminoguanidine (AMG), classically described as an inhibitor of advanced glycation end products, turned out to be also efficient in animal models as an antioxidant against lipid peroxidation. The originality of the present study was based on the simultaneous assessment of the oxidation of LDL lipid and protein moieties in order to characterize the molecular sites of AMG protection. Oxidation of the LDL lipid moiety was monitored by measuring conjugated dienes (CD) and hydroperoxide molecular species from cholesteryl esters (CEOOH) and phosphatidylcholines (PCOOH). LDL protein oxidative modifications were assessed by evaluating apoB carbonylation and fragmentation. The LDL oxidation was mediated by water gamma radiolysis, which has the advantage of being quantitative and highly selective with regard to the free radicals produced. Here, we reported that AMG resulted in a protection of LDLs against lipid peroxidation (both in the lag phase and in the propagation phase) and against apoB fragmentation in a concentration-dependent manner, due to the scavenging effect of AMG toward lipid peroxyl radicals. Paradoxically, AMG was poorly efficient against apoB carbonylation that began during the lag phase. We hypothesize that, even in the presence of AMG, a nonnegligible proportion of (*)OH radicals remained able to initiate oxidation of the LDL protein moiety, leading to apoB carbonylation.     

Serum non-transferrin-bound iron and low-density lipoprotein oxidation in heterozygous hemochromatosis

Non-transferrin-bound iron (NTBI) is implicated in lipid peroxidation but the relation with oxidative modification of low-density lipoprotein (LDL) is not known. We assessed variables reflecting in vitro and in vivo LDL oxidation in two age- and sex-matched groups (n=23) of hereditary hemochromatosis heterozygotes (C282Y), characterized by a clear difference in mean serum NTBI (1.55+/-0.57 micromol/L vs 3.70+/-0.96 micromol/L). Plasma level of oxidized LDL (absolute and relative to plasma apolipoprotein B), and IgG and IgM antibodies to oxidized LDL, markers of in vivo LDL oxidation, did not differ between the groups with low and high serum NTBI. Mean lag-phase of in vitro LDL oxidation was also not significantly different between both study groups. Conclusion: these findings do not support the hypothesis that NTBI promotes oxidative modification of plasma LDL.     

Effect of hemodialysis on the antioxidative properties of serum

In patients with chronic renal failure undergoing regular hemodialysis (HD), oxidative stress is involved in the development of dialysis-related pathologies. The aim of the study was to measure the effect of HD treatment on the general antioxidative status of serum with special consideration of the specific oxidizability of lipids and proteins. Indicators for the oxidative/antioxidative status of plasma were monitored at the beginning and at the end of a dialysis session on the arterial and venous side of the dialyzer. A decrease in the antioxidant status was accompanied by an increased oxidizability of proteins as well as lipids during HD treatment. During the first passage of the dialyzer, the lag time of lipid oxidation decreased from 114.0+/-19.8 to 81.5+/-18.9 min, the lag time of protein oxidation decreased from 105.0+/-24.6 to 72.9+/-21.3 min and the total antioxidative status decreased from 518+/-24 to 252+/-124 microM trolox equivalents. The carbonyl content of serum proteins was high in patients with end stage renal disease (ESRD) (3.9+/-1.1 vs. 0.9+/-0.1 nmol/mg in controls) but did not change significantly during dialysis procedure. Our data demonstrate that the susceptibility of serum lipids and proteins to oxidative modification is severely increased by HD treatment.     

Oxidation of low-density lipoproteins: effect of antioxidant content,fatty acid composition and intrinsic phospholipase activity on susceptibility to metal ion-induced oxidation

The oxidative modification of low-density lipoprotein (LDL) may play an important role in atherogenesis. Our understanding of the mechanism of LDL oxidation and the factors that determine its susceptibility to oxidation is still incomplete. We have isolated LDL from 45 healthy individuals and studied the relationship between LDL fatty acid, vitamin E and β-carotene composition, intrinsic phospholipase A₂-like activity and parameters of LDL oxidation. LDL was exposed to a copper ion-dependent oxidising system and the kinetics of oxidation studied by monitoring formation of fatty acid conjugated dienes. The length of the lag phase of inhibited lipid peroxidation was measured as well as the rate of lipid peroxidation during the propagation phase. There was no significant correlation between LDL antioxidant vitamin or fatty acid composition and lag time to LDL oxidation. Oleic acid was negatively correlated with the rate of LDL oxidation (r = −0.41, P < 0.01) whilst linoleic acid was significantly correlated with the extent of LDL oxidation measured by the production of total dienes (r = 0.34, P < 0.05). Interestingly, LDL vitamin E content was positively correlated with both the rate (r = 0.28, P < 0.05) and extent of LDL oxidation (r = 0.43, P < 0.01). LDL isolated from this group of subjects showed significant intrinsic phospholipase-like activity. The phospholipase activity, whilst not correlated with lag time, was significantly correlated with both rate (r = 0.43, P < 0.01) and total diene production (r = 0.44, P < 0.01) of LDL oxidation. We conclude that antioxidant content, fatty acid composition and intrinsic phospholipase activity have little influence on the lag time of Cu-induced LDL oxidation. These components do however, significantly influence both the rate and extent of LDL oxidation, with increased vitamin E, linoleic acid content and phospholipase activity associated with faster and more extensive oxidation. The possible pro-oxidant effect of vitamin E has interesting implications for the postulated ‘protective’ effects of vitamin E on atherogenesis.     

The effect of histidine modification on copper-dependent lipid peroxidation in human low-density lipoprotein

Summary

Lipid peroxidation and subsequent oxidative modification of low-density lipoprotein (LDL) have been implicated as causal events in atherosclerosis. Cu²⁺ may play an important role in LDL oxidation by binding to histidine residues of apolipoprotein B-100 (apo B) and initiating and propagating lipid peroxidation. To investigate the role of histidine residues, we used diethylpyrocarbonate (DEPC), a lipid-soluble histidine-specific modifying reagent. When LDL (0.1 mg protein/ml, or 0.2 µM) was incubated with DEPC (1 mM), at least 76 ± 7% of the histidine residues in apo B were modified. Treatment of LDL with DEPC led to an increase in the rate of Cu²⁺-induced initiation of lipid peroxidation (R_i), but a significant decrease in the rate of propagation. These changes resulted in an overall increased resistance of LDL to oxidation, with a significantly increased lag phase preceding the propagation phase of lipid peroxidation. In contrast to DEPC, ascorbate completely prevented the initiation of LDL oxidation (R_i = 0). Our data indicate that there are two types of copper/histidine binding sites on apo B: those facing the lipid core of the LDL particle, which mediate the propagation of lipid peroxidation and are modified by DEPC; and those found on the surface of the LDL particle exposed to the aqueous environment, which are responsible for mediating the initiation of lipid peroxidation and are modifiable by ascorbate in the presence of Cu²⁺.     

Resveratrol inhibits copper ion-induced and azo compound-initiated oxidative modification of human low density lipoprotein.

To investigate whether resveratrol, a polyphenolic compound in red wine, affects the oxidation of human low density lipoprotein (LDL), LDL purified from normolipidemic subjects was subjected to Cu(2+)-induce and azo compound-initiated oxidative modification, with and without the addition of varying concentrations of resveratrol. Modification of LDL was assessed by the formation of thiobarbituric acid reactive substances (TBARS) and changes in the relative electrophoretic mobility (REM) of LDL on agarose gels. Resveratrol (50 microM) reduced TBARS and REM of LDL during Cu(2+)-induced oxidation by 70.5% and 42.3%, respectively (p < 0.01), and prolonged the lag phase associated with the oxidative modification of LDL by copper ion or azo compound. These in vitro results suggest that resveratrol may afford protection of LDL against oxidative damage resulting from exposure to various environmental challenges, possibly by acting as a free radical scavenger.     

Manganese-porphyrin reactions with lipids and lipoproteins

Manganese porphyrin complexes serve to catalytically scavenge superoxide, hydrogen peroxide, and peroxynitrite. Herein, reactions of manganese 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP(5+)) with lipids and lipid hydroperoxides (LOOH) are examined. In linoleic acid and human low-density lipoprotein (LDL), MnTE-2-PyP(5+) promotes oxidative reactions when biological reductants are not present. By redox cycling between Mn(+3) and Mn(+4) forms, MnTE-2-PyP(5+) initiates lipid peroxidation via decomposition of 13(S)hydroperoxyoctadecadienoic acid [13(S)HPODE], with a second-order rate constant of 8.9 x 10(3) M(-1)s(-1)and k(cat) = 0.32 s(-1). Studies of LDL oxidation demonstrate that: (i) MnTE-2-PyP(5+) can directly oxidize LDL, (ii) MnTE-2-PyP(5+) does not inhibit Cu-induced LDL oxidation, and (iii) MnTE-2-PyP(5+) plus a reductant partially inhibit lipid peroxidation. MnTE-2-PyP(5+) (1-5 microM) also significantly inhibits FeCl(3) plus ascorbate-induced lipid peroxidation of rat brain homogenate. In summary, MnTE-2-PyP(5+) initiates membrane lipid and lipoprotein oxidation in the absence of biological reductants, while MnTE-2-PyP(5+) inhibits lipid oxidation reactions initiated by other oxidants when reductants are present. It is proposed that, as the Mn(+3) resting redox state of MnTE-2-PyP(5+) becomes oxidized to the Mn(+4) redox state, LOOH is decomposed to byproducts that propagate lipid oxidation reactions. When the manganese of MnTE-2-PyP(5+) is reduced to the +2 state by biological reductants, antioxidant reactions of the metalloporphyrin are favored.     

Antioxidant/prooxidant effects of dietary non-flavonoid phenols on the Cu2+-induced oxidation of human low-density lipoprotein (LDL)

A central role in the oxidative development of atherosclerotic lesions has been ascribed to the peroxidation of plasma low-density lipoprotein (LDL). Dietary supplementation with virgin olive oils increases the total plasma antioxidant status and the resistance of low-density lipoprotein to ex vivo oxidation. We have studied the effects of some dietary non-flavonoid phenols from Olea europaea L., both in purified form or in complex mixtures obtained by biotransformation of olive leaf extracts, on the LDL oxidation induced by Cu2+ ions. Cu2+-Induced LDL oxidation is inhibited by oleuropein and hydroxytyrosol in the initiation phase of the reaction at concentrations of phenols higher than that of Cu2+ ions. Interestingly, at lower concentration, both phenols anticipated the initiation process of LDL oxidation, thus exerting prooxidant capacities. Although similar effects are already described for flavonoids, such as quercetin, rutin, and apigenin, it is the first time that a prooxidant effect of dietary non-flavonoid phenols, such as oleuropein and hydroxytyrosol, on the LDL oxidation is reported. Our results show that a net effect of oleuropein and hydroxytyrosol on Cu2+-induced LDL peroxidation is determined by a balance of their pro- and antioxidant capacities. It is worth to underline that, during Cu2+-induced LDL oxidation in the presence of bioreactor eluates, we have evidence of a synergistic effect among phenolic compounds that enhance their antioxidant capacities so avoiding the prooxidant effects.     

Intracellular generation of MDA-LYS epitope in foam cells.

Oxidative stress plays a central role in atherogenesis. Antioxidants, such as probucol, inhibit oxidation of LDL, retard secretion of interleukin-1, growth factors and chemoattractants, and thus inhibit progression of atherosclerosis. Other antioxidants with an ability to inhibit LDL oxidation, however, could not prevent progression of atherosclerosis. The inconsistency between antioxidant potencies indicated oxidative events might have occurred at locations other than LDL. MDA-lysine epitope (MDA-lys) is closely associated with atherogenesis and was recognized as marker for oxidation. We traced formation of MDA-lys during oxidation of LDL and formation of foam cells. The results indicated that thiobarbituric acid reactive substance (TBARS) was primarily present in lipid fraction of ox-LDL not associated with protein fraction after Cu2+ oxidation in vitro. Oxidized LDL did not increase significant immunoreactivity of MDA-lys epitope under our experimental conditions. Foam cells, however, showed the presence of MDA-lys epitope suggesting that intracellular oxidation events occurred to internalized lipids. The uptake of non-oxidatively modified LDL (acetylated LDL) was sufficient to generate MDA-lys epitope in foam cells, consistent with the hypothesis that atherosclerosis is associated with oxidative events in addition to LDL oxidation. We hypothesized that MDA-lys may be generated through intracellular lipid metabolism during the formation of foam cells.     

Red wine mitigates the postprandial increase of LDL susceptibility to oxidation

The aim of the present study was to verify the extent of oxidative stress induced by a meal at plasma and LDL level, and to investigate the capacity of red wine to counteract this action. In two different sessions, six healthy men ate the same test meal consisting of "Milanese" meat and fried potatoes. The meal was taken either with 400 ml red wine or with an isocaloric hydroalcoholic solution. Oxidative stress at plasma level was estimated through the measure of ascorbic acid, alpha-tocopherol, protein SH groups, uric acid, and antioxidant capacity, measured before and 1 and 3 h after the meal. The change in the resistance of LDL to oxidative modification was taken as an index of exposure to pro-oxidants. The susceptibility to Cu(II)-catalyzed oxidation of baseline and postprandial LDL was measured as conjugated dienes formation, tryptophan residues, and relative electrophoretic mobility. The experimental meal taken with wine provoked a significant increase in the total plasma antioxidant capacity and in the plasma concentration of alpha-tocopherol and SH groups. Postprandial LDL was more susceptible to metal-catalyzed oxidation than the homologous baseline LDL after the ethanol meal. On the contrary, postprandial LDL obtained after the wine meal was as resistant or more resistant to lipid peroxidation than fasting LDL.     

Mechanisms of oxidative modification of low density lipoproteins under conditions of oxidative and carbonyl stress

Low-molecular-weight aldehydes (glyoxal, methylglyoxal, 3-deoxyglucosone) generated on autooxidation of glucose under conditions of carbonyl stress react much more actively with amino groups of L-lysine and epsilon-amino groups of lysine residues of apoprotein B-100 in human blood plasma low density lipoproteins (LDL) than their structural analogs (malonic dialdehyde (MDA), 4-hydroxynonenal) resulting on free radical oxidation of lipids under conditions of oxidative stress. Glyoxal-modified LDL aggregate in the incubation medium with a significantly higher rate than LDL modified by MDA, and MDA-modified LDL are markedly more poorly absorbed by cultured human macrophages and significantly more slowly eliminated from the rat bloodstream upon intravenous injection. Studies on kinetics of free radical oxidation of rat liver membrane phospholipids have shown that ubiquinol Q(10) is the most active lipid-soluble natural antioxidant, and suppression of ubiquinol Q(10) biosynthesis by beta-hydroxy-beta-methylglutaryl coenzyme A reductase inhibitors (statins) is accompanied by intensification of lipid peroxidation in rat liver biomembranes and in LDL of human blood plasma. Injection of ubiquinone Q(10) protects the human blood plasma LDL against oxidation and prevents oxidative stress-induced damages to rat myocardium. A unified molecular mechanism of atherogenic action of carbonyl-modified LDL in disorders of lipid and carbohydrate metabolism is discussed.