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.     

Flavonoid metabolites and susceptibility of rat lipoproteins to oxidation

Flavonoids are ingested with vegetables and beverages and exert a beneficial effect on cardiovascular disease. Studies in animals in vitro and in humans ex vivo on the resistance of lipoproteins to oxidation are not consistent and the mechanisms by which flavonoids protect against atherosclerosis are a matter of debate. In the present study, we investigated the effects of administering diets containing 0.3% (wt/wt) quercetin, 0.3% (wt/wt) catechin, or 35% (vol/wt) dealcoholated red wine (DRW) for 10 days in healthy rats on markers of oxidative damage in lipoproteins and in plasma. The antioxidant levels in low-density lipoproteins (LDL) or the lag phase, oxidation rate, and maximum level of conjugated dienes during ex vivo LDL oxidation did not differ between control and treated rats. Plasma levels of alpha-tocopherol and retinol were similar in all groups. The total antioxidant status of the plasma from rats fed either quercetin or DRW diet was higher than in control rats. Only glucuronide and sulfate compounds of quercetin were detected in plasma from rats fed the quercetin-rich diet, and no flavonoids or their metabolites were detected in plasma or LDL from rats fed the catechin- or the DRW-rich diet. No significant differences in malondialdehyde or in conjugated dienes in plasma were observed. These results indicate that although metabolites from quercetin are present in plasma, they are not detected in lipoproteins and do not modify the level of other antioxidants. In conclusion, in the absence of any pathology or of oxidative stress the intake of quercetin, catechin, or DRW did not protect lipoproteins from oxidation ex vivo.     

Synergistic interaction between the probucol phenoxyl radical and ascorbic acid in inhibiting the oxidation of low density lipoprotein.

Chain-breaking antioxidants such as butylated hydroxytoluene, alpha-tocopherol, and probucol have been shown to decrease markedly the oxidative modification of low density lipoprotein (LDL). Their mechanism of action appears to involve scavenging of LDL-lipid peroxyl radicals. The purpose of this study was to investigate the occurrence of radical reactions produced during oxidation of LDL and LDL-containing probucol initiated by lipoxygenase or copper. In addition, we have investigated the possibility of a synergistic interaction between ascorbate and probucol in inhibiting the oxidation of LDL. Incubation of LDL-containing probucol and lipoxygenase produced a composite electron spin resonance (ESR) spectrum due to the endogenous alpha-tocopheroxyl radical and probucol-derived phenoxyl radical. The spectral assignment was further verified by chemical oxidation of alpha-tocopherol and probucol. In the presence of ascorbic acid, these radicals in the LDL particle were reduced to their parent compounds with concomitant formation of the ascorbate radical. In both the peroxidation of linoleic acid and the copper-initiated peroxidation of LDL, the antioxidant activity of probucol was significantly increased by low (3-6 microM) concentrations of ascorbate. The probucol-dependent inhibition of LDL oxidation was enhanced in the presence of ascorbic acid. We conclude that the reaction between the phenoxyl radical of probucol and ascorbate results in a synergistic enhancement of the antioxidant capacity of these two compounds and speculate that such reactions could play a role in maintaining the antioxidant status of LDL during oxidative stress in vivo.     

Postprandial LDL phenolic content and LDL oxidation are modulated by olive oil phenolic compounds in humans

Olive oil phenolic compounds are potent antioxidants in vitro, but evidence for antioxidant action in vivo is controversial. We examined the role of the phenolic compounds from olive oil on postprandial oxidative stress and LDL antioxidant content. Oral fat loads of 40 mL of similar olive oils, but with high (366 mg/kg), moderate (164 mg/kg), and low (2.7 mg/kg) phenolic content, were administered to 12 healthy male volunteers in a cross-over study design after a washout period in which a strict antioxidant diet was followed. Tyrosol and hydroxytyrosol, phenolic compounds of olive oil, were dose-dependently absorbed (p<0.001). Total phenolic compounds in LDL increased at postprandial state in a direct relationship with the phenolic compounds content of the olive oil ingested (p<0.05). Plasma concentrations of tyrosol, hydroxytyrosol, and 3-O-methyl-hydroxytyrosol directly correlated with changes in the total phenolic compounds content of the LDL after the high phenolic compounds content olive oil ingestion. A 40 mL dose of olive oil promoted a postprandial oxidative stress, the degree of LDL oxidation being lower as the phenolic content of the olive oil administered increases. In conclusion, olive oil phenolic content seems to modulate the LDL phenolic content and the postprandial oxidative stress promoted by 40 mL olive oil ingestion in humans.     

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.     

(+)-Catechin as antioxidant: mechanisms preventing human plasma oxidation and activity in red wines

We evaluated the antioxidant effect of (+)-catechin (CTCH), in the presence of physiological antioxidant levels of ascorbic acid (AA), alpha-tocopherol (AT) and beta-carotene (BC), in human plasma oxidised with AAPH. Following a five-hour incubation, the formation of lipid oxidation products (TBARS) was almost doubled, and the concentrations of lipid soluble antioxidants were 10 to 30% from the initial levels. In these conditions, AA was consumed within the first hour of incubation. The addition of CTCH prevented AT and BC depletion and TBARS formation, but had no effect on AA consumption. When the kinetics of oxidation were analysed CTCH oxidation preceded lipid soluble antioxidant depletion, but no consumption of CTCH was associated to AA oxidation. Considering that CTCH could contribute to the antioxidant activity of red wine, we first characterised both the antioxidant capacity and CTCH content of several wines. The wines with highest content of CTCH and antioxidant activity were also the most effective in preventing AAPH-mediated oxidation of plasma vitamin E. Results support the idea that CTCH could have a role as a physiological antioxidant in human plasma, and that CTCH of wine could contribute to the antioxidant status of human plasma.     

Effect of dietary supplementation with alpha-tocopherol on the oxidative modification of low density lipoprotein.

Much data has accumulated supporting a proatherogenic role for oxidized low density lipoprotein (Ox-LDL). Micronutrient antioxidants such as alpha-tocopherol, the principal lipid-soluble antioxidant, assume potential significance because levels can be manipulated by dietary measures without resulting in side effects. Co-incubation of LDL in vitro with alpha-tocopherol inhibits its oxidative modification. Hence the effect of dietary supplementation with alpha-tocopherol on the time course of copper-catalyzed oxidation of LDL was tested in a randomized placebo-controlled single-blind study. Two groups of 12 male subjects were given either placebo or alpha-tocopherol (800 IU/day) for a period of 12 weeks. Alpha-tocopherol therapy did not result in any side effects or exert an adverse effect on the plasma lipid and lipoprotein profile. While the lipid standardized alpha-tocopherol levels were similar at baseline, the supplemented group had 3.3-fold and 4.4-fold higher levels compared to placebo at 6 and 12 weeks, respectively. In the 15 subjects in whom both plasma and LDL alpha-tocopherol levels were quantitated, there was a significant correlation (r = 0.79, P less than 0.0001). At baseline there were no significant differences in the time course curves of thiobarbituric acid-reacting substances (TBARS) activity or conjugated diene formation between the alpha-tocopherol and placebo groups. However, at both 6 and 12 weeks the mean levels of TBARS activity and conjugated diene formation were lower in the alpha-tocopherol group; the most significant differences were manifest at the 3-h time point. Also at both 6 and 12 weeks the mean rate of oxidation was lower in the alpha-tocopherol group.2+_     

Cocoa procyanidin chain length does not determine ability to protect LDL from oxidation when monomer units are controlled

Cocoa flavan-3-ols (catechin, epicatechin and oligomeric procyanidins) were tested for their ability to decrease LDL oxidative susceptibility and spare alpha-tocopherol (alpha-toc) in vitro. Physiologic concentration (0.10-0.50 &mgr;M) of flavanols were used. The flavanols increased LDL conjugated diene lag times dose-dependently from 23-207% and 15-143% in response to copper and AAPH oxidation, respectively, and delayed alpha-toc consumption. Sparing of LDL alpha-toc represents a possible mechanism for flavanols to enhance the resistance of plasma and LDL to oxidative stress. Procyanidins decreased LDL oxidative susceptibility with increasing chain length. However, when based on equivalent amounts of monomeric units, they inhibited LDL oxidation to a similar extent. This suggests that antioxidant activity of procyanidins with biologic substrates is not attributable to chain length or charge delocalization through polymeric linkages, but primarily to ring structures and catechol groups. Additionally, human plasma was analyzed for the presence of oligomeric procyanidins following consumption of a flavanol-rich cocoa product. Procyanidin dimers were detected in plasma concordant with the appearance of monomeric flavanols, with a peak of 0.08 +/- 0.01 &mgr;mol/L (n = 6) at two hours after consumption. Thus, this paper confirms the occurrence of procyanidins in human plasma, and extends previous structure-function observations regarding flavanoid protection of LDL.     

Comparison of LDL trap assay to other tests of antioxidant capacity; effect of vitamin E and lovastatin treatment

Oxidized low density lipoprotein (LDL) has a major impact in the development of atherosclerosis. Risk for oxidative modification of LDL is usually determined indirectly by measuring the capability of LDL to resist radical insult. We compared three different methods quantifying the antioxidative capacity of LDL ex vivo in dyslipidemic patients with coronary heart disease. Plasma samples were obtained from two double-blinded cross-over trials. The duration of all interventions (placebo, lovastatin 60 mg/day, RRR-alpha-tocopherol 300 mg/day and lovastatin + RRR-alpha-tocopherol combined) was 6 weeks. The total radical capturing capacity of LDL (TRAP) in plasma was determined using 2,2-azo-bis(2,4-dimethyl-valeronitrile) (AMVN) -induced oxidation, and measuring the extinction time of chemiluminescence. TRAP was compared to the variables characterizing formation of conjugated dienes in copper-induced oxidation. Also the initial concentrations and consumption times of reduced alpha-tocopherol (alpha-TOH) and ubiquinol in AMVN-induced oxidation were determined. Repeatability of TRAP was comparable to that of the lag time in conjugated diene formation. Coefficient of variation within TRAP assay was 4.4% and between TRAP assays 5.9%. Tocopherol supplementation produced statistically significant changes in all antioxidant variables except those related to LDL ubiquinol. TRAP increased by 57%, the lag time in conjugated diene formation by 34% and consumption time of alpha-TOH by 88%. When data of all interventions were included in the analyses, TRAP correlated with the lag time (r = 0.75, p < 10(-6)), with LDL alpha-TOH (r = 0.50, p < 0.001) and with the consumption time of alpha-TOH (r = 0.58, p < 0.0001). In the baseline data, the associations between different antioxidant variables were weaker. TRAP correlated with the lag time (r = 0.55, p < 0.001) and alpha-TOH consumption time (r = 0.48, p < 0.05), and inversely with apolipoprotein Al (r = -0.51, p < 0.05). Lag time at the baseline did not correlate with ubiquinol or tocopherol parameters, or with any plasma lipid or lipoprotein levels analyzed. Lovastatin treatment did not significantly affect the antioxidant capacity of LDL. In conclusion, TRAP reflects slightly different properties of LDL compared to the lag time. Thus, LDL TRAP assay may complement the other methods used to quantify the antioxidant capacity of LDL. However, TRAP and the lag time react similarly to vitamin E supplementation.     

Effect of oral supplementation with D-alpha-tocopherol on the vitamin E content of human low density lipoproteins and resistance to oxidation.

Twelve clinically healthy subjects participated in a vitamin E supplementation study. Eight were given daily dosages of 150, 225, 800, or 1200 IU RRR-alpha-tocopherol for 21 days (two persons per dose) and four received placebo. Prior, during, and after the supplementation period, alpha-tocopherol, gamma-tocopherol, and carotenoids were determined in plasma and low density lipoprotein (LDL). The maximum levels of alpha-tocopherol were 1.7- to 2.5-times the baseline values in plasma and 1.7- to 3.1-times in LDL. A high correlation existed between alpha-tocopherol in plasma and LDL. gamma-Tocopherol significantly decreased in plasma and LDL during vitamin E supplementation. No significant influence on the lipoprotein and lipid status and carotenoid levels of the participants occurred throughout the supplementation. The resistance of LDL against copper-mediated oxidation was also measured. The oxidation resistance of LDL was significantly higher during vitamin E supplementation. However, the efficacy of vitamin E in protecting LDL varied from person to person. The statistical evaluation of all data gave a correlation of r2 = 0.51 between alpha-tocopherol in LDL and the oxidation resistance as measured by the length of the lag-phase preceding the oxidation of LDL. No association was seen between levels of carotenoids and vitamin E in plasma and LDL. The present study clearly shows that in humans the oxidation resistance of LDL can be increased by vitamin E supplementation.     

Differential antioxidant properties of red wine in water soluble and lipid soluble peroxyl radical generating systems

Red wine and its components have been shown to possess cardioprotective and anti-atherogenic effects. Additionally, red wine and many of its components like catechin, epicatechin, rutin, transresveratrol and quercetin possess antioxidant properties. Oxidized low density lipoprotein (LDL) is involved in the development of an atherosclerotic lesion. Red wine, therefore, may be anti-atherogenic because of its antioxidant effects on LDL modification. This study examined the antioxidant effects of catechin, epicatechin, rutin, transresveratrol, quercetin and Merlot wines on LDL oxidation. Merlot was chosen because although other red wines have been tested, limited information exists for this variety. Oxidation was carried out with AAPH (2,2-Azo-bis(2-amidinopropane) dihydrochloride) and AMVN (2,2-Azo-bis(2,4-dimethylvaleronitrile)), as water and lipid soluble peroxyl radical generating systems (FRGS), respectively. This allowed us to determine the lipophilic antioxidant characteristics of the wine and its components. Conjugated diene assays were used to measure LDL oxidation over 6 hrs. In an AAPH system, all polyphenolic compounds except transresveratrol displayed an antioxidant effect. LDL oxidation by AAPH was also inhibited by aliquots of Merlot wine. No antioxidant effects were observed in an AMVN environment except for a mild antioxidant effect by quercetin. Surprisingly, incubation of LDL with Merlot wine strongly protected against oxidation by AMVN. In summary, the five phenolic compounds displayed antioxidant effects in a water soluble free radical generating system, but only quercetin showed this in a lipid soluble one. However, red wine inhibited LDL oxidation by both water and lipid soluble free radical generating systems. Our data suggest, therefore, that red wines contain unidentified antioxidants that provide protection against LDL oxidation within a lipid soluble environment. (Mol Cell Biochem 263: 211–215, 2004)     

Biomarkers of oxidative stress study: are plasma antioxidants markers of CCl(4) poisoning?

Antioxidants in the blood plasma of rats were measured as part of a comprehensive, multilaboratory validation study searching for noninvasive biomarkers of oxidative stress. For this initial study an animal model of CCl(4) poisoning was studied. The time (2, 7, and 16 h) and dose (120 and 1200 mg/kg, intraperitoneally)-dependent effects of CCl(4) on plasma levels of alpha-tocopherol, coenzyme Q (CoQ), ascorbic acid, glutathione (GSH and GSSG), uric acid, and total antioxidant capacity were investigated to determine whether the oxidative effects of CCl(4) would result in losses of antioxidants from plasma. Concentrations of alpha-tocopherol and CoQ were decreased in CCl(4)-treated rats. Because of concomitant decreases in cholesterol and triglycerides, it was impossible to dissociate oxidation of alpha-tocopherol and the loss of CoQ from generalized lipid changes, due to liver damage. Ascorbic acid levels were higher with treatment at the earliest time point; the ratio of GSH to GSSG generally declined, and uric acid remained unchanged. Total antioxidant capacity showed no significant change except for 16 h after the high dose, when it was increased. These results suggest that plasma changes caused by liver malfunction and rupture of liver cells together with a decrease in plasma lipids do not permit an unambiguous interpretation of the results and impede detection of any potential changes in the antioxidant status of the plasma.     

Molecular bases of the treatment of Alzheimer's disease with antioxidants: prevention of oxidative stress

Alzheimer's disease is associated with a systemic oxidative stress situation which can be followed in vivo by determining biomarkers such as plasma lipoperoxides and TBARS levels and the oxidation degree of glutathione in red blood cells. It has been observed that Alzheimer's patients show an increased level of plasma TBARS, which indicates a higher free radical oxidation of plasma unsaturated phospholipids, and an increased oxidation of red blood cells glutathione, which indicates oxidative stress in peripheral cells. This latter, glutathione oxidation, was found to correlate statistically with the cognitive status of the patients. Treatment with vitamin E resulted in an improved cognitive performance only of those patients in which the tocopherol acted as an antioxidant, according to blood indicative markers of oxidative stress. Indeed, the effect of vitamin E on Alzheimer's disease patients showed considerable variations both in its antioxidant function and in its capacity to improve cognitive functions. An important conclusion from the reported results is that epidemiological or clinical studies that aim to test the effect of antioxidant supplementation on given functions should include the determination of the antioxidant status of the patients by the measurement of blood markers of oxidative stress.     

Oral alpha-tocopherol supplementation inhibits lipid oxidation in established human atherosclerotic lesions

BACKGROUND: Much experimental evidence suggests that lipid oxidation is important in atherogenesis and in epidemiological studies dietary antioxidants appear protective against cardiovascular events. However, most large clinical trials failed to demonstrate benefit of oral antioxidant vitamin supplementation in high-risk subjects. This paradox questions whether ingestion of antioxidant vitamins significantly affects lipid oxidation within established atherosclerotic lesions. METHODS AND RESULTS: This placebo-controlled, double blind study of 104 carotid endarterectomy patients determined the effects of short-term alpha-tocopherol supplementation (500 IU/day) on lipid oxidation in plasma and advanced atherosclerotic lesions. In the 53 patients who received alpha-tocopherol there was a significant increase in plasma alpha-tocopherol concentrations (from 32.66 +/- 13.11 at baseline to 38.31 +/- 13.87 (mean +/- SD) micromol/l, p < 0.01), a 40% increase (compared with placebo patients) in circulating LDL-associated alpha-tocopherol (p < 0.0001), and their LDL was less susceptible to ex vivo oxidation than that of the placebo group (lag phase 115.3 +/- 28.2 and 104.4 +/- 15.7 min respectively, p < 0.02). Although the mean cholesterol-standardised alpha-tocopherol concentration within lesions did not increase, alpha-tocopherol concentrations in lesions correlated significantly with those in plasma, suggesting that plasma alpha-tocopherol levels can influence lesion levels. There was a significant inverse correlation in lesions between cholesterol-standardised levels of alpha-tocopherol and 7beta-hydroxycholesterol, a free radical oxidation product of cholesterol. CONCLUSIONS: These results suggest that within plasma and lesions alpha-tocopherol can act as an antioxidant. They may also explain why studies using < 500 IU alpha-tocopherol/day failed to demonstrate benefit of antioxidant therapy. Better understanding of the pharmacodynamics of oral antioxidants is required to guide future clinical trials.     

Photoactivation of phthalocyanine-loaded low density lipoproteins induces a local oxidative stress that propagates to human erythrocytes: protection by caffeic acid

Toxic effects imposed to human erythrocytes by low density lipoproteins carrying phthalocyanines used in photodynamic therapy (PDT) of tumors are described. This study was aimed at evaluating cytotoxic effects induced by reactive species produced locally in photosensitizer-loaded lipoproteins and further transferred to the cells. The experimental set up designed to examine these interactions starts with the loading of human plasma with the photosensitizer, the subsequent rapid purification and dialysis of the LDL fraction and incubation with human erythrocytes. This experimental model was assessed by following leakage of endogenous K+ from cells, electrochemical detection of oxygen, spectroscopic determination of conjugated dienes, phthalocyanine, SH groups and hemoglobin, analysis of fatty acids by gas chromatography and identification of a-tocopherol by HPLC. Photosensitizer-loaded lipoproteins become more susceptible to oxidation, exhibiting shorter lag phases of lipid oxidation, higher rates of oxidation and increased loss of endogenous alpha-tocopherol when challenged with peroxyl radicals and copper, as compared with native lipoproteins from the same plasma sample. Incubation of photosensitized lipoproteins with erythrocytes under light (>560 nm) results in a sigmoidal efflux of K+ followed by hemolysis. The phenolic antioxidant caffeic acid inhibits lipoprotein oxidation induced by peroxyl radicals, either in native or photosensitizer-loaded fractions, delays hemolysis of erythrocytes and partially prevents membrane loss of SH groups in ghosts, but not the efflux of K+. Mechanistically, a chain lipid peroxidation reaction does not participate in the toxic effects to cells but a specific pool of membrane SH groups sensitive to caffeic acid is likely to be involved. This study suggests that an oxidative stress occurring locally in phthalocyanine-loaded low density lipoproteins may further induce cytotoxic effects by targeting specific SH groups at the cell membrane level. The physiological relevance of these findings and the beneficial use of antioxidants are discussed in the context of PDT.     

Oxidative Stress in Severely Obese Persons Is Greater in Those With Insulin Resistance

The postprandial state seems to have a direct influence on oxidative status and insulin resistance. We determined the effect of an increase in plasma triglycerides after a high‐fat meal on oxidative stress in severely obese patients with differing degrees of insulin resistance. The study was undertaken in 60 severely obese persons who received a 60‐g fat overload with a commercial preparation. Measurements were made of insulin resistance, the plasma activity of various antioxidant enzymes, the total antioxidant capacity (TAC) and the plasma concentration of thiobarbituric acid reactive substances (TBARS). The patients with greater insulin resistance had a lower plasma superoxide dismutase (SOD) activity (P < 0.05) and a greater glutathione peroxidase (GSH‐Px) activity (P < 0.05). The high‐fat meal caused a significant reduction in SOD activity and an increase in the plasma concentration of TBARS in all the patients. Only the patients with lower insulin resistance experienced a significant increase in plasma catalase activity (2.22 ± 1.02 vs. 2.93 ± 1.22 nmol/min/ml, P < 0.01), remaining stable in the patients with greater insulin resistance. These latter patients had a reduction in plasma TAC (6.92 ± 1.93 vs. 6.29 ± 1.80 mmol/l, P < 0.01). In conclusion, our results show a close association between the degree of insulin resistance and markers of oxidative stress, both before and after a high‐fat meal. The postprandial state causes an important increase in oxidative stress, especially in severely obese persons with greater insulin resistance. However, we are unable to determine from this study whether there is first an increase in oxidative stress or in insulin resistance.     

A comprehensive study of oxidative stress and antioxidant status in preeclampsia and normal pregnancy

Oxidative stress has been increasingly postulated as a major contributor to endothelial dysfunction in preeclampsia (PE), although evidence supporting this hypothesis remains inconsistent. This study aimed to analyze in depth the potential role of oxidative stress as a mechanism underlying endothelial damage in PE and the pregnant woman's susceptibility to the disease. To this end, indicative markers of lipoperoxidation and protein oxidation and changes in antioxidant defense systems were measured in blood samples from 53 women with PE and 30 healthy pregnant controls. Results, analyzed in relation to disease severity, showed PE women, compared with women with normal pregnancy, to have: (1) significantly enhanced antioxidant enzyme SOD and GPx activities in erythrocytes; (2) similar plasma alpha-tocopherol levels and significantly increased alpha-tocopherol/lipids in both mild and severe PE; (3) significantly decreased plasma vitamin C and protein thiol levels; (4) similar erythrocyte glutathione content, total plasma antioxidant capacity, and whole plasma oxidizability values; (5) significantly elevated plasma total lipid hydroperoxides, the major initial reaction products of lipid peroxidation, in severe PE; (6) no intracellular or extracellular increases in any of the secondary end-products of lipid peroxidation, malondialdehyde or lipoperoxides; (7) similar oxidative damage to proteins quantified by plasma carbonyl levels, immunoblot analysis, and advanced oxidation protein products assessment; and (8) significantly elevated and severity-related soluble vascular cell adhesion molecule-1 serum levels reflecting endothelial dysfunction. No correlations were found among plasma levels of circulating adhesion molecules with regard to lipid and protein oxidation markers. Globally, these data reflect mild oxidative stress in blood of preeclamptic women, as oxidative processes seem to be counteracted by the physiologic activation of antioxidant enzymes and by the high plasma vitamin E levels that would prevent further oxidative damage. These results do not permit us to conclude that oxidative stress might be a pathogenetically relevant process causally contributing to the disease.     

In vitro inhibition by estrogens of the oxidative modifications of human lipoproteins

Estrogens exert protective actions against atherosclerosis, part of these effects having been ascribed to their antioxidant properties. The aim of this work was to assess the ability of estrogens to prevent the oxidative modifications of low density lipoproteins (LDL) and other plasma lipoprotein fractions whose relationship with atherosclerosis has been less studied. For this purpose, different estrogen compounds were used: natural and synthetic estrogens, and catecholestrogens. The molecules were added in vitro to human LDL and very low density lipoproteins (VLDL) in the presence of Cu2+. The lipoprotein oxidative modifications were determined by measuring the formation of thiobarbituric acid reactive substances, the appearance of conjugated dienes and the degradation of tryptophan groups from the apoproteins. In VLDL, 2-hydroxyestradiol and diethylstilbestrol exerted potent antioxidant effects similar to those found for alpha-tocopherol and probucol. 17beta-Estradiol and 4-hydroxyestradiol also prevented VLDL oxidation, but to a lesser extent. When LDL were used, estrogens similarly exerted antioxidant actions, 2-hydroxyestradiol being the most potent inhibitor. These results show that estrogens, whose antioxidant actions have been demonstrated in other experimental models, also possess the ability to prevent in vitro the oxidative modifications of human plasma LDL and VLDL.     

Strictinin as an efficient antioxidant in lipid peroxidation

The antioxidant effect of strictinin (SOH), which was extracted from green tea leaves, against the peroxidation of linoleic acid in sodium dodecyl sulfate (SDS) and cetyl trimethylammonium (CTAB) micelles, against the peroxidation of low-density lipoprotein (LDL) and against oxidative hemolysis of human red blood cells (RBCs), has been studied. The peroxidation of linoleic acid and LDL, and oxidative hemolysis of RBCs were initiated thermally by a water-soluble azo initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), and the reaction kinetics in micelles and LDL were monitored by uptake of oxygen. The synergistic antioxidant effect of SOH with alpha-tocopherol (Vitamin E) was also studied by following the decay kinetics of alpha-tocopherol. Kinetic analysis of the antioxidation process demonstrates that SOH, used either alone or in combination with alpha-tocopherol, is an effective antioxidant against lipid peroxidation, but its effects significantly depend on the reaction medium.     

Modulation of rat liver cytochrome P450 activity by prolonged red wine consumption

Cytochrome P450-dependent oxidation of lauric acid, p-nitrophenol and ethanol by liver microsomal fractions were studied in control rats and in animals given either ethanol, red wine, or alcohol-free red wine for 10 weeks. Ethanol increased the total cytochrome P450 and the isoenzyme 2E1 content, as well as the p-nitrophenol hydroxylation and ethanol oxidation. These effects of ethanol treatment were attenuated by red wine administration. Red wine increased the total antioxidant capacity of plasma, whereas the alcohol-free red wine decreased the cytochrome P450 content and decreased the oxidation of lauric acid, p-nitrophenol and ethanol to values lower than control. It is concluded that red wine administration attenuates the ethanol-induced enhancement in liver microsomal parameters dependent on cytochrome P450 2E1 activity, an affect that seems to be accomplished by the non-alcoholic constituents of red wine known to have antioxidant properties.