Low density lipoprotein composition and oxidizability in coronary disease — apparent favourable effect of beta blockers

Acute myocardial infarction leads to acceleration of atherosclerosis

Patients who experience acute myocardial infarction (AMI) are at increased risk of recurrent events in the weeks to months following the initial event. The underlying etiology for this vulnerable period following MI is unclear but could be related to the same underlying triggers responsible for the initial MI. Alternatively, the recurrent cardiac event could be promoted by the incident event. For example, several biomarkers reflecting inflammatory activity have been shown to be elevated for weeks to months following MI and this inflammatory response could aggravate existing atherosclerotic lesions by accelerating their growth and/or promoting plaque instability. The purpose of this review is to highlight recent preclinical and clinical studies supporting links between AMI and atherosclerosis and to consider potential therapeutic interventions.

Changes in small dense low-density lipoprotein levels following acute coronary syndrome

Low-density lipoprotein (LDL), especially small dense LDL (sdLDL), plays a role in atherogenesis. We compared baseline sdLDL levels between healthy controls and patients with acute coronary syndrome (ACS). Blood samples were taken from patients diagnosed with myocardial infarction ([MI] n = 104) and unstable angina ([UA] n = 100). Both sdLDL and high-sensitivity C-reactive protein (hsCRP) levels were determined on admission and in the next 24 hours after the onset of symptoms. Baseline concentration of sdLDL was significantly higher in patients presenting with ACS than controls (P < .05). In the 24 hours following ACS, the sdLDL levels decreased insignificantly in both groups of patients with ACS (P > .05). The changes in sdLDL values were not significantly different between MI and UA participants (P > .05). Patients with ACS have higher concentration of sdLDL compared with the controls.

The relationship between paraoxonase1-192 polymorphism and activity with coronary artery disease

OBJECTIVE

We tested the association between PON1 polymorphism, PON1 activity, oxidative susceptibility of LDL and coronary artery disease in Egyptians.

METHODS

PON1 polymorphism, serum PON1 activity, lipoprotein oxidation susceptibility and lipid profile were measured.

RESULTS

Levels of HDL and paraoxonase activity were significantly decreased in CAD patients compared to control group, and in patients with three vessels compared to those of single or two vessels disease. High-activity allele (R) has a more atherogenic lipid profile than for the low activity allele (Q). PON1 RR genotype has nine fold risks to develop CAD in Egyptians while those with PON1 QR genotype have four fold risks.

CONCLUSION

The PON1 activity is lower in subject with CAD and there is a significant relationship between activity of PON1 and the severity of coronary atherosclerosis. Also, we provide evidence of a significant association between R allele of the PON1 polymorphism and the development of coronary artery disease.

Lipid and protein oxidation and antioxidant status in patients with angiographically proven coronary artery disease

OBJECTIVES

We aimed to evaluate the association of lipid peroxidation, protein oxidation and antioxidant system, and to assess an association with the severity of the disease, in patients with and without coronary artery disease (CAD) documented by coronary angiography.

DESIGN AND METHODS

The population included 208 patients, undergoing clinically indicated coronary angiography. While the subjects with normal coronary angiograms (n=54) were evaluated as controls, the patients with CAD (n=154) were divided into three categories according to the number of diseased coronaries; one-vessel (n=50), two-vessels (n=51) and three-vessels (n=53). Lipid parameters were determined by routine laboratory methods. Plasma malondialdehyde and vitamin E concentrations were determined with the high-performance liquid chromatography. Other oxidant and antioxidant parameters were studied spectrophotometrically.

RESULTS

While plasma malondialdehyde levels, the susceptibilities of erythrocyte and apolipoprotein B containing lipoproteins to in vitro induced oxidative stress, serum protein carbonyls, low density lipoprotein-cholesterol, triglyceride, apolipoprotein B and lipoprotein (a) levels had significantly increased, high-density lipoprotein-cholesterol and apolipoprotein AI levels, erythrocyte glutathione peroxidase, glutathione reductase, glucose 6 phosphate dehydrogenase, serum catalase, paraoxonase and arylesterase activities, plasma vitamin E and C and carotenoid levels had significantly decreased. The odds ratios for one-, two-, and three-vessel disease increased across especially higher tertiles of concentrations for oxidation parameters and lower tertiles of concentrations for antioxidant parameters.

CONCLUSIONS

According to the results, we suggest that increased lipid and protein oxidation products and decreased antioxidant enzymes and vitamins contribute to increased oxidative stress which in turn is related to the severity of the disease.

Increased plasma malondialdehyde and protein carbonyl levels and lymphocyte DNA damage in patients with angiographically defined coronary artery disease

We investigated the oxidative modifications of lipids, proteins and DNA, three potential molecular targets of oxidative stress, in 30 patients with angiographically defined coronary artery disease (CAD) and 30 healthy control subjects. In addition, we examined relationships between these oxidative modifications and the severity of vascular lesions in patients with CAD. Malondialdehyde (MDA) and protein carbonyl (PC) levels, as well as ferric reducing antioxidant power (FRAP), were measured in the plasma. DNA damage was evaluated as single strand breaks (SSBs), formamidopyrimidine glycosylase (Fpg) and endonuclease III (E-III)-sensitive sites by the comet assay in DNA isolated from lymphocytes. MDA and PC levels increased, but FRAP values decreased, in patients as compared to controls. However, these values did not vary with the number of affected coronary vessels and were not correlated with Duke score, a parameter of the severity of vascular lesions in patients with CAD. We also found that lymphocyte DNA damage (SSBs, Fpg and E-III sites) were increased in patients. Although there were no significant differences in SSBs values in patients grouped according to affected vessel number, Fpg and E-III sites increased. We also detected significant correlations between Duke scores and SSBs and Fpg sites. Serum cholesterol, triglyceride and LDL-cholesterol levels were found to increase, but HDL-cholesterol levels decreased in CAD patients, but these lipids were not correlated with Duke scores. The results of this study reinforce the presence of increased combined oxidative modifications in lipid, protein and DNA in patients with CAD. However, lymphocyte DNA damage seems to be a more reliable assay than MDA and PC determinations to detect the severity of vascular lesions in patients.

Potent Antioxidant Properties of 4-Hydroxyl-propranolol

The antioxidant properties of 4-HO-propranolol (4HOP), a major metabolite of propranolol, were studied and compared with that of propranolol and vitamin E (Trolox). When isolated hepatic microsomal membranes were peroxidized by an iron-catalyzed.OH-generating system [dihydroxyfumarate +Fe (III)], 4HOP potently and concentration-dependently inhibited lipid peroxidation; the IC50 value was 1.1 microM, whereas those for Trolox and propranolol were 4.3 and 168 microM, respectively. When isolated human low-density lipoprotein (LDL) was oxidized by 7.5 microM Cu(II) for 9 h, 4HOP at 3 microM delayed the lag phase significantly by 108 min, which was comparable with that of probucol (98-min delay) but was far greater than that provided by propranolol (6 min) or Trolox (47 min). At 1 microM 4HOP, the delay was 45 min. When confluent cultured bovine aortic endothelial cells were exposed to the Fe-catalyzed oxy-radical system, acute loss of glutathione occurred (55% decrease in 50 min). Pretreatment of the cells with 0.067 to 6.7 microM 4HOP for 30 min provided increasing degrees of protection against the glutathione loss; the EC50 value was 1.2 microM, whereas those for Trolox and propranolol were 7.9 and 49 microM, respectively. The loss of cell survival due to the radical stress was also effectively preserved by 4HOP. In separate experiments, when the endothelial glutathione was oxidatively depleted by a peroxynitrite-generating system (3-morpholinosydnonimine), 4HOP also provided potent protective activities. In conclusion, 4HOP is 4- to 8-fold more potent than vitamin E and >100-fold more active than propranolol as a "chain-breaking" antiperoxidatant against membrane and LDL oxidation and can provide superior endothelial cytoprotective efficacy against oxygen- or nitrogen-derived oxidant-mediated cell injury. Being a major metabolite in human and with its plasma level approaching that of propranolol, 4-HO-propranolol may contribute, in part, to the cardiovascular therapeutic benefits of propranolol.

Antioxidant activity of prenylated flavonoids from the West African medicinal plant Dorstenia mannii

The antioxidant activities of three prenylated flavonoids from Dorstenia mannii (6,8-diprenyleriodictyol, dorsmanin C and dorsmanin F) were compared to the common, non-prenylated flavonoid, quercetin. The prenylated flavonoids were found to be potent scavengers of the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH), and are more potent than butylated hydroxy toluene (BHT), a common antioxidant used as a food additive. The prenylated flavonoids also inhibited Cu(2+)-mediated oxidation of human low density lipoprotein (LDL). Dose-response studies indicated that the prenylated flavonoids were effective inhibitors of lipoprotein oxidation with IC50 values <1 microM and had similar inhibitory potency compared to quercetin, but was not directly related to Cu binding. Unlike quercetin, they did not show any pro-oxidant activity at high doses in the Cu(2+)-mediated lipoprotein oxidation system. The medicinal action of Dorstenia mannii may be related to the high concentration of potent antioxidant prenylated flavonoids in this species.

Similarity in the distribution of F(2)-isoprostanes in the lipid subfractions of atherosclerotic plaque and in vitro oxidised low density lipoprotein

Oxidation of low density lipoprotein (LDL) in vivo is thought to play a critical role in the initiation of atherosclerosis. F(2)-isoprostanes are compounds resulting from non-enzymatic oxidation of arachidonic acid and elevated levels are present in human atherosclerotic plaque. However, little is known about the formation of F(2)-isoprostanes in plaque lesions or their distribution in lipid subclasses. Given that LDL and tissue lipid subfractions (such as phospholipids, cholesterol esters and triglycerides) all contain significant levels of arachidonic acid, the aim of this study was to examine the relative distribution of F(2)-isoprostanes in the different lipid fractions of LDL oxidised in vitro, and compare this to the distribution in atherosclerotic plaque. The results reveal that while the majority of F(2)-isoprostanes are present in the phospholipid or surface lipid fractions, the core lipids (cholesterol esters/triglycerides) contribute at least 10% of the total F(2)-isoprostanes in both LDL oxidised in vitro and human atherosclerotic plaque. The remarkably similar profiles between the oxidised LDL and advanced atherosclerotic plaque suggests oxidation in vivo, is predominantly via non-enzymatic processes directed towards the surface lipids.

Significance of small dense low-density lipoproteins and other risk factors in patients with various types of coronary heart disease

BACKGROUND

It remains unclear how closely the small dense low-density lipoprotein (LDL) (diameter < or =25.5 nm) is associated with various types of coronary heart disease (CHD) in Japanese patients, an ethnic group with lower serum cholesterol levels and less massive obesity compared with Western populations.

METHODS AND RESULTS

We measured mean LDL particle diameter by gradient gel electrophoresis in 571 patients with CHD and in 263 healthy subjects who served as control patients. Patients with CHD were classified into acute coronary syndrome (ACS), stable CHD and vasospastic angina. High-density lipoprotein cholesterol and apolipoprotein-A1 and -B were significantly different between patients with CHD and controls. LDL size in patients with CHD was markedly smaller than that in controls in both men and women (25.5 +/- 0.7 vs 25.9 +/- 0.4 and 25.7 +/- 0.7 vs 26.0 +/- 0.5 nm, respectively). LDL cholesterol was significantly higher in patients with ACS than in other groups. Plasma levels of high-density lipoprotein cholesterol decreased as the number of diseased vessels or angiographic coronary severity evaluated by Gensini score increased, but the LDL size was comparable irrespective of the type of CHD and the extent and severity of the lesions. Multiple logistic regression analysis revealed that small dense LDL was independently associated with the incidence of CHD in both sexes (odds ratio [OR] 3.5, 95% CI 2.1-5.7, and OR 2.9, 95% CI 1.5-5.6, P <.005).

CONCLUSION

Our study suggests that the small dense LDL is strongly associated with various types of CHD, independent of traditional and nontraditional coronary risk factors, but is not related to the severity and extent of the coronary lesions.

Enhanced Susceptibility to Oxidation and Diminished Vitamin E Content of LDL from Patients with Stable Coronary Artery Disease

Background: Convincing evidence points to oxidative modification of LDL as an important trigger in a complex chain of events leading to atherosclerosis. We investigated the occurrence of enhanced susceptibility of LDL to oxidation and decreased vitamin E concentration in LDL as additional risk factors promoting atherosclerosis among patients with established coronary artery disease (CAD).

Methods: We examined 132 patients with angiographically confirmed CAD and compared them with 111 healthy control individuals. We measured conjugated diene production to assess susceptibility of LDL to copper-mediated oxidation. Vitamin E content of LDL was measured by HPLC.

Results: The mean lag time of LDL oxidation and LDL α-tocopherol/LDL-cholesterol ratio were lower in the patients with CAD (55 ± 14 min and 2.4 ± 1.0 mmol/mmol) than in the controls (63 ± 13 min and 2.9 ± 1.1 mmol/mmol; P &lt;0.0001 and &lt;0.001, respectively). Multiple stepwise regression analysis demonstrated the lag time (odds ratio, 1.96; 95% confidence interval, 1.34–2.87; P &lt;0.0001) and concentration of vitamin E in LDL (odds ratio, 1.65; 95% confidence interval, 1.16–2.33; P &lt;0.005) as independent determinants of CAD. Significant inverse Spearman rank correlations were found between lag time (r = −0.285; P &lt;0.001) or concentration of vitamin E in LDL (r = −0.197; P &lt;0.002) and severity of CAD. Lag times were not significantly correlated with serum C-reactive protein or ferritin.

Conclusions: Our data suggest that a short LDL oxidation lag time and a low concentration of vitamin E in LDL might be independent coronary risk factors for stable CAD in Iranian people.

Red wine polyphenols, in the absence of alcohol, reduce lipid peroxidative stress in smoking subjects

Phenolic compounds in red wine can exert antioxidant effects on in vitro lipoprotein oxidation. This has led to speculation that red wine consumption mediates unique anti-atherosclerotic effects compared to other alcoholic beverages. However, studies assessing the effects of red wine consumption on lipoprotein oxidation ex vivo have not been conclusive. The recent identification of the F2-isoprostanes as oxidative products of arachidonic acid has provided a reliable measure of in vivo lipid peroxidation. This randomized trial investigated changes in plasma and urinary F2-isoprostane concentrations following red wine, white wine, or dealcoholized red wine consumption in humans. Eighteen male smokers consumed, in random order, red wine, white wine, or dealcoholized red wine, for two weeks with one week washout between beverages. Plasma and urinary F2-isoprostane concentrations were measured before and after each beverage. Serum gamma-glutamyl transpeptidase (gamma-GT) and urinary 4-O -methylgallic acid were measured as markers of alcohol consumption and phenolic acid absorption, respectively. Plasma F2-isoprostanes (p < .05) decreased significantly with dealcoholized red wine but not with the alcohol-containing beverages. Urinary excretion of F2-isoprostanes showed a similar trend. gamma-GT decreased significantly with dealcoholized red wine and increased with both alcohol-containing beverages (p < .01). Urinary excretion of 4-O-methylgallic acid increased significantly (p < .001) in the 24 h urine samples following red wine or dealcoholized red wine ingestion, but not with white wine. Serum urate increased and beta-carotene decreased with both alcoholic beverages relative to dealcoholized red wine. There was no change in the antioxidants alpha- and gamma-tocopherol or vitamin C with any of the beverages. The results suggest that polyphenols in dealcoholized red wine can reduce in vivo lipid peroxidation as measured by F2-isoprostanes in smoking subjects. However, no reduction in lipid peroxidation was observed following red or white wine consumption, suggesting that any protective effects of wine drinking on cardiovascular disease are unlikely to be related to inhibition of lipid oxidation.

Inhibition of lipoprotein oxidation by prenylated xanthones derived from mangostin

Oxidative damage is thought to play a critical role in cardiovascular and other chronic diseases. This has led to considerable interest in the antioxidant activity of dietary compounds. Flavonoids have received the most attention and much is known about the structural requirements for antioxidant activity. However, little is known about the antioxidant activity of other plant derived phenolic compounds such as the xanthones. We have previously shown that the prenylated xanthone, mangostin, can inhibit the oxidation of low density lipoprotein. In order to examine the effects of structure modification on antioxidant activity of this class of compound we have prepared a number of derivatives of mangostin and tested antioxidant activity in an isolated LDL and plasma assay. The results of this study show that structural modification of mangostin can have a profound effect on antioxidant activity. Derivatisation of the C-3 and C-6 hydroxyl groups with either methyl, acetate, propane diol or nitrile substantially reduces antioxidant activity. In contrast, derivatisation of C-3 and C-6 with aminoethyl derivatives enhanced antioxidant activity, which may be related to changes in solubility. Cyclisation of the prenyl chains had little influence on antioxidant activity.

Vitamin E and Coronary Heart Disease in Tunisians

Background: Vitamin E (VE) is thought to be effective in preventing atherosclerosis. However, to date no consistent relationship has been identified between VE and coronary heart disease (CHD). This study was designed to assess the degree of association between VE and CHD in a sample of the Tunisian population.

Methods: Sixty-two angiographically confirmed coronary atherosclerotic patients and 65 age- and sex-matched controls were included. VE was measured in plasma and in the LDL fraction by HPLC. Cholesterol, triglycerides, and phospholipids were measured by enzymatic methods.

Results: A trend toward a meaningful decrease of plasma VE was observed in affected patients compared with controls (P = 0.06). VE concentrations standardized for cholesterol and lipid concentrations were significantly lower (P &lt;0.02) in coronary patients than in controls (4.35 ± 1.03 vs 4.82 ± 1.23 mmol/mol for cholesterol-adjusted VE and 2.35 ± 0.56 vs 2.66 ± 0.65 mmol/mol for lipid-adjusted VE, respectively). In the LDL fraction, only cholesterol-standardized VE was significantly lower in cases than controls (3.84 ± 1.13 vs 4.41 ± 1.16 mmol/mol). This association between VE and CHD remained unchanged independent of age, sex, smoking habit, hypertension, and diabetes. In CHD patients, lower lipid-adjusted VE was associated with enhanced LDL susceptibility to oxidation but without alteration of the serum fatty acid profile.

Conclusions: These results support the hypothesis that VE plays a role in preventing atherosclerosis.

Oxidation of LDL and extent of peripheral atherosclerosis

Evidence has accumulated for oxidative modification of low-density lipoproteins (LDL) to play an important role in the atherogenic process. Therefore, we investigated the relation between susceptibility of LDL to oxidation and risk of peripheral atherosclerosis among 249 men between 45 and 80 years of age. The ankle-arm index was calculated for both legs as the ratio of systolic blood pressure in the leg divided by the arm systolic blood pressure. The lowest of both ankle-arm indices was used to categorize subjects. Thirty-nine men with an ankle-arm index < 1.00 (20% cut-off point of distribution) were classified as subjects with peripheral atherosclerosis. Subjects with peripheral atherosclerosis reported more often the use of a special diet and the use of antihypertensive medication, aspirin and coumarin derivatives. No significant differences in total, LDL and HDL cholesterol and triglycerides were present between groups. Resistance time and maximum rate of oxidation were measured ex vivo using copper-induced LDL oxidation. Subjects with peripheral atherosclerosis had a significantly lower resistance time, whereas the maximum rate of oxidation tended to be increased in subjects with peripheral atherosclerosis. Odds ratios (ORs, and 95% confidence interval) for the successive tertiles of resistance time were 1.00 (reference), 0.37 (0.15-0.89) and 0.37 (0.16-0.86) (p(trend) < 0.01). ORs for the successive tertiles of maximum rate of oxidation were 1.00 (reference), 1.34 (0.47-3.82) and 1.50 (0.55-4.15). This inverse association was borderline significant (p(trend) = 0.07). These results support an association between LDL oxidation and the development of peripheral atherosclerosis.

Re-evaluation of the ferrous oxidation in xylenol orange assay for the measurement of plasma lipid hydroperoxides

The ferrous oxidation in xylenol orange version 2 (FOX2) assay coupled with triphenylphosphine has recently been employed for the measurement of total plasma hydroperoxides (ROOHs). In this study, we have evaluated sample handling and the effect of storage conditions on ROOH levels in human plasma (n = 32). Mean level of ROOHs in fresh plasma was 8.35 +/- 3.09 mumol/l (range 4.03-19.5 mumol/l). Addition of butylated hydroxytoluene (BHT) immediately after sample collection had no effect on the concentration of ROOHs. Storage of samples at -70 degrees C for 6 weeks was associated with a variable degree of loss of detectable ROOHs. A mean ROOH level of 6.00 +/- 2.23 mumol/l (range 2.88-13.5 mumol/l) was recorded after 6 weeks of storage at -70 degrees C. There was no difference in the mean level of ROOHs between samples stored for 6 and 60 weeks at -70 degrees C. Inclusion of BHT had no effect on the stability of plasma ROOHs during prolonged storage. Intra-assay coefficients of variation were < 12%, with the lowest variation in fresh samples (7.6%). In conclusion, these results suggest that the FOX2 assay should be a useful tool for measurement of ROOHs in fresh plasma samples but not in stored samples.

LDL oxidation: therapeutic perspectives

The peroxidation step of lipid transormation is considered to be essential in the pathogenesis of atherosclerosis. Although data concerning the mechanisms by which lipid peroxidation occurs in vivo are scarce, several lines of evidence suggest that some endogenous and exogenous compounds with antioxidant activity could have some beneficial effects in the prevention of atherosclerosis. Ascorbic acid (vitamin C) and alpha-tocopherol (vitamin E) act as the most important hydrophilic and lipophilic antioxidants, respectively in vivo. Accordingly, animal and human studies suggest that these compounds may have some preventive effect against the development of clinical coronary heart disease. Many plant phenols and flavonoids may be important dietary antioxidants and it has been speculated that these compounds in red wine or in the Mediterranean diet could explain the 'French paradox'. Several studies show that antioxidants such as probucol and butylated hydroxytoluene can inhibit development of atherosclerotic lesions in Watanabe and cholesterol-fed rabbits. Some drugs such as beta-blockers, calcium antagonists, hypolipodemic drugs,...appear to have at least in vitro antioxidant effects but the clinical relevance of these properties remains unkonwn. Moreover, some interventions aimed to decrease the LDL-oxidative susceptibility have not been shown to attenuate atherogenesis when cholesterol levels remain markedly elevated.

LDL oxidation and extent of coronary atherosclerosis

Accumulated evidence indicates that oxidative modification of LDL plays an important role in the atherogenic process. Therefore, we investigated the relation between coronary atherosclerosis and susceptibility of LDL to oxidation in a case-control study in men between 45 and 80 years of age. Case subjects and hospital control subjects were selected from subjects undergoing a first coronary angiography. Subjects with severe coronary stenosis (> or = 85% stenosis in one and > or = 50% stenosis in a second major coronary vessel) were classified as case subjects (n=91). Hospital control subjects with no or minor stenosis (< or = 50% stenosis in no more than two of the three major coronary vessels, n=94) and population control subjects free of plaques in the carotid artery (n=85) were pooled for the statistical analysis into one control category. Enrollment procedures allowed for similar distributions in age and smoking habits. Case subjects had higher levels of total and LDL cholesterol and triglycerides and lower levels of HDL cholesterol. Resistance time, maximum rate of oxidation, and maximum diene production were measured ex vivo using copper-induced LDL oxidation. A borderline significant inverse trend was observed for coronary atherosclerosis risk at increasing resistance time. Odds ratios (95% confidence interval) for the successive quartiles were 1.0 (reference), 0.77 (0.39 to 1.53), 0.67 (0.33 to 1.34), and 0.55 (0.27 to 1.15) (ptrend=0.07). No relation with maximum rate of oxidation was found, and higher maximum diene levels were found in control subjects (P<.01). The main determinant of oxidation was the fatty acid composition of LDL. No effect of smoking or use of medication was observed. We conclude that although LDL resistance to oxidation may be a factor in atherogenesis, the ex vivo measure is not a strong predictor of severity of coronary atherosclerosis.

Clinical predictors of oxidized low-density lipoprotein in patients with coronary artery disease

Oxidized low-density lipoprotein (LDL) may play a key role in the initiation and progression of atherosclerosis. Risk factors for elevated levels of oxidized LDL are not well established and may be important in identifying individuals who may benefit from antioxidant supplementation or interventions to reduce oxidant stress. The purpose of this study was to determine if clinical parameters predict levels of oxidized LDL. We evaluated the relation between clinical parameters and oxidized LDL in 45 nonsmoking, nondiabetic patients (39 men and 6 women) with coronary artery disease. Oxidized LDL was assessed by measurement of conjugated dienes, lipid peroxides, and thiobarbituric reactive substances (TBARS) at 0 hours to evaluate baseline oxidant stress and postincubation with an oxidizing agent to assess the capacity of LDL for peroxidation. Results were lipid standardized and were not materially altered by multivariate adjustment. Significant predictors of increased oxidized LDL included female sex, family history of premature cardiovascular disease, increased percent body fat, increased body mass index, increased heart rate at rest, history of smoking, exercise <4 times per week, and no regular wine consumption. These data suggest that clinical parameters correlate with levels of oxidized LDL and may be useful in identifying patients at risk for increased oxidant stress.

Scavenging of hypochlorous acid by carvedilol and ebselen in vitro

1. The antihypertensive drug carvedilol and the antiinflammatory selenoorganic compound ebselen were tested for their ability to react with the reactive oxygen species hypochlorous acid (HOCl) in vitro. 2. Carvedilol scavenges HOCl at a rate sufficient to protect a model molecule catalase against inactivation by HOCl. 3. Ebselen was resistant to HOCl when its glutathione-peroxidase mimetic property was compared with that of glutathione peroxidase.

Beta-blockers inhibit the modification of low-density lipoproteins by sodium hypochlorite in vitro

The effect of beta-blockers (alprenolol, oxprenolol, atenolol, acebutolol) and the non-steroidal anti-inflammatory drug, diclofenac, on modification of low-density lipoproteins (LDL) by sodium hypochlorite (NaOCl) was investigated in vitro. Beta-blockers and diclofenac inhibit the formation of thiobarbituric acid reactive substances in LDL modified by NaOCl. Beta-blockers, but not diclofenac, inhibit the hypochlorite-induced aggregation of LDL which was determined by photon correlation spectroscopy. The intracellular accumulation of cholesterol esters in J774 macrophages is inhibited by addition of beta-blockers, but not diclofenac, to LDL prior to the addition of NaOCl. The modification inhibiting effect of beta-blockers is inversely correlated to the binding capabilities of these substances to LDL which were assessed by laser electrophoresis. Inhibition of LDL modification in vivo by beta-blockers may reduce the risk of atherosclerosis and, therefore, compensate for the cholesterol-raising effect of these drugs in human plasma.

Lipid peroxidation-associated oxidative stress during percutaneous transluminal coronary angioplasty in humans

Animal studies suggest that myocardial ischemia/reperfusion causes oxidative stress. We, therefore, examined whether routinely performed percutaneous transluminal coronary angioplasty (PTCA) might be a human ischemia/reperfusion model for oxidative stress-induced lipid peroxidation. Fasting antecubital venous blood was sampled from 13 patients on the morning of PTCA, and 2 d after PTCA. Venous and coronary arterial blood were sampled just before and 10 min after the first balloon inflation. Samples were analyzed for plasma and LDL lipid hydroperoxide levels, in vitro oxidation of LDL, and LDL antioxidant levels. Lipid hydroperoxide levels in plasma and LDL remained unchanged throughout the study. During the first 10 min of PTCA, the lag time during oxidation of LDL in vitro did not change, but the maximum rate of oxidation decreased in venous and arterial samples (Wilcoxon signed rank test: p < .002). At the same time, total tocopherol levels in LDL significantly increased by 6.3% (p = .048) in arterial, but not in venous samples. Total carotenoid levels increased by 3.8% (p = .127) in arterial samples and decreased by 2.9% (p = .040) in venous samples. Forty hours after PTCA, LDL oxidation parameters and LDL antioxidant levels were similar to baseline, except for about 17% lower levels of delta-tocopherol (p = .037) and gamma-tocopherol (p = .014). Our results, therefore, do not support that PTCA in humans is associated with oxidative stress-induced lipid peroxidation.

The role of copper reduction by alpha-tocopherol in low-density lipoprotein oxidation

The oxidation of lipoproteins is thought to be an important early step in atherogenesis. The measurement of lipid peroxidation in low-density lipoprotein (LDL) challenged with Cu2+ has become a widespread test to determine the "susceptibility" of LDL to oxidation. The determination of lag time to oxidation is thought to be a measure of the total antioxidant capacity of the LDL. However, we and others have failed to observe any correlation between lag time and the LDL content of its major lipid antioxidant, alpha-tocopherol. In fact, several studies now suggest a pro-oxidant role for tocopherol under some conditions of LDL oxidation. In the present study we sought to determine if there was a relationship between Cu2+ reduction by LDL and kinetic parameters of LDL oxidation. LDL (0.3 mmol/l cholesterol, approximately 0.1 mg protein/ml) was incubated at 30 degrees C with 2 microM Cu2+ and the formation of conjugated dienes measured over a 4-h period. Using neocuproine, an indicator molecule that specifically complexes Cu+ but not Cu2+, the reduction of Cu2+ by LDL was monitored. The final Cu concentration in these assays was 100 microM and neocuproine 750 microM. Cu+ formation was measured by absorbance at 454 nm. A strong negative correlation was observed between copper reduction by LDL and lag time to oxidation (r = -0.66, p < .005, n = 16). Further experiments showed that (1) LDL was able to reduce Cu2+ to Cu+ in a time and concentration-dependent manner; (2) blocking of free -SH groups on LDL apoprotein B by preincubation with dithionitrobenzoic acid (DTNB) had no significant effect on the rate and extent of Cu2+ reduction; (3) consumption of tocopherol in LDL undergoing oxidation with Cu was very rapid (rate = 6 x 10(-10) M s(-1)). When Cu+ formed during incubation with LDL was complexed with neocuproine, there was significant inhibition of LDL oxidation, as indicated by lipid peroxide formation and mobility on agarose gel electrophoresis. Surprisingly, tocopherol consumption was even more rapid in the presence of neocuproine, consistent with a shift in Cu2+/Cu+ equilibrium and faster reduction of Cu2+ by alpha-tocopherol. These results indicate that under these conditions tocopherol is a major reducing agent in LDL, converting Cu2+ to Cu+, and therefore, may play an important role in promoting LDL oxidation. However, there was no correlation between LDL tocopherol content and reduction of Cu2+. Examination of the time course of Cu2+ reduction in tocopherol enriched and depleted LDL indicates that tocopherol may determine Cu reduction at early time points but that the eventual capacity of LDL to reduce Cu may depend on more complex interactions between tocopherol and other LDL components.

Low-density lipoprotein composition and oxidability in atherosclerotic cardiovascular disease

OBJECTIVES

To characterize low-density lipoprotein (LDL) chemical composition and oxidability in normolipidemic and dyslipidemic patients with atherosclerotic cardiovascular disease, as compared with matched control subjects. To evaluate LDL susceptibility to oxidation, we determined the cutoff points of thiobarbituric reactive substances (TBARS) in LDL after oxidative stress, as well as its resistance to oxidation.

DESIGN AND METHODS

LDL (density 1.019-1.063 g/mL) of 24 men with atherosclerotic cardiovascular disease (12 normolipidemic and 12 dyslipidemic patients) and 18 age-matched healthy control men. LDL chemical composition was determined and apo B/cholesterol ratio was calculated. TBARS in native LDL and after 60 and 120 min of LDL oxidation with copper were measured. The conjugated diene production kinetics during LDL incubation with copper were also studied, lag time being an oxidation resistance marker. Cutoff points for the positivity criterion of apoB/cholesterol ratio in LDL and TBARS in native and oxidized LDL were evaluated using the receiver operator characteristic (ROC) graphic method.

RESULTS

LDL were triglyceride-enriched, the apoB/cholesterol ratio being higher in patients than in controls, without differences between normolipidemic and dyslipidemic subgroups. We have established the following cutoff values to differentiate between patients and controls: 0.43 mg/mg for the apo B/cholesterol ratio in LDL; 3.0 nmol malondialdehyde/mg protein for TBARS in native LDL; 22 and 80 nmol malondialdehyde/mg protein after 60- and 120-min postoxidative stress, respectively. We did not find differences in the conjugated diene production kinetics between patients and controls.

CONCLUSIONS

The enrichment in triglycerides and the high apoB/ cholesterol ratio suggest the presence of an abnormal LDL particle in normolipidemic and dyslipidemic patients. This LDL particle was more susceptible to oxidation. In the ROC analysis, the TBARS plot at 120 min exhibited greater accuracy and better performance than the other LDL oxidability markers.

Oxidative susceptibility of low-density lipoproteins--influence of regular alcohol use

In population studies, a low-to-moderate intake of alcohol has been consistently linked to a lower risk of coronary artery disease. The recent suggestion that alcoholic beverages may be conferring this decrease in risk because they contain antioxidant phenolic compounds that reduce the oxidizability of low-density lipoprotein (LDL) has to be reconciled with the possible counteracting influence of a pro-oxidant effect of alcohol. In a controlled crossover study, we have now measured the oxidizability of LDL in 27 regular beer drinkers during consecutive 4-week periods, wherein they consumed a high versus low alcohol beer (4.9 vs. 0.9% alcohol v/v, respectively), with the two beers being similar in phenolic content. This resulted in a decrease in alcohol consumption by approximately 80% (408 +/- 25 ml/week vs. 75 +/- 11 ml/week). During the low alcohol period, there was no change in LDL vitamin E or its cholesterol or protein content. Analysis of LDL oxidation kinetics revealed an increase in oxidizability during the high alcohol phase. This was despite a decrease in arachidonic acid content of LDL and a corresponding increase in palmitic acid during high alcohol intake--a change in fatty acid composition that has the potential to favor a decrease in oxidizability. Our results suggest that alcohol ingestion increases LDL oxidation, despite reducing the polyunsaturated fatty acid composition. The overall effect of alcoholic beverages on LDL oxidation may be a balance between the pro-oxidant and antioxidant activity of its various constituents. The predominant pro-oxidant effect demonstrated in these beer drinkers, although not relevant to any potential decrease in coronary artery disease, may be important in the pathogenesis of alcohol-related disease in other organ systems.

Vitamin E deficiency in variant angina

BACKGROUND

Oxidative modification of LDL has been suggested to increase coronary vasoreactivity to agonists. A deficiency of vitamin E, a major antioxidant, may be related to the occurrence of coronary artery spasm.

METHODS AND RESULTS

Vitamin E levels were determined with the use of high-performance liquid chromatography in normolipidemic subjects, including 29 patients with active variant angina (group 1), 13 patients with inactive stage of variant angina without anginal attacks during the past 6 months (group 2), 32 patients with a significant (>75%) organic coronary stenosis and stable effort angina (group 3), and 30 patients without coronary artery disease (group 4). Total lipid levels in blood were calculated as total cholesterol plus triglyceride levels. The plasma alpha-tocopherol levels as well as alpha-tocopherol/lipids were significantly lower in group 1 than in groups 2 through 4. Also, the plasma gamma-tocopherol levels were significantly lower in group 1 than in groups 2 through 4. The vitamin E levels were not significantly different between group 1 patients with and those without a significant organic stenosis. In group 1, both alpha- and gamma-tocopherol levels were significantly elevated after a > or = 6-month angina-free period. The alpha-tocopherol levels in the LDL fraction were significantly lower in group 1 than in group 4. Plasma alpha-tocopherol levels were significantly correlated with those in the LDL fractions. In 6 patients of group 1 still having anginal attacks while receiving calcium channel blockers, the addition of vitamin E acetate (300 mg/d) significantly elevated plasma alpha-tocopherol levels and inhibited the occurrence of angina.

CONCLUSIONS

Plasma vitamin E levels were significantly lower in patients with active variant angina than in subjects without coronary spasm, suggesting an association between vitamin E deficiency and coronary artery spasm.

Lipid peroxidation: a review of causes, consequences, measurement and dietary influences

In this review the process of lipid peroxidation and the atherogenicity of peroxidied lipids are discussed. Recent findings with regard to the effect of selected dietary factors on susceptibility of lipids to oxidative stress and on antioxidant defences are analysed with particular reference to their potential use in the prevention and treatment of atherogenesis and, by extension, coronary heart disease. Laboratory methods of assessing antioxidant defences, lipid peroxidation and the effects of lipid peroxidation are also reviewed and discussed with particular reference to their ability to assess in vivo oxidative stress and lipid peroxidation status. A range of oxidative stress indices are presented and their limitations discussed, but the main focus is on the most commonly used laboratory test for lipid peroxidation, the thiobarbituric acid reacting substances (TBARS) test. Finally, the influence of selected dietary factors on measured peroxidation status is discussed, with particular reference to the antioxidant vitamins C (ascorbic acid) and E (alpha tocopherol) and the type of fatty acids (mono- and poly-unsaturated) in the diet.

Protective effects of carvedilol, a vasodilating beta-adrenoceptor blocker, against in vivo low density lipoprotein oxidation in essential hypertension

Low density lipoprotein (LDL) oxidation plays a crucial role in the development and progression of atherosclerosis and is enhanced in patients with essential hypertension. This finding has stimulated a search for antihypertensive drugs with high intrinsic antioxidant properties. We investigated the antihypertensive and antioxidant effects of carvedilol, a new vasodilating beta-adrenoceptor blocking agent in a group of patients with mild to moderate essential hypertension after 4-month treatment. Carvedilol administration markedly increased the resistance to oxidation of LDL isolated from treated patients to values comparable to those of control, nonhypertensive subjects. This effect was achieved despite a significant loss in LDL-associated vitamin E. The increased resistance of LDL to oxidation promoted by carvedilol was not related to the normalization of previously increased blood pressure (BP). Indeed, the administration of other conventional antihypertensive drugs, capable of decreasing arterial BP but without high intrinsic antioxidant properties, to a control group of matched hypertensive patients failed to ameliorate LDL oxidation parameters. Carvedilol treatment also reduced the extent of in vivo LDL oxidation, as reflected by the decrease in antioxidized LDL autoantibody titer. This effect as well was detected only in the group of carvedilol-treated hypertensive patients and not after the simple reduction in BP obtained with antihypertensive drugs different from carvedilol.

Women have a larger and less atherogenic low density lipoprotein particle size than men

Some epidemiological studies have shown that serum total cholesterol increases with age. especially in women. On the other hand, the risk of coronary artery disease is smaller in women than in men. Earlier studies have shown that a small dense low density lipoprotein (LDL) is more atherogenic than a large LDL. We studied LDL size and apolipoprotein E (apo E) phenotypes in premenopausal and postmenopausal women and in men at the same age. In this study 342 subjects participating in a health screening study were examined. There were four subgroups: 40-year-old men (n = 85), 40-year-old women (n = 80), 70-year old men (n = 88) and 70-year-old women (n = 89). In the present study LDL size was larger (P < 0.01) in women (26.39 +/- 0.07 nm) than in men (25.95 +/- 0.07 nm). We found that LDL size correlated highly positively (r = 0.606; P < 0.001) with serum high density lipoprotein (HDL) concentration and inversely with serum triglyceride concentration (r = -0.627; P < 0.001). Measuring serum HDL cholesterol and triglycerides in health screening studies gives information indirectly about LDL size and its atherogenicity. Apo E phenotype was not significantly associated with serum triglycerides, but was associated with LDL size, LDL cholesterol, total cholesterol and HDL cholesterol. In our sample LDL size decreased and LDL cholesterol and total cholesterol increased according to the most prevalent apo E phenotypes in the order E2/3, E3/3, E3/4 and E4/4. Subjects with phenotype apo E4/4 had the smallest LDL size (25.70 +/- 0.19 nm), the highest total cholesterol (6.53 +/- 0.35 mmol/l) and the lowest HDL cholesterol values (1.28 +/- 0.04 mmol/l). We conclude that there was a significant interaction between sex and age in serum total cholesterol which was highest in older women. However, their LDL size was larger and their LDL is less atherogenic. Apo E phenotype had a significant influence on LDL size.

Characterization of drugs as antioxidant prophylactics

There is growing interest in the evaluation of drugs (prescription only medicines and over-the-counter medicines) as antioxidant prophylactics. Although free radical mechanism in human degenerative diseases is now generally recognised, the mechanisms of tissue injury in humans are very complex and it may not be possible to clearly identify the role played by free radicals in the process. This review examines the current evidence to support the notion that drugs for a particular therapeutic category might possess useful antioxidant capacity hence minimising tissue injury due to free radicals.

Absence of increased susceptibility of LDL to oxidation in type 1 diabetics

Insulin-dependent diabetics have a greatly increased risk of developing premature coronary artery disease which is not entirely explained by known risk factors. A possible explanation may be enhanced oxidative modification of low density lipoprotein (LDL). The aim of this study was to determine firstly, whether or not LDL from moderately well controlled type 1 diabetics is more readily oxidisable than LDL from healthy non-diabetics and, secondly, to assess whether potential predictors of LDL oxidisability differ between type 1 diabetics and controls. Twenty type 1 diabetic men were carefully matched with healthy non-diabetic men on the basis of age and body mass index and each pair attended the department on the same morning for blood sampling. LDL oxidisability was assessed using both copper in PBS, 15 and 30 mM glucose, and with AAPH. There was no difference between type 1 diabetics and controls in the susceptibility of the LDL to either copper-dependent or non-transition metal-dependent oxidation. Furthermore, there was no difference between the groups for LDL vitamin E content, LDL fatty acid composition in cholesteryl esters, triglycerides or phospholipids, or LDL copper reductive capacity, but LDL glycation was elevated in the IDDM subjects. Given the absence of increased LDL oxidisability in these subjects, the recommendation of vitamin E supplementation in type 1 diabetics should be considered a secondary priority to achieving adequate glucose control.

Susceptibility of plasma low density lipoprotein to cupric ion-induced peroxidation in patients with variant angina

OBJECTIVES

The purpose of this study was to investigate the peroxidative susceptibility of plasma low density lipoprotein in patients with active variant angina and to compare it with that in subjects without coronary spasm.

BACKGROUND

Oxidized or modified low density lipoprotein can impair endothelium-dependent vasoregulation and has atherogenic properties; it may be related to the genesis of coronary artery spasm by potentiating agonist-induced vasoconstriction.

METHODS

The sensitivity of plasma low density lipoprotein for cupric ion (Cu2+)-induced peroxidation was examined. Low density lipoprotein was isolated from plasma in 112 patients: 21 with active variant angina, 18 with inactive variant angina without anginal attacks during the preceding 6 months, 39 with significant organic coronary artery stenoses but without rest angina and 34 control subjects without coronary artery disease. Lipid peroxidation products in low density lipoprotein were assayed as thiobarbituric acid-reactive substances before and after incubation with various concentrations of Cu2+ at 37 degrees C for 24 h.

RESULTS

Significantly higher levels of generation of thiobarbituric acid-reactive substances from plasma low density lipoprotein after incubation with Cu2+ were seen in patients with active variant angina than in patients in the other three groups. The dose-response curve of low density lipoprotein peroxidation induced by Cu2+ shifted to the left in this group as compared with the curve in the other three groups. The vitamin E (alphatocopherol) content of low density lipoprotein fraction in these patients was significantly lower than that in the other groups. After > or = 6 months of an angina-free period in five patients with active variant angina, thiobarbituric acid-reactive substances induced by 0.5 mumol/liter Cu2+ in low density lipoprotein were significantly decreased and vitamin E content was significantly increased.

CONCLUSIONS

These results indicate that vitamin E-deficient plasma low density lipoprotein in patients with active variant angina is highly susceptible to peroxidative modification.

Mangostin inhibits the oxidative modification of human low density lipoprotein

The oxidation of low density lipoprotein (LDL) may play an important role in atherosclerosis. We investigated the possible antioxidant effects of mangostin, isolated from Garcinia mangostana, on metal ion dependent (Cu2+) and independent (aqueous peroxyl radicals) oxidation of human LDL. Mangostin prolonged the lagtime to both metal ion dependent and independent oxidation of LDL in a dose dependent manner over 5 to 50 microM as monitored by the formation of conjugated dienes at 234 nm (P < 0.001). There was no significant effect of mangostin on the rate at which conjugated dienes were formed in the uninhibited phase of oxidation. Levels of thiobarbituric reactive substances (TBARS) generated in LDL were measured 4 and 24 hours after oxidation with 5 microM Cu2+ in the presence or absence of 50 microM or 100 microM mangostin. We observed an inhibition of TBARS formation with 100 microM mangostin at 4 hours (P = 0.027) but not at 24 hours (P = 0.163). Similar results were observed in the presence of 50 microM mangostin. Mangostin, at 100 microM, retarded the relative electrophoretic mobility of LDL at both 4 and 24 hours after Cu2+ induced oxidation. Mangostin (100 microM) significantly inhibited the consumption of alpha-tocopherol in the LDL during Cu2+ initiated oxidation over a 75 minute period (P < 0.001). From these results, we conclude that mangostin is acting as a free radical scavenger to protect the LDL from oxidative damage in this in vitro system.

Oxidation of low density lipoproteins from patients with renal failure or renal transplants

Peroxidation of low density lipoproteins (LDL) may be involved in the development of atherosclerosis which is prevalent in patients with chronic renal failure and renal transplant recipients. We determined the copper ion catalyzed oxidation in vitro, vitamin E content, and chemical and fatty acid composition of LDL isolated from 38 patients with renal disease and 15 healthy subjects. Also the acute effect of hemodialysis treatment on LDL oxidation variables was tested. The lag time in conjugated diene formation during oxidation was significantly (P = 0.011) shorter in LDL from renal transplant recipients (66 min, N = 18) mainly due to significantly (P < 0.05) shorter times in women (47 min, N = 7), compared with healthy subjects (83 min, N = 15), patients on hemodialysis (91 min, N = 13) and patients treated by continuous ambulatory peritoneal dialysis (CAPD) (82 min, N = 7). The maximum rate and the extent of LDL oxidation were significantly (P < 0.01) lower in all patients with renal disease compared with healthy subjects. The triglyceride content of LDL was significantly (P < 0.001) higher in women with kidney grafts (7.3%) compared with levels in the corresponding men (5.3%) and healthy women (5.0%), and was correlated significantly with the lag time in LDL oxidation in renal transplant recipients (Spearmans r = -0.502, P = 0.034). The percentage oleic acid in LDL was significantly higher (P = 0.002) and the percentage linoleic acid was significantly lower (P = 0.046) in patients with renal disease, and may largely account for their lower rates and extent of LDL oxidation. Levels of the LDL oxidation variables and organic lipid peroxide content of LDL were not significantly different before and after hemodialysis and 24 hours later. These results suggest that LDL from women with renal transplants may be abnormally susceptible to oxidation possibly due to increased triglyceride content.

Effect of low-dose simvastatin on cholesterol levels, oxidative susceptibility, and antioxidant levels of low-density lipoproteins in patients with hypercholesterolemia: a pilot study

In this pilot study, 12 patients (6 men, 6 postmenopausal women) with hypercholesterolemia were treated with low-dose (5 mg/d) simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, for 4 weeks. Low-density lipoprotein (LDL) samples were isolated at the beginning (week 0) and at the end (week 4) of the treatment regimen. Simvastatin caused significant decreases of total cholesterol (-18.1%), LDL cholesterol (-27.6%), and apolipoprotein B (-21.8%), and significantly reduced total cholesterol, free cholesterol, cholesterol esters, phospholipids, and protein in LDL without significantly changing the component ratios and fatty acid levels of LDL. However, simvastatin therapy had no major effects on either antioxidant levels in LDL or the oxidative susceptibility of LDL. We conclude that low-dose simvastatin significantly reduces LDL cholesterol levels without increasing the oxidative susceptibility of LDL or decreasing the antioxidant levels of LDL, and thus may reduce the risk of coronary artery disease.

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 beta-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.

LDL oxidation in patients with severe carotid atherosclerosis. A study of in vitro and in vivo oxidation markers

Among the various risk factors involved in the development and progression of carotid atherosclerosis, the oxidation of LDL has been proposed to play a relevant role. LDL oxidation has been investigated in 94 patients with severe carotid atherosclerosis undergoing elective carotid artery endarterectomy and in 42 matched control subjects. LDL oxidation was evaluated in all patients as (1) the susceptibility to in vitro oxidation, (2) vitamin E concentration and its efficiency in LDL, and (3) the presence of autoantibodies against oxidatively modified lipoprotein to monitor the occurrence of the oxidative processes taking place in vivo. No difference was detected between control subjects and patients concerning vitamin E concentration and the kinetics of conjugated diene formation in isolated LDL exposed to CuSO4. However, vitamin E efficiency was lower (9.6 +/- 4.2 versus 30.2 +/- 7.6 min/nmol vitamin E) and the duration of the vitamin E-independent lag phase was longer (105.5 +/- 16.5 versus 58 +/- 11.8 minutes) in the patient group. Autoantibodies against oxidatively modified lipoproteins were measured with an ELISA method using native LDL, Cu(2+)-oxidized LDL (oxLDL), or malondialdehyde-derivatized LDL (MDA-LDL) as antigens. To monitor cross-reactivity of the antibodies detected with other oxidatively modified proteins, human serum albumin (HSA) and MDA-derivatized HSA (MDA-HSA) were also employed. The antibody titer was calculated as the ratio of antibodies against modified versus native proteins.(ABSTRACT TRUNCATED AT 250 WORDS)