Oxidative susceptibility of unfractionated serum or plasma: response to antioxidants in vitro and to antioxidant supplementation

BACKGROUND: The susceptibility of plasma lipids to oxidation is thought to be a factor contributing to atherogenic risk. Various groups have studied the in vitro oxidizability of isolated LDL and examined the effects of conventional antioxidants. The drawbacks associated with the isolation of LDL for evaluation of in vitro oxidizability, however, have limited the application of this measurement in large-scale studies. METHODS: We developed and evaluated an assay that can be used to directly assess the oxidative susceptibility of unfractionated serum or plasma lipids, obviating the need for isolation of lipoprotein fractions. Oxidative conditions were initiated in vitro with cuprous chloride and 2,2'-azobis(2-amidinopropane) hydrochloride. The effects of antioxidants added in vitro, and as an oral supplement, were monitored by conjugated diene formation. RESULTS: The addition of ascorbic acid (0-50 micromol/L) in vitro elicited a dose-dependent protective effect, increasing the lag time to oxidation (P < 0.001). In contrast, alpha-tocopherol demonstrated prooxidant behavior at increasing concentrations (0-50 micromol/L), although we observed a decrease in the maximum rate of oxidation. Our findings are supported by the results from plasma samples of participants in a randomized antioxidant (vitamins C and E) intervention study after acute ischemic stroke. The group receiving vitamins C and E for 14 days showed an increased lag time to plasma lipid oxidation in vitro compared with the nonsupplemented group (P < 0.05). CONCLUSION: The susceptibility of unfractionated plasma or serum lipids to oxidation in vitro offers an alternative to LDL for evaluating the efficacy of antioxidant regimens.     

糖尿病患者血清低密度脂蛋白亚组分的分布及氧化易感性

为探讨糖尿病（ＤＭ）患者血浆低密度脂蛋白（ＬＤＬ）亚组分的异常特性。本文采用密度工超速离心直接分离ＬＤＬ亚组分,并对其分布及体外铜离子介导的氧化易感性进行分析。结果表示单纯ＤＭ患者、ＤＭ合并症患者及对照组间ＬＤＬ亚组分分布无差别;ＤＭ患者ＬＤＬ各组分氧化延滞时间显著缩短,尤以ＤＭ合并症患者明显,示其易于氧化,血浆脂质巡氧化程度亦增高。认为ＤＭ患者动脉粥样硬化的高发生率同其ＬＤＬ易于氧化的我相关联。     

Vitamin E supplementation in hyperlipidaemic patients: effect of increasing doses on in vitro and in vivo low-density lipoprotein oxidation

BACKGROUND: Vitamin E supplementation is associated with a reduced risk of developing atherosclerotic events; probably because it inhibits low-density lipoprotein (LDL) oxidation, an initial step in atherosclerosis. Metal ion-dependent LDL oxidation is a commonly used method to estimate oxidizability of LDL, but the effect of antioxidant supplementation on the levels of autoantibodies to oxidised LDL (ox-LDL), an in vivo indicator of LDL oxidation, is unknown. DESIGN: This double-blind, placebo-controlled study investigated the susceptibility of LDL to copper induced oxidation and malondialdehyde (MDA) derivatized-LDL (MDA-LDL) in hyperlipidaemic patients on supplements of vitamin E. The vitamin E group (n = 20) took vitamin E 100 IU daily and the dose was doubled at six-weekly intervals to 1600 IU daily. The control group (n = 17) received placebo in the same fashion. Blood samples were obtained at baseline and each subsequent visit to measure vitamin E status and oxidation of LDL. RESULTS: A significant increase in both alpha-tocopherol levels and the lengths of lag phase was seen in the vitamin E group after first week of supplementation (100 IU day-1). This continued to rise in a dose-dependent fashion with a doubling of the lag phase on 1600 IU daily. However, the titre of antibodies to MDA-LDL was not altered. CONCLUSIONS: The results suggest that although regarded as an in vivo marker of LDL oxidation, antibodies to MDA-LDL may not be a suitable measure to evaluate the effect of short-term antioxidant supplementation. The failure of autoantibody titres to fall despite reduced oxidizability of LDL may possibly be attributable to a long half-life of the antibody or, once initiated, a continuous immunological response to ox-LDL contained in atherosclerotic lesions of the arterial wall.     

Susceptibility of LDL to oxidation in vitro and antioxidant capacity in familial combined hyperlipidemia: comparison of patients with different lipid phenotypes

BACKGROUND: There is increasing evidence that oxidation of low-density lipoprotein (LDL) plays an important role in atherogenesis. AIM: To explore the LDL oxidizability and its determinants in familial combined hyperlipidemia (FCHL) patients with different phenotypes. METHOD: The study included 59 FCHL family members with different lipid phenotypes, 39 non-affected relatives, and 30 spouses as healthy controls. RESULTS: The lag time for LDL oxidation was significantly shorter in FCHL patients with different lipid phenotypes as compared to healthy controls. There were no significant differences in the propagation rate and conjugated diene formation and alpha-tocopherol content in LDL between the FCHL groups and healthy controls. Plasma concentrations of alpha-tocopherol in all FCHL patients and uric acid in FCHL patients with IIB and IV phenotypes were significantly higher than in healthy controls. Plasma total peroxyl radical trapping capacity measured (TRAPmea) and TRAPcalc tended to be higher in affected FCHL groups, but the difference was significant only for IIB phenotype. The peak LDL particle size in the combined group of FCHL patients was significantly smaller than in healthy controls. The lag time for LDL oxidation correlated significantly with LDL size both in the group of FCHL family members (r = 0.477, P<0.001) and in the healthy controls (r = 0.482, P<0.01). CONCLUSIONS: LDL from FCHL patients irrespectively of lipid phenotypes is more susceptible to oxidation in vitro than LDL from healthy controls. This increased susceptibility of LDL to oxidation in vitro seems to be attributed to the abundance of small dense LDL particles and not to the defect of antioxidant capacity in FCHL     

Effects of atorvastatin and simvastatin on low-density lipoprotein subfraction profile, low-density lipoprotein oxidizability, and antibodies to oxidized low-density lipoprotein in relation to carotid intima media thickness in familial hypercholesterolemia.

BACKGROUND: Little is known about the effects of statins on the quality of circulating low-density lipoprotein (LDL) in relation to atherosclerosis progression. METHODS: In a double-blind, randomized trial of 325 patients with familial hypercholesterolemia (FH), we assessed the effects of high-dose atorvastatin (80 mg) and conventional-dose simvastatin (40 mg) on LDL subfraction profile (n = 289), LDL oxidizability (n = 121), and circulating autoantibodies to oxidized LDL (n = 220). Progression of atherosclerosis was measured by carotid intima media thickness (IMT) (n = 325). RESULTS: At baseline, the patients showed an intermediate LDL subfraction profile composed of three LDL subfractions (LDL1, LDL2, LDL3), with LDL2 as the predominant subfraction. A strong negative correlation was found between plasma triglycerides and the LDL subfraction profile (r = -.64, p = .000). Both plasma levels of triglycerides and small dense LDL3 correlated weakly with baseline IMT (r = .11, p = .04 and r = .15, p = .01, respectively; n = 289). No association was found between baseline IMT and oxidation parameters or circulating antibodies to oxidized LDL. Atorvastatin reduced triglycerides, LDL cholesterol, and all LDL subfractions to a greater extent than did simvastatin and led to regression of carotid IMT. However, LDL subfraction pattern and plasma levels of autoantibodies to oxidized LDL remained unchanged in both treatment groups, and LDL oxidizability increased minimally to a similar extent in both groups. Significant treatment differences were found for the rate of in vitro oxidation of LDL and the amount of dienes formed during in vitro oxidation of LDL, which both decreased more following atorvastatin than after simvastatin. CONCLUSION: Change of IMT after statin treatment was associated with baseline IMT (r = .41), LDL cholesterol (r = -.20), and the amount of dienes formed during in vitro oxidation of LOL (r = .28) but not with plasma levels of antibodies to oxidized LDL, in vitro LDL oxidizability, and LDL subfraction profile.     

连续多次单采血浆者低密度脂蛋白及相关复合物的氧化易感性分析

目的探讨连续多次单采血浆者氧化低密度脂蛋白(ox-LDL)、β2-糖蛋白I/氧化低密度脂蛋白(β2-GPI/ox-LDL)复合物的水平,并分析其体内低密度脂蛋白(LDL)的氧化易感性。方法分别检测60例连续多次单采血浆者和60例初次血浆单采者的ox-LDL、β2-GPI/ox-LDL复合物的水平,同时分析其LDL氧化易感性的变化。结果与初次血浆单采者相比,连续多次单采血浆者的血浆ox-LDL、β2-GPI/ox-LDL复合物水平的差异均无统计学意义,其LDL氧化延滞时间延长、氧化速率及总氧化值下降,但差异均无统计学意义。结论连续多次的血浆单采对体内ox-LDL、β2-GPI/ox-LDL复合物的水平以及LDL氧化易感性均无明显影响,不会增加其心血管疾病的风险。     

Differences in LDL oxidizability by glycemic status: the insulin resistance atherosclerosis study

OBJECTIVE: To investigate differences in LDL oxidizability by glycemic status within the Insulin Resistance Atherosclerosis Study cohort. RESEARCH DESIGN AND METHODS: LDL oxidizability (lag time and oxidation rate) after exposure to copper was compared among 352 subjects with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), newly diagnosed type 2 diabetes, and known type 2 diabetes. RESULTS: After adjustment for age, clinic, ethnicity, sex, and smoking status, LDL oxidation rates differed by glycemic status (P = 0.001), with a strong trend (P = 0.0001) for reduced LDL oxidation rate with increasing extent and duration of glucose intolerance (2,378 +/- 54, 2,208 +/- 65, 2,145 +/- 71, and 2,115 +/- 48 arbitrary units [mean +/- SE] for NGT, IGT, newly diagnosed type 2 diabetes, and known type 2 diabetes, respectively). Differences in LDL oxidation rate among groups were relatively unaltered by adjustment for lipids and lipoproteins, hypertension, BMI, and waist-to-hip ratio (WHR) and remained significant even after further adjustment for dietary antioxidants and fatty acids, as well as medications. LDL lag times differed marginally by glycemic status (P = 0.058), with similar values for NGT, IGT, and newly diagnosed type 2 diabetes (57-60 min) but higher values for known type 2 diabetes (65 +/- 2). These differences were eliminated by further adjustment for lipids and lipoproteins, hypertension, BMI, and WHR. CONCLUSIONS: We found that glycemic status influenced LDL oxidizability, with a paradoxical reduction in LDL oxidizability, as indicated by a lower LDL oxidation rate with increased extent and duration of glucose intolerance. This difference was only slightly attenuated by adjustment for relevant demographic, metabolic, dietary, and pharmacological factors that potentially influence LDL oxidation.     

Susceptibility of LDL to oxidation in vitro and antioxidant capacity in familial combined hyperlipidemia: comparison of patients with different lipid phenotypes

BACKGROUND. There is increasing evidence that oxidation of low-density lipoprotein (LDL) plays an important role in atherogenesis. AIM. To explore the LDL oxidizability and its determinants in familial combined hyperlipidemia (FCHL) patients with different phenotypes. METHOD. The study included 59 FCHL family members with different lipid phenotypes, 39 non-affected relatives, and 30 spouses as healthy controls. RESULTS. The lag time for LDL oxidation was significantly shorter in FCHL patients with different lipid phenotypes as compared to healthy controls. There were no significant differences in the propagation rate and conjugated diene formation and &#102 -tocopherol content in LDL between the FCHL groups and healthy controls. Plasma concentrations of &#102 -tocopherol in all FCHL patients and uric acid in FCHL patients with IIB and IV phenotypes were significantly higher than in healthy controls. Plasma total peroxyl radical trapping capacity measured (TRAP mea ) and TRAP calc tended to be higher in affected FCHL groups, but the difference was significant only for IIB phenotype. The peak LDL particle size in the combined group of FCHL patients was significantly smaller than in healthy controls. The lag time for LDL oxidation correlated significantly with LDL size both in the group of FCHL family members (r = 0.477, P < 0.001) and in the healthy controls (r = 0.482, P < 0.01). CONCLUSIONS. LDL from FCHL patients irrespectively of lipid phenotypes is more susceptible to oxidation in vitro than LDL from healthy controls. This increased susceptibility of LDL to oxidation in vitro seems to be attributed to the abundance of small dense LDL particles and not to the defect of antioxidant capacity in FCHL.     

Increased serum iron may contribute to enhanced oxidation of low-density lipoprotein in smokers in part through changes in lipoxygenase and catalase

BACKGROUND: Increased oxidative stress is considered to be causative for cardiovascular disease (CVD) in smokers, but its mechanisms are still unclear. We compared oxidative stress markers between male smokers and male nonsmokers. METHODS: Twenty-three healthy men (11 nonsmokers and 12 smokers) were enrolled, and blood samples after 12 h of fasting were collected to assess plasma lipids and oxidative stress markers. The effects of iron loading on 12-lipoxygenase (12-LO) expression and activity in human umbilical vein endothelial cells (HUVECs) were tested in vitro to investigate the relevance of iron to oxidation potential in vivo. RESULTS: Higher levels of plasma-oxidized low-density lipoprotein (LDL) and lipid peroxide (LPO), and higher oxidizability of LDL were observed in smokers than in nonsmokers. Higher levels of serum iron and lower levels of plasma vitamin E were observed in smokers than in nonsmokers. Stepwise multiple regression analysis showed that serum iron was an independent determinant for both plasma-oxidized LDL and lag time of LDL oxidation. Iron loading enhanced 12-LO expression threefold and its activity 1.5-fold. Moreover, iron loading decreased catalase expression by 50% and significantly reduced its activity by 75%. CONCLUSIONS: Enhanced oxidative stress in smokers may be due to increased iron levels. Iron-induced modulation of expression and activity of 12-LO and catalase may be relevant to increased iron-related oxidative stress as observed in smokers.     

Effect of atorvastatin on LDL oxidation and antioxidants in normocholesterolemic type 2 diabetic patients

BACKGROUND: Oxidative stress in diabetes increases lipid peroxidation, which stimulates the development of atherosclerosis. METHODS: We investigated in a 3-month placebo-controlled study with 19 normocholesterolemic type 2 diabetic patients whether treatment with 10-mg atorvastatin influenced antioxidants and reduced LDL oxidizability, assessed by in vitro production of conjugated dienes after copper-induced LDL oxidation. RESULTS: The lag phase, as a measure of the resistance of LDL to oxidation, did not change (62.8+/-8.2 respectively 59.6+/-9.7 min, p=n.s.), while conjugated dienes decreased (512+/-74 respectively 487+/-50 nmol, p=0.012). Plasma alpha-tocopherol and ubiquinol levels decreased, while their ratios to LDL cholesterol remained stable. CONCLUSIONS: Atorvastatin favourably influences some parameters of LDL oxidation. Whether this effect is clinically relevant remains to be determined.     

Plasma lipid oxidation and susceptibility of low-density lipoproteins to oxidation in male patients with stable coronary artery disease

Objectives: Oxidative modifications of low-density lipoproteins (LDL) are considered to be important in the pathogenesis of atherosclerosis. However, the data on the association between LDL oxidation and severity of clinical manifestations of coronary artery disease (CAD) are contradictory. Previous reports were concerned mostly with unstable angina patients. The present study was undertaken to evaluate plasma lipid oxidation status in patients with stable CAD.

Design and Methods: 37 male patients with angiographically confirmed CAD (asymptomatic or suffering from stable angina pectoris) and 32 control subjects were used in the study. Plasma levels of vitamin E and products of lipid peroxidation, as well as parameters of the test for oxidizability of LDL in vitro were measured.

Results: We did not find differences between 2 groups of individuals regarding the levels of products of lipid peroxidation, vitamin E levels, lag time, maximal rate of oxidation, and total amount of conjugated dienes in the test for oxidizability of LDL.

Conclusion: The results of our study challenge, but do not disprove, the oxidative hypothesis of atherosclerosis. Real atherosclerotic modifications of plasma LDL occur apparently in the vascular wall after trapping of LDL by the interstitial matrix. The rise in oxidative parameters in unstable angina reported in the literature may not be the cause of the disease but, rather, the consequence of the multiple brief episodes of ischemia-reperfusion.     

A comparison of the antiatherogenic effects of probucol and of a structural analogue of probucol in low density lipoprotein receptor-deficient rabbits.

The efficacies of probucol and a close structural analogue as antioxidants in the prevention of atherogenesis in LDL receptor-deficient rabbits were compared. The antioxidant potency of the analogue in vitro was equal to that of probucol. Its biological availability was much greater: almost comparable concentrations in total plasma were achieved by feeding 1% probucol (wt/wt) and 0.05% analogue (wt/wt). Total plasma concentrations were comparable, but the concentration of probucol within the LDL fraction was about twice that of the analogue. Probucol slowed lesion progression by almost 50%, confirming earlier reports; the analogue, however, showed no detectable inhibitory effect on atherogenesis. Resistance of LDL to oxidation was measured at the end of the study by incubating it with Cu2+ and measuring the rate of diene conjugation. Probucol prolonged diene conjugation lag time from the control value of 130 min to values > 1,000 min. The analogue approximately tripled the lag time (mean, 410 min) and yet failed to slow the atherogenic process. The results suggest that LDL resistance to oxidation must reach some threshold level before there is significant protection against atherogenesis. However, probucol has additional biological effects, possibly not shared by the analogue, that could contribute to its antiatherogenic potential.     

Decreased in vitro oxidizability of low-density lipoprotein in hypercholesterolaemic patients treated with 3-hydroxy-3-methyIgIutaryl-CoA reductase inhibitors

Abstract. We studied the effects of the 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitors simvastatin and pravastatin on the in vitro susceptibility of low-density lipoprotein (LDL) to oxidation. Twenty-three hypercholesterolaemic patients (mean serum cholesterol 9.7 mmol 1^-1) were treated with increasing doses of either simvastatin or pravastatin for 18 weeks. No significant differences in effect on lipid levels between the two drugs were found. Treatment resulted in lowering of total cholesterol and LDL-cholesterol by maximally 30% and 34%, respectively. Chemical composition analysis showed that LDL particles contained relatively more protein and less free cholesterol and cholesteryl-ester after treatment. The LDL cholesterol/protein ratio decreased from 1.24 ± 0.21 to 0.97 ± 0.23 ( n = 20). By continuous monitoring of in vitro oxidation it appeared that LDL was less susceptible to oxidation after drug treatment. Maximal rate of diene production was significantly decreased from 19.7 ± 3.1 to 18.5 ± 3.3 nmol min^-1 mg^-1 LDL; total diene production decreased significantly from 420.3 ± 67.6 to 380.5 ± 49.1 nmol mg-¹ LDL; the lag time was unchanged throughout the study. These studies show that HMG-CoA reductase inhibitors reduce the oxidizability of LDL by altering its composition.     

Effect of antioxidants on oxidative modification of LDL.

Human low density lipoprotein (LDL) with a molecular mass of 2.5 million contains on average 1300 molecules of polyunsaturated fatty acids (PUFAs) bound in the different lipid classes. The predominant antioxidant in LDL is alpha-tocopherol, with an average of 6 molecules in each LDL particle. The other substances with potential antioxidant activity are: gamma-tocopherol, beta-carotene, alpha-carotene, lycopene, cryptoxanthin, cantaxanthin, phytofluene and ubiquinol-10. Each is present in amounts of only 1/20th to 1/300th of that of alpha-tocopherol. If LDL is exposed to oxidative conditions (Cu++ ions, macrophages) a lag phase precedes the oxidation of PUFAs. During the lag phase the antioxidants disappear with alpha-tocopherol the first to go and beta-carotene the last. The lag phase, which can readily be determined, is an index of the oxidation resistance of LDL. If LDL is loaded with vitamin E in vitro its oxidation resistance increases linearly with its alpha-tocopherol content according to the equation, y = kx+a. The same relationship is applicable if the alpha-tocopherol content of LDL is increased by taking oral vitamin E. Daily doses of 150, 225, 800 and 1200 IU RRR-alpha-tocopherol increased the LDL alpha-tocopherol on average to 138%, 158%, 144% and 215% of the initial value, the oxidation resistance being increased to 118%, 156%, 135% and 175%, respectively. The efficiency of vitamin E-dependent (= k) and the vitamin independent (= a) oxidation resistance seem to be subject specific with strong individual variation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of Antioxidants on Oxidative Modification of LDL

Human low density lipoprotein (LDL) with a molecular mass of 2.5 million contains on average 1300 molecules of polyunsaturated fatty acids (PUFAs) bound in the different lipid classes. The predominant antioxidant in LDL is a-tocopherol, with an average of 6 molecules in each LDL particle. The other substances with potential antioxidant activity are: gamma-tocopherol, β-carotene, a-carotene, lycopene, cryptoxanthin, cantaxanthin, phytofluene and ubiquinol-10. Each is present in amounts of only 1/ 20th to 1/300th of that of a-tocopherol. If LDL is exposed to oxidative conditions (Cuions, macrophages) a lag phase precedes the oxidation of PUFAs. During the lag phase the antioxidants disappear with a-tocopherol the first to go and β-carotene the last.

The lag phase, which can readily be determined, is an index of the oxidation resistance of LDL. If LDL is loaded with vitamin E in vitro its oxidation resistance increases linearly with its a-tocopherol content according to the equation, y=kx+a. The same relationship is applicable if the a-tocopherol content of LDL is increased by taking oral vitamin E. Daily doses of 150, 225, 800 and 1200 IU RRR-a-tocopherol increased the LDL a-tocopherol on average to 138%, 158%, 144% and 215% of the initial value, the oxidation resistance being increased to 118%, 156%, 135% and 175%, respectively. The efficiency of vitamin E-dependent (=k) and the vitamin E independent (=a) oxidation resistance seem to be subject specific with strong individual variation. The k values ranged from 1.38 to 34.1 min (mean 4.5±3.3, n = 36) and the value of a ranged from — 49 to +97 min (mean 43.9±31.5). The variability of k and a explains why the a-tocopherol content of an individual LDL sample is per se not predictive for its resistance to oxidation.     

The effect of acetaminophen on oxidative modification of low-density lipoproteins in hypercholesterolemic rabbits

Oxidative modification of low-density lipoproteins (LDL) contributes to the pathology of atherosclerosis. Antioxidants may protect LDL against oxidative modification. Acetaminophen, a widely used analgesic and antipyretic agent, has significant antioxidant properties. However, there is little evidence to suggest that acetaminophen acts as an antioxidant for LDL oxidation in vivo. In this study, we investigated the in vivo effect of acetaminophen on LDL oxidation in hypercholesterolemic rabbits. The oxidative modification of LDL was identified by conjugated dienes and thiobarbituric acid-reactive substances (TBARS). In the cholesterol group which rabbits were fed a diet contained 1% g cholesterol for 8 weeks, TBARS contents and conjugated diene levels in the plasma and isolated LDL samples significantly increased compared with the control rabbits (p<0.05). However, in the cholesterol + acetaminophen group, the TBARS contents and conjugated diene levels were significantly lower than that of the cholesterol group (p<0.05). The results from in vitro studies also demonstrated that the LDL isolated from serum was oxidized by Cu(++) ions and this oxidation reduced in the presence of acetaminophen. The reduced oxidative modification of LDL by acetaminophen may be of therapeutic value in preventing the development and progression of atherosclerosis.     

Effect of Soybean Hypocotyl Extract on Lipid Peroxidation in GK Rats

Vascular complications, as a consequence of atherosclerosis, are main causes of morbidity and mortality in patients with diabetes mellitus. There is increasing evidence that lipid peroxidation and oxidative modification of low density lipoprotein (LDL) is important in atherogenesis. In this study we investigated the effect of soybean hypocotyl extract (SHE), rich in isoflavones and saponins, on lipid peroxide (LPO) levels in liver, plasma and lipoproteins in GK diabetic rats, and its efficacy on the reduction of susceptibility of LDL and high density lipoprotein (HDL) to oxidation. The oxidative modification of LDL and HDL was determined with the lag time of copper ion-induced oxidation curve identified by the conjugated dienes. In SHE group which were fed diet containing 40 g/kg of SHE for 16 weeks, LPO levels in liver, plasma and HDL fraction were significantly decreased compared with the control group. The lag phage of LDL oxidation curve was prolonged noticeably by a mean of 27 min in SHE group as compared to the control group, indicating a reduced susceptibility to oxidation. The results suggest that intake of soybean hypocotyl extract might be useful for the prevention and treatment of diabetes mellitus and diabetes-associated diseases.     

Long chain polyunsaturated fatty acids may account for higher low-density lipoprotein oxidation susceptibility in Lithuanian compared to Swedish men

OBJECTIVES: Mortality in coronary heart disease among middle-aged men is four times higher in Lithuania than in Sweden. Traditional risk factors cannot account for this difference. We earlier reported that low-density lipoprotein (LDL) in Lithuanian men showed a lower resistance to oxidation, measured as LDL lag time during copper oxidation, than that in Swedish men. Serum concentrations of several fat-soluble antioxidant vitamins were lower among Lithuanian men. The aim of this study was to investigate whether differences in LDL fatty acid composition could account for the difference in LDL oxidation susceptibility between men in the two countries. METHODS: This cross-sectional study included randomly selected healthy 50-year-old men from Vilnius, Lithuania (n=50) and Link?ping, Sweden (n=50). Main outcome measures were fatty acids in LDL, phospholipid (PL) and cholesterol ester (CE) fractions of LDL and LDL oxidation susceptibility. RESULTS: The mean proportions of PL 20:5n3 (eicosapentaenoic acid, EPA) were higher in Vilnius men (2.09 +/- 1.05 vs. 1.53 +/- 0.58%, p= 0.004). LDL lag time was shorter in Vilnius men, mean +/- SD (75.4 +/- 13.6 vs. 89.5 +/- 13.1 mins, p<0.0001) than in Link?ping men. Mean serum gamma-tocopherol was lower in Vilnius men (0.07 +/- 0.05 vs. 0.12 +/- 0.04 microg/mmol, p<0.0001) but alpha-tocopherol did not differ. In a multiple regression analysis controlled for city, high PL-EPA, low alpha-tocopherol, and high plasma triglycerides significantly contributed to a short LDL lag time, r2=0.53. CONCLUSIONS: Fat quality, i.e. poly unsaturated fatty acids, especially LDL-EPA, plasma triglycerides and antioxidative vitamins may partly account for the increased LDL oxidation susceptibility found in Vilnius men compared with Link?ping men.     

Acute and long-term effects of low-density lipoprotein (LDL)-apheresis on oxidative damage to LDL and reducing capacity of erythrocytes in patients with severe familial hypercholesterolaemia

Several studies have suggested that the oxidative modification of low-density lipoprotein (LDL) could play a key role in the early stages of atherosclerosis. The susceptibility of LDL to oxidation has been found to be greater in patients with coronary heart disease. Familial hypercholesterolaemia (FH) is a powerful clinical model in which to study the predictive role of LDL in atherogenesis. LDL-apheresis is a treatment that is able to decrease lipid levels in plasma. This study was aimed at investigating the reducing capacity of erythrocytes and the in vitro susceptibility to oxidation of LDL isolated from patients with homozygous, heterozygous and double-heterozygous FH, who were treated fortnightly with LDL-apheresis or left untreated. In 14 FH patients, at baseline and after a cycle of treatment, the susceptibility of LDL to oxidative modification was analysed by studying the kinetics of conjugate diene formation. Plasma hydroperoxides, polyunsaturated fatty acid content, LDL electrophoretic mobility on agarose, the titre of auto-antibodies against oxidized LDL and serum paraoxonase activity were also measured. Furthermore, in order to evaluate a potential relationship between LDL oxidation and redox status, erythrocyte GSH and ATP levels were determined in FH patients treated regularly or never treated previously by LDL-apheresis. Unlike in the control group, the oxidative status of LDL in all FH patients was modified by LDL-apheresis, as revealed by the higher negative charge and the increase in levels of hydroperoxides and antibodies against oxidized LDL in the plasma. Our findings suggest both an acute effect and a long-term effect of LDL-apheresis in FH patients treated with dextran sulphate cellulose apheresis. The acute effect of LDL-apheresis on the susceptibility to oxidation of plasma and LDL was demonstrated by significant decreases in plasma hydroperoxide content, total LDL concentration and polyunsaturated fatty acid content. The increased resistance of LDL to oxidation was shown by prolongation of the lag time (P<0.05) in samples after a single cycle of treatment. The long-term effect of LDL-apheresis was demonstrated by the comparable values for lag phases (obtained from the kinetics of conjugate diene formation) in patients under active treatment and controls. Compared with healthy controls and untreated patients, the erythrocyte GSH content was significantly higher (P相似文献   

Vitamin E supplementation and oxidative damage to DNA and plasma LDL in type 1 diabetes.

OBJECTIVE: To determine the effect of 400 IU/day of the antioxidant vitamin E on the susceptibility of plasma LDL and lymphocyte DNA to oxidative damage in type 1 diabetes. RESEARCH DESIGN AND METHODS: We studied 42 patients with type 1 diabetes and 31 age- and sex-matched control subjects in a randomized prospective double-blind placebo-controlled trial by using 400 IU/day of oral vitamin E for 8 weeks. Measurements were made of single-strand breaks in lymphocyte DNA at baseline and after hydrogen peroxide-induced stress (comet assay) and of copper-induced LDL oxidization and plasma antioxidant profiles. RESULTS: Plasma LDL and lymphocyte DNA were more resistant to induced oxidative change in the type 1 diabetes group than in control subjects. Vitamin E supplementation reduced LDL oxidizability in the control subjects but not in the type 1 diabetes group and had no effect on oxidative DNA damage in either group. The type 1 diabetes group had a significantly poorer plasma antioxidant profile with lower mean serum concentrations of alpha-tocopherol and most carotenoids than control subjects. CONCLUSIONS: Plasma LDL and lymphocyte DNA appear to be more resistant to oxidative change in type 1 diabetic subjects than in control subjects, and there was no evidence of oxidatively induced DNA or LDL change in type 1 diabetes. This study does not support the hypothesis of oxidative damage in these patients, and a dose of vitamin E (400 IU/day) that reduced LDL oxidative susceptibility in control subjects did not do so in patients with type 1 diabetes.