Lag Time Of Low-density Lipoprotein Oxidation Research Articles

Studies of LDL particle size and susceptibility to oxidation and association with glucose metabolism in children after heart transplantation

Background Increased concentrations of serum triglyceride and low-density lipoprotein (LDL) cholesterol are common after heart transplantation (HTx). These abnormalities may promote transplant vascular disease and atherosclerosis, especially if LDL is small, dense, and oxidized. There have been no previous studies of LDL particle size and LDL susceptibility to oxidation in children after HTx. Methods Twenty-three HTx recipients (aged 3–19 years) who received triple-drug immunosuppression therapy after HTx and 181 controls within the same age range participated in the study. Total, high-density lipoprotein, and LDL-cholesterol concentrations; triglyceride concentration, and glucose and insulin concentrations during oral glucose tolerance tests were determined an average of 3 years after HTx (range, 1–7 years). Moreover, we determined serum lipoprotein (a) concentration, apolipoprotein E phenotype, LDL particle size, and indices of LDL susceptibility to copper-induced oxidation in 12 HTx recipients. Results We found hypertriglyceridemia in 56.5% and hyperinsulinemia in 30.4% of patients. Triglyceride concentration and body mass index were associated significantly with insulin concentration ( p < 0.008 for both). Low-density lipoprotein particle size, LDL susceptibility to in vitro oxidation, and lipoprotein (a) concentrations did not differ significantly between HTx patients and controls. Low-density lipoprotein particle size was associated inversely with cyclosporine through level (Neoral, r = –0.59, p = 0.045), whereas weight-adjusted dosage of cyclosporine correlated positively with longer lag time of LDL oxidation ( r = 0.69, p = 0.013). Conclusions Hypertriglyceridemia and hyperinsulinemia were common in children receiving triple-drug immunosuppression therapy after HTx. Increased cyclosporine through concentration was associated with small LDL particle size but did not increase LDL susceptibility to oxidation.

Effects of α-tocopherol and astaxanthin on LDL oxidation and atherosclerosis in WHHL rabbits

The aim of this study was to evaluate the influence of α-tocopherol and astaxanthin on low-density lipoprotein (LDL) oxidation lag time and atherosclerotic lesion formation in Watanabe heritable hyperlipidemic (WHHL) rabbits. Thirty-one, 3-month-old WHHL rabbits were divided into three experimental groups. One group ( n=10) was fed standard rabbit feed alone and served as a control, a second group ( n=11) was supplied with the same feed containing 500 mg α-tocopherol/kg and a third group ( n=10) was given a feed containing 100 mg astaxanthin/kg. Plasma lipids, lipoproteins and LDL oxidation lag time were followed for 24 weeks. At the end of the treatment period, the animals were killed and the thoracic aorta was used for evaluation of the degree of atherosclerosis. Colour photographs of the intimal surface of the vessel were taken for determination of the atherosclerotic area. Cross-sections of the thoracic aorta were used for histological examination and for determination of intimal thickening. Specimens of the vessel were used for determination of the tissue cholesterol content. Plasma cholesterol remained at a high level during the time of the experiment and there were no differences between the experimental groups. After 24 weeks, the LDL oxidation lag time was 53.7±1.7 min, 109±4 min ( P<0.001) and 56.4±3.4 min ( P=0.47) in the control, α-tocopherol and astaxanthin groups, respectively. In the thoracic aorta, the atherosclerotic area was 80.7±5.1%, 67.1±6.7% ( P=0.13) and 75.2±5.7% ( P=0.49) in the control, α-tocopherol and astaxanthin groups, respectively. The intimal thickening was 45.6±3.2%, 44.0±4.1% ( P=0.89) and 40.0±4.5% ( P=0.33) in the control, α-tocopherol and astaxanthin groups, respectively. Finally, the cholesterol content was 107±9 μmol/g, 95.7±11.5 μmol/g ( P=0.31) and 101±5 μmol/g ( P=0.33) in the control, α-tocopherol and astaxanthin groups, respectively. It can be concluded that α-tocopherol but not astaxanthin prolonged the LDL oxidation lag time. The two antioxidative substances did not prevent atherogenesis in WHHL rabbits in this setting.

Effect of genistein supplementation on tissue genistein and lipid peroxidation of serum, liver and low-density lipoprotein in hamsters

The aim of this study was to investigate the effects of genistein supplementation in a vitamin E-deficient diet on the genistein concentrations and the lipid oxidation of serum, liver and low-density lipoprotein (LDL) of hamsters. Thirty-six male hamsters were randomly divided into three groups and fed a vitamin E-deficient semisynthetic diet (AIN-76) containing different levels of genistein, i.e., G0 (control group, genistein-free diet), G50 (50 mg genistein/kg diet) and G200 (200 mg genistein/kg diet) for 5 weeks. The concentrations of genistein in serum and liver significantly increased with the increase of genistein supplementation. The vitamin E contents in LDL were higher in hamsters fed G50 or G200 diets than in hamsters fed genistein-free diet. Genistein supplementation to hamsters significantly reduced the propagation rate during conjugated diene formation of LDL oxidation, and the lag time of LDL oxidation in hamsters fed G200 diets was significantly lower than that of G0 diets. In addition, genistein supplementation significantly raised serum total antioxidant capacity and decreased the thiobarbituric acid-reactive substances (TBARS) of LDL and liver in hamsters. However, no significant differences in TBARS were found in serum, irrespective of genistein addition. On the other hand, the relative contents of polyunsaturated fatty acids in LDL were decreased after genistein supplementation. There was a negative correlation between lag time and P/S ratio, and a positive correlation between lag time and vitamin E contents. These data demonstrate that genistein supplementation markedly increased its concentrations in body tissues and reduced oxidative stress of lipid oxidation of serum, liver and LDL.

Copper-mediated LDL oxidation by homocysteine and related compounds depends largely on copper ligation

Oxidation of low-density lipoprotein (LDL) is thought to be a major factor in the pathophysiology of atherosclerosis. Elevated plasma homocysteine is an accepted risk factor for atherosclerosis, and may act through LDL oxidation, although this is controversial. In this study, homocysteine at physiological concentrations is shown to act as a pro-oxidant for three stages of copper-mediated LDL oxidation (initiation, conjugated diene formation and aldehyde formation), whereas at high concentration, it acts as an antioxidant. The affinity for copper of homocysteine and related copper ligands homocysteine, cystathionine and djenkolate was measured, showing that at high concentrations (100 microM) under our assay conditions, they bind essentially all of the copper present. This is used to rationalise the behaviour of these ligands, which stimulate LDL oxidation at low concentration but generally inhibit it at high concentration. Albumin strongly reduced the effect of homocystine on lag time for LDL oxidation, suggesting that the effects of homocystine are due to copper binding. In contrast, copper binding does not fully explain the pro-oxidant behaviour of low concentrations of homocysteine towards LDL, which appears in part at least to be due to stimulation of free radical production. The likely role of homocysteine in LDL oxidation in vivo is discussed in the light of these results.

Impact of a high-monounsaturated-fat diet on lipid profile in subjects with type 1 diabetes

Objective Controversy persists regarding the use of a high-monounsaturated-fat diet in people with type 1 diabetes. The purpose of this study was to compare the effects of a high-monounsaturated-fat diet containing 43% to 46% carbohydrates and 37% to 40% fat (17% to 20% monounsaturated fat) with those of a high-carbohydrate diet containing 54% to 57% carbohydrates and 27% to 30% fat (10% to 13% monounsaturated fat) on the quantitative and qualitative lipoprotein profile in type 1 diabetes. Design A randomized crossover study was conducted. Two months before the dietary trial, subjects were monitored on their intensive insulin regimen to normalize glycemic and lipid levels. Subjects Twenty-six individuals followed each diet for 2 months. Eight subjects lost or gained >2 kg, and three had the same dietary intakes during the two diets. For the remaining 15, seven adhered to the two diet prescriptions and eight followed one of the two diets. Statistical analysis Analysis of variance for crossover design (intent-to-treat group of 26) and Wilcoxon signed rank test (group of seven) were used to assess differences between the two diets. Results For the intent-to-treat group (n=26), low-density lipoprotein cholesterol, although within normal range, was lower by 7% (P=.034) at the end of the high-monounsaturated-fat diet. The other 17 lipid parameters tested were not statistically significant. For those who adhered to the two diets (n= 7), lower plasma total triglycerides by 18% (P=.027), lower very low-density lipoprotein triglycerides by 26% (P=.043), lower very low-density lipoprotein cholesterol by 48% (P=.043), higher apolipoprotein A1 by 7% (P=.018), smaller low-density lipoprotein particle size by 1% (P=.043), and longer low-density lipoprotein oxidation lag time by 25% (P=.043) were found after the high-monounsaturated-fat diet. Applications/conclusions A high-monounsaturated-fat diet seemed to have a favorable effect on fasting lipoprotein profile in people with type 1 diabetes. Further research is needed with a larger sample to recommend a high-monounsaturated-fat diet as an alternative diet therapy in type 1 diabetes. J. Am Diet Assoc. 2003;103:467-474.

Anti-Atherogenic Effects of Fermented Fresh Coffee Bean, Soybean and Rice Bran Extracts

Fermented fresh coffee bean, soybean and rice bran extracts (FCSRE, GuardoxTM) is a mixture of aqueous extract of fresh coffee beans, rice bran, and soybeans fermented with Bacillus subtilis Natto. Superoxide anion and hydroxy radical were effectively trapped by FCSRE, as shown by electron spin resonance experiments. Thiobarbituric acid reacting substance (TBARS) formation in human low-density lipoprotein (LDL) induced by copper ion was inhibited by adding FCSRE (0.1 mg/dl) in vitro. Male New Zealand white rabbits were assigned to two groups, control rabbits (n=8) were fed a diet containing 1% cholesterol for 12 weeks, and experimental rabbits (n=8) were fed a 1% cholesterol diet with added 5% FCSRE (2 g/kg body weight/day). Although plasma cholesterol levels rapidly increased after initiation of the high cholesterol diet, no statistical difference was observed between the control and experimental groups. After 12 weeks, sera were sampled, rabbits were sacrificed, and aortas were removed. TBARS formation in LDL induced by copper ion was significantly lower in the experimental group compared with the control group. Lag time of LDL oxidation was also significantly longer in the experimental group. FCSRE administration significantly inhibited the TBARS formation in the aorta compared with the control animals. There was a significant difference in the aortic area covered with atherosclerotic lesions between the experimental and the control groups (53.7±16.3% vs. 36.2±8.18%, p<0.05). These results suggest that FCSRE may be a promising material for the prevention of atherosclerosis.

Efficacy of a complex multivitamin supplement

Objectives: Multivitamin supplements are often sold to consumers with the claim that supplements modify risk factors associated with disease. Because few products are validated scientifically, we examined the effects of a 24-ingredient multivitamin formula in an open-label pilot investigation. Methods: We examined 150 subjects for specific endpoints including blood concentrations of selected vitamins, homocysteine, lipids, and low-density lipoprotein (LDL) oxidation indices at baseline and at 12 and 24 wk. Results: One hundred forty-one subjects were successfully assayed for and showed significant time effects for homocysteine and vitamin B6 (as pyridoxal-5′-phosphate), B12, and folic acid concentrations during treatment ( P < 0.0001). Vitamin B6, B12, and folic acid concentrations were significantly elevated at weeks 12 and 24 ( P < 0.05). Homocysteine concentration decreased significantly during the same periods (7.9 ± 2.4 versus 6.7 ± 1.7 versus 6.7 ± 1.9 mM/mL; P < 0.05). There were correlations relating homocysteine to vitamins B6 ( P = 0.001, r 2 = 0.03), B12 ( P < 0.001, r 2 = 0.09), and folic acid ( P = 0.001, r 2 = 0.10). Significant time effects were noted for 121 subjects successfully assayed for vitamin C, E, β-carotene, LDL oxidation rate, and LDL lag time ( P < 0.0001). Post hoc assessment showed elevations in vitamin C, E, and β-carotene concentrations at 12 and 24 wk ( P < 0.05). LDL oxidation lag time at baseline (57.5 ± 13.9 min) increased by 12 wk (63.5 ± 19.0 min; P < 0.05) and 24 wk (63.8 ± 16.3 min; P < 0.05). LDL oxidation rate at baseline (9.7 ± 3.0 μM · min −1 · g −1) was reduced at 12 wk (7.1 ± 2.5 μM · min −1 · g −1; P < 0.05) and 24 wk (6.0 ± 2.0 μM · min −1 · g −1; P < 0.05). Only vitamin C was significantly correlated with LDL oxidation rate ( P = 0.05, r 2 = 0.003). Conclusions: A multi-ingredient vitamin formula with antioxidant properties has measurable effects on homocysteine and LDL oxidation indices.

Association between carotid intima-media thickness and low-density lipoprotein size and susceptibility of low-density lipoprotein to oxidation in asymptomatic members of familial combined hyperlipidemia families.

In addition to low-density lipoprotein (LDL) cholesterol, small, dense LDL particles and oxidative modification of LDL have been linked to the pathogenesis of atherosclerosis. The present study was aimed at investigating the association between carotid artery intima-media thickness (IMT) and LDL particle size and susceptibility of LDL to oxidation in vitro in asymptomatic members of familial combined hyperlipidemia (FCHL) families. LDL particle size, susceptibility of LDL to oxidation in vitro, and carotid IMT were measured in 148 asymptomatic FCHL family members. LDL particle size and lag time for LDL oxidation were reduced in hyperlipidemic compared with normolipidemic family members. LDL particle size, serum total cholesterol, and alpha-tocopherol in LDL were independently associated with lag time for LDL oxidation in multivariate analysis. LDL particle size was associated with carotid mean IMT independently of clinical, lipid, and antioxidant variables in multivariate analysis. Although the susceptibility of LDL to oxidation in vitro was correlated with mean IMT, it did not have a significant independent contribution to variation in mean IMT in the multivariate model. We conclude that LDL particle size but not susceptibility of LDL to oxidation in vitro is independently associated with carotid IMT in asymptomatic FCHL family members. These results imply that small, dense LDL as an inherent feature of FCHL is an important diagnostic indicator for coronary artery disease risk in FCHL.

Influence of dietary fat saturation on lipid peroxidation of serum and low density lipoprotein in rats

The purpose of this study was to investigate the influence of different P/S (polyunsaturated/saturated) ratios on lipid peroxidation of plasma, liver and low-density lipoprotein (LDL) in rats, using dietary fats with different saturation levels. Male Sprague-Dawley rats weighing about 300 g were randomly divided into five groups and fed a semisynthetic diet containing 10% (w/w) fat for 6 weeks. The fat was composed of 100, 75, 50, 25, 0% corn oil and 0, 25, 50, 75, 100% lard (CO100, CO75, CO50, CO25 and LA groups, with P/S ratios of 3.81, 2.13, 1.21, 0.64, and 0.28, respectively) respectively. The body and liver weight of rats fed dietary fat with different P/S ratios were comparable among 5 groups. The CO100 group had higher plasma TBARS (thiobarbituric acid-reactive substances) than the CO25 and LA groups. The TBARS of LDL in LA and CO25 groups were lower than those of the other (CO100, CO75 and CO50) groups. In addition, the rats fed P/S ratio ≦1.21 (i.e., CO50, CO25, and LA groups) had lower LDL TBARS than rats fed P/S ratio >1.21 (i.e., CO100 and CO75 groups) when LDL were incubated with Cu 2+ at 37 °C for 2 or 5 h. On the other hand, rats fed diets with P/S ratio ≦1.21 experienced significantly increase lag time of conjugated diene formation in LDL than those fed P/S >1.21. The fatty acid content of 18:2 (n-6) in LDL was reduced by decreasing the ratio of P/S in dietary fat. The ratio of linoleic acid content to oleic acid content was inversely correlated with the lag time of LDL oxidation. However, different P/S ratio in the diet did not affect 18:1 (n − 9), vitamin E levels and the TBARS values in liver of rats. The results suggested that P/S ratios in the diet influenced the LDL oxidation, and the lipid peroxidation might have a threshold of P/S ratios between 1.21 and 0.64.

Effects of eprosartan versus hydrochlorothiazide on markers of vascular oxidation and inflammation and blood pressure (renin-angiotensin system antagonists, oxidation, and inflammation)

Antagonists of the renin-angiotensin system, such as angiotensin type 1 (AT 1) receptor inhibitors and angiotensin-converting enzyme inhibitors, are becoming increasingly popular agents in treating patients with systemic hypertension and minimizing organ damage. In the present study, we compared the effects of eprosartan, an AT 1 receptor inhibitor, with the diuretic hydrochlorothiazide in a group of newly diagnosed hypertensive patients with multiple risk factors for atherosclerosis. The subjects were monitored and tested at 0 and 4 weeks to determine their individual effects on vascular and inflammatory markers. Although blood pressure reduction was comparable between the 2 agents, there were notable differences in their effects on markers of inflammation and oxidation. We observed a 28% reduction in neutrophil superoxide anion generating capacity, a 34% reduction in soluble monocyte chemotactic protein-1, and a 35% reduction in soluble vascular cell adhesion molecule with eprosartan therapy (all p <0.05 from the start of therapy). In addition, eprosartan showed further benefit in its ability to increase low-density lipoprotein oxidation lag time, suggesting an increased resistance to oxidation and/or modification of low-density lipoprotein. Although hydrochlorothiazide was effective in blood pressure reduction, there were no significant changes in any of the above parameters after 4 weeks of treatment. These findings suggest that eprosartan, an AT 1 receptor inhibitor, effectively reduces systemic blood pressure and, compared with hydrochlorothiazide, suggests additional benefits in the vasculature by inhibiting mechanisms of inflammation and oxidation.

Green tea flavonoids inhibit the LDL oxidation in osteogenic disordered rats fed a marginal ascorbic acid in diet

Osteogenic Disorder Shionogi (ODS) rats can not synthesize ascorbic acid (AA). We have examined the capacity of green tea flavonoids (GTF) to modify low-density lipoprotein (LDL) oxidation in ODS rats with dietary AA restriction. In the first experiment, ODS rats were fed diets containing 300 (AA300 diet) or 0 (AA0 diet) mg AA/kg diets for 20 d. In comparison with the AA300 diet, the AA0 diet significantly decreased the concentrations of plasma AA and α-tocopherol in LDL and significantly shortened the lag time of LDL oxidation in vitro. In the second experiment, ODS rats were fed one of the following three diets: the AA300 diet, the diet containing 25 mg AA (AA25, marginal AA)/kg diet (AA25 diet), or the diet containing 25 mg AA + 8 g GTF/kg diet (AA25 + GTF diet) for 20 d. Plasma AA concentration were significantly lower in rats fed AA25 compared with AA300 but not in those fed AA25 + GTF. LDL oxidation lag time was significantly longer in rats fed AA25 + GTF compared with the other two groups. Lag time for LDL oxidation was significantly and positively correlated with LDL α-tocopherol ( r = 0.6885, P = 0.0191). These results suggest that dietary flavonoids suppress the LDL oxidation through the sparing effect on LDL α-tocopherol and/or plasma AA when AA intake is marginal in the ODS rats.

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 f -tocopherol content in LDL between the FCHL groups and healthy controls. Plasma concentrations of f -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.

Irbesartan, an angiotensin type 1 receptor inhibitor, regulates the vascular oxidative state in patients with coronary artery disease

OBJECTIVESThe aim of this study was to determine the effect of angiotensin II type 1 (AT1) receptor antagonists on pro-oxidant species observed in the pathogenesis of atherosclerosis. Parameters such as low-density lipoprotein (LDL) susceptibility, monocyte binding capacity, superoxide generation and lipid peroxidation were examined in the presence of the AT1receptor antagonist irbesartan.BACKGROUNDLow-density lipoprotein oxidation is a key component in the process of atherogenesis. This modification may involve various mechanisms, including changes in nitric oxide levels and superoxide levels. Additionally, compounds that suppress these mechanisms may retard or inhibit the pathogenesis of atherosclerosis.METHODSForty-seven patients with documented coronary artery disease were treated with irbesartan for a 12-week period. Patients were randomized to receive irbesartan or placebo. Lipid peroxidation, superoxide levels, monocyte binding and LDL oxidation were measured at 0, 4 and 12 weeks. Findings were statistically evaluated by two-way repeated measures analysis of variance with p < 0.05 being significant.RESULTSTreatment with irbesartan significantly decreased the pro-oxidative environment seen in our study population. Lag time for LDL oxidation increased 32% at 12 weeks, suggesting an increased resistance of LDL modification in the serum. Thiobarbituric acid reactive substances activity indicated that lipid peroxidation decreased by 36% in comparison to placebo. In addition, superoxide levels and monocyte-binding capacity were also significantly reduced in coronary artery disease patients receiving irbesartan.CONCLUSIONSOur results indicate that irbesartan may suppress the atherosclerotic process by inhibiting the intravascular oxidative state and the production of reactive oxygen species, compounds that may cause damage to the vasculature.

Cranberry proanthocyanidins associate with low‐density lipoprotein and inhibit in vitro Cu2+‐induced oxidation

AbstractAntioxidant activity of six fractions of cranberry phenolic compounds was determined by inhibition of Cu2+‐induced low‐density lipoprotein (LDL) oxidation. The phenolic composition of each fraction was determined by high‐performance liquid chromatography. The phenolic fractions were mixed with aliquots of modified human serum prior to LDL isolation. The serum was modified to remove very‐low‐density lipoprotein and chylomicrons that may bind phenolic compounds. Only fractions 5 and 6 that contained proanthocyanidins (PAs) significantly increased the lag time of LDL oxidation, and the lag time for fraction 6 was significantly higher than for fraction 5. The mass distribution of PAs in these fractions was obtained by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry, a technique that allows rapid characterisation of the molecular weight distribution in mixtures of oligomeric compounds. Fraction 5 contained trimers through heptamers, whereas fraction 6 contained pentamers through nonamers. In addition, fraction 6 contained PA oligomers with more doubly linked, A‐type interflavan bonds. Results indicate that PAs specifically associate with LDL in modified serum and increase the lag time of Cu2+‐induced oxidation. Differences between fractions 5 and 6 in PA structure and effects on LDL oxidation suggest that the degree of polymerisation and the nature of the interflavan bond influence antioxidant properties.© 2001 Society of Chemical Industry

Apple Juice Consumption Reduces Plasma Low-Density Lipoprotein Oxidation in Healthy Men and Women

ABSTRACT Epidemiological studies show that consumption of fruits and vegetables is associated with beneficial effects on human health including reduced risk of coronary artery disease (CAD). Fruits and their juices contain phytochemicals that inhibit in vitro low-density lipoprotein (LDL) oxidation and may account, in part, for their protective effect. However, reports of in vivo antioxidant effects from fruit intake are limited. We conducted a human trial to examine the in vivo effect of consumption of apples (both whole and juice) in an unblinded, randomized, crossover design. Healthy men and women added 375 ml of unsupplemented apple juice or 340 g of cored whole apple to their daily diet for 6 weeks, then crossed over to the alternate product for 6 weeks. Blood samples were obtained at baseline and after each dietary period. Compliance was monitored via biweekly 5-day food records, bodyweight checks, and meetings with study personnel. There were no significant differences between groups in intake of dietary fat, cholesterol, total carbohydrate, sugar, or calories throughout the study. Dietary fiber intake increased by 22% with whole apple consumption. Body weight, fasting serum lipid concentration, and other lipoprotein parameters were unchanged. Apple juice consumption increased ex vivo copper (Cu(++))-mediated LDL oxidation lag time by 20% compared with baseline. Apples and apple juice both reduced conjugated diene formation. Moderate apple juice consumption provides in vivo antioxidant activity. In view of the current understanding of CAD, the observed effect on LDL might be associated with reduced CAD risk and supports the inclusion of apple juice in a healthy human diet.

Fluvastatin, an HMG-CoA reductase inhibitor, protects LDL from oxidative modification in hypercholesterolemic rabbits.

The antioxidative effect of fluvastatin sodium (fluvastatin) on low-density lipoprotein (LDL) was evaluated in vivo and in vitro. Since ex vivo measurement of the LDL oxidizability is reported to reflect the response of the atherosclerotic process, LDL isolated from rabbits fed a high cholesterol diet for 4 weeks with or without fluvastatin, pravastatin or alpha-tocopherol administration was oxidized by copper ions to estimate conjugated diene formation. Fluvastatin but not pravastatin significantly prolonged the lag time of LDL oxidized by copper ions ex vivo without affecting plasma cholesterol levels at a dose of 3 mg/kg after four weeks of treatment. Alpha-tocopherol-treated rabbits showed dramatically elongated LDL oxidation lag time at a dose of 150 mg/kg. In order to assess the mechanism, the content of alpha-tocopherol, a major endogenous antioxidant in LDL was measured, and we found that only LDL isolated from alpha-tocopherol-treated rabbits contained a significantly larger amount of alpha-tocopherol than that from high cholesterol control rabbits. To elucidate the mechanism further, the effect of fluvastatin on conjugated diene formation during copper-induced LDL oxidation in vitro was studied. Fluvastatin not only prolonged lag time, but also suppressed the rate of LDL oxidation, both in a dose dependent manner above 1 microM, while pravastatin showed no effect. These results suggest the direct antioxidative effect of fluvastatin on LDL oxidation in vivo. Since oxidation of LDL is an important step in the initiation and progression of atherosclerosis, fluvastatin may reduce the risk of this condition not only by lowering plasma cholesterol but also by protecting LDL from oxidation.

Flavonoids protect against oxidative damage to LDL in vitro: Use in selection of a flavonoid rich diet and relevance to LDL oxidation resistance ex vivo?

The ability of a range of dietary flavonoids to inhibit low-density lipoprotein (LDL) oxidation in vitro was tested using a number of different methods to assess oxidative damage to LDL. Overall quercetin was the most effective inhibitor of oxidative damage to LDL in vitro. On this basis, a diet enriched with onions and black tea was selected for a dietary intervention study that compared the effect on the Cu2+ ion-stimulated lag-time of LDL oxidation ex vivo in healthy human subjects of a high flavonoid diet compared with a low flavonoid diet. No significant difference was found in the Cu2+ ion-stimulated lag-time of LDL oxidation ex vivo between the high flavonoid and low flavonoid dietary treatments (48 ± 1.6 min compared to 49 ± 2.1 min).

Susceptibility of LDL to oxidation is not associated with the presence of coronary heart disease or renal dysfunction in NIDDM patients

Coronary heart disease (CHD) is the leading cause of death among patients with non-insulin-dependent diabetes mellitus (NIDDM) and the oxidation of low-density lipoprotein (LDL) may be an essential factor in the development of atherosclerotic lesions. Therefore, we studied the in vitro susceptibility of LDL to copper-induced oxidation in 72 NIDDM patients and 94 well-matched non-diabetic control subjects. There was no significant difference in the lagtime of LDL oxidation between NIDDM patients and control subjects (68.1±8.8 vs. 66.7±9.2 min, respectively, P=0.29). The plasma α-tocopherol/LDL-ratio was the most significant determinant of the lagtime in multiple regression analysis. High level of serum triglycerides was associated with decreased lagtime in control subjects, but not in NIDDM patients. Blood glucose balance was not associated with LDL susceptibility to oxidation in NIDDM patients. Subjects with CHD did not have LDL susceptibility to oxidation different from that of subjects without CHD in either of the study groups. Urinary albumin excretion or glomerular filtration rate was not associated with the lagtime of LDL oxidation in NIDDM patients. In conclusion, these data suggest that diabetes and hyperglycemia per se do not affect the susceptibility of LDL to oxidation. The presence of CHD or renal dysfunction were not associated with LDL susceptibility to oxidation.

Beneficial effect of gemfibrozil on the chemical composition and oxidative susceptibility of low density lipoprotein: a randomized, double-blind, placebo-controlled study

Previous reports have shown that administration of fibrates can reduce coronary events and also improve plasma lipid levels. Oxidative modification of low density lipoprotein has been implicated in the pathogenesis of atherosclerosis, and the resistance of low density lipoprotein (LDL) to in vitro oxidation has been found to be correlated with the extent of atherosclerosis. We performed a double-blind, placebo-controlled intervention trial to establish whether gemfibrozil could improve resistance of LDL to oxidation in patients with hyperlipidemia. Patients were randomly assigned to treatment with gemfibrozil (450 mg, twice a day, n=10) or placebo ( n=9) for 8 weeks. Blood samples were obtained after an overnight (12 h) fast. Gemfibrozil administration significantly reduced total plasma cholesterol and triglyceride levels and changed the LDL from small, dense particles (pattern B, ≤25.5 nm) to larger, more buoyant particles (pattern A, >25.5 nm). Gemfibrozil significantly increased the lag time of LDL oxidation in vitro by 18.2% from 45.5±8.0 min at week 0 to 53.4±11.4 min at week 8, but did not change LDL vitamin E and β-carotene concentrations. Surprisingly, gemfibrozil significantly decreased LDL lipid peroxides by −33.1% and increased the LDL vitamin E/lipid peroxide ratio by 67.6% from 1.3±0.5 at week 0 to 2.1±0.9 at week 8. These results demonstrate that gemfibrozil treatment can render LDL less susceptible to oxidative modification while reducing plasma cholesterol and triglyceride and improving LDL subclass pattern. This antioxidative effect of gemfibrozil on LDL may be one of the factors which could delay the progression of atherosclerosis.

Potent Inhibitory Activities of Hydrophobic aci-Reductones (2-Hydroxytetronic Acid Analogs) Against Membrane and Human Low-Density Lipoprotein Oxidation

The effects of selected aci-reductones, which are hydrophobic ascorbate-related analogs including 4-chlorophenyl-2-hydroxytetronic acid (Cpd A), 4-(1,1′-biphenyl)-2-hydroxytetronic acid (Cpd B), and 4-(4′-chloro-1,1′-biphenyl)-2-hydroxytetronic acid (Cpd C), on membrane and low density lipoprotein (LDL) oxidation were assessed. Hepatic microsomal lipid peroxidation was induced by the ascorbate + Fe(II) chemical system. All three agents inhibited membrane lipid peroxidation in a concentration-dependent manner with the order of potency: Trolox (vitamin E) ≤ Cpd A ≪ Cpd B < Cpd C; based on the ec 50 values, Cpd B and Cpd C were 11- and 19-fold, respectively, more potent than Trolox. In contrast to ascorbic acid, all three agents did not display any membrane prooxidative effect in the presence of iron. When human LDL was incubated with 10 μM of Cu(II), LDL oxidation, determined by the formation of thiobarbituric acid reactive substances, followed a typical sigmoidal curve with an initial lag phase. Preincubation of the LDL samples with low micromolar concentrations (1 and 3 μM) of each agents for 30 min before the addition of copper resulted in significant delays of the lag time of LDL oxidation, and the effectiveness of Cpd B and Cpd C was more prominent than that mediated by either Trolox or probucol. Since clinical evidence strongly supports the hypothesis that atherogenesis is initiated by LDL oxidation, the results suggest that these aryl tetronic acid analogs may serve as promising candidates for future therapeutic use as anti-atherogenic agents.