Low-density Lipoprotein Vitamin Research Articles

High plasma levels of CD40 are associated with low coenzyme Q and vitamin E content of low‐density lipoprotein in healthy men

Objective. There is a growing body of evidence to suggest that low‐density lipoprotein (LDL) cholesterol, inflammation and oxidative stress are pivotal in the development of cardiovascular disease, but their interconnections are not well known. The objective of this study was to determine whether immunological activation, reflected by the plasma levels of soluble CD40 (sCD40), interleukin (IL)‐1β, tumor necrosis factor‐α and IL‐6 are associated with the antioxidant potential of LDL particles or with common lipid, immunological or thrombotic markers in 51 young healthy men. Material and methods. We determined the coenzyme Q level from an oxidized LDL fraction, obtaining the concentration for ubiquinone, which indicates total coenzyme Q levels. Results. The plasma level of sCD40 was negatively correlated with LDL ubiquinone (r = −0.45, p = 0.001) and E vitamin (r = −0.37, p = 0.008) and positively correlated with plasma concentration of plasminogen activator inhibitor‐1 (PAI‐1, r = 0.52, p = 0.002) and caspase‐1 (r = 0.40, p = 0.004). No correlation was detected between sCD40 and plasma lipid or C‐reactive protein concentrations. As sCD40 was strongly correlated with the content of LDL ubiquinone and vitamin E, their values were compared according to groups formed by sCD40 tertiles. Analysis of variance showed that there were significant differences in LDL ubiquinone (p<0.0001) and vitamin E (p = 0.004) concentrations between sCD40 tertiles. Conclusions. The data indicate that increased activation of the CD40 system is related to low levels of LDL ubiquinone and vitamin E. This suggests that chronic or increased immunological activation may consume the antioxidant potential of LDL particles.

Nebivolol decreases oxidative stress in essential hypertensive patients and increases nitric oxide by reducing its oxidative inactivation

To obtain further insight into the mechanism underlying the vasodilator effect of nebivolol. Since oxidative inactivation of nitric oxide (NO) is regarded as an important cause of its decreased biological activity, we studied (1) the effect of nebivolol on some oxidative parameters in essential hypertensive patients; (2) the effect of plasma of nebivolol-treated patients on reactive oxygen species production and NO availability in endothelial cells. A total of 20 healthy subjects and 20 matched essential hypertensive patients treated with atenolol or nebivolol according to a double-blind, randomized design participated in the study. We measured low-density lipoprotein (LDL) and plasma hydroperoxides, 8-isoprostanes, oxidized LDL, susceptibility of LDL to oxidation (lag phase) and LDL vitamin E and the effect of plasma of nebivolol- and atenolol-treated patients on reactive oxygen species production and NO availability in endothelial cells exposed to oxidative stress. In hypertensive patients, nebivolol and atenolol significantly reduced blood pressure values after 4 weeks of treatment. Plasma and LDL hydroperoxides, plasma 8-isoprostanes, plasma ox-LDL and LDL lag phase were significantly improved only in the patients receiving nebivolol compared with the atenolol group. Similarly there was a reduction of reactive oxygen species (ROS) and O2*- concentration in endothelial cells exposed to oxidative stress after incubation of the cells with plasma of the patients enrolled in the trial only in the patients receiving nebivolol compared to atenolol group. Furthermore, the reduction of basal and stimulated NO induced by oxidative stress in endothelial cells was significantly lower in the patients receiving nebivolol compared to atenolol group. The findings of the present study indicate that nebivolol, through its antioxidant properties, increases NO also by decreasing its oxidative inactivation.

Age-related changes of serum lipoprotein oxidation in rats

Oxidation of low-density lipoprotein (LDL) may be a prelude to atherogenesis and directly age related. To assess whether there may be relationship between age and plasma lipoprotein (LP) oxidation, we studied copper-mediated LP oxidation isolated from the blood of 2 months, 7 months, and 15 months old rats. We determined whether the susceptibility of LP to oxidation might be related to vitamin C levels in serum, vitamin E levels in LP, or the total antioxidant capacity (TAC) of serum or LP. Serum vitamin C content was inversely related to age, malondialdehyde (MDA) propagation rate, and maximum change of MDA concentrations. However, there were no significant relationships between age and serum TAC, LP TAC, serum vitamin E, or the ratio of LP vitamin E to serum vitamin C content. The lag phase of MDA formation was significantly decreased with age and the ratio of LP vitamin E content to serum vitamin C content, increased with age. Maximum change of MDA concentration was positively correlated with the ratio of LP vitamin E contents to serum vitamin C concentration. Thus, as the rat ages, vitamin C status decreases with an increased LP susceptibility to oxidation. It is tempting to speculate that enhanced LP oxidation in older rats may reflect a reduced amount of recycling of LDL vitamin E by serum vitamin C.

Quantity versus quality of LDL cholesterol in patients with familial hypercholesterolemia—which is more important?

Background: The aim of this study was to determine the effects of low-density lipoprotein (LDL) particle size and composition on the susceptibility of LDL to oxidation in subjects with Familial Hypercholesterolemia (FH). Methods: LDL was isolated from 20 FH homozygotes, 20 FH heterozygotes and 20 normal controls. Susceptibility of LDL to ex vivo copper-mediated oxidation was assessed by measuring conjugated diene production at 234 nm. Other factors known to influence LDL oxidation, namely particle size, vitamin E levels, and fatty acid composition of the LDL particles were also measured. Results: The mean duration of the lag phase was 1.42-fold longer in the FH homozygotes, and 1.21-fold longer in the FH heterozygotes than in the normal controls. LDL particle size was significantly larger in the FH homozygotes (26.45±0.37 nm) and FH heterozygotes (26.01±0.40 nm) compared to the normal control group (25.17±0.39 nm). LDL vitamin E concentrations, when expressed relative to LDL cholesterol concentrations, were similar in all the groups. In addition, no significant differences were observed in the total saturated, monounsaturated or polyunsaturated fatty acid content of LDL in the three groups of subjects. Conclusion: These results suggest that it is the great excess in LDL quantity, rather than LDL ‘quality’, that is responsible for the severe and premature atherosclerosis in patients with FH.

The Effect of Vitamin E and Vitamin C Supplementation on LDL Oxidizability and Neutrophil Respiratory Burst in Young Smokers

Objective: The purpose of this study was to determine the effect of vitamin E and/or vitamin C supplementation on low-density lipoprotein (LDL) oxidizability and neutrophil (PMN) superoxide anion production in young smokers.Methods: Thirty smokers with a <5 pack-year history were randomly assigned to take placebo; vitamin C (1 g/day); vitamin E (400 IU/day); or both vitamins in a double-blind fashion. Subjects took the supplements for 8 weeks. At weeks 0 and 8, blood was collected for isolation of LDL and PMN, and for antioxidant vitamin analysis. LDL was oxidized with a copper (Cu) catalyst, and oxidation was measured by formation of conjugated dienes over a 5-hour time course. Lag times and maximum oxidation rates were calculated from the time course data. PMN superoxide anion release was assessed by respiratory burst after stimulation with phorbol ester and opsonized zymosan, and their ability to oxidize autologous LDL following treatment with the above stimuli was measured with the conjugated diene assay.Results: Subjects who received vitamin E alone had a significant increase in the lag phase of Cu-catalyzed LDL oxidation (week 0, 118 ± 31 min vs. week 8, 193 ± 80 min, mean ± SD, p < 0.05), whereas the vitamin C and placebo groups had no changes in LDL oxidation kinetics. The group receiving both vitamins E and C had a significant reduction in oxidation rate (week 0, 7.4 ± 2.3 vs. week 8, 5.1 ± 2.1, p < 0.05). There were no significant changes for any group in PMN superoxide anion production or PMN LDL oxidation after stimulation with either phorbol ester or opsonized zymosan. Plasma and LDL vitamin E concentrations were significantly increased in both groups that received vitamin E. The subjects who received vitamin C alone had no significant change in plasma vitamin C concentrations; however, when data were pooled from both groups who received vitamin C, the increases were significant.Conclusion: Vitamin E supplementation of young smokers was effective in reducing Cu-catalyzed LDL oxidizability; however, vitamin E and/or C supplementation showed few significant effects on the more physiologically relevant PMN function. This casts doubt on the ability of antioxidant supplementation to reduce oxidative stress in smokers in vivo. Therefore, smoking cessation remains the only means by which young smokers can prevent premature coronary heart disease.

Effect of menopause on low-density lipoprotein oxidation: is oestrogen an important determinant?

Objectives: Significantly increased risk for developing cardiovascular disease in post-menopausal women is linked with the fall of oestrogen. Although supraphysiological levels of oestrogen may inhibit oxygen free radical mediated low-density lipoprotein (LDL) oxidation, the effect of physiological level of oestrogen on LDL oxidation is unknown. Methods: The present study compared oxidizability of LDL in healthy pre- and post-menopausal women by using a commonly employed copper ion-dependent method. Results: Pre-menopausal women ( n=20, mean age 27) had significantly higher serum oestradiol level (576±109 pmol/l) in comparison to post-menopausal women ( n=23, mean age 51, oestradiol 64±18 pmol/l, P<0.001). The oxidation of LDL in two groups was not different by measuring either the lag phase of conjugated dienes formation (54±12 vs. 55±14 min, P>0.05) or the generation of thiobarbituric acid reactive substances over 4 h of oxidation. The major lipid soluble antioxidant in LDL, vitamin E (determined as α-tocopherol) is similar in two groups (2.34±0.48 vs. 2.40±0.56 nmol/mg LDL, pre- and post-menopausal subjects, respectively, P>0.05). Linear regression analysis found a weak but significant correlation between LDL vitamin E level and oxidizability of LDL in both groups but did not show effect of serum oestradiol levels. Conclusion: The results suggest that physiological levels of oestrogen may not be able to affect in vitro LDL oxidation.

Endothelial vasodilator function is related to low-density lipoprotein particle size and low-density lipoprotein vitamin E content in type 1 diabetes

OBJECTIVESWe sought to determine whether endothelial vasodilator function (EVF) in patients with type 1 diabetes was related to low-density lipoprotein (LDL) particle size (LDLPS), LDL vitamin E content (LDLVE) or the susceptibility of LDL to oxidation (OxLDL).BACKGROUNDImpaired EVF is an early feature of diabetic vascular disease and may be related to oxidant stress. Although small, dense LDL and oxidized LDL are features of type 2 diabetes and predict the development of coronary artery disease, their role in type 1 diabetes is less clear.METHODSEndothelium-dependent vasodilation was assessed in the brachial artery (flow-mediated vasodilation [FMD]) and in the forearm resistance circulation using venous occlusion plethysmography in response to graded doses of intrabrachial acetylcholine (ACh). Thirty-seven patients with type 1 diabetes mellitus (DM) and 45 matched controls underwent flow-mediated dilation, while a subset of 19 DM and 20 controls underwent plethysmography.RESULTSTotal, LDL and high-density lipoprotein cholesterol or triglycerides were not different in DM compared with controls, but LDLPS was smaller (25.6 ± 0.06 vs. 26.1 ± 0.1 nm, p < 0.05) and LDLVE was reduced (2.0 ± 0.25 vs. 2.6 ± 0.18 μmol/mmol LDL, p < 0.05). Oxidative susceptibility of LDL was not different. Flow-mediated vasodilation was impaired in DM compared with controls (3.6 ± 0.6% vs. 7.1 ± 0.5%, p < 0.005), as was the vasodilator response to ACh (p < 0.05). Flow-mediated vasodilation was directly related to LDLPS and LDLVE in both the entire study cohort and DM alone (p < 0.05), but not to other parameters of the standard lipid profile. Similarly, endothelium-dependent vasodilation in the resistance circulation was directly related to LDLPS and LDLVE, but not to OxLDL.CONCLUSIONThese results suggest, but do not prove, that LDL particle size and LDL vitamin E may be determinants of conduit and resistance vessel endothelial vasodilator function in type 1 diabetes. Further work will be required to prove cause and effect.

Low-density lipoprotein susceptibility to oxidation and cytotoxicity to endothelium in sickle cell anemia

Patients with sickle-cell anemia exhibit pro-oxidative metabolic perturbations. We hypothesize that because of chronic oxidative stress, plasma low-density lipoprotein (LDL) from patients with sickle-cell anemia is more susceptible to oxidation. To test this hypothesis, LDL susceptibility to copper-mediated oxidation was measured in 24 patients with sickle-cell anemia and 48 control subjects. Sickle-cell LDL was more susceptible to oxidation than control LDL, measured by a 22% shorter mean lag time between LDL exposure to CuSO4 and conjugated diene formation (97 vs 124 minutes; P = .023). LDL vitamin E, iron, heme, and cholesterol ester hydroperoxide (CEOOH) levels were also measured. LDL vitamin E levels were significantly lower in patients with sickle-cell anemia compared with control subjects (1.8 vs 2.9 mol/mol LDL; P = .025), but there was no correlation with lag time. Pro-oxidant heme and iron levels were the same in sickle-cell and control LDL. LDL CEOOHs were not significantly different in sickle and control LDL (3.1 vs 1.2 mmol/mol of LDL unesterified cholesterol, P = .15), but LDL CEOOH levels were inversely correlated with lag times in patients with sickle-cell anemia (r2 = 0.38; P = .018). The cytotoxicity of partially oxidized LDL to porcine aortic endothelial cells was inversely correlated with lag times (r2 = 0.48; P = .001). These preliminary data suggest that increased LDL susceptibility to oxidation could be a marker of oxidant stress and vasculopathy in patients with sickle-cell anemia.

LDL isolated from Greek subjects on a typical diet or from American subjects on an oleate-supplemented diet induces less monocyte chemotaxis and adhesion when exposed to oxidative stress.

The mechanisms underlying the cardiovascular benefits of Mediterranean-style diets are not fully understood. The high content of monounsaturated fatty acids in Mediterranean-style diets derived from oleate-rich olive oil may be beneficial in reducing low density lipoprotein (LDL) oxidation and its subsequent development of atherogenic properties. This study sought to assess the proinflammatory potential of LDL isolated from subjects consuming a diet naturally rich in olive oil. LDL was isolated from 18 Greek, 18 American, and 11 Greek-Americans subjects, all of whom were living in the United States. Fatty acid composition and vitamin E levels of LDL were determined, as was the extent of copper-mediated LDL oxidation. LDL was also mildly oxidized by exposure to fibroblasts overexpressing 15-lipoxygenase and tested in vitro for bioactivity by determining its ability to stimulate monocyte chemotaxis and adhesion to endothelial cells. To confirm that dietary fatty acids influence the proinflammatory properties of mildly oxidized LDL, LDL was also isolated from 13 healthy American subjects after consumption of an 8-week liquid diet supplemented with either oleic (n=6) or linoleic (n=7) acid and tested for bioactivity in a similar fashion. There were no differences in the baseline lipid profiles among the Greeks, Americans, or Greek-Americans. Oleic acid content in LDL was 20% higher in the Greek compared with the American or Greek-American subjects (P<0.001). The extent of in vitro LDL oxidation, measured by conjugated diene formation, was lower in the Greek subjects (P<0.02), but there was no difference in the lag time. Induction of monocyte chemotaxis and adhesion by mildly oxidized LDL was decreased by 42% in the Greek group compared with the American subjects (P<0.001). There was an inverse correlation between the oleic acid content of LDL and stimulation of monocyte chemotaxis (r=-0.64, P<0.001) and a positive correlation between the polyunsaturated fatty acid content of LDL (total linoleate and arachidonic acids levels in LDL) and stimulation of monocyte chemotaxis (r=0.51, P<0.01) in the entire cohort. There were no differences in LDL vitamin E content between the groups. In the liquid-diet groups, the oleic acid-supplemented group had a 113% higher oleic acid content in LDL and a 46% lower linoleic acid content in LDL than the linoleate-supplemented group (P<0.001), whereas the vitamin E content in LDL was equal in both groups. When exposed to oxidative stress, the LDL enriched in oleic acid promoted less monocyte chemotaxis (52% lower) and reduced monocyte adhesion by 77% in comparison with linoleate-enriched LDL (P<0.001). There was a strong, negative correlation between oleic acid LDL content and monocyte adhesion (r=-0.73, P<0.001) and a strong, positive correlation between polyunsaturated fatty acid LDL content and monocyte adhesion (r=0.87, P<0.001). This study demonstrates that dietary enrichment of LDL with oleic acid is realistic and readily achieved by using diets currently in use in Mediterranean countries. In addition, these data suggest that LDL enriched with oleic acid and reduced in polyunsaturated fatty acids may be less easily converted to a proinflammatory, minimally modified LDL.

Oxidative Modification of Low-Density Lipoprotein and Atherogenetic Risk in β-Thalassemia

We investigated the oxidative state of low-density lipoprotein (LDL) in patients with beta-thalassemia to determine whether there was an association with atherogenesis. Conjugated diene lipid hydroperoxides (CD) and the level of major lipid antioxidants in LDL, as well as modified LDL protein, were evaluated in 35 beta-thalassemia intermedia patients, aged 10 to 60, and compared with age-matched healthy controls. Vitamin E and beta-carotene levels in LDL from patients were 45% and 24% of that observed in healthy controls, respectively. In contrast, the mean amount of LDL-CD was threefold higher and lysil residues of apo B-100 were decreased by 17%. LDL-CD in thalassemia patients showed a strong inverse correlation with LDL vitamin E (r = -0.784; P <.0001), while a negative trend was observed with LDL-beta-carotene (r = -0.443; P =.149). In the plasma of thalassemia patients, malondialdehyde (MDA), a byproduct of lipid peroxidation, was increased by about twofold, while vitamin E showed a 52% decrease versus healthy controls. LDL-CD were inversely correlated with plasma vitamin E (r = -0.659; P <.0001) and correlated positively with plasma MDA (r = 0.621; P <. 0001). Plasma ferritin was positively correlated with LDL-CD (r = 0.583; P =.0002). No correlation was found between the age of the patients and plasma MDA or LDL-CD. The LDL from thalassemia patients was cytotoxic to cultured human fibroblasts and cytotoxicity increased with the content of lipid peroxidation products. Clinical evidence of mild to severe vascular complications in nine of the patients was then matched with levels of LDL-CD, which were 36% to 118% higher than the mean levels of the patients. Our results could account for the incidence of atherogenic vascular diseases often reported in beta-thalassemia patients. We suggest that the level of plasma MDA in beta-thalassemia patients may represent a sensitive index of the oxidative status of LDL in vivo and of its potential atherogenicity.

Oxidative Modification of Low-Density Lipoprotein and Atherogenetic Risk in β-Thalassemia

We investigated the oxidative state of low-density lipoprotein (LDL) in patients with β-thalassemia to determine whether there was an association with atherogenesis. Conjugated diene lipid hydroperoxides (CD) and the level of major lipid antioxidants in LDL, as well as modified LDL protein, were evaluated in 35 β-thalassemia intermedia patients, aged 10 to 60, and compared with age-matched healthy controls. Vitamin E and β-carotene levels in LDL from patients were 45% and 24% of that observed in healthy controls, respectively. In contrast, the mean amount of LDL-CD was threefold higher and lysil residues of apo B-100 were decreased by 17%. LDL-CD in thalassemia patients showed a strong inverse correlation with LDL vitamin E (r = −0.784; P &lt; .0001), while a negative trend was observed with LDL-β–carotene (r = −0.443; P = .149). In the plasma of thalassemia patients, malondialdehyde (MDA), a byproduct of lipid peroxidation, was increased by about twofold, while vitamin E showed a 52% decrease versus healthy controls. LDL-CD were inversely correlated with plasma vitamin E (r = −0.659; P &lt; .0001) and correlated positively with plasma MDA (r = 0.621; P &lt; .0001). Plasma ferritin was positively correlated with LDL-CD (r = 0.583; P =.0002). No correlation was found between the age of the patients and plasma MDA or LDL-CD. The LDL from thalassemia patients was cytotoxic to cultured human fibroblasts and cytotoxicity increased with the content of lipid peroxidation products. Clinical evidence of mild to severe vascular complications in nine of the patients was then matched with levels of LDL-CD, which were 36% to 118% higher than the mean levels of the patients. Our results could account for the incidence of atherogenic vascular diseases often reported in β-thalassemia patients. We suggest that the level of plasma MDA in β-thalassemia patients may represent a sensitive index of the oxidative status of LDL in vivo and of its potential atherogenicity.

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.

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.

Increased susceptibility of low-density lipoprotein (LDL) to oxidation by γ-radiolysis with age

The susceptibility to oxidation of freshly isolated LDL from healthy normolipidemic individuals in three age groups was estimated by exposure of LDL to ionizing radiation followed by analyses of vitamin E, TBARS, conjugated dienes, and fluorescent products. The results clearly showed that LDL from elderly subjects was the most susceptible to oxidative damage in vitro. In particular, the greater susceptibility of LDL from elderly subjects in comparison to that from young subjects may be attributed to the much lower (4-fold) concentration of LDL vitamin E in the elderly subjects. The present study reinforces the notion that the susceptibility of LDL to oxidation increases with age.

Cadmium and atherosclerosis in the rabbit: Reduced atherogenesis by superseding of iron?

This study evaluated the effect of dietary cadmium (Cd) on atherosclerosis in the rabbit. Cholesterol was added to the diet to initiate and/or accelerate atherogenesis. Cd was added to the diet at two dose levels. Uptake of Cd was 55 μg/kg body weight (BW)/day at the low dose level and 1350 μg/ kg BW/day at the high dose level. Five groups of rabbits were fed five different diets for 9 months: (l) basal diet without additional constituents; (2) background diet, which was basal diet to which cholesterol had been added; (3) the low-dose level Cd diet, which was background diet to which 2 mg Cd/kg had been added; (4) high-dose level Cd diet, which was background diet to which 50 mg Cd/kg had been added; and (5) basal diet to which 50 mg Cd/kg had been added. Dietary cholesterol increased blood total leucocyte count, serum and liver total cholesterol concentrations, serum total bilirubin concentration, low-density lipoprotein vitamin E concentration and induction of atherosclerotic plaques in the aorta and coronary arteries. Cd in the diet increased liver and kidney Cd concentrations in a dose-dependent way, decreased prothrombin time and temporarily increased urea and creatinine clearances. Slight kidney damage was induced by Cd only in animals fed the high-dose level Cd diet (with or without cholesterol). Dietary Cd partly counteracted the dietary cholesterol-induced increases of serum and liver total cholesterol concentrations, and tended to reduce plaque formation in the aorta. Dietary Cd in rabbits fed cholesterol-containing diets influenced cholesterol metabolism and tended to decrease atherosclerosis in a dose-related fashion. This is in contrast with limited epidemiological human data. Dietary Cd also decreased serum ferritin concentration and increased serum transferrin concentration. Free iron concentration is associated with myocardial infarction in man and augments the development of atherosclerosis in rabbits. It is concluded that the observed reduction in atherogenesis is related to dietary Cd-induced changes in cholesterol metabolism, increased rheology of blood and/or, most likely, reduced free iron concentration.

Inverse relation between the concentration of low-density-lipoprotein vitamin E and severity of coronary artery disease

Oxidation of low-density lipoprotein (LDL) is believed to play an important role in atherogenesis, and antioxidant vitamins are thought to protect against coronary artery disease (CAD). We investigated whether the vitamin E concentrations in serum and LDL were associated with the severity of CAD as assessed by a semiquantitative scoring system in which coronary angiograms are analyzed for the number and size of distinct stenotic lesions (global stenosis score). The study group consisted of 64 consecutive male survivors of myocardial infarction aged < 45 y. Lipid-adjusted serum and LDL vitamin E concentrations were significantly lower in the patients than in 35 age-matched male control subjects, whereas the absolute serum and LDL vitamin E concentrations did not differ significantly. No associations were found between the serum concentration or lipid-adjusted serum values of vitamin E and the stenosis score. In contrast, significant inverse correlation was found between the LDL vitamin E concentration, whether adjusted to the lipid (r=-0.477,P<0.001) or protein (r=-0.375, P<0.01) content of LDL, and the global coronary stenosis score. We conclude that a low LDL vitamin E concentration might play a role in the development of stenoses in coronary arteries and may contribute to clinically manifest CAD.

Dietary non-tocopherol antioxidants present in extra virgin olive oil increase the resistance of low density lipoproteins to oxidation in rabbits

Consumption of a range of dietary antioxidants may be beneficial in protecting low density lipoprotein (LDL) against oxidative modification, as studies have demonstrated that antioxidants other than vitamin E may also function against oxidation of LDL in vitro. In the present study, the effect of polyphenol antioxidants on the susceptibility of LDL to copper-mediated oxidation was investigated after feeding semi-purified diets to 3 groups of New Zealand white (NZW) rabbits. All diets comprised 40% energy as fat with 17% energy as oleic acid. Dietary fatty acid compositions were identical. Oils with different polyphenol contents were used to provide the dietary source of oleic acid — refined olive oil, extra virgin olive oil and Trisun high oleic sunflower seed oil. Polyphenolic compounds (hydroxytyrosol and p-tyrosol) could only be detected in the extra virgin olive oil. Vitamin E was equalised in all diets. LDL oxidizability in vitro was determined by continuously monitoring the copper-induced formation of conjugated dienes after 6 weeks of experimental diet feeding. The lag phase before demonstrable oxidation occurred was significantly increased in the high polyphenol, extra virgin olive oil group ( P < 0.05) when compared with combined results from the low polyphenol group (refined olive oil and Trisun), even though the LDL vitamin E concentration in the high polyphenol group was significantly lower. The rate of conjugated diene formation was not influenced by the presence of dietary polyphenols. Results demonstrate that antioxidants, possibly phenolic compounds which are present only in extra virgin olive oil, may contribute to the endogenous antioxidant capacity of LDL, resulting in an increased resistance to oxidation as determined in vitro.

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.

Vitamin C prevents metal ion-dependent initiation and propagation of lipid peroxidation in human low-density lipoprotein

Lipid peroxidation and oxidative modification of low-density lipoprotein (LDL) have been implicated as causal factors in the pathogenesis of atherosclerosis, and prevention of LDL oxidation by antioxidants may be an effective strategy to inhibit the progression of the disease. We investigated the effects of the reduced form of vitamin C ( l-ascorbic acid, AA) and its two-electron oxidation product (dehydro- l-ascorbic acid, DHA) upon metal ion-dependent oxidative modification of human LDL. We found that low micromolar concentrations of both AA and DHA protect LDL against oxidation induced by Cu 2+ or by hemin and hydrogen peroxide. In a dose-dependent manner, AA and DHA prevented the initiation of lipid peroxidation in LDL, as determined by a sensitive and selective assay for lipid hydroperoxides utilizing HPLC with chemiluminescence detection. AA and DHA also preserved the LDL-associated antioxidants α-tocopherol, β-carotene, and lycopene, but not ubiquinol-10. Furthermore, AA was able to stop propagation of lipid peroxidation in LDL, whereas DHA lacked this ability. The addition of 60 μM AA to LDL containing up to 38 nmol/mg protein of pre-formed lipid hydroperoxides led to their rapid disappearance; this activity of AA was dependent on the presence of redox-active copper, but did not lead to the formation of lipid hydroxides, the reduced form of lipid hydroperoxides. Our data show that in Cu 2+-exposed LDL (i) vitamin C primarily spares, rather than regenerates, α-tocopherol and other endogenous antioxidants, except for ubiquinol-10; (ii) AA and DHA, unlike the LDL-associated antioxidants, act as preventive rather than chain-breaking antioxidants, i.e., AA and DHA prevent initiation of lipid peroxidation in LDL; and (iii) AA can terminate lipid peroxidation, thereby protecting partially oxidized LDL against further oxidative modification.

Susceptibility of low density lipoprotein to oxidation in familial hypercholesterolaemia

There is increasing evidence that oxidative modification of low density lipoprotein (LDL) plays an important role in the pathogenesis of atherosclerosis. Subjects with familial hypercholesterolaemia (FH) have elevated concentrations of LDL and develop premature atherosclerosis. The aim of the study was to determine whether the susceptibility of LDL to in vitro oxidation is increased in FH subjects. LDL was isolated from 15 FH homozygotes (mean age ± SD, 19 ± 10 years; mean LDL-cholesterol 16.86 ± 3.55 mmol/1), 15 FH heterozygotes (38 ± 13 years; LDL-cholesterol 5.58 ± 1.78 mmol/1) and 15 normocholesterolaemic subjects ( 31 ± 8 years; LDL-cholesterol 3.07 ± 0.77 mmol/1). Susceptibility of LDL to in vitro copper-mediated oxidation was assessed by measuring conjugated diene production at 234 nm, the lag phase being a measure of the resistance of LDL to oxidation. Unexpectedly, the mean duration of the lag phase was 2.2 fold longer in the FH homozygotes (123.8 ± 45.0 min) and 1.75-fold longer in the FH heterozygotes (99.9 ± 40.6 min) than in the controls (57.1 ± 27.9 min; P < 0.0001). Serum and LDL vitamin E levels were higher in the FH patients, but not when expressed relative to LDL-cholesterol concentration. There was also no correlation between LDL vitamin E concentration and duration of the lag phase. LDL bulk rather than the susceptibility of LDL to oxidation is probably the more important factor for the initiation and progression of atherosclerosis in FH patients.