Lag Time Of Low-density Lipoprotein Oxidation Research Articles

Does Acute Exercise Affect the Susceptibility of Low Density Lipoprotein to Oxidation?

This study describes the effect of an acute exercise bout on the susceptibility of isolated low density lipoprotein (LDL) to in vitro oxidation. LDL was isolated from 23 subjects (exercisers, n = 11; sedentary, n = 12) immediately before and after a single bout of exercise (30 min of treadmill work at 55% & 70% peak oxygen consumption (VO2 peak) for exercisers and sedentary, respectively). A statistically significant decrease in lag time for LDL oxidation was observed following exercise compared to baseline (96.1 ± 23.5 min vs. 92.1 ± 23.3 minutes; n = 23, p ≤ .03) using a 5 μM copper system. There was a statistically significant increase in plasma myeloperoxidase (MPO) levels following exercise compared to baseline values (1.58 ± .91 ng/dl versus 2.08 ± 1.2 ng/dl; n = 12, p ≤ .03). These results suggest that the 30 min exercise bout at a moderate intensity and duration was a sufficient oxidative stress to increase the susceptibility of LDL to in vitro oxidation. Additionally, the exercise bout appeared to activate neutrophils, subsequently releasing MPO protein.

Effect of alpha-tocopherol on LDL oxidation and glycation: in vitro and in vivo studies

Much data support a role for both low density lipoprotein (LDL) oxidation and glycation in atherogenesis. While alpha-tocopherol decreases the oxidative susceptibility of LDL, its role in decreasing LDL glycation is unclear. Hence we tested the effect of alpha-tocopherol both in vitro and in vivo on LDL oxidation and glycation. LDL was isolated after enrichment of plasma with alpha-tocopherol. This resulted in a 2-fold increase in alpha-tocopherol in LDL (AT-LDL). During a 6-day incubation of control LDL (C-LDL) and AT-LDL with 25 mM glucose, there were no significant differences in the degree of glycation on days 1, 3, and 6. Also, apoB advanced glycosylation end product levels were not significantly different between C-LDL and AT-LDL. There was a progressive increase in the susceptibility of LDL to oxidation with increasing LDL glycation as evidenced by reduced lag time of copper-catalyzed LDL oxidation. However, AT-LDL was more resistant to copper-catalyzed oxidation. Similar findings were observed when the LDLs were incubated with endothelial cells. The data from the alpha-tocopherol supplementation study confirmed our in vitro findings that alpha-tocopherol significantly decreases oxidative susceptibility of LDL, but does not affect its glycation. Therefore, while glycation increases LDL oxidative susceptibility, alpha-tocopherol decreases the oxidation of glycated LDL but not LDL glycation.

Inhibitory effect of ebselen on the oxidation of low density lipoprotein.

The inhibitory effect of a synthesized glutathione peroxidase (GSHPX) mimic- ebselen, and its cofactor glutathione (GSH), on the oxidation of low density lipoprotein (LDL) induced by Cu(2+) was studied by determination of hydroperoxides and thiobarbituric acid reactive substances (TBARS). Ebselen alone had a strong inhibitory effect on the oxidation of LDL. The lag time of LDL oxidation was prolonged with an increase in the concentration of ebselen. The inhibitory effect of 5 μM ebselen was equivalent to that of 50 μM α-tocopherol. When GSH was present, ebselen exhibited stronger inhibitory effect than when present alone. With 50 μM GSH, ebselen at a concentration as low as 5 μM could inhibit oxidation of LDL induced by 5 μM Cu(2+) completely for at least 24 h. Ebselen at high concentrations (100 μM) decomposed hydroperoxides in pre-oxidized LDL and effectively prevented its further oxidation, but not in the present of EDTA. Low concentration of ebselen (5 μM) plus GSH (50 μM) decomposed hydroperoxides in pre-oxidized LDL whether EDTA was added or not.

Effects of Vitamin E on Susceptibility of Low-Density Lipoprotein and Low-Density Lipoprotein Subfractions to Oxidation and on Protein Glycation in NIDDM

To evaluate the effect of vitamin E supplementation on the susceptibility of low-density lipoprotein (LDL) and LDL subfractions to oxidation and on protein glycation in non-insulin-dependent diabetes mellitus (NIDDM). Twenty-one men with NIDDM (HbA1c = 6-10%), ages 50-70, were randomly assigned to either 1,600 IU/day of vitamin E or placebo for 10 weeks after a 4-week placebo period. LDL and LDL subfractions were isolated after 4 weeks of placebo and after 6 and 10 weeks of therapy. Susceptibility of LDL to copper-mediated oxidation was measured by conjugated diene formation (lag time) and formation of thiobarbituric acid-reactive substances (TBARS). Fasting serum glucose, mean weekly blood glucose, HbA1c, and glycated plasma protein concentrations were also determined at these time points. Vitamin E content in plasma and LDL increased 4.0- and 3.7-fold, respectively, in the vitamin E-treated group. Vitamin E decreased the susceptibility of LDL to oxidation in comparison with placebo (lag time, 243 +/- 46 vs. 151 +/- 22 min, P < 0.01; 3 h TBARS, 24 +/- 12 vs. 66 +/- 18 nmol malondialdehyde/mg LDL, P < 0.05). Vitamin E content also increased significantly in both buoyant and dense LDL subfractions, and their oxidation was dramatically reduced. The lag time of LDL oxidation correlated well with the content of vitamin E in both LDL and its subfractions (r = 0.69-0.92). Glycemic indexes did not change significantly in either group during the study. Protein glycation, including glycated hemoglobin, glycated albumin, glycated total plasma proteins, and glycated LDL were unchanged in the vitamin E group. Supplementation of vitamin E in NIDDM leads to enrichment of LDL and LDL subfractions and reduced susceptibility to oxidation. Despite a greater percentage increase in vitamin E content in small dense LDL, it remained substantially more susceptible to oxidation than was buoyant LDL. This suggests that dense, LDL may gain less protection against oxidation from antioxidant supplementation than does larger, more buoyant LDL. In contrast to previous reports, vitamin E supplementation did not reduce glycation of intracellular or plasma proteins.

Oxidation of low-density lipoproteins: effect of antioxidant content, fatty acid composition and intrinsic phospholipase activity on susceptibility to metal ion-induced oxidation

The oxidative modification of low-density lipoprotein (LDL) may play an important role in atherogenesis. Our understanding of the mechanism of LDL oxidation and the factors that determine its susceptibility to oxidation is still incomplete. We have isolated LDL from 45 healthy individuals and studied the relationship between LDL fatty acid, vitamin E and β-carotene composition, intrinsic phospholipase A 2-like activity and parameters of LDL oxidation. LDL was exposed to a copper ion-dependent oxidising system and the kinetics of oxidation studied by monitoring formation of fatty acid conjugated dienes. The length of the lag phase of inhibited lipid peroxidation was measured as well as the rate of lipid peroxidation during the propagation phase. There was no significant correlation between LDL antioxidant vitamin or fatty acid composition and lag time to LDL oxidation. Oleic acid was negatively correlated with the rate of LDL oxidation ( r = −0.41, P < 0.01) whilst linoleic acid was significantly correlated with the extent of LDL oxidation measured by the production of total dienes ( r = 0.34, P < 0.05). Interestingly, LDL vitamin E content was positively correlated with both the rate ( r = 0.28, P < 0.05) and extent of LDL oxidation ( r = 0.43, P < 0.01). LDL isolated from this group of subjects showed significant intrinsic phospholipase-like activity. The phospholipase activity, whilst not correlated with lag time, was significantly correlated with both rate ( r = 0.43, P < 0.01) and total diene production ( r = 0.44, P < 0.01) of LDL oxidation. We conclude that antioxidant content, fatty acid composition and intrinsic phospholipase activity have little influence on the lag time of Cu-induced LDL oxidation. These components do however, significantly influence both the rate and extent of LDL oxidation, with increased vitamin E, linoleic acid content and phospholipase activity associated with faster and more extensive oxidation. The possible pro-oxidant effect of vitamin E has interesting implications for the postulated ‘protective’ effects of vitamin E on atherogenesis.

Effects of Ca-antagonists on oxidative susceptibility of low density lipoprotein (LDL).

Twelve adults (age 32-61 years) with essential hypertension were recruited from the outpatient clinics of National Defense Medical College hospital to serve as subjects in the present study. They were treated with nilvadipine, a Ca-antagonist, 4 mg b.i.d. for 4 weeks. LDL samples were isolated by ultracentrifugation at the beginning (week 0) and at the end (week 4) of the treatment regimen. The formation of conjugated dienes was measured by incubating 100 micrograms of LDL protein with 2 mumol CuSO4 in 2 ml phosphate buffered saline (PBS). There were no significant differences between lipids levels, composition and anti-oxidant levels of LDL at weeks 0 and 4. The lag time of LDL oxidation was 71.1 +/- 11.3 min at week 0 and 81.3 +/- 13.2 min at week 4 (p < 0.05). In vitro studies of LDL oxidation, evaluated by thiobarbituric acid reactive substances (TBARS) and by agarose electrophoretic mobility, indicated that nilvadipine inhibited the oxidative modification of LDL while amlodipine, used as control, did not. Nilvadipine, a lipophilic Ca-antagonist, significantly prolonged the lag time of conjugated diene formation of LDL by 12.6% but amlodipine, a hydrophilic Ca-antagonist, had no major effect on LDL oxidation. These results suggest that Ca-antagonists are effective for the prevention of atherosclerosis but the effect is dependent upon the lipophilicity of the drugs.