Plasma lipid composition and LDL oxidation.

Low-density lipoprotein (LDL) oxidation in vivo depends on lipid composition and on plasma antioxidant status. The aim of our study was to investigate the relationship between plasma lipid composition and LDL oxidation and, in particular, to explore whether LDL-cholesterol/triglycerides ratio (LDL-C/TG) and LDL-cholesterol/high-density lipoprotein (HDL)-cholesterol ratio (LDL-C/HDL-C) can be used as predictive parameters of LDL oxidation in vivo. In 87 volunteers over a wide range of age plasma lipids and LDL oxidation were studied. Blood was collected after 12 h overnight fast. LDL oxidation was estimated by the level of conjugated diene (BDC) in the lipid fraction isolated from plasma after gradient ultra-centrifugation. The results were expressed as micromol/l (BDC/l) to evaluate the level of oxidized LDL, and as nmol of BDC for mg of LDL-cholesterol (BDC/LDL-C) for the evaluation of LDL oxidation degree. BDC/l correlated significantly with age, total and LDL-C, apolipoprotein B and TG, while BDC/LDL-C negatively correlated with total cholesterol, apolipoprotein B, LDL/TG and LDL/HDL ratios. Age of subjects significantly correlated with total and LDL-C and apolipoprotein B. TG have a significant inverse correlation with HDL-C. Our results support the hypothesis that among the several factors involved in LDL oxidation the most important determinants are LDL/TG. Plasma triglycerides appear to be very important even when circulating cholesterol levels are within normal limits. Moreover, we found that the LDL/HDL ratio is also very important with regard to the putative protective role of HDL against LDL oxidation in vivo. In conclusion, plasma lipid parameters must be evaluated not only for their absolute values but also for their mutual ratios as expression of plasma lipid homeostasis. Both LDL/TG and LDL/HDL ratios can be used as predictive parameters of in vivo LDL oxidation.     

LDL susceptibility to oxidation and HDL antioxidant capacity in patients with renal failure

Objectives

This study examines the susceptibility to oxidation and the ability to stimulate reactive oxygen species of LDL from hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD) patients. It was also designed to evaluate the antioxidant activity of HDL from uremic patients.

Design and methods

Lipoprotein properties were determined in 28 HD patients, 30 CAPD patients and 30 control subjects by spectrophotometric, chemiluminescence and electrophoresis methods.

Results

CAPD LDL were more resistant to oxidation than control LDL. HD and control LDL, in contrast to CAPD LDL, stimulated reactive oxygen species generation in granulocytes. The HDL ability to protect LDL against oxidation was impaired in renal patients.

Conclusions

The risk of atherosclerosis development in patients with renal failure does not appear to be related to less resistance of LDL to oxidation, but rather to the decreased HDL antioxidant capacity.     

Beneficial effects of virgin coconut oil on lipid parameters and in vitro LDL oxidation

OBJECTIVES: The present study was conducted to investigate the effect of consumption of virgin coconut oil (VCO) on various lipid parameters in comparison with copra oil (CO). In addition, the preventive effect of polyphenol fraction (PF) from test oils on copper induced oxidation of LDL and carbonyl formation was also studied. DESIGN AND METHODS: After 45 days of oil feeding to Sprague-Dawley rats, several lipid parameters and lipoprotein levels were determined. PF was isolated from the oils and its effect on in vitro LDL oxidation was assessed. RESULTS: VCO obtained by wet process has a beneficial effect in lowering lipid components compared to CO. It reduced total cholesterol, triglycerides, phospholipids, LDL, and VLDL cholesterol levels and increased HDL cholesterol in serum and tissues. The PF of virgin coconut oil was also found to be capable of preventing in vitro LDL oxidation with reduced carbonyl formation. CONCLUSION: The results demonstrated the potential beneficiary effect of virgin coconut oil in lowering lipid levels in serum and tissues and LDL oxidation by physiological oxidants. This property of VCO may be attributed to the biologically active polyphenol components present in the oil.     

Effects of soy and other natural products on LDL:HDL ratio and other lipid parameters: A literature review

Abnormal lipid levels contribute significantly to the risk of coronary heart disease, a major cardiovascular disease and a serious health problem. Various dietary and pharmacologic treatments have been devised to reduce elevated blood cholesterol levels. Soy protein, soluble fiber, and plant sterol/ester-containing margarines are promising new food-component candidates that may help to realize this goal. Of particular interest in this context is the LDL:HDL ratio, a strong predictor of cardiac events. This report is a review of more than 50 recent trials to determine how such dietary components and garlic affect the LDL:HDL ratio and other lipid parameters. Consumption of new soy products containing high, fixed levels of isoflavones, cotyledon soy fiber, and soy phospholipids (Abaco and Abalon) significantly reduced the LDL:HDL ratio by up to 27%. Soluble dietary fibers such as psyllium and beta glucan from oat bran had a variable effect on LDL-cholesterol levels in the studies analyzed. Plant sterol esters, when consumed in margarines, lowered the LDL:HDL ratio by up to 22%. On average, Abacor and Abalon reduced the LDL:HDL ratio by 20%, LDL cholesterol by 15%, total cholesterol by 10%, and triglycerides by 6%, and increased HDL cholesterol by 5%. The new soy-based supplements may therefore play a valuable role in reducing cardiovascular risk.     

Mechanism of in vitro heme-induced LDL oxidation: effects of antioxidants

BACKGROUND: Heme protein toxicity, owing to generation of reactive oxygen species most likely by direct interaction between heme iron and hydrogen peroxide (H2O2), may be involved in various pathologies, including atherogenesis and pigmentary acute renal failure. The aim of this study was to investigate the mechanism of heme cytotoxicity and the effects of antioxidant therapies in an in vitro model of heme-induced low-density lipoprotein (LDL) oxidation. MATERIALS AND METHODS: Human LDLs were exposed to heme, iron (Fe), protoporphyrin (PPIX) and PPIX-Zinc (Zn) with or without H2O2. Lipid peroxidation was monitored by measurement of conjugated diene formation (at the 234-nm absorbance). The effect of various antioxidants, such as vitamin E and vitamin C, reduced glutathione (GSH), and oxidized glutathione (GSSG), mannitol and desferoxamine (DFO) was further investigated in the established in vitro model of LDL oxidation. RESULTS: Incubation of LDLs in the presence of heme/H2O2 induced lipid peroxidation with the optimal oxidation rate being at 5 microm heme/100 microm H2O2 doses. By contrast, incubation of LDL with H2O2, Fe, Fe/H2O2, PPIX, PPIX/H2O2, heme or PPIX-Zn did not initiate any LDL oxidation. In vitro, the vitamin E load protected native LDLs against heme/H2O2 oxidative modifications. Incubation of LDLs with increasing doses of vitamin C, GSH and DFO conferred a dose-dependent protection, while mannitol and GSSG had no effect. CONCLUSIONS: Initiation and propagation of heme-induced lipid peroxidation is not mediated by a Fenton reaction but depends on specific interactions between heme and H2O2. It may result from the generation of ferryl and perferryl radicals derived from hemic Fe and H2O2 interactions. A protective effect of vitamins E, C, GSH and DFO was demonstrated in this model.     

Coenzyme Q10, Alpha-Tocopherol and Free Cholesterol in HDL and LDL Fractions

Twenty-three randomly selected plasma samples from apparently healthy, middle aged men were analysed for coenzyme Q₁₀ (CoQ₁₀), alpha-tocopnerol (AT) and free cholesterol (FC) in: 1) whole plasma, 2) the HDL lipoprotein fraction after LDL precipitation (VLDL + LDL). CoQ₁₀, AT and FC in plasma averaged 0.69 ±. 11,6.74 ± 1.78 μg ± ml^?1 and 0.59 ±. 11 mg ± ml^?1 and in HDL 0.17, 3.24 μg × ml^?1 and 0.17 mg × ml^?1 or 29, 48 and 29% of plasma values. Amounts of CoQ₁₀ and AT were correlated to that of FC in all pools. The amount of HDL-CoQ₁₀ but not of HDL-AT fell, with the HDL-FC expressed as the fraction of plasma FC. In all pools, N-AT versus AT initially increased and then levelled off, indicating saturation like conditions in contrast to CoQ₁₀. Thus, CoQ₁₀ and AT are differently allocated in HDL and LDL. This might have a bearing both on the suggested lipoprotein protection against peroxidation by these two antioxidants, but also on the distribution and allocation in different organs of CoQ₁₀ and AT by HDL and LDL transportation.     

Ednit influence on oxidation resistance of LDL lipoproteins in hypertensive subjects]

AIM: Evaluation of resistance of low density lipoproteins (LDLP) of the serum to oxidation in patients with essential hypertension (EH) before and after course treatment with ednit. MATERIALS AND METHODS: 10 patients with mild or moderate EH aged 38-58 years were given ednit for 1 or 2 months. 10 healthy males aged 35-48 years served control. RESULTS: EH patients had high baseline levels of lipid peroxidation products in LDLP, while antioxidant resistance of LDPL was diminished by 67% (p < 0.05) compared to controls. Ednit treatment for 1 and 2 months enhanced this resistance in mild and moderate EH (p < 0.05). CONCLUSION: Ednit raises resistance of LDLP to oxidation and as ACE inhibitor lowers arterial pressure. Therefore it can be used in EH.     

Anti-inflammatory HDL becomes pro-inflammatory during the acute phase response. Loss of protective effect of HDL against LDL oxidation in aortic wall cell cocultures.

We previously reported that high density lipoprotein (HDL) protects against the oxidative modification of low density lipoprotein (LDL) induced by artery wall cells causing these cells to produce pro-inflammatory molecules. We also reported that enzyme systems associated with HDL were responsible for this anti-inflammatory property of HDL. We now report studies comparing HDL before and during an acute phase response (APR) in both humans and a croton oil rabbit model. In rabbits, from the onset of APR the protective effect of HDL progressively decreased and was completely lost by day three. As serum amyloid A (SAA) levels in acute phase HDL (AP-HDL) increased, apo A-I levels decreased 73%. Concomitantly, paraoxonase (PON) and platelet activating factor acetylhydrolase (PAF-AH) levels in HDL declined 71 and 90%, respectively, from days one to three. After day three, there was some recovery of the protective effect of HDL. AP-HDL from human patients and rabbits but not normal or control HDL (C-HDL) exhibited increases in ceruloplasmin (CP). This increase in CP was not seen in acute phase VLDL or LDL. C-HDL incubated with purified CP and re-isolated (CP-HDL), lost its ability to inhibit LDL oxidation. Northern blot analyses demonstrated enhanced expression of MCP-1 in coculture cells treated with AP-HDL and CP-HDL compared to C-HDL. Enrichment of human AP-HDL with purified PON or PAF-AH rendered AP-HDL protective against LDL modification. We conclude that under basal conditions HDL serves an anti-inflammatory role but during APR displacement and/or exchange of proteins associated with HDL results in a pro-inflammatory molecule.     

Lipid modification in type 2 diabetes: the role of LDL and HDL

Patients with type 2 diabetes feature important modification of both low density lipoprotein (LDL) and high density lipoprotein particles which are likely to play an important role in the development of atherosclerosis. Although plasma LDL cholesterol level is usually normal in type 2 diabetic patients, LDLs show a significant increase in their plasma residence time which may promote cholesterol deposition in the arterial wall. Moreover, important qualitative abnormalities of LDLs, potentially atherogenic, are observed in type 2 diabetic patients: small dense, triglyceride-rich, LDL particles (known as subclass B), oxidized LDL and glycated LDL. All these qualitative modification of LDLs amplify the atherosclerotic process.
Plasma high density lipoprotein (HDL) cholesterol is decreased in type 2 diabetes related to increased catabolism of HDL particles. One of the mechanism responsible for increased catabolism of HDLs is hypertriglyceridemia, promoting through cholesteryl ester transfer protein (CETP) the transfer of triglycerides (TG) to HDL leading to the formation of TG-rich HDLs which are very good substrates for hepatic lipase, enzyme in charge of HDLs catabolism. The reduction in plasma adiponectin level, observed in type 2 diabetes may be another mechanism involved in the diminution of HDL cholesterol. Furthermore, qualitative abnormalities of HDLs are described in type 2 diabetes: enrichment in triglycerides and glycation, which may impair HDL-mediated cholesterol efflux and reverse cholesterol transport. In addition to their role in reverse cholesterol transport, HDLs usually show antioxidative, anti-inflammatory, anti-thrombotic and endothelium-dependent vasorelaxant effects. It has been shown that HDLs from patients with type 2 diabetes have a significant reduction in their antioxidative and endothelium-dependent vasorelaxant properties.     

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     

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.     

Serum LDL cholesterol,the LDL/HDL cholesterol ratio and liver microsomal enzyme induction evaluated by antipyrine kinetics

The association of serum LDL and HDL cholesterol with hepatic microsomal enzyme induction, assessed by plasma antipyrine kinetics was investigated in 30 epileptics. Patients on enzyme-inducing anticonvulsants had reduced LDL/HDL cholesterol ratios and elevated HDL cholesterol concentrations and HDL/total cholesterol ratios, indicating a cholesterol transfer from LDL to HDL. Strong hepatic microsomal enzyme induction was associated with reduced LDL cholesterol. The LDL/HDL cholesterol ratio was negatively proportional and the HDL/total cholesterol ratio positively proportional to the antipyrine clearance rate. Epileptics, particularly those with a high antipyrine clearance, had a cholesterol distribution pattern characteristic of a low probability of developing coronary atherosclerosis. The results support the view that hepatic microsomal enzyme induction favourably alters the cholesterol distribution in the body.     

Oxidation of LDL enhances the cholesteryl ester transfer protein (CETP)-mediated cholesteryl ester transfer rate to HDL, bringing on a diminished net transfer of cholesteryl ester from HDL to oxidized LDL

Cholesteryl ester transfer protein (CETP) plays a controversial role in atherogenesis by contributing to the net transfer of high density lipoprotein (HDL) cholesteryl ester (CE) to the liver via apolipoprotein-B-containing lipoproteins (apoB-LP). We evaluated in vitro the CETP-mediated bidirectional transfer of CE from HDL to the chemically modified pro-atherogenic low density lipoprotein (LDL) particles. Acetylated or oxidized (ox) LDL, either unlabeled or [3H]-CE labeled, were incubated with [14C]-CE-HDL in the presence of the lipoprotein-deficient plasma fraction (d>1.21 g/ml) as the source of CETP. The amount of radioactive CE transferred was determined after dextran sulfate/MgCl(2) precipitation of LDL. The results showed a 1.4-2.8-fold lower HDL-CE transfer to acetylated LDL while no effect was observed on the CE transfer to oxidized LDL. However, the reverse transfer rate of [3H]CE-LDL to HDL was 1.4-3.6 times greater when LDL was oxidized than when it was intact. Overall, HDL(2) was better than HDL(3) as donor of CE to native LDL, probably reflecting the relatively greater CE content of HDL(2). Oxidation of LDL enhanced the CETP-mediated cholesteryl ester transfer rate to HDL, bringing on a reduced net transfer rate of cholesteryl ester from HDL to ox LDL. This may diminish the oxLDL particle's atherogenic effect.     

Serum LDL cholesterol, the LDL/HDL cholesterol ratio and liver microsomal enzyme induction evaluated by antipyrine kinetics

The association of serum LDL and HDL cholesterol with hepatic microsomal enzyme induction, assessed by plasma antipyrine kinetics was investigated in 30 epileptics. Patients on enzyme-inducing anticonvulsants had reduced LDL/HDL cholesterol ratios and elevated HDL cholesterol concentrations and HDL/total cholesterol ratios, indicating a cholesterol transfer from LDL to HDL. Strong hepatic microsomal enzyme induction was associated with reduced LDL cholesterol. The LDL/HDL cholesterol ratio was negatively proportional and the HDL/total cholesterol ratio positively proportional to the antipyrine clearance rate. Epileptics, particularly those with a high antipyrine clearance, had a cholesterol distribution pattern characteristic of a low probability of developing coronary atherosclerosis. The results support the view that hepatic microsomal enzyme induction favourably alters the cholesterol distribution in the body.     

Reagent-free, simultaneous determination of serum cholesterol in HDL and LDL by infrared spectroscopy

BACKGROUND: The purpose of this study was to assess the feasibility of infrared (IR) spectroscopy for the simultaneous quantification of serum LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) concentrations. METHODS: Serum samples (n = 90) were obtained. Duplicate aliquots (5 microL) of the serum specimens were dried onto IR-transparent barium fluoride substrates, and transmission IR spectra were measured for the dry films. In parallel, the HDL-C and LDL-C concentrations were determined separately for each specimen by standard methods (the Friedewald formula for LDL-C and an automated homogeneous HDL-C assay). The proposed IR method was then developed with a partial least-squares (PLS) regression analysis to quantitatively correlate IR spectral features with the clinical analytical results for 60 randomly chosen specimens. The resulting quantification methods were then validated with the remaining 30 specimens. The PLS model for LDL-C used two spectral ranges (1700-1800 and 2800-3000 cm(-1)) and eight PLS factors, whereas the PLS model for HDL-C used three spectral ranges (800-1500, 1700-1800, and 2800-3500 cm(-1)) with six factors. RESULTS: For the 60 specimens used to train the IR-based method, the SE between IR-predicted values and the clinical laboratory assays was 0.22 mmol/L for LDL-C and 0.15 mmol/L for HDL-C (r = 0.98 for LDL-C; r = 0.91 for HDL-C). The corresponding SEs for the test spectra were 0.34 mmol/L (r = 0.96) and 0.26 mmol/L (r = 0.82) for LDL-C and HDL-C, respectively. The precision for the IR-based assays was estimated by the SD of duplicate measurements to be 0.11 mmol/L (LDL-C) and 0.09 mmol/L (HDL-C). CONCLUSIONS: IR spectroscopy has the potential to become the clinical method of choice for quick and simultaneous determinations of LDL-C and HDL-C.     

Coenzyme Q10, alpha-tocopherol and free cholesterol in HDL and LDL fractions.

Twenty-three randomly selected plasma samples from apparently healthy, middle aged men were analysed for coenzyme Q10 (CoQ10), alpha-tocopherol (AT) and free cholesterol (FC) in: 1) whole plasma, 2) the HDL lipoprotein fraction after LDL precipitation (VLDL + LDL). CoQ10, AT and FC in plasma averaged 0.69 +/- .11, 6.74 +/- 1.78 micrograms x ml-1 and 0.59 +/- .11 mg x ml-1 and in HDL 0.17, 3.24 micrograms x ml-1 and 0.17 mg x ml-1 or 29, 48 and 29% of plasma values. Amounts of CoQ10 and AT were correlated to that of FC in all pools. The amount of HDL-CoQ10 but not of HDL-AT fell, with the HDL-FC expressed as the fraction of plasma FC. In all pools, N-AT versus AT initially increased and then levelled off, indicating saturation like conditions in contrast to CoQ10. Thus, CoQ10 and AT are differently allocated in HDL and LDL. This might have a bearing both on the suggested lipoprotein protection against peroxidation by these two antioxidants, but also on the distribution and allocation in different organs of CoQ10 and AT by HDL and LDL transportation.     

Serum total, HDL, LDL cholesterol, and triglyceride levels in patients with rheumatoid arthritis

Patients with rheumatoid arthritis are at risk of increased prevalence of coronary heart disease. In general, the plasma level of high density lipoprotein cholesterol (HDL) correlates with the risk of incidence of ischemic heart disease. The levels of total, HDL, low density (LDL) cholesterol, and triglycerides were measured in sera of patients with rheumatoid arthritis and in healthy controls. In patients with rheumatoid arthritis (26 men and 103 women), the serum total and LDL cholesterol were higher, whereas the HDL cholesterol and triglycerides were lower (p less than 0.001) compared to the values observed in controls (625 men and 749 women). Similar patterns were seen when results of age and sex matched controls were compared to the results of patients suffering from rheumatoid arthritis. The lipid parameters of patients with rheumatoid arthritis were not different when the patients were treated with steroidal or nonsteroidal anti-inflammatory drugs.