Vitamin E reduces cholesterol esterification and uptake of acetylated low density lipoprotein in macrophages

The effects of vitamin E on cholesteryl ester (CE) metabolism in 1774 cells were examined. Pretreatment of 1774 cells with vitamin E at concentrations above 50 μM significantly decreased acetylated low density lipoprotein (LDL)-induced incorporation of [¹⁴C]oleate into CF in cells in a dose-dependent manner. This was partly due to vitamin E Also significantly inhibiting the uptake of [³H]CE-labeled acetylated LDL by 1774 cells. A trend existed toward suppression of acyl-CoA:cholesterol acyltransferase (ACAT) activity in the cell lysate at high vitamin E concentration, but there was no effect on hydrolysis of CE. These data indicate that vitamin E reduces the uptake of modified LDL and suppresses ACAT activity, resulting in less cholesterol esterification in macrophages; a novel mechanism underlying the antiatherogenic properties of vitamin E.     

Protective effect of olive oil and its phenolic compounds against low density lipoprotein oxidation

The protective effect of phenolic compounds from an olive oil extract, and of olive oils with (extra-virgin) and without (refined) phenolic components, on low density lipoprotein (LDL) oxidation was investigated. When added to isolated LDL, phenolics [0.025–0.3 mg/L caffeic acid equivalents (CAE)] increased the lag time of conjugated diene formation after copper-mediated LDL oxidation in a concentration-dependent manner. Concentrations of phenolics greater than 20 mg/L inhibited formation of thiobarbituric-acid reactive substances after AAPH-initiated LDL oxidation. LDL isolated from plasma after preincubation with phenolics (25–160 mg/L CAE) showed a concentration-dependent increase in the lag time of conjugated diene formation after copper-mediated LDL oxidation. Refined olive oil (0 mg/L CAE) and extra-virgin olive oil (0.1 and 0.3 mg/L CAE) added to isolated LDL caused an increase in the lag time of conjugated diene formation after copper-mediated LDL oxidation that was related to olive oil phenolic content. Multiple regression analysis showed that phenolics were significantly associated with the increase in lag time after adjustment for effects of other antioxidants; α-tocopherol also achieved a statistically significant effect. These results indicate that olive oil phenolic compounds protect LDL against peroxyl radical-dependent and metal-induced oxidation in vitro and could associate with LDL after their incubation with plasma. Both types of olive oil protect LDL from oxidation. Olive oil containing phenolics, however, shows more antioxidant effect on LDL oxidation than refined olive oil.     

Enhancement of low density lipoprotein binding to both low density lipoprotein receptor-positive and- negative cells by tetracycline antibiotics

Some tetracycline (TC) antibiotics, including TC and anhydrotetracycline, have been found to enhance specific binding of low density lipoprotein (LDL) to both LDL receptor-positive and-negative cells at relatively higher concentrations. When incubated at 37°C, the ability of LDL receptor-negative human fibroblasts to bind ¹²⁵I-LDL was increased from<2 to 45 ng/mg by 170 μM TC. In normal human fibroblasts and Hep G2 cells, ¹²⁵I-LDL binding was elevated 1.4- to 2-fold by 113 μM TC. The ¹²⁵I-LDL binding in the presence of TC was diminished by both heparin and EDTA. The enhancement by TC was not observed when ¹²⁵I-LDL binding was assayed at 4°C. TC enhanced LDL binding to paraformaldehyde-fixed Hep G2 cells, excluding LDL receptor induction in the mechanism. These results demonstrated that TC enhanced cellular LDL binding through a process not involving functional LDL receptors.     

Effects of dietary virgin olive oil phenols on low density lipoprotein oxidation in hyperlipidemic patients

The aim of this study was to assess the effects of the dietary intake of extra virgin olive oil on the oxidative susceptibility of low density lipoproteins (LDL) isolated from the plasma of hyperlipidemic patients. Ten patients with combined hyperlipidemia (mean plasma cholesterol 281 mg/dL, triglycerides 283 mg/dL) consumed a low-fat, low-cholesterol diet, with olive oil (20 g/d) as the only added fat, with no drug or vitamin supplementation for 6 wk. Then they were asked to replace the olive oil they usually consumed with extra virgin olive oil for 4 wk. LDL were isolated at the beginning, and after the 4 wk of dietary treatment. LDL susceptibility to CuSO₄-mediated oxidation was evaluated by measuring the extent of lipid peroxidation. We also determined fatty acid composition and vitamin E in plasma and LDL and plasma phenolic content. Extra virgin olive oil intake did not affect fatty acid composition of LDL but significantly reduced the copper-induced formation of LDL hydroperoxides and lipoperoxidation end products as well as the depletion of LDL linoleic and arachidonic acid. A significant increase in the lag phase of conjugated diene formation was observed after dietary treatment. These differences are statistically correlated with the increase in plasma phenolic content observed at the end of the treatment with extra virgin olive oil; they are not correlated with LDL fatty acid composition or vitamin E content, which both remained unmodified after the added fat change. This report suggests that the daily intake of extra virgin olive oil in hyperlipidemic patients could reduce the susceptibility of LDL to oxidation, not only because of its high monounsaturated fatty acid content but probably also because of the antioxidative activity of its phenolic compounds.     

Sedimentation equilibrium of human low density lipoprotein subfractions

The molecular weights of low density lipoprotein (LDL) subfractions were determined precisely by meniscus depletion sedimentation equilibrium. Equilibrium speeds ranged from 9743 to 5896 rpm. The average molecular weights of various LDL subfractions of S_f ^o values 9.49, 7.94, 6.42, 5.17, and 3.71 determined by sedimentation equilibrium were 2.97×10⁶; 3.13×10⁶; 2.89×10⁶; 2.45 ×10⁶; and 2.61×10⁶ daltons, respectively; and their respective densities were 1.0267, 1.0306, 1.0358, 1.0422, and 1.0492 g/ml. Minimal hydrated molecular weights for these fractions determined by flotation velocity at 37,020 rpm were 2.57×10⁶; 2.37×10⁶; 2.09×10⁶; 1.94×10⁶; and 1.81 ×10⁶ daltons; whereas similar molecular weights determined at 52,640 rpm were 2.53×10⁶; 2.27 ×10⁶; 1.99×10⁶; 1.86×10⁶; and 1.74×10⁶ daltons for the respective LDL subfractions. Higher molecular weights of fractions 2 and 5 compared to their adjacent fractions 1 and 4 by sedimentation equilibrium are of great interest. The calculated frictional ratio f/f^o from sedimentation equilibrium and flotation velocity data ranges from 1.10 to 1.31, suggesting complexity and asymmetry of LDL subfraction molecules. There is also evidence that compressibility of LDL molecules may be different than that for the salt solution under high g-force. Assuming that redistributed LDL molecules at equilibrium under low g-force are spherical, it is possible that the shape of LDL molecules undergoing flotation velocity determinations may be distorted in high g-force conditions. Such distortion may be consistent with the high f/f^o values obtained and may also be a basis for structural rearrangement and/or lipoprotein degradation with prolonged preparative ultracentrifugation at high g-force and pressure.     

Proteolytic susceptibility of platelet low density lipoprotein receptor

In order to further characterize low density lipoprotein (LDL)-platelet interaction, we investigated the effect of protease pretreatment of human platelets on the subsequent binding of iodinated LDL (¹²⁵I-LDL). Our results showed that the platelet LDL receptor had a proteolytic susceptibility different from that of both classical LDL receptors and the fibrinogen receptor. Platelet pretreatment with chymotrypsin, trypsin, and pronase (at 50 μg/mL) had no effect on¹²⁵I-LDL binding, whereas fibroblast¹²⁵I-LDL binding was markedly reduced. Mild proteolytic digestion, however (up to 1 mg/mL), was helpful in characterizing the platelet LDL receptor. Scatchard analysis showed that chymotrypsin did not modify LDL binding characteristics, whereas trypsin and pronase altered maximal number of binding sites (B_max) without variation in dissociation constant. Trypsin increased B_max approximately twofold (2156±327 binding sites on control platelets vs. 5246±296 on treated platelets,P<0.001, mean±SEM, n=5), but pronase decreased B_max about 50% (2017±275 control vs. 1153±195 treated,P<0.001). A minimum of 30 min preincubation was required to detect significant effects, and apparent equilibrium was reached by 60 min. Maximal increase in platelet LDL binding sites induced by trypsin was observed at a protein concentration of 1 mg/mL at 37°C, whereas at 4°C no effect was found. In contrast, maximal pronase-inhibitory effect also was observed at 37°C but at higher protein concentration (10 mg/mL). Aprotinin, phenylmethylsulfonylfluoride, and soybean trypsin inhibitor were capable of fully blocking both the stimulation and the inhibition of platelet LDL binding induced by trypsin and pronase, respectively. Platelet pretreatment with both chymotrypsin and pronase (0.5 mg/mL) activated fibrinogen binding sites to a similar extent as ADP (100 μM). Furthermore, LDL (at a protein concentration of 0.3 mg/mL) increased by 81±6% the binding of fibrinogen to both protease- and ADP-stimulated platelets, but was unable to activate fibrinogen binding sites in unstimulated platelets. Over-all, the results suggest that platelet LDL receptor presents a different proteolytic susceptibility in comparison with both “classical” LDL receptor and fibrinogen receptor. Portions of this work were presented at the 17th Meeting of the European Lipoprotein Club, Tutzing, Germany, September 12–15, 1994.     

Protective effect of oleuropein, an olive oil biophenol, on low density lipoprotein oxidizability in rabbits

On the basis of the results obtained with pilot studies conducted in vitro on human low density lipoprotein (LDL) and on cell cultures (Caco-2), which had indicated the ability of certain molecules present in olive oil to inhibit prooxidative processes, an in vivo study was made of laboratory rabbits fed special diets. Three different diets were prepared: a standard diet for rabbits (diet A), a standard diet for rabbits modified by the addition of 10% (w/w) extra virgin olive oil (diet B), a modified standard diet for rabbits (diet C) differing from diet B only in the addition of 7 mg kg⁻¹ of oleuropein. A series of biochemical parameters was therefore identified, both in the rabbit plasma and the related isolated LDL, before and after Cu-induced oxidation. The following, in particular, were selected: (i) biophenols, vitamins E and C, uric acid, and total, free, and ester cholesterol in the plasma; (ii) proteins, triglycerides, phospholipids, and total, free, and ester cholesterol in the native LDL (for the latter, the dimensions were also measured); (iii) lipid hydroperoxides, aldehydes, conjugated dienes, and relative electrophoretic mobility (REM) in the oxidized LDL (ox-LDL). In an attempt to summarize the results obtained, it can be said that this investigation has not only verified the antioxidant efficacy of extra virgin olive oil biophenols and, in particular, of oleuropein, but has also revealed a series of thus far unknown effects of the latter on the plasmatic lipid situation. In fact, the addition of oleuropein in diet C increased the ability of LDL to resist oxidation (less conjugated diene formation) and, at the same time, reduced the plasmatic levels of total, free, and ester cholesterol (−15, −12, and −17%, respectively), giving rise to a redistribution of the lipidic components of LDL (greater phospholipid and cholesterol amounts) with an indirect effect on their dimesions (bigger by about 12%).     

Effect of dietary fish oil on the rate of very low density lipoprotein triacylglycerol formation and on the metabolism of chylomicrons

The mechanism by which ω3 fatty acids lower plasma triacylglycerol levels was investigated. Rats were fed fish oil, olive oil (10% fat by weight) or a nonpurified diet 4% fat by weight) for 15 days. Lipoprotein lipase was inhibited by intra-arterial administration of Triton WR 1339 to estimate hepatic triacylglycerol output. Rats fed the olive oil diet showed a higher rate of triacylglycerol formation than rats fed the ω3 fatty acid diet or the low-fat diet. All three groups showed identical rates of removal from plasma of intraarterially administered artificial chylomicrons that had simultaneously been labeled with cholesteryl [1-¹⁴C]oleate and [9,10(n)-³H]triolein. Liver radioactivity and total fat content were lowest in rats fed the fish oil diet, indicating that ω3 fatty acids were preferentially metabolized in liver. Chylomicrons obtained from donor rats fed either fish oil containg [¹⁴C]cholesterol or olive oil containing [³H]cholesterol were removed at similar rates when infused together intraarterially into recipient animals. A slower formation of plasma very low density lipoprotein triacylglycerols in rats fed fish oil is probably due to a faster rate of oxidation of the fatty acid chains in the liver resulting in decreased plasma triacylglycerol concentrations.     

Effect of ethanol on low density lipoprotein and platelet composition

The present study was designed to investigate the effect of ethanol (EtOH) dose on low density lipoprotein (LDL) and platelet composition. Male squirrel monkeys were divided into three groups designated Control, Low, and High EtOH, and fed isocaloric liquid diets containing 0%, 12%, and 24% of calories as EtOH, respectively. After four months of treatment, monkeys fed the 12% alcohol dose had LDL and platelet cholesterol concentrations similar to Controls. By contrast, platelet membranes from High EtOH animals contained significantly more cholesterol which was associated with higher levels of plasma LDL cholesterol and apolipoprotein B. Blood platelet count, size, and mass were similar for all groups and circulating platelet aggregates were absent in the two alcohol cohorts. Despite elevations in platelet cholesterol mass and thromboxane A₂ (TXA₂) precursor, phospholipid arachidonate, platelet responsiveness, measured as thromboxane formed in response to a collagen challengein vitro, and the cholesterol/phospholipid molar ration, were not significantly altered by high dose alcohol. Normal platelet activity in High EtOH monkeys may have resulted from a significant increase in the platelet phospholipid polyunsaturated/saturated fatty acid ratio and a non-significant increase in platelet phospholipid mass, both of which would have a fluidizing effect on platelet membranes. Our data indicate that low EtOH intake has no effect on platelet composition and function while unfavorable platelet cholesterol enrichment following consumption of high dose ethanol may arise from elevations in plasma LDL. Potentially thrombogenic (TXA₂ formation, platelet aggregate formation) consequences of increased platelet cholesterol in squirrel monkeys fed high levels of alcohol may be averted by compensatory physicochemical changes in platelet membrane lipid composition although persistent elevations in circulating LDL may contribute to increased risk of cardiovascular disease.     

通过控制醇凝胶强度常压制备低密度疏水SiO2气凝胶

常压干燥制备低密度气凝胶是促进高性能气凝胶发展应用的重要途径。以正硅酸乙酯为硅源,采用溶胶-凝胶和常压干燥工艺制备出低密度(<100 kg·m^-3)的疏水SiO₂气凝胶,通过工艺参数的控制制备出不同压缩模量的醇凝胶,探讨了反应物配比对醇凝胶压缩模量和气凝胶密度间的影响关系,获得了通过控制醇凝胶压缩模量制备低密度疏水SiO₂气凝胶的方法;发现将醇凝胶压缩模量控制在0.25~2.5 kPa范围内,可制备出密度小于100 kg·m^-3的疏水SiO₂气凝胶,该研究可以为低密度疏水SiO₂气凝胶的低成本常压制备及其控制方法提供指导。     

Dialysis and gel filtration of isolated low density lipoproteins do not cause a significant loss of low density lipoprotein tocopherol and carotenoid concentration

The resistance of isolated low density lipoprotein (LDL) to copper-initiated oxidation is often used as a measure of effectiveness of an antioxidant intervention. Prior to oxidation excess salt and EDTA are removed via dialysis or gel filtration of the LDL sample. However, there is concern over whether the antioxidant content of dialyzed or gel-filtered LDL is truly representative of native LDL extracted from a blood sample. Previously, the experiments done after the storage of native and dialyzed LDL at −80°C showed that the dialysis step can cause a loss of up to 60% in the tocopherol and carotenoid content of LDL. In the present study, a comparison of the micronutrient concentration in freshly prepared dialyzed and native LDL from 35 subjects showed that after the correction for cholesterol, only lycopene (13%, P<0.001) and to a lesser extent α-carotene (8%, P<0.02) were significantly decreased, and the absolute fall in concentration was far smaller than previously reported. Other experiments done with smaller numbers of samples suggested that there were minimal micronutrient losses following gel filtration and that it was important to include 10 μmol/L EDTA in the dialysis and elution buffer; otherwise micronutrient losses did occur. In summary, immediate dialysis of freshly isolated LDL in the presence of 10 μmol/L. EDTA does not cause any major loss in the concentration of tocopherol and most carotenoids.     

Partial specific volume and preferential hydration of low density lipoprotein subfractions

We have determined the partial specific volume ( ) for five low density lipoprotein (LDL) subfractions (n=5–7) and evaluated preferential hydration (n=2) for LDL subfraction 3 in normolipoproteinemic subjects in order to characterize these highly atherogenic components of the human plasma lipoprotein spectra. Values for at 1 g were determined by sixth place density measurements of the solvent and lipoprotein solutions and carbon, hydrogen and nitrogen (CHN) absolute mass of the lipoprotein concentrations. Mean values for were 0.9757±0.0019, 0.9701±0.0007, 0.9674±0.0016, 0.9616±0.0016 and 0.9550±0.0025 ml/g for subfractions 1, 2, 3, 4 and 5, respectively. However, molecular densities (σ) obtained from ϱ(rho)=1/ for respective LDL subfractions were 1.0249, 1.0308, 1.0337, 1.0399 and 1.0471 g/ml, respectively. The preferential hydration of lipoprotein subfraction 3 (n=2) in NaCl/H₂O solutions was 2.9–4.8 wt percent, whereas values were much lower (0.3–0.6 wt percent) in NaCl/NaBr/H₂O solvent system. Unhydrated densities for LDL subfraction 3 (n=2) at 1 g (sixth-place density meter) were 1.0287 and 1.0269 g/ml, whereas at 200,000 × g (used in D₂O flotation ηF^o vs ϱ determinations) both values were 1.0308 g/ml, indicating that these similar LDL fractions have 23 and 53% higher compressibility than the solvent at 200,000 × g force. It was observed that the linearity of ηF^o vs ϱ may not be valid for solvents NaCl/NaBr/H₂O of density as high as 1.4744 g/ml. Thus, flotation velocity data using extreme salt concentrations (1.4744 g/ml and higher) may be viewed with caution.     

Lipid composition influences the shape of human low density lipoprotein in vitreous ice

Earlier cryo-electron microscopic studies have indicated that the normal low density lipoprotein (N-LDL) has a discoid shape when its core is in the liquid-crystalline state. In the present study, we investigated whether the shape of LDL depends on the physical state and/or the lipid composition of the lipoprotein core. Using a custom-built freezing device, we vitrified N-LDL samples from either above or below the phase-transition temperature of the core (42 and 24°C, respectively). Cryo-electron microscopy revealed no differences between these samples and indicated a discoid shape of the N-LDL particle. In contrast, TG-enriched LDL (T-LDL) did not have discoid features and appeared to be quasi-spherical in preparations that were vitrified from either 42 or 24°C. These results suggest that the shape of N-LDL is discoid, regardless of the physical state of its core, whereas T-LDL is more spherical. Aspects that may influence the shape of LDL are discussed.     

低密度油井水泥的研究与生产

通过对生物灰、硅灰、粉煤灰、矿粉等减轻材料的性能研究,结合多种减轻材料不同比例的掺加对低密度水泥浆的性能影响,确定最佳配比方案,制备出密度低、流动度好、稠化时间长、不同温度下强度优异的低密度油井水泥。     

Low pH enhances the transfer of carotene from carrot juice to olive oil

A current model for carotenoid transport and absorption in the gut proposes an initial solubilization in the oil phase of dietary emulsions followed by incorporation of the carotenoids in mixed bile salt micelles. To assess the relevance of the first stage of this model to what is observed in vivo we have examined the transfer of carotene from carrot juice to olive oil. Increased acidity enhanced the transfer from both whole juice and carotene crystals isolated from both whole juice and carotene crystals isolated from carrot chromoplasts. The transfer was significantly slower from whole juice. By using exogenous β-carotene and measuring its transfer to oil in the presence and absence of carrot juice we have demonstrated that the inhibition of the transfer in juice arises, at least in part, from soluble juice factors. The inhibition is relieved by a fall in pH, which leads to lowering of the electric potential at the oil/aqueous phase interface and aggregation of carrot tissue including crystalline carotene. Under conditions of low pH, oil droplets adhere to the tissue aggregates, allowing carotene to pass into the oil. Our results provide an explanation for why carotene absorption in vivo is depressed by conditions of low gastric acidity.     

Involvement of phospholipids in apolipoprotein B modification during low density lipoprotein oxidation

An increased amount of phospholipids remained attached on delipidated apolipoprotein B originated from oxidized low density lipoprotein (LDL). ³¹P nuclear magnetic resonance analysis of such apolipoprotein showed an organic phosphorus peak at −0.55 ppm, which suggests the formation of adducts (most probably Schiff bases) of oxidized phospholipids with apolipoprotein B. The above reaction occurs in parallel with the hydrolysis of oxidized phospholipids, catalyzed by the LDL-attached platelet-activating factor acetylhydrolase, and may contribute to the proatherogenic effect of oxidatively modified low density lipoprotein.     

Quantitative determination of low density lipoprotein oxidation by FTIR and chemometric analysis

This study was conducted to develop a quantitative FTIR spectroscopy method to measure LDL lipid oxidation products and determine the effect of oxidation on LDL lipid and protein. In vitro LDL oxidation at 37°C for 1 h produced a range of conjugated diene (CD) (0.14–0.26 mM/mg protein) and carbonyl contents (0.9–3.8 μg/g protein) that were used to produce calibration sets. Spectra were collected from the calibration set and partial least squares regression was used to develop calibration models from spectral regions 4000-650, 3750-3000, 1720-1500, and 1180-935 cm⁻¹ to predict CD and carbonyl contents. The optimal models were selected based on their standard error of prediction (SEP), and the selected models were performance-tested with an additional set of LDL spectra. The best models for CD prediction were derived from spectral regions 4000-650 and 1180-935 cm⁻¹ with the lowest SEP of 0.013 and 0.013 mM/mg protein, respectively. The peaks at 1745 (cholesterol and TAG ester C=O stretch), 1710 (carbonyl C-O stretch), and 1621 cm⁻¹ (peptide C=O stretch) positively correlated with LDL oxidation. FTIR and chemometrics revealed protein conformation changes during LDL oxidation and provided a simple technique that has potential for rapidly observing structural changes in human LDL during oxidation and for measuring primary and secondary oxidation products.     

新型骨架油封的性能研究

文中对一种新型的非金属骨架油封进行了性能研究,并把它和常用的金属骨架与织物骨架作了对比(如价格,耐温性能,刚性)等,并对影响该骨架性能的各个方面进行了研究。