Dietary fatty acids regulate hepatic low density lipoprotein (LDL) transport by altering LDL receptor protein and mRNA levels.

The concentration of LDL in plasma is strongly influenced by the amount and the type of lipid in the diet. Recent studies in the hamster have shown that dietary fatty acids differentially affect circulating LDL levels primarily by altering receptor-dependent LDL uptake in the liver. To investigate the mechanistic basis of this effect, rates of receptor-dependent LDL transport in the liver were correlated with LDL receptor protein and mRNA levels in hamsters fed safflower oil or coconut oil and varying amounts of cholesterol. Hepatic LDL receptor activity was significantly lower in animals fed coconut oil than in animals fed safflower oil at all levels of cholesterol intake (26, 53, and 61% lower at cholesterol intakes of 0, 0.06, and 0.12%, respectively). These fatty acid-induced changes in hepatic LDL receptor activity were accompanied by parallel changes in hepatic LDL receptor protein and mRNA levels, suggesting that dietary fatty acids regulate the LDL receptor pathway largely at the mRNA level.     

Interaction of dietary cholesterol and triglycerides in the regulation of hepatic low density lipoprotein transport in the hamster.

These studies report the effects of dietary cholesterol and triglyceride on rates of receptor-dependent and receptor-independent LDL transport in the liver of the hamster. In animals fed diets enriched with 0.1, 0.25, or 1% cholesterol for 1 mo, receptor-dependent LDL transport in the liver was suppressed by 43, 63, and 77%, respectively, and there were reciprocal changes in plasma LDL-cholesterol concentrations. In addition, dietary triglycerides modified the effect of dietary cholesterol on hepatic LDL transport and plasma LDL concentrations so that at each level of cholesterol intake, polyunsaturated triglycerides diminished and saturated triglycerides accentuated the effect of dietary cholesterol. When animals were raised from weaning on diets containing small amounts of cholesterol, the decline in receptor-dependent LDL transport was nearly abolished by the addition of polyunsaturated or monounsaturated triglycerides, but was markedly augmented by the addition of saturated lipids. When animals raised on diets containing cholesterol and saturated triglycerides were returned to the low cholesterol, low triglyceride control diet, hepatic receptor-dependent LDL transport and plasma LDL-cholesterol concentrations returned essentially to normal within 2 wk. Neither receptor-independent LDL transport nor the receptor-dependent uptake of asialofetuin was significantly altered by dietary cholesterol or triglyceride suggesting that the effect of these lipids on hepatic LDL receptor activity was specific and not due to a generalized alteration in the physiochemical properties of hepatic membranes. These studies demonstrate the important role of saturated triglycerides in augmenting the effect of cholesterol in suppressing hepatic LDL receptor activity and elevating LDL-cholesterol levels.     

Regulation of low density lipoprotein receptor activity in freshly isolated human lymphocytes.

Circulating human lymphocytes freshly isolated from venous blood of 15 normal subjects exhibited a low capacity to bind, take up, and degrade 125I-labeled low density lipoprotein (LDL). However, when these cells were incubated for 72 h in the absence of lipoproteins, they gradually acquired in increased number of high affinity cell surface receptors for LDL. The increase in the number of LDL receptors was associated with a 16-fold increase in the rate at which the cells were able to take up and degrade the lipoprotein. The LDL binding and degradation processes that developed in normal lymphocytes exhibited the following characteristics; (a) high affinity (saturation was achieved at LDL concentrations below 50 mug protein/ml); (b) specificity (unlabeled LDL was much more effective than human high density lipoprotein or other plasma proteins in competing with 125I-LDL for binding to the LDL receptor); and(c) feedback regulation (the increase in the number of LDL receptors that appeared after incubation of freshly isolated lymphocytes in lipoprotein-deficient medium was prevented by exposure of the cells to either LDL or a mixture of 25-hydroxycholesterol plus cholesterol but not to HDL). Freshly isolated lymphocytes obtaine from three subjects with the homozygous form of familial hypercholesterolemia failed to develop normal amounts of LDL receptor activity when incubated in medium devoid of lipoproteins. The current data indicate: (a) that the LDL receptors that appear on the surface of cholesterol-deprived, normal human lymphocytes are genetically identical to the previously characterized LDL receptors of cultured human fibroblasts and long-term lymphoid cells and (b) that at least one cell type in the human body, the circulating human lymphocyte, has the capacity to produce a high affinity LDL receptor that mediates the cellular uptake and degradation of plasma LDL.     

Genetics of the low density lipoprotein receptor. Diminished receptor activity in lymphocytes from heterozygotes with familial hypercholesterolemia.

Using circulating mononuclear cells as a readily available tissue and using the rate of high affinity degradation of 125-I-labeled low density lipoprotein (LDL) as an index of cell surface LDL receptor activity, we have measured receptor activity in cells from 53 individuals. This group includes 32 healthy subjects, 15 subjects with the heterozygous form of familial hypercholesterolemia, and 6 subjects with hyperlipidemic disorders other than familial hypercholesterolemia. 7 of the healthy subjects and 10 of the heterozygotes were members of a single large kindred with five-generation transmission of the mutant familial hypercholesterolemia gene. LDL receptor activity was assayed in blood mononuclear cells under two sets of conditions. First, 125I-LDL degradation was measured in purified lymphocytes that had been incubated for 3 days in the absence of lipoproteins so as to induce a high level of LDL receptor activity. Phase-contrast autoradiograms of cells incubated with 125I-LDL and electron micrographs of cells incubated with ferritin-labeled LDL confirmed the existence of LDL receptors on lymphocytes. Second, 125I-LDL degradation was measured in mixed mononuclear cells (85-90% lymphocytes and 5-15% monocytes) immediately after their isolation from the bloodstream. This assay represented an attempt to assess the number of receptors actually expressed on the cells when they were in the circulation. Under both sets of conditions, cells from the familial hypercholesterolemia heterozygotes expressed an average of about one-half the normal number of LDL receptors. The current findings are consistent with the conclusion that heterozygotes with familial hypercholesterolemia possess only one functional allele at the LDL receptor locus and that the consequent deficiency of LDL receptors produces the clinical syndrome of heterozygous familial hypercholesterolemia.     

Interaction between free fatty acids and insulin in the acute control of very low density lipoprotein production in humans.

Changes in VLDL triglyceride and VLDL apo B production were determined semiquantitatively in healthy young men by examining the effect of altering plasma insulin and/or FFA levels on the change in the slopes of the specific activity of VLDL [3H]triglyceride glycerol or the 131I-VLDL apo B versus time curves. In one study (n = 8) insulin was infused for 5 h using the euglycemic hyperinsulinemic clamp technique. Plasma FFA levels declined by approximately 80% (0.52 +/- 0.01 to 0.11 +/- 0.02 mmol/liter), VLDL triglyceride production decreased by 66.7 +/- 4.2% (P = 0.0001) and VLDL apo B production decreased by 51.7 +/- 10.6% (P = 0.003). In a second study (n = 8) heparin and Intralipid (Baxter Corp., Toronto, Canada) were infused with insulin to prevent the insulin-mediated fall in plasma FFA levels. Plasma FFA increased approximately twofold (0.43 +/- 0.05 to 0.82 + 0.13 mmol/liter), VLDL triglyceride production decreased to a lesser extent than with insulin alone (P = 0.006) (-31.8 +/- 9.5%, decrease from baseline P = 0.03) and VLDL apo B production did not decrease significantly (-6.3 +/- 13.6%, P = NS). In a third study (n = 8) when heparin and Intralipid were infused without insulin, FFA levels rose approximately twofold (0.53 +/- 0.04 to 0.85 +/- 0.1 mmol/liter), VLDL triglyceride production increased by 180.1 +/- 45.7% (P = 0.008) and VLDL apo B production increased by 94.2 +/- 28.7% (P = 0.05). We confirm our previous observation that acute hyperinsulinemia suppresses VLDL triglyceride and VLDL apo B production in healthy humans. In addition, we have demonstrated that elevation of plasma FFA levels acutely stimulates VLDL production in vivo in healthy young males. Elevating plasma FFA during hyperinsulinemia attenuates but does not completely abolish the suppressive effect of insulin on VLDL production, at least with respect to VLDL triglycerides. Therefore, in normal individuals the acute inhibition of VLDL production by insulin in vivo is only partly due to the suppression of plasma FFA, and may also be due to an FFA-independent process.     

Dietary fish oil stimulates hepatic low density lipoprotein transport in the rat.

These studies were undertaken to examine the effect of fish oil, safflower oil, and hydrogenated coconut oil on the major processes that determine the concentration of low density lipoprotein (LDL) in plasma, i.e., the rate of LDL production and the rates of receptor-dependent and receptor-independent LDL uptake in the various organs of the body. When fed at the 20% level, fish oil reduced plasma LDL-cholesterol levels by 38% primarily by increasing LDL receptor activity in the liver. Dietary safflower oil also increased hepatic LDL receptor activity; however, since the rate of LDL production also increased, plasma LDL-cholesterol levels remained essentially unchanged. Hydrogenated coconut oil had no effect on LDL receptor activity but increased the rate of LDL-cholesterol production causing plasma LDL-cholesterol levels to increase 46%. Dietary fish oil had no effect on the receptor-dependent transport of asialofetuin by the liver, suggesting that the effect of fish oil on hepatic LDL receptor activity was specific and not due to a generalized alteration in the physical properties of hepatic membranes. Finally, dietary fish oil increased hepatic cholesteryl ester levels and suppressed hepatic cholesterol synthesis rates, suggesting that the up-regulation of hepatic LDL receptor activity in these animals was not simply a response to diminished cholesterol availability in the liver.     

Comparison of glucosylated low density lipoprotein with methylated or cyclohexanedione-treated low density lipoprotein in the measurement of receptor-independent low density lipoprotein catabolism.

We previously showed that glucosylation of lysine residues of low density lipoproteins (LDL) blocks high-affinity degradation by cultured human fibroblasts, and markedly slows LDL turnover in guinea pigs. The present studies were done to evaluate glucosylated (GLC) LDL as a tracer of receptor-independent LDL catabolism, and to compare it with two other modified LDL, methylated (MET) LDL, and cyclohexanedione (CHD)-treated LDL, which have been used previously for this purpose. Glucosylation of LDL did not affect receptor-independent degradation in vivo, as the turnover of GLC-LDL and native LDL were similar in the LDL receptor-deficient, Watanabe heritable hyperlipidemic rabbit. Each modified radiolabeled LDL preparation was injected into eight guinea pigs, and fractional catabolic rates (FCR) determined. The FCR of GLC-LDL (0.024 +/- 0.005 h-1; SD) was similar to that of MET-LDL (0.023 +/- 0.006 h-1), and approximately 22% of that of native LDL (0.105 +/- 0.02 h-1). The FCR of CHD-LDL was greater than that of the other modified LDL, and it varied depending on how soon after preparation the CHD-LDL was injected: when used within 2 h of preparation, the mean FCR was 0.044 +/- 0.007 h-1 (n = 4); when used after overnight dialysis at 4 degrees C, the mean FCR was 0.082 +/- 0.03 h-1 (n = 4). This suggests that CHD-LDL overestimates the amount of LDL degraded by receptor-independent pathways, perhaps because the CHD modification is spontaneously reversible. The present studies indicate that GLC-LDL is a useful tracer of receptor-independent LDL catabolism in animals.     

Soybean protein diet increases low density lipoprotein receptor activity in mononuclear cells from hypercholesterolemic patients.

The effect of two diets containing different protein sources (animal vs. soybean) on the low density lipoprotein (LDL) receptor activity was tested in freshly isolated mononuclear cells from 12 individuals with severe type II hyperlipoproteinemia. The two diets, both taken for 4 wk in a crossover design were of otherwise identical composition. During the soybean protein diet period, total cholesterol was reduced by 15.9% and LDL-cholesterol by 16.4%. The diet containing animal proteins exerted no significant change in plasma lipid levels vs. the baseline findings. The soybean diet regimen dramatically affected the degradation of LDL by mononuclear cells. Degradation was increased 16-fold vs. the basal activity and 8-fold compared with the standard low lipid diet with animal proteins. There was, however, no clear relationship between the reduction of total and LDL-cholesterolemia and the increased LDL degradation. These findings confirm similar data previously obtained in cholesterol-fed rats and suggest that some factor/s, most likely of a protein nature, may regulate the expression of lipoprotein receptors in peripheral cells, particularly when receptor activity is suppressed by experimental diets and/or spontaneous hypercholesterolemia.     

Protective effect of high density lipoprotein associated paraoxonase. Inhibition of the biological activity of minimally oxidized low density lipoprotein.

Our group has previously demonstrated that oxidized phospholipids in mildly oxidized LDL (MM-LDL) produced by oxidation with lipoxygenase, iron, or cocultures of artery wall cells increase monocyte-endothelial interactions and this sequence of events is blocked by HDL. To obtain further insight into the mechanism by which HDL abolishes the activity of MM-LDL we investigated the effect of the HDL-associated ester hydrolase paraoxonase (PON). Treatment of MM-LDL with purified PON significantly reduced the ability of MM-LDL to induce monocyte-endothelial interactions. Inactivation of PON by pretreating HDL with heat or EDTA reduced the ability of HDL to inhibit LDL modification. HPLC analysis of phospholipids isolated from MM-LDL before and after treatment with purified PON showed that the 270 nm absorbance of phospholipids was decreased, while no effect was observed on 235 nm absorbance. Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (Ox-PAPC) and specific fractions of Ox-PAPC isolated by HPLC induced the same monocyte-endothelial interactions as did MM-LDL. Biologically active and inactive HPLC fractions of Ox-PAPC were compared by fast atom bombardment-mass spectrometry which revealed that active fractions possessed ions with a mass to charge [correction of change] ratio greater than native PAPC by multiples of 16 D suggesting the addition of 3 and 4 oxygen atoms to PAPC. Comparison of Ox-PAPC by fast atom bombardment-mass spectrometry before and after PON treatment showed that PON destroyed these multi-oxygenated molecules found in biologically active fractions of Ox-PAPC. These results suggest that PON in HDL may protect against the induction of inflammatory responses in artery wall cells by destroying biologically active lipids in mildly oxidized LDL.     

Glucocorticoid-stimulated biosynthesis of low density lipoprotein receptor in cultured fibroblasts

Preincubation of human skin fibroblasts in the presence of 10(-6)-10(-5) mol/l glucocorticoids (dexamethasone) causes a concentration and time-dependent increase of receptor-mediated internalisation of [125I]LDL. This increase is due to a glucocorticoid-specific stimulation by 40-50% of LDL receptor synthesis as demonstrated by an increased incorporation of [35S]methionine into immune precipitated receptor protein. In contrast the rate of synthesis of total cell protein and of lysosomal cathepsin D is not significantly influenced by dexamethasone. The increased LDL receptor synthesis is accompanied by an enhanced synthesis of cholesterol from [2-3H]mevalonolactone and [1-14C]acetate. The glucocorticoid-induced enhancement of LDL receptor and cholesterol synthesis is abolished by preincubation of the cells with dexamethasone in combination with 25-hydroxycholesterol.     

Multiplex PCR assay for screening deletions in the low density lipoprotein receptor gene.

Background: In different populations of the world, more than 150 genetic alterations of the LDL receptor gene have been identified; each of which can result in hypercholesterolaemia, but no hot spots in the gene were detected so far. Because of the existence of very variable genetic alterations in different ethnic communities, none of the assays developed for screening mutations/deletions in a population defined can be adapted to study the possible genetic defects. The present study was designed to develop a new, multiplex PCR-based, molecular biological method to screen the whole coding region of the LDL receptor gene. Methods: Using primer pairs completely flanking the promoter and the entire exonal region, in the PCR reactions 83-386-bp long, DNA sequences were synthesised in seven different reaction mixtures. The reaction conditions of the multiplex PCR system were optimised in order to synthesise all exons and the promoter region of the gene using only two annealing temperatures. The products could be visualised separately by agarose gel electrophoresis/ethidium bromide staining. Results: A rapid, effective test enabling the screening of DNA alterations in the entire LDL receptor gene was developed. Using this simple multiplex PCR assay, deletions affecting more than 10 bp in any part of the gene can be easily detected by a single agarose gel electrophoresis. Conclusions: The simplicity, specificity and versatility of the assay make it suitable system for routine screening of LDL receptor gene mutations in large population samples. This PCR assay can be recommended for screening of LDL-RG deletions in populations or groups at high risk for cardiovascular diseases.     

Mechanisms by which saturated triacylglycerols elevate the plasma low density lipoprotein-cholesterol concentration in hamsters. Differential effects of fatty acid chain length.

These studies were designed to elucidate how shorter (MCT) and longer (HCO) chain-length saturated triacylglycerols and cholesterol interact to alter steady-state plasma LDL-cholesterol levels. When either MCT or HCO was fed in the absence of cholesterol, there was little effect on receptor-dependent LDL transport but a 36-43% increase in LDL-cholesterol production. Cholesterol feeding in the absence of triacylglycerol led to significant suppression of receptor-dependent LDL transport and a 26-31% increase in LDL-cholesterol production. However, when the longer chain-length saturated triacylglycerol was fed together with cholesterol there was a marked increase in the suppression of receptor-dependent LDL transport and an 82% increase in production rate. Together, these two alterations accounted for the observed eightfold increase in plasma LDL-cholesterol concentration. In contrast, feeding the shorter chain-length saturated triacylglycerol with cholesterol actually enhanced receptor-dependent LDL transport while also causing a smaller increase (52%) in the LDL-cholesterol production rate. As a result of these two opposing events, MCT feeding had essentially no net effect on plasma LDL-cholesterol levels beyond that induced by cholesterol feeding alone.     

Smoking and plasma lipoproteins in man: effects on low density lipoprotein cholesterol levels and high density lipoprotein subfraction distribution

Abstract. In a survey of a healthy population (n = 197), LDL cholesterol, plasma triglycerides and VLDL triglycerides were found to be substantially increased and plasma HDL cholesterol decreased in smokers. The lipid-associated atherogenic risk in smokers as assessed by the LDL/HDL ratio was significantly higher [2.89 (SD 1.18, n= 63)] than in non-smokers [2.38 (SD 0.98, n= 86) P < 0.01]. The lower HDL level found in smokers was explained by a lower HDL-2 subfraction as determined by analytical ultracentrifugation. HDL 2b, 2a and 3a, measured by gradient gel electrophoresis, were all lower in the smokers but this was only significant for HDL 2a. Smoking had no effect on Lp(a) levels. HDL cholesterol and HDL-2 were strongly negatively correlated whereas LDL cholesterol and LDL/HDL ratio were strongly positively correlated with the plasma triglyceride concentration. There was a small but significant reduction in plasma CETP activity [non-smokers 49%t/μl (SD 17, n= 90), smokers 43%t/μl (SD 17, n= 66) P < 0.05] but CETP activity was not correlated with any measure of HDL in this population. Smoking was found to be an important independent contributor to the variation in plasma triglyceride, HDL, HDL-2 and LDL/HDL ratio. After correcting for sex, age, BMI, alcohol consumption, oral contraceptive use and plasma triglycerides smoking was still found to be significantly associated with HDL and the LDL/HDL ratio. Upon adjustment for covariant factors the mean differences between smokers and non-smokers for HDL cholesterol, HDL-2 and LDL/HDL were 0.15 mM, 16 mg dl-¹ and 0.39 respectively. There appeared to be important sex differences in the influence of smoking on plasma lipoproteins. In women the main impact of smoking was on triglyceride levels and they in turn affected LDL and HDL. In contrast, in men, smoking had little impact on triglycerides and affected HDL more directly. We conclude that smoking cigarettes has an important effect on plasma lipoprotein metabolism through multiple mechanisms.     

Identification of a lymphocyte surface receptor for low density lipoprotein inhibitor, an immunoregulatory species of normal human serum low density lipoprotein.

The present study demonstrates the existence on human peripheral blood lymphocytes of a saturable cell surface receptor for low density lipoprotein inhibitor (LDL-In), a subset of normal human serum low density lipoprotein (LDL) that has been previously demonstrated to suppress selected lymphocyte functions in vivo and in vitro. The binding of radioiodinated LDL-In of demonstrable biological activity occurs rapidly and is quantitatively augmented by prior cultivation of the lymphocytes in lipoprotein-depleted serum, suggesting regulation of receptor density by lipoproteins in vivo. Binding is temperature dependent, facilitated by calcium ions, saturable at 4 degrees C within 40-60 min, and blocked by prior exposure to unlabeled LDL-In. The lymphocyte receptor is trypsin sensitive and regenerates in vitro with a t1/2 of 3.6 h. LDL-In receptors are calculated to have a maximum density of 4,860 +/- 460 per cell if uniformly distributed on all lymphocyte subsets. These receptors have an estimated average association constant of 1.47 X 10(7) liters/mol. When considered in context of the estimated concentration of LDL-In in blood, the receptors should be partially occupied in vivo by endogenous plasma LDL-In. Prior site occupancy inhibition experiments designed to analyze the specificity of LDL-In binding demonstrate that (a) LDL-In is 13.7-fold more effective than whole LDL in blocking the subsequent binding of 125I-LDL-In to cells; and that (b) LDL is 11-fold more effective than LDL-In in blocking the binding of 125I-LKL. This is consistent with the degree of contamination of each lipoprotein with the other lipoprotein. An independent identity of the LDL-In receptor is also supported by observations that in contrast to the previously described LDL receptor, synthesis and expression of the LDL-In receptor on lymphocytes are not suppressed by cultivation of the cells in the presence of 25-hydroxycholesterol and cholesterol. These findings suggest the existence of a previously undescribed and discrete receptor on lymphocytes for LDL-In, and that the modulation of lymphocyte function by LDL-In may be mediated by a specific cell surface receptor pathway.     

Cholesterol lowering in low density lipoprotein receptor knockout mice overexpressing apolipoprotein E.

Apo E is a key molecule in the lipoprotein metabolism; thus, genetic manipulation of apo E may prove useful in the treatment of hypercholesterolemia. To test the feasibility of this idea, we have generated low density lipoprotein receptor (LDLR) knockout mice that overexpress the rat apo E transgene (ETg+/+:LDLRKO), and compared their plasma lipoprotein profiles with those of nonexpressing LDLR knockout mice (ETg-/-:LDLRKO). On a normal chow diet, the mean plasma cholesterol level of ETg+/+:LDLRKO mice was significantly lower than that of ETg-/-:LDLRKO mice (189 versus 240 mg/dl, P < 0. 01). The LDL fraction was selectively reduced in the ETg+/+:LDLRKO mice. Despite the challenge with an atherogenic diet, cholesterol lowering was persistently observed and fatty streak lesions in the aortic sinus were significantly suppressed in the mice overexpressing apo E. These results imply that stimulation of hepatic production of apo E may be used as a promising adjunctive therapy for homozygous familial hypercholesterolemia.     

Role of the low density lipoprotein receptor in the flux of cholesterol through the plasma and across the tissues of the mouse.

These studies were undertaken to quantify cholesterol balance across the plasma space and the individual organs of the mouse, and to determine the role of the low density lipoprotein receptor (LDLR) in these two processes. In the normal mouse (129 Sv), sterol was synthesized at the rate of 153 mg/d per kg body weight of which 78% occurred in the extrahepatic tissues while only 22% took place in the liver. These animals metabolized 7.1 pools of LDL-cholesterol (LDL-C) per day, and 79% of this degradation took place in the liver. Of this total turnover, the LDLR accounted for 88% while the remaining 12% was receptor independent. 91% of the receptor-dependent transport identified in these animals was located in the liver while only 38% of the receptor-independent uptake wsa found in this organ. When the LDLR was deleted, the LDL-C production rate increased 1.7-fold, LDL-C turnover decreased from 7.1 to 0.88 pools/d, and the plasma LDL-C level increased 14-fold, from 7 to 101 mg/dl. Despite these major changes in the circulating levels of LDL-C, however, there was no change in the rate of cholesterol synthesis in any extrahepatic organ or in the whole animal, and, further, there was no change in the steady-state cholesterol concentration in any organ. Thus, most extrahepatic tissues synthesize their daily sterol requirements while most LDL-C is returned directly to the liver. Changes in LDLR activity, therefore, profoundly alter the plasma LDL-C concentration but have virtually no affect on cholesterol balance across any extrahepatic organ, including the brain.     

低密度、氧化低密度脂蛋白对内皮细胞分泌内皮素的影响

目的 观察低密度脂蛋白（LDL）、氧化低密度脂蛋白（ox-LDL）对内皮细胞分泌内皮素（ET）的影响，以及后者在体外是否对前者具有氧化修饰作用.方法 采用不同浓度的LDL、ox-LDL及LDL＋ox-LDL与脐静脉内皮细胞株ECV-304进行孵育，24 h后分别收集细胞和上清液，采用放免分析法测定ET含量.结果 LDL、ox-LDL均能促进内皮细胞合成、分泌ET，但ox-LDL的作用更显著，而LDL＋ox-LDL组上清ET浓度大于两者单独作用之和.结论 LDL、ox-LDL均能促进内皮细胞合成、分泌ET，但后者的作用更为明显，且在体外对LDL具有氧化修饰作用。