低水平大豆异黄酮对血清脂蛋白氧化修饰的影响

目的 :　评价低水平 (0 .5～ 1 0μmol/L)大豆异黄酮组分 (染料木素、大豆素和染料木甙 )对血清脂蛋白氧化修饰过程作用的效果及其特点。方法 :　采用 Cu2 +诱导全血清脂蛋白氧化修饰模型 ,通过检测体系中共轭双烯和硫代巴比妥酸反应物质 (TBARS)生成量变化反映异黄酮组分对脂蛋白氧化修饰过程和结局的影响。结果 :　启动氧化前向血清脂蛋白体系中加入 0 .5～1 0 μmol/L的染料木素、大豆素或染料木甙和 α-生育酚均显著减少共轭双烯和 TBARS的生成 ,并存在剂量相关关系。当血清脂蛋白氧化启动后 ,加入 1 0μmol/L异黄酮组分仍显示有较强的抑制作用 ,只是作用强度比启动前加入时减弱 ;而相同浓度的α-生育酚仅对共轭双烯生成显示有一定抑制作用 ,对 TBARS生成甚至呈现促进趋势。结论 :　低水平异黄酮组分即能对血清脂蛋白氧化修饰产生抑制作用 ,且在氧化启动后的效果优于 α-生育酚     

镁对人体低密度脂蛋白氧化修饰的影响

目的 :　观察镁对人体低密度脂蛋白 (LDL)氧化修饰的影响。方法 :　一次性密度梯度超速离心法制备人天然 LDL,共轭二烯法检测 Mg2 +对 Cu2 +介导的 LDL氧化反应敏感性的影响 ,硫代巴比妥酸反应物 (TBARS)法检测 Mg2 +对 Cu2 +和内皮细胞介导的 LDL氧化修饰程度的影响。结果 :　 1 .LDL+Cu2 + +Mg2 +各剂量组 LDL氧化反应潜伏期较 LDL+Cu2 +组明显延长 ;2 .LDL+Cu2 + +0 .3mmol/L Mg2 +组和 LDL+Cu2 + +0 .6mmol/L Mg2 +组 TBARS低于 LDL+Cu2 + 组 ,P<0 .0 1 ;3.在内皮细胞介导的 LDL氧化体系中 ,补 Mg2 + 各剂量组 TBARS低于空白对照组 ,LDL+Mg2 +各剂量组 TBARS低于 LDL组 ,差异均具有显著性 (P<0 .0 5)。结论 :　在一定实验条件下 Mg2 +可阻断 LDL的氧化反应     

维生素E和β胡萝卜素对巨噬细胞氧化修饰低密度脂蛋白的影响

目的 :　研究维生素 E(VE)、β胡萝卜素 (βC)对巨噬细胞 (MΦ )介导的低密度脂蛋白 (LDL)氧化修饰能力的影响。方法 :　于培养成熟的 MΦ中分别加入不同剂量的 VE(40、1 0 0、2 0 0 μmol/L)和 βC(0 .5、1 .0、2 .0 μmol/L) 37℃孵育 2 4 h,通过测定培养物上清液中硫代巴比妥酸反应物 (TBARS)、荧光物质 (Lipofusin)、LDL电泳迁移率 (Rf)及共轭二烯 (Dienes)的形成 ,反映LDL的氧化修饰程度。结果 :　体外补充 VE可以显著降低培养物上清液中 TBARS、荧光物质以及共轭二烯的形成 ,明显抑制 LDL的电泳迁移率 ,随剂量增大作用加强 ;βC低剂量组 (0 .5μmol/L)可显著降低培养物上清液中 TBARS、荧光物质以及共轭二烯的形成 ,明显抑制 LDL的电泳迁移率 ,其余各组无明显影响。结论 :　 VE、βC均可抑制 MΦ介导 LDL氧化修饰的能力 ,并具一定的量效关系 ,提示在 MΦ氧化修饰 LDL的可调节因子中 ,抗氧化营养素是一种有效措施     

镁对氧化低密度脂蛋白致内皮细胞损伤的保护作用

为探讨镁对内皮细胞的保护作用 ,用一次性密度梯度超速离心法制备人低密度脂蛋白 (LDL) ,以共轭二烯法和改良八木法检测Mg2 +(0 3、0 6、1 2和 2 4mmol L)对Cu2 +介导LDL氧化反应潜伏期和氧化修饰程度的影响。另将传至 2～ 3代的人脐静脉内皮细胞分为正常对照组、ox LDL对照组、补镁组和ox LDL +Mg2 +组 ,改良八木法测定细胞脂质过氧化物水平 ,黄嘌呤氧化法测定细胞外SOD活性 ,DTNB法测定含硒和不含硒GSH Px活性。结果显示 ,(1)Mg2 +各剂量组明显延长Cu2 +介导LDL氧化反应潜伏期 ,0 3和 0 6mmol LMg2 +显著降低TBARS的生成 ;(2 )与ox LDL组相比 ,ox LDL +Mg2 +各剂量组TBARS生成量显著下降 ,SOD活性显著升高 ,含硒GSH Px酶活力显著升高 ,不含硒GSH Px活力显著升高。提示镁抑制LDL的氧化修饰 ,补镁能降低细胞脂质过氧化物水平 ,增强抗氧化酶的的活性     

维生素C在低密度脂蛋白氧化修饰中作用的体外实验

目的：研究维生素C（VC）在预防低密度脂蛋白（LDL）氧化修饰中的作用。方法：在Cu^2 介导的无细胞体系中分别加入VC10,50,100,200μmol/L,巨噬细胞体中分别加入VC50,100,200μmol/L,以维生素（200μmol/L）为阳性对照,不添加维生素C组（VC0）为阴性对照,测定荧光物质（lipofusin),硫代巴比妥酸反应物质（TBARS）,LDL电泳迁移率（Rf),氧化型低密度脂蛋白（Ox-LDL),LDL氧化过程中的停滞时间等LDL的氧化修饰情况。结果：Cu^2 介导的无细胞体系中,高剂量VC（100,200μmol/L）在3,6,9h均能发挥其抗氧化作用,抑制TBARS,Ox-LDL生成,而VC低剂量（10,50μmol/L）则无此作用,相反在3h表现出促Ox-LDL生成作用,在巨噬细胞体系中,高剂量组（100,200μmol/L)能显著降低荧光物质,TBARS和LDL电泳迁移率（Rf),延长LDL氧化过程中的停滞时间,并存在剂量反应关系。结论：VC在LDL氧化修饰中具有双重作用,低剂量时能促进LDL氧化,高剂量时表现出抗氧化作用。     

大豆异黄酮对大鼠血脂和过氧化状态的影响

目的　观察大豆异黄酮 ( SI)对大鼠血脂水平及体内过氧化状态的影响。方法　 48只 Wistar大鼠随机分成四组 ,分别接受正常饲料、高脂饲料、高脂饲料添加 SI糖甙 30 0 mg/kg和高脂饲料添加 SI甙元 30 0 mg/kg处理。实验期 7周。结果　SI显著抑制高脂饲料所致的血浆甘油三酯水平升高 ,但对血浆总胆固醇 ,低密度脂蛋白胆固醇及高密度脂蛋白胆固醇变化几乎无影响。SI对进食高脂饲料引起的体内过氧化物水平升高具有显著拮抗作用 ,表现在降低肝脏及心肌中的自由基水平 ,升高肝脏超氧化物歧化酶和肝脏及心肌中谷胱甘肽过氧化物酶活性 ,减少血清及肝脏、心肌和主动脉中的脂质过氧化物含量。SI糖甙与其甙元的作用特征一致 ,仅在作用程度上略有差异。结论　 SI对高血甘油三酯有降低作用 ,并能改善高脂所致体内过氧化状态异常 ,减轻对机体的过氧化损伤。在大鼠饲料中 SI甙元的效果略优于 SI糖甙     

大豆异黄酮对糖尿病大鼠脂蛋白氧化的影响

目的 研究大豆异黄酮对糖尿病大鼠血浆脂蛋白脂质过氧化的影响。方法 给糖尿病大鼠饲喂添加大豆异黄酮的饲料8周，检测其血浆脂蛋白过氧化脂质程度以及氧化易感性的变化。结果 食用大豆异黄酮的糖尿病大鼠血浆总过氧化脂质低密度脂蛋白(LDL)和高密度脂蛋白(HDL)过氧化脂质含量明显减少，且在体外进行氧化修饰时，LDL氧化延滞时间明显延长，提示LDL氧化易感性下降。结论 大豆异黄酮显降低糖尿病大鼠LDL和HDL脂质过氧化程度，降低LDL氧化易感性，对糖尿病及其并发症的发生和发展能起到有效的防治作用。     

高水平维生素E对大鼠血脂、肝脂及肝脂质过氧化的作用

采用成年Wistar大鼠为实验动物,雌雄各半。1组为基础饲料对照组,2组为高脂饲料对照组,3、4、5组分别以维生素E30、60、120mg/d灌胃,同时喂饲高脂饲料。实验8周后停止灌胃并改饲基础饲料5周至实验结束。 研究表明:1.高水平维生素E(60和120mg/d)对高脂饲料诱导的大鼠肝实质细胞中性脂肪蓄积及肝脏(体内)脂质过氧化的增加均有明显抑制作用。2.高水平维生素E(30、60和120mg/d)无明显降低大鼠血清胆固醇、甘油三酯及增加血清高密度脂蛋白胆固醇的作用。大鼠血清维生素E与胆固醇水平呈正相关关系,与高密度脂蛋白胆固醇无明显相关。提示维生素E可能并无抑制高脂血症的作用。3.喂饲高脂饲料时雌鼠血清胆固醇的反应比雄鼠敏感,维生素E灌胃时雌鼠血清维生素E的反应比雄鼠敏感,提示存在性别差异。     

不同水平维生素E和β-胡萝卜素对Cu~(2 )氧化修饰低密度脂蛋白的影响

研究不同浓度的维生素 E(VE)和β-胡萝卜素 (βC)对 Cu2 诱导的氧化修饰低密度脂蛋白 (L DL )作用的影响 ,通过测定硫代巴比妥酸反应物质 (TBARS)、L DL 的电泳迁移率 (Rf)以及荧光物质 (L ipofusin)扫描 ,反映 L DL的氧化修饰程度。结果表明 :VE、βC均可减少 TBARS的产生、减小 L DL的 Rf,并且具有剂量 -效应关系 ,随浓度增加 ,VE抑制作用加强而 βC抑制作用减弱 ,而且 VE对 TBARS的影响比 βC小 ,对 Rf的影响比βC大。二者对荧光物质均有降低作用 ,但无剂量 -效应关系。提示 VE、βC均可不同程度的抑制Cu2 氧化修饰 L DL 的作用 ,在降低机体脂质过氧化反应、减少氧化修饰型 L DL(OX- L DL)的形成方面具有重要作用 ,但二者作用机理可能并不相同     

饮食诱导肥胖易感和肥胖抵抗大鼠HSL和LPL基因表达的研究

目的探讨高脂饮食诱导肥胖易感(OP)大鼠和肥胖抵抗(OR)大鼠,激素敏感性脂肪酶(HSL)和脂蛋白脂肪酶(LPL)基因表达的差别。方法健康雄性SD大鼠80只,高脂饲料喂饲5周后,筛选出OP大鼠和OR大鼠,再将所有大鼠转为基础饲料喂饲10周后,处死动物,收集血清和白色脂肪组织,应用RT-PCR方法比较白色脂肪组织HSL和LPL基因的表达。结果高脂饲料喂饲5周后,OP大鼠白色脂肪组织HSL基因表达显著低于OR大鼠,而LPL基因表达显著高于OR大鼠;而转成基础饲料喂饲10后,OP大鼠HSL基因表达与OR大鼠无显著差异,但LPL基因表达仍显著高于OR大鼠。结论HSL基因表达水平下降和LPL基因表达水平升高,通过抑制脂肪分解促进脂肪合成,导致高脂饮食诱导肥胖易感大鼠的形成。HSL基因高表达更多是由高脂饮食诱导产生的,而LPL基因表达升高才是肥胖大鼠的特征性基因表达改变。     

不同水平维生素E和β—胡萝卜素对Cu^2＋氧化修饰低密度脂蛋白的影响

研究不同浓度的维生素Ｅ（ＶＥ）和β－胡萝卜素（βＣ）对Ｃｕ＾２＋诱导的氧化修饰低密度脂蛋白（ＬＤＬ）作用的影响,通过测定硫代巴比妥酸反应物质（ＴＢＡＲＳ）、ＬＤＬ的电泳迁移率（Ｒｆ?以及荧光物质（Ｌｉｐｏｆｕｓｉｎ）扫描,反映ＬＤＬ的氧化修饰程度。结果表明：ＶＥ、βＣ均可减少ＴＢＡＲＳ的产生、减小ＬＤＬ的Ｒｆ,并且具有剂量－效应关系,随浓度增加,ＶＥ抑制作用加强而βＣ抑制作用减弱,而且ＶＥ对ＴＢＡ     

Lowering dietary saturated fat and total fat reduces the oxidative susceptibility of LDL in healthy men and women

The present study examined the effects of reducing dietary total fat and saturated fat (SFA) on LDL oxidative susceptibility in 27 healthy men and women (age 24-65 y). Each subject consumed each of three diets for 8 wk: an average American diet (AAD, 34% energy from fat, 15% from SFA), a Step-1 diet (29% fat, 9% SFA) and a very low SFA diet (Low-Sat, 25% fat, 6% SFA). In vitro LDL oxidation was assessed by copper-mediated oxidation, as measured by the kinetics of conjugated diene formation and lipid peroxide formation. Compared with the AAD, plasma LDL-cholesterol (LDL-C) and HDL cholesterol levels were 8% lower (P: = 0.16 and P: = 0.11, respectively), in subjects when they consumed the Step-1 diet and 11% (P: < 0.03) and 14% (P: < 0.057) lower, respectively, when they consumed the Low-Sat diet. Conjugated diene production and oxidation rate were 7% (P: < 0. 05) and 9% (P: < 0.05) lower, respectively. The reduction of lipid peroxide formation was 9% (P: < 0.05) in subjects when they consumed the Low-Sat diet vs. the AAD. In addition, lipid peroxide and conjugated diene formation were positively correlated with plasma total and LDL-C and apolipoprotein B (apo B) levels (r = 0.5-0.6, P: < 0.001), suggesting that quantity of LDL is an important determinant of oxidative modification. Furthermore, at the same level of apo B or LDL-C, LDL from subjects when they consumed either Step-1 or Low-Sat diets was less susceptible (P: < 0.05) to oxidation than those when they consumed the AAD, suggesting that qualitative changes also affect LDL oxidative susceptibility. Therefore, the benefits of lowering dietary SFA may extend beyond decreasing LDL-C levels and include favorable qualitative changes in LDL that further decrease risk of coronary heart disease.     

Abstracts of Recent Articles on Nutrition and Cancer

This study was designed to determine the effect of diets enriched with plant and animal fats on oxidative stress and glutathione metabolism in rabbit liver tissues. This study was conducted to investigate whether the type of dietary fat will impact fatty acid composition and oxidant/antioxidant status in tissues.

Rabbits were fed diets containing 2 g corn oil/100 g diet (low fat diet, LF) and LF supplemented with 16 g/100 g diet of either corn oil (CO), CO with added cholesterol (CO + C), milk fat (MF), chicken fat (CF), beef tallow (BT), or lard (L) for 30 days. After the feeding period, livers were analyzed for total fatty acid composition, thiobarbituric acid reactive substances (TBARS), conjugated dienes, and reduced glutathione (GSH), as well as for activities of glutathione peroxidase (GP) and glutathione reductase (GR). Moreover, to fully determine the oxidative stability and free radical trapping capacity, TBARS levels were measured after additional exposure of liver homogenates to 10 mM 2,2(1)-azo-bis-amidinopropane- hydrochloride (AAPH) for up to 21 hours.

CO and CF, but not saturated fats such as MF, increased liver conjugated diene and TBARS levels and decreased liver GSH levels and GP activity. In tissues additionally exposed to AAPH, the maximum oxidation, measured as TBARS, was reached between 6 and 7 hours of treatment, independent of dietary fat. In addition, there was a marked effect of AAPH on the maximum rate of TBARS formation with the following descending order: CO > CF > CO + C > L > MF > BT > LF. This high susceptibility to oxidative stress in liver tissues of rabbits fed the CO diet may be explained in part by the significant elevation in linoleic acid (18:2n-6).

There appears to be an inverse correlation between dietary fat-mediated oxidative stress and antioxidant enzyme activities. The present data suggest that high levels of dietary unsaturated fat should be avoided if oxidative stress is a critical issue in nutrition-related diseases. In addition, these data support our hypothesis that diets rich in MF provide a lipid environment with low susceptibility to oxidative stress.     

Feasibility of using an oleate-rich diet to reduce the susceptibility of low-density lipoprotein to oxidative modification in humans

Oxidized low-density lipoprotein (LDL) is more atherogenic than native LDL. The initial step in the oxidation is the peroxidation of polyunsaturated fatty acids. Thus, decreasing the concentration of polyunsaturated fatty acids should reduce the susceptibility of LDL to oxidation. Therefore, we tested the possibility that diets enriched in oleate might result in LDL that is less susceptible to oxidative modification. LDL isolated from subjects consuming an oleate-enriched diet, compared with LDL from subjects on a linoleate-enriched diet, contained significantly more oleate (28.7% vs 11.5%) and less linoleate (31.9% vs 50.9%). Generation of conjugated dienes was significantly lower in the LDL from the oleate group. Most important, after incubation with endothelial cells, LDL from the oleate group underwent less degradation by macrophages. These studies demonstrate the feasibility of altering the diet in a way that will not raise LDL cholesterol concentrations and yet will decrease the susceptibility of LDL to oxidative modification.     

Effect of curcumin on LDL oxidation in vitro, and lipid peroxidation and antioxidant enzymes in cholesterol fed rabbits

In this study we examined the antioxidant effect of curcumin on lipid oxidation in vitro and in vivo. In vitro, curcumin at 5 microgM concentration completely prevented low-density lipoprotein (LDL) oxidation by CuS0(4), indicating that curcumin is an effective antioxidant in vitro. In vivo, feeding a pure cholesterol (PC)-rich diet to rabbits significantly increased the plasma and liver lipids as well as thiobarbituric acid reactive substances (TBARS) levels. Addition of curcumin to the PC diet did not show any effect on either plasma lipid and TBARS or liver lipids. Liver TBARS tended to decrease but that decrease was not significant. Erythrocyte glutathione peroxidase (GSH-Px) activity was significantly decreased while catalase activity was significantly increased in rabbits fed a PC diet. The addition of curcumin to a PC diet did not show any significant effect on erythrocyte enzyme activities compared to the rabbits fed a PC diet. The liver GSH-Px and catalase activities were significantly decreased in rabbits fed a PC diet, but the addition of curcumin to the PC diet enhanced the liver GSH-Px activity, which became nonsignificantly different from the control group. These results were discussed considering that curcumin may not be well absorbed and it did not reach a level high enough in vivo to overcome the severe hypercholesterolemia and oxidative stress produced by the PC-rich diet.     

Long-chain n-3 polyunsaturated fatty acid from fish oil modulates aortic nitric oxide and tocopherol status in the rat

In spite of their high oxidisability, long-chain n-3 PUFA protect against CVD. Dietary fatty acids modulate the fatty acid composition of lipoproteins involved in atherosclerosis. We thought that if long-chain n-3 PUFA were able to increase NO production by the aorta, then by its antioxidant activity the NO will prevent lipid peroxidation. However, the beneficial effect of NO in vivo on VLDL + LDL oxidation would only be possible if NO could diffuse to their lipidic core. Rats were fed maize oil- or fish oil as menhaden oil- (MO) rich diets for 8 weeks, to study the effects of MOon aortic NO production, NO diffusion into VLDL + LDL, the extent of oxidation in native VLDL + LDL and their oxidisability ex vivo. Aortic NO production and its alpha-tocopherol content were increased and n-3 PUFA were incorporated into the VLDL + LDL. In spite of the higher peroxidisability and the low alpha-tocopherol in native VLDL + LDL from rats fed MO, native VLDL + LDL from the two groups shared similar electrophoretic patterns, conjugated dienes, thiobarbituric acid-reactive substances, total antioxidant capacity, and NO diffusibility on VLDL + LDL, indicative of an in vivo protection against oxidation. However, these results do not correlate with the ex vivo oxidisability of VLDL+ LDL, as NO is lacking. Thus, the in vivo beneficial effects can be explained by increased a-tocopherol in aorta and by a compensatory effect of NO onVLDL + LDL against the low alpha-tocopherol levels, which may contribute to the anti-atherogenic properties of fish oil.     

Iron supplementation does not affect the susceptibility of LDL to oxidative modification in women with low iron status

Elevated iron stores may or may not promote atherogenesis by increasing free radical formation and oxidative stress, but controlled diet and supplement trials are lacking. We tested the hypothesis that iron supplementation does not increase the susceptibility of LDL to undergo oxidative modification in women with low iron status. A randomized, double-blind, 2-period crossover study design (n=26) was used to examine the effects of the following diets on measures of LDL oxidation: average American diet (AAD) [36% of energy as fat; 15% saturated fatty acids (SFA)], and a Step 2 diet (26% fat; 7% SFA). In addition, subjects received either a supplement containing 160 mg of ferrous sulfate (50 mg elemental iron) or a placebo twice daily [supplement group received a total of 320 mg ferrous sulfate (100 mg elemental iron) daily]. After supplementation, serum ferritin differed between the supplement and placebo groups (P=0.008). Measures of LDL oxidation were not affected by supplement intake; however, they were affected by diet. Lag time was shorter after the women consumed the AAD diet than after the Step 2 diet (P<0.0001). The diets did not affect the rate of oxidation or total dienes. Although iron status was improved by aggressive iron supplementation, LDL oxidative susceptibility was not affected. As expected, lag time was increased after the women consumed the low fat, low SFA diet. Therefore, the results of this study do not support a relationship between iron status and LDL oxidation.     

Effects of a dietary oxidized fat on cholesterol in plasma and lipoproteins and the susceptibility of low-density lipoproteins to lipid peroxidation in guinea pigs fed diets with different concentrations of vitamins E and C

To investigate the effect of a dietary oxidized fat on the concentrations of cholesterol in liver, plasma, and lipoproteins and the susceptibility of low-density lipoproteins (LDL) to lipid peroxidation, and to explore the effects of vitamins E and C, male guinea pigs were divided into five groups. Four groups were fed diets with an oxidized fat supplemented with 35 or 175 mg alpha-tocopherol equivalents/kg and 300 or 1000 mg of vitamin C/kg for 29 days. One group, used as a control, was fed the same basal diet with fresh fat with 35 mg alpha-tocopherol equivalents/kg and 300 mg of vitamin C/kg. Guinea pigs fed the oxidized-fat diets, irrespective of dietary vitamin E and C concentrations, had significantly lower concentrations of total cholesterol in the liver and a lower concentration of cholesterol in LDL than the control animals fed the fresh fat. According to the lag time before onset of lipid peroxidation, LDL of guinea pigs fed the oxidized-fat diet with 35 mg alpha-tocopherol equivalents and 300 mg vitamin C/kg were significantly more susceptible to copper-induced lipid peroxidation than those of guinea pigs fed the fresh fat diet. Within the groups fed the oxidized fat diets, increasing the dietary vitamin E concentration from 35 to 175 mg/kg significantly (p < 0.05) and increasing the dietary vitamin C concentration from 300 to 1000 mg/kg in tendency (p < 0.10) reduced the susceptibility of LDL to oxidation. LDL of guinea pigs fed the oxidized fat diets with 175 mg alpha-tocopherol equivalents/kg were even more resistant to oxidation than LDL of guinea pigs fed the fresh diet. In conclusion, the study shows that dietary oxidized fat influences the cholesterol metabolism and the susceptibility of LDL to lipid peroxidation; the latter can be modified by dietary vitamins E and C.