雷公藤红素通过激活LXRα/ABCA1通路和细胞自噬抑制巨噬细胞脂质蓄积

巨噬细胞源性泡沫细胞转化被认为是动脉粥样硬化(atherosclerosis,AS)形成与发展的早期变化,其细胞内蓄积的过量脂质可通过促进血管内膜生长与坏死核形成,继而诱发斑块破裂及血栓形成等严重后果.近期研究发现,雷公藤红素可显著调节脂质代谢,对泡沫细胞转化进程具有潜在的治疗意义.本研究表明,雷公藤红素(Celasrol,CeT)呈浓度依赖性减少巨噬细胞Raw264.7内的脂滴积蓄,并上调胆固醇转运关键分子ABCA1、LXRA蛋白质表达.进一步研究显示,CeT可逆转ABCA1敲低介导的脂质蓄积与ABCA1表达下调.此外,CeT处理Raw264.7细胞24 h时观察到自噬标志物LC3Ⅱ/Ⅰ增加、p62减少,且采用自噬抑制剂3MA可恢复细胞内脂质水平.综上,CeT可能通过上调LXRα/ABCA1信号及激活荷脂细胞自噬,抑制巨噬细胞内脂质蓄积.因此,深入探究CeT在巨噬细胞源性泡沫细胞转化及AS发生发展中的作用,是研究AS治疗新的着力点,并为药物干预提供新的靶点.     

Adipophilin在动脉粥样硬化病变和脂质负荷细胞中的作用研究(英文)

Adipophilin是细胞内脂质聚集和与脂质聚集有关疾病的标志物 ,巨噬细胞源性泡沫细胞的形成是动脉粥样硬化性疾病发生的重要环节 .为了探讨adipophilin在动脉粥样硬化性疾病的作用 ,通过高胆固醇饲料喂养新西兰白兔 12周 ,复制动脉粥样硬化疾病模型 ,同时测定血脂的变化和动脉壁胆固醇 ,使用HE染色、苏丹Ⅳ染色观察动脉粥样硬化病变的形成 ,使用免疫组织化学的方法观察动脉粥样硬化病变处和动物肝脏中adipophilin的表达 .结果发现 ,高胆固醇饲料喂养组血清总胆固醇、低密度脂蛋白胆固醇和动脉壁胆固醇明显增高 ,动脉粥样硬化病变面积增加到 (40 0 6± 7 2 9) % ,动脉粥样硬化病变处adipophilin表达呈阳性 ;而adipophilin在肝脏中的表达无论是高胆固醇饲料喂养组或对照组均为阴性 .使用80mg/L OxLDL与小鼠腹膜巨噬细胞共孵育 ,复制脂质负荷细胞 ,然后把构建的 1mmol/Ladipophilin反义寡核苷酸与该细胞共孵育 .结果发现 ,使用油红O染色观察的细胞内脂滴明显减少 ,生化测定细胞内胆固醇酯显著降低 ,与对照组相比 ,差别有显著性 .说明adipophilin与动脉粥样硬化病变有密切的关系 ,控制adipophilin的表达能够减少巨噬细胞细胞内胆固醇酯的聚集     

Adipophilin在动脉粥样硬化病变和脂质负荷细胞中的作用研究(英)

Adipophilin是细胞内脂质聚集和与脂质聚集有关疾病的标志物,巨噬细胞源性泡沫细胞的形成是动脉粥样硬化性疾病发生的重要环节.为了探讨adipophilin在动脉粥样硬化性疾病的作用,通过高胆固醇饲料喂养新西兰白兔12周,复制动脉粥样硬化疾病模型,同时测定血脂的变化和动脉壁胆固醇,使用HE染色、苏丹Ⅳ染色观察动脉粥样硬化病变的形成,使用免疫组织化学的方法观察动脉粥样硬化病变处和动物肝脏中adipophilin的表达.结果发现,高胆固醇饲料喂养组血清总胆固醇、低密度脂蛋白胆固醇和动脉壁胆固醇明显增高,动脉粥样硬化病变面积增加到(40.06±7.29)%,动脉粥样硬化病变处adipophilin表达呈阳性;而adipophilin在肝脏中的表达无论是高胆固醇饲料喂养组或对照组均为阴性.使用80 mg/L OxLDL与小鼠腹膜巨噬细胞共孵育,复制脂质负荷细胞,然后把构建的1 mmol/L adipophilin反义寡核苷酸与该细胞共孵育.结果发现,使用油红O染色观察的细胞内脂滴明显减少,生化测定细胞内胆固醇酯显著降低,与对照组相比,差别有显著性.说明adipophilin与动脉粥样硬化病变有密切的关系,控制adipophilin的表达能够减少巨噬细胞细胞内胆固醇酯的聚集.     

氧化修饰与丙二醛修饰的低密度脂蛋白对巨噬细胞高密度脂蛋白结合量及胆固醇酯聚集的影响

本文用Cu~(2+)(引发氧化修饰)和脂质过氧化降解产物丙二醛(MDA)对低密度脂蛋白(LDL)进行修饰,观察了两种修饰的LDL对巨噬细胞高密度脂蛋白_3(HDL_3)结合量及细胞内胆固醇酯聚集的影响。结果说明:1.Cu~(2+)和MDA修饰的LDL都可使巨噬细胞HDL_3结合量下降,细胞内脂质过氧化物(LPO)含量升高,但当处理细胞在含10％无脂血清(LPDS)培养液中继续培养时,由MDA修饰的LDL(MDA-LDL)导致的HDL_3结合量降低又有一定的恢复,细胞内LPO含量不再升高,而Cu~(2+)修饰的LDL(Cu~(2+)-LDL)处理的细胞继续培养时,HDL_3结合量则继续下降,细胞LPO含量则继续升高。2.由Cu~(2+)-LDL导致的巨噬细胞HDL_3结合量下降与细胞LPO含量升高之间呈负相关(r=-0.81,P<0.01)。3.MDA-LDL和Cu~(2+)-LDL都可造成巨噬细胞胆固醇酯聚集,但MDA-LDL造成的胆固醇酯可被HDL_3大量清除而Cu~(2+)-LDL造成的胆固醇酯聚集则不能。     

β-榄香烯对RAW264.7巨噬细胞源性泡沫细胞作用的研究

目的:研究β-榄香烯抗巨噬细胞源性泡沫细胞的形成及抑制巨噬细胞炎症因子分泌的作用。为探讨β-榄香烯抗动脉粥样硬化(AS)的作用提供依据。方法:采用氧化低密度脂蛋白(ox-LDL)诱导小鼠单核/巨噬细胞(RAW264.7)建立巨噬细胞源性泡沫细胞模型,采用油红O染色鉴定泡沫细胞形成。给予不同浓度(0.5,5,50μM)β-榄香烯干预后,ELISA方法检测巨噬细胞源性泡沫细胞内胆固醇含量和肿瘤坏死因子-α(TNF-α),白介素-6(IL-6)分泌量的变化。结果:β-榄香烯可降低巨噬细胞源性泡沫细胞内总胆固醇(P0.05或P0.01),胆固醇酯含量(P0.01),减少炎症因子TNF-α,IL-6的分泌(P0.05或P0.01),并且呈现出一定的浓度依赖性。结论:β-榄香烯抑制巨噬细胞对ox-LDL的摄取,降低细胞内胆固醇的含量,抑制泡沫细胞的形成,同时改善巨噬细胞的炎症状态从而发挥抗动脉粥样硬化的作用。     

重组人可溶性凝血酶调节蛋白对单核细胞源性泡沫细胞形成的影响

目的:研究可溶性凝血酶调节蛋白(Soluble thrombomodulin,sTM)结合的血浆低密度脂蛋白对细胞胆固醇代谢的影响,探索sTM参与或影响动脉粥样硬化发病过程的初步机制。方法:以THP-1巨噬细胞为模型,通过油红O染色、高效液相色谱检测胆固醇含量等方法,以体外重组人可溶性凝血酶调节蛋白结合的低密度脂蛋白(sTM-LDL)作用于巨噬细胞,观察sTM-LDL对细胞胆固醇代谢的影响。结果:研究发现:正常人LDL对细胞内胆固醇代谢影响较小;而sTM-LDL处理细胞72小时后,细胞内大量脂滴形成,细胞内胆固醇含量明显增多,符合典型泡沫细胞的特征;运用NH-1单抗中和／干扰sTM的作用,不能阻断sTM-LDL诱导的THP-1细胞内胆固醇聚集。结论:sTM对LDL的修饰可能改变了LDL的理化特性和代谢途径,可导致细胞内胆固醇聚集和泡沫细胞的形成,且这种作用与sTM本身对细胞的影响可能无明显关系。     

氧化修饰低密度脂蛋白对巨噬细胞一氧化氮合酶基因表达的影响

氧化修饰LDL(OX-LDL)可抑制脂多糖(LPS)诱导的巨噬细胞NO释放, 而正常(N-LDL)和乙酰化LDL(AC-LDL)则没有抑制作用.OX-LDL对NO释放的抑制作用随LDL修饰程度的升高而增强,且具有浓度和时间效应.狭缝杂交结果显示OX-LDL处理可使LPS诱导的巨噬细胞NOS mRNA含量下降,提示OX-LDL对NO释放的抑制作用可能发生在转录水平.     

beta- 榄香烯对RAW264.7 巨噬细胞源性泡沫细胞作用的研究

目的:研究β-榄香烯抗巨噬细胞源性泡沫细胞的形成及抑制巨噬细胞炎症因子分泌的作用。为探讨β-榄香烯抗动脉粥样硬化(AS)的作用提供依据。方法:采用氧化低密度脂蛋白(ox-LDL)诱导小鼠单核/巨噬细胞(RAW264.7)建立巨噬细胞源性泡沫细胞模型,采用油红O染色鉴定泡沫细胞形成。给予不同浓度(0.5,5,50μM)β-榄香烯干预后,ELISA方法检测巨噬细胞源性泡沫细胞内胆固醇含量和肿瘤坏死因子-α(TNF-α),白介素-6(IL-6)分泌量的变化。结果:β-榄香烯可降低巨噬细胞源性泡沫细胞内总胆固醇(P<0.05或P<0.01),胆固醇酯含量(P<0.01),减少炎症因子TNF-α,IL-6的分泌(P<0.05或P<0.01),并且呈现出一定的浓度依赖性。结论:β-榄香烯抑制巨噬细胞对ox-LDL的摄取,降低细胞内胆固醇的含量,抑制泡沫细胞的形成,同时改善巨噬细胞的炎症状态从而发挥抗动脉粥样硬化的作用。     

Krüppel样因子4通过支持PPARγ信号通路维持细胞稳态以保护血管平滑肌细胞免受泡沫细胞样表型转化的损害（英文）

动脉粥样硬化(AS)被普遍认为是一种血管壁细胞(包括内皮细胞和血管平滑肌细胞)、循环细胞以及固有免疫原性细胞(例如单核细胞/巨噬细胞)等多种细胞综合作用引起的炎症性疾病。其中血管平滑肌细胞(VSMCs)胆固醇超负荷形成的泡沫细胞可能在动脉粥样硬化的进展中发挥重要作用。Krüppel样因子4(KLF4)是一种关键的抗炎转录因子,尤其在心血管疾病方面,已被证实发挥了重要的血管功能保护作用。然而,目前尚不清楚KLF4是否在AS过程胆固醇对VSMCs的损伤中发挥保护作用。该研究旨在探讨KLF4在AS进展过程中VSMCs泡沫细胞样表型转化的作用及其分子机制。小鼠AS造模结果显示,KLF4缺失增加动脉粥样硬化斑块面积(P<0.05),并增加动脉壁脂质蓄积(P<0.05)及血清胆固醇含量(P<0.05),加速AS进展。细胞内油红O染色及胆固醇含量测定研究证实,KLF4缺失促进VSMCs内胆固醇蓄积(P<0.05)。QRT-PCR和Western印迹结果证实,KLF4缺失促进VSMCs胆固醇摄取、合成、促炎因子分泌及巨噬细胞黏附和胆固醇损伤诱导的巨噬细胞标志物的表达(P<...     

Wnt5a/PKCδ信号通路介导氧化低密度脂蛋白诱导的巨噬细胞自噬

研究发现动脉粥样硬化(atherosclerosis,AS)斑块中巨噬细胞摄取氧化低密度脂蛋白(oxidized low-density lipoprotein, ox-LDL)和巨噬细胞极化等关键变化与失调性自噬关系密切. Wnt5a (wingless-type MMTV integration site family member 5a)在AS病变的富含巨噬细胞区域中高表达,然而Wnt5a是否参与巨噬细胞自噬尚未明确.本研究发现,60 mg/L ox-LDL处理Raw264.7细胞6 h时,自噬标志物LC3Ⅱ/Ⅰ显著增加,p62显著减少,且Wnt5a、PKCδ及STAT3的表达均增加.小分子干扰RNA (small interference RNA,si RNA)敲低Wnt5a后,逆转ox-LDL诱导的LC3Ⅱ/Ⅰ和PKCδ表达,上调p62表达,减少细胞内脂质蓄积. PKCδ抑制剂Rottlerin干预后,LC3Ⅱ/Ⅰ和STAT3减少,p62增加,降低细胞内脂质含量.综上,ox-LDL可能通过Wnt5a/PKCδ信号通路诱导巨噬细胞自噬.因此,深入研究Wnt5a/PKCδ通路在巨噬细胞及AS发生发展中的作用,是研究自噬机制新的着力点,并为药物干预提供新的靶点.     

Lipid peroxide and transition metals are required for the toxicity of oxidized low density lipoprotein to cultured endothelial cells

The toxicity of oxidized low density lipoprotein (Ox-LDL) to cultured vascular endothelial cells was investigated. The modification of low density lipoprotein (LDL) by copper led to the production of thiobarbituric acid-reacting substance (TBARS) and lipid hydroperoxide (LPO). TBARS was distributed not only in lipoprotein, but also in the aqueous phase, whereas LPO was observed only in the lipoprotein particle. During the incubation of LDL with copper, the copper bound to lipoprotein and formed a complex. The toxicity of products resulting from the oxidation of LDL to endothelial cells was recognized in Ox-LDL particles, not in the aqueous phase. Following dialysis of Ox-LDL against EDTA, copper which had bound to the Ox-LDL particle was released and the toxicity of Ox-LDL disappeared. The addition of copper to the dialyzed Ox-LDL restored the cytotoxicity. To a lesser extent this effect was also observed with the addition of iron. A study of the time-course of LDL oxidation showed that the toxicity of Ox-LDL depends upon the level of LPO, not upon the content of TBARS, the extent of negative charge or the protein adduct of aldehydes. These results demonstrate that transition metal is required for Ox-LDL toxicity and that the toxic moiety of the products resulting from LDL oxidation is LPO associated with the Ox-LDL particle.     

Differences in the metabolism of oxidatively modified low density lipoprotein and acetylated low density lipoprotein by human endothelial cells: inhibition of cholesterol esterification by oxidatively modified low density lipoprotein

The rate of degradation of oxidatively modified low density lipoprotein (Ox-LDL) by human endothelial cells was similar to that of unmodified low density lipoprotein (LDL), and was approximately 2-fold greater than the rate of degradation of acetylated LDL (Ac-LDL). While LDL and Ac-LDL both stimulated cholesterol esterification in endothelial cells, Ox-LDL inhibited cholesterol esterification by 34%, demonstrating a dissociation between the degradation of Ox-LDL and its ability to stimulate cholesterol esterification. Further, while LDL and Ac-LDL resulted in a 5- and 15-fold increase in cholesteryl ester accumulation, respectively, Ox-LDL caused only a 1.3-fold increase in cholesteryl ester mass. These differences could be accounted for, in part, by the reduced cholesteryl ester content of Ox-LDL. However, when endothelial cells were incubated with Ac-LDL in the presence and absence of Ox-LDL, Ox-LDL led to a dose-dependent inhibition of cholesterol esterification without affecting the degradation of Ac-LDL. This inhibitory effect of Ox-LDL on cholesteryl ester synthesis was also manifest in normal human skin fibroblasts incubated with LDL and in LDL-receptor-negative fibroblasts incubated with unesterified cholesterol to stimulate cholesterol esterification. Further, the lipid extract from Ox-LDL inhibited cholesterol esterification in LDL-receptor negative fibroblasts. These findings suggest that the inhibition of cholesterol esterification by oxidized LDL is independent of the LDL and scavenger receptors and may be a result of translocation of a lipid component of oxidatively modified LDL across the cell membrane.     

Human serum paraoxonase (PON 1) is inactivated by oxidized low density lipoprotein and preserved by antioxidants

Human serum paraoxonase (PON1) can protect low density lipoprotein (LDL) from oxidation induced by either copper ion or by the free radical generator azo bis amidinopropane hydrochloride (AAPH). During LDL oxidation in both of these systems, a time-dependent inactivation of PON arylesterase activity was observed. Oxidized LDL (Ox-LDL) produced by lipoprotein incubation with either copper ion or with AAPH, indeed inactivated PON arylesterase activity by up to 47% or 58%, respectively. Three possible mechanisms for PON inactivation during LDL oxidation were considered and investigated: copper ion binding to PON, free radical attack on PON, and/or the effect of lipoprotein-associated peroxides on the enzyme. As both residual copper ion and AAPH are present in the Ox-LDL preparations and could independently inactivate the enzyme, the effect of minimally oxidized (Ox-LDL produced by LDL storage in the air) on PON activity was also examined. Oxidized LDL, as well as oxidized palmitoyl arachidonoyl phosphatidylcholine (PAPC), lysophosphatidylcholine (LPC, which is produced during LDL oxidation by phospholipase A2-like activity), and oxidized cholesteryl arachidonate (Ox-CA), were all potent inactivators of PON arylesterase activity (PON activity was inhibited by 35%-61%). PON treatment with Ox-LDL (but not with native LDL), or with oxidized lipids, inhibited its arylesterase activity and also reduced the ability of the enzyme to protect LDL against oxidation. PON Arylesterase activity however was not inhibited when PON was pretreated with the sulfhydryl blocking agent, p-hydroxymercurybenzoate (PHMB). Similarly, on using recombinant PON in which the enzyme's only free sulfhydryl group at the position of cysteine-284 was mutated, no inactivation of the enzyme arylesterase activity by Ox-LDL could be shown. These results suggest that Ox-LDL inactivation of PON involves the interaction of oxidized lipids in Ox-LDL with the PON's free sulfhydryl group. Antioxidants such as the flavonoids glabridin or quercetin, when present during LDL oxidation in the presence of PON, reduced the amount of lipoprotein-associated lipid peroxides and preserved PON activities, including its ability to hydrolyze Ox-LDL cholesteryl linoleate hydroperoxides. We conclude that PON's ability to protect LDL against oxidation is accompanied by inactivation of the enzyme. PON inactivation results from an interaction between the enzyme free sulfhydryl group and oxidized lipids such as oxidized phospholipids, oxidized cholesteryl ester or lysophosphatidylcholine, which are formed during LDL oxidation. The action of antioxidants and PON on LDL during its oxidation can be of special benefit against atherosclerosis since these agents reduce the accumulation of Ox-LDL by a dual effect: i.e. prevention of its formation, and removal of Ox-LDL associated oxidized lipids which are generated during LDL oxidation.     

Influence of Angelicae sinensis extract on lipid accumulation in rabbit aortic smooth muscle cells induced by oxidized LDL

Objective: To further establish a definite basic of the application value of sodium ferulate (SF) for prevention and cure of acute coronary heart disease, we examined the effects of SF on LDL oxidation and lipid accumulation in rabbit aortic smooth muscle cells induced by modified-LDL.Methods: LDL oxidation was carried out in the presence and absence of SF. Cultured rabbit aortic smooth muscle cells were used as the model. To investigate the effects of SF on intracellular lipid accumulation, cells were incubated with Ox-LDL and SF. The lipid content (cholesterol and triglycerides) of the cells were determined.Results: Intracellular cholesterol and triglycerides were significantly increased in cell-modified LDL group. The enhancements of above indexes were decreased after addition of SF (200 microg/ml). On the other hand, incubation of LDL with SF resulted in a significant decrease in TBARS activity and electrophoretic mobility.Conclusion: The results indicated that SF assume significance both in the protection of LDL against oxidation and inhibition of cell-modified LDL effects on intracellular lipid with the potential to prevent cell foamation.     

Uptake of modified low-density lipoproteins alters actin distribution and locomotor forces in macrophages

It is postulated thatmacrophage-derived foam cells accumulate in the arterial wall becausethey lose the ability to migrate after excessive ingestion of modifiedforms of low-density lipoproteins (LDL). To assess changes in locomotorforce generating capacity of foam cells, we measured isometric forcesin J774A.1 macrophages after cholesterol loading with oxidized (Ox-LDL)or aggregated (Agg-LDL) LDL using a novel magnetic force transducer.Ox-LDL loading reduced the ability of J774A.1 macrophages to generate isometric forces by 50% relative to control cells. Changes in forcefrequency consistent with reduced motility were detected as well.Agg-LDL loading was also detrimental to J774A.1 motility but to alesser extent than Ox-LDL. Ox-LDL loading significantly reduced totalactin levels and induced changes in the F-actin to G-actindistribution, whereas Agg-LDL loaded cells had significantly increasedlevels of total actin. These data provide evidence that cholesterolloading and subsequent accumulation decreases macrophage motility byreducing the cells' force generating capacity and that Ox-LDL appearsto be more effective than Agg-LDL in disrupting the locomotor machinery.

     

Oxidized low density lipoproteins regulate synthesis of monkey aortic smooth muscle cell proteoglycans that have enhanced native low density lipoprotein binding properties

Oxidized low density lipoproteins (Ox-LDL) affect several biological processes involved in atherogenesis. However, it is not known whether Ox-LDL can regulate proteoglycan expression and thus affect arterial wall lipoprotein retention. This study evaluated whether Ox-LDL, as compared with native LDL, regulates proteoglycan expression by monkey arterial smooth muscle cells in vitro and whether proteoglycans synthesized in the presence of Ox-LDL exhibit altered lipoprotein binding properties. Ox-LDL stimulated glycosaminoglycan synthesis, as measured by (35)SO(4) incorporation, by 30-50% over that of native LDL. The effect was maximal after 72 h of exposure to 5 microg/ml of Ox-LDL. The molecular sizes of versican, biglycan, and decorin increased in response to Ox-LDL, as indicated by size exclusion chromatography and SDS-polyacrylamide gel electrophoresis. These effects could be mimicked by the lipid extract of Ox-LDL. These size increases were largely due to chain elongation and not to alterations in the ratio of (35)SO(4) to [(3)H]glucosamine incorporation. Affinity chromatography indicated that Ox-LDL stimulated the synthesis of proteoglycans with high affinity for native LDL. Ox-LDL also specifically stimulated mRNA expression for biglycan (but not versican or decorin), which was correlated with increased expression of secreted biglycan. Thus, Ox-LDL may influence lipoprotein retention by regulating synthesis of biglycan and also by altering glycosaminoglycan synthesis of vascular proteoglycans so as to enhance lipoprotein binding properties.     

Antioxidant effects of fructosyl arginine, a Maillard reaction product in aged garlic extract

The amino-carbonyl (Maillard) reaction of amino acids with sugars is a nonenzymatic browning reaction that takes place during the processing, cooking, and storage of foods. Maillard reaction products (MRPs) have been shown to possess interesting chemical and biological properties including antimutagenic and antioxidant activity. In this study, we determined the antioxidant effects of fructosyl arginine (Fru-Arg), a MRP in aged garlic extract. Low density lipoprotein (LDL) was incubated with Cu(2+) at 37 degrees C and 5% CO(2) for 24 hours, which resulted in an increase of thiobarbituric acid reactive substances (TBARS) indicating lipid peroxidation. Coincubation of Cu(2+) with Fru-Arg and LDL resulted in a significant inhibition of TBARS formation. Pulmonary artery endothelial cells (PAEC) were exposed to 0.1 mg/mL oxidized LDL (Ox-LDL) at 37 degrees C and 5% CO(2) for 24 hours. Lactate dehydrogenase (LDH) release, as an index of cell membrane damage, and TBARS were measured. Ox-LDL caused an increase of LDH release and TBARS formation. Pretreatment of PAEC with Fru-Arg inhibited these changes. Murine macrophages were incubated with Ox-LDL, and the release of peroxides was measured using a fluorometric assay. Ox-LDL caused an increased release of peroxides. Coincubation of macrophages with Fru-Arg and Ox-LDL inhibited the release of peroxides dose-dependently. In a cell free system, Fru-Arg was shown to scavenge hydrogen peroxide. These data suggest that Fru-Arg is a potent antioxidant, and thus may be useful for the prevention of atherosclerosis and other disorders associated with oxidative stress.     

Differential effects of oxidized LDL on apolipoprotein AI and B synthesis in HepG2 cells

Oxidized low-density lipoproteins (Ox-LDL) are key elements in atherogenesis. Apolipoprotein AI (apoAI) is an active component of the antiatherogenic high-density lipoproteins (HDL). In contrast, plasma apolipoprotein B (apoB), the main component of LDL, is highly correlated with coronary risk. Our results, obtained in HepG2 cells, show that Ox-LDL, unlike native LDL, leads to opposite effects on apoB and apoAI, namely a decrease in apoAI and an increase in apoB secretion as evaluated by [(3)H]leucine incorporation and specific immunoprecipitation. Parallel pulse-chase studies show that Ox-LDL impaired apoB degradation, whereas apoAI degradation was increased and mRNA levels were decreased. We also found that enhanced lipid biosynthesis of both triglycerides and cholesterol esters was involved in the Ox-LDL-induced increase in apoB secretion. Our data suggest that the increase in apoB and decrease in apoAI secretion may in part contribute to the known atherogenicity of Ox-LDL through an elevated LDL/HDL ratio, a strong predictor of coronary risk in patients.     

Metabolism of modified LDL and foam cell formation in murine macrophage-like RAW 264 cells.

The uptake of modified low density lipoprotein (LDL) by arterial macrophages is a key event in the atherogenesis. We studied 1) the uptake and degradation of modified LDL, 2) LDL recognition by specific receptors, and 3) the foam cell formation with murine macrophage-like RAW 264 cells in vitro. The cells took up and degraded effectively 125I-labeled acetylated LDL (Ac-LDL) and aggregated LDL (Aggr-LDL). Also oxidized LDL (Ox-LDL) was taken up but it was degraded poorly. The degradation of 125I-Ac-LDL was efficiently competed by both unlabeled Ac-LDL and Ox-LDL, whereas the degradation of 125I-Ox-LDL was partially competed by unlabeled Ox-LDL and Aggr-LDL but not at all by unlabeled Ac-LDL. The incubation with increasing concentrations of Ac-LDL, Aggr-LDL or Ox-LDL resulted in marked foam cell formation in the RAW 264 cells. Ox-LDL was cytotoxic at 500 to 1000 microg/ml concentrations. The results show that RAW 264 cells have at least two classes of receptors for modified lipoproteins: one that recognizes both Ox-LDL and Ac-LDL, and is similar to the scavenger receptors, and another that recognizes Ox-LDL but not Ac-LDL. RAW 264 cells are a convenient model cell line for examining the metabolism of modified lipoproteins, not only that of Ac-LDL but also that of Ox-LDL and Aggr-LDL, and cellular accumulation of lipids derived from modified LDL.     

Panax quinquefolium saponins protects low density lipoproteins from oxidation

Oxidized low-density lipoprotein (Ox-LDL) is believed to be involved in the pathogenesis of atherosclerosis. Panax quinquefolium saponins (PQS) are extracted from the stems and leaves of the North American form of ginseng, Panax quinquefolium. Earlier studies have suggested that this extract improves the lipid profile of hyperlipidemic rats and has antioxidant properties in cultured rat cardiac myocytes. The aims of the present study were to investigate the potential of PQS in reducing LDL oxidation as well as limiting the ability of Ox-LDL to impair endothelium-dependent relaxation in rat aortic rings. LDL was isolated from the plasma of healthy human donors by sequential ultracentrifugation. Native LDL (0.2 or 0.3 mg/ml) was incubated with PQS (0.25-1 mg/ml) for 30 min at 20 degrees C. For comparison, vitamin C (50 microM) was added in place of PQS. Oxidative modification was initiated with 5 microM CuSO4 at 37 degrees C for 0-24 h. In our hands, PQS concentration-dependently reduced lipid peroxide levels as measured by the amount of thiobarbituric acid reactive substances formed. This range of PQS also retarded the alterations in relative electrophoretic mobility of Ox-LDL in a similar manner. Furthermore, measurement of phospholipid fractions content indicated that PQS could reduce the conversion of phosphatidylcholine to lysophosphatidylcholine in Ox-LDL. Functional studies demonstrated that PQS-pretreated Ox-LDL was less potent than untreated Ox-LDL at impairing endothelium-dependent relaxation in rat aortic rings. In conclusion, our results suggest that PQS has antioxidant properties and that reduction of LDL oxidation by PQS may provide a protective effect against the detrimental actions of Ox-LDL.