Aviram M
Lipid Research Unit, Rambam Medical Center, Haifa, Israel.
J Biol Chem. 1992 Jan 5;267(1):218-25.
Oxidation of low density lipoprotein (LDL) by cells of the arterial wall or in the presence of copper ions was shown to result in the peroxidation of its fatty acids as well as its cholesterol moiety. LDL incubation with cholesterol oxidase (CO) resulted in the conversion of up to 85% of the lipoprotein unesterified cholesterol (cholest-5-en-3-ol) to cholestenone (cholest-4-en-3-one) in a dose- and time-dependent pattern. Plasma very low density lipoprotein (VLDL) and high density lipoprotein (HDL) could be similarly modified by CO. In cholesterol oxidase-modified LDL (CO-LDL), unlike copper ion-induced oxidized LDL (Cu-Ox-LDL), there was no fatty acids peroxidation, and lipoprotein size or charge as well as LDL cholesteryl ester, phospholipids, and triglycerides content were not affected. CO-LDL, however, demonstrated enhanced susceptibility to oxidation by copper ions in comparison to native LDL. Upon incubation of CO-LDL with J-774 A.1 macrophage-like cell line, cellular uptake and degradation of the lipoprotein was increased by up to 62% in comparison to native LDL but was 15% lower than that of Cu-Ox-LDL. Similarly, the binding of CO-LDL to macrophages increased by up to 80%, and cellular cholesterol mass was increased 51% more than the mass obtained with native LDL. Several lines of evidence indicate that CO-LDL was taken up via the LDL receptor: 1) Excess amounts of unlabeled LDL, but not acetyl-LDL (Ac-LDL), effectively competed with 125I-CO-LDL for the uptake by cells. 2) The degradation of CO-LDL by various types of macrophages and by fibroblasts could be dissociated from that of Ac-LDL and was always higher than that of native LDL. 3) A monoclonal antibody to the LDL receptor (IgG-C7) and a monoclonal antibody to the LDL receptor binding domains on apoB-100 (B1B6) inhibited macrophage degradation of CO-LDL. The receptor for Cu-Ox-LDL, which is not shared with Ac-LDL, was also partially involved in macrophage uptake of CO-LDL, since Cu-Ox-LDL demonstrated some competition capability with CO-125I-LDL for its cellular degradation. CO-LDL cellular degradation was inhibited by chloroquine, thus implying lysosomal involvement in the cellular processing of the lipoprotein. Incubation of macrophages with LDL in the presence of increasing concentrations of cholestenone resulted in up to 52% enhanced lipoprotein cellular degradation suggesting that the cholestenone in CO-LDL might be involved in the enhanced cellular uptake of the modified lipoprotein.(ABSTRACT TRUNCATED AT 400 WORDS)
动脉壁细胞或在铜离子存在的情况下，低密度脂蛋白（LDL）的氧化被证明会导致其脂肪酸以及胆固醇部分的过氧化。LDL与胆固醇氧化酶（CO）孵育会使高达85%的脂蛋白未酯化胆固醇（胆甾-5-烯-3-醇）以剂量和时间依赖性方式转化为胆甾烯酮（胆甾-4-烯-3-酮）。血浆极低密度脂蛋白（VLDL）和高密度脂蛋白（HDL）也可被CO类似地修饰。在胆固醇氧化酶修饰的LDL（CO-LDL）中，与铜离子诱导的氧化LDL（Cu-Ox-LDL）不同，不存在脂肪酸过氧化，并且脂蛋白大小或电荷以及LDL胆固醇酯、磷脂和甘油三酯含量均未受影响。然而，与天然LDL相比，CO-LDL对铜离子氧化的敏感性增强。将CO-LDL与J-774 A.1巨噬细胞样细胞系孵育后，与天然LDL相比，脂蛋白的细胞摄取和降解增加了高达62%，但比Cu-Ox-LDL低15%。同样，CO-LDL与巨噬细胞的结合增加了高达80%，细胞胆固醇量比天然LDL获得的量增加了51%。几条证据表明CO-LDL是通过LDL受体摄取的：1）过量的未标记LDL，但不是乙酰化LDL（Ac-LDL），能有效竞争125I-CO-LDL被细胞摄取。2）各种类型的巨噬细胞和成纤维细胞对CO-LDL的降解可与Ac-LDL的降解分离，且总是高于天然LDL的降解。3）针对LDL受体的单克隆抗体（IgG-C7）和针对载脂蛋白B-100上LDL受体结合域的单克隆抗体（B1B6）抑制巨噬细胞对CO-LDL的降解。Cu-Ox-LDL的受体与Ac-LDL不共享，也部分参与了巨噬细胞对CO-LDL的摄取，因为Cu-Ox-LDL对其细胞降解表现出与125I-CO-LDL的一定竞争能力。CO-LDL的细胞降解被氯喹抑制，因此意味着溶酶体参与了脂蛋白的细胞处理过程。在胆甾烯酮浓度增加的情况下，巨噬细胞与LDL孵育导致脂蛋白细胞降解增强高达52%，这表明CO-LDL中的胆甾烯酮可能参与了修饰脂蛋白细胞摄取的增强。（摘要截断于400字）
