School of Biological Sciences and Institute of Cardiovascular and Metabolic Research, Hopkins Building, Whiteknights, University of Reading, Reading RG6 6UB, UK.
Biochemistry. 2012 May 8;51(18):3767-75. doi: 10.1021/bi2017975. Epub 2012 Apr 25.
Low-density lipoprotein (LDL) has recently been shown to be oxidized by iron within the lysosomes of macrophages, and this is a novel potential mechanism for LDL oxidation in atherosclerosis. Our aim was to characterize the chemical and physical changes induced in LDL by iron at lysosomal pH and to investigate the effects of iron chelators and α-tocopherol on this process. LDL was oxidized by iron at pH 4.5 and 37 °C and its oxidation monitored by spectrophotometry and high-performance liquid chromatography. LDL was oxidized effectively by FeSO(4) (5-50 μM) and became highly aggregated at pH 4.5, but not at pH 7.4. The level of cholesteryl esters decreased, and after a pronounced lag, the level of 7-ketocholesterol increased greatly. The total level of hydroperoxides (measured by the triiodide assay) increased up to 24 h and then decreased only slowly. The lipid composition after 12 h at pH 4.5 and 37 °C was similar to that of LDL oxidized by copper at pH 7.4 and 4 °C, i.e., rich in hydroperoxides but low in oxysterols. Previously oxidized LDL aggregated rapidly and spontaneously at pH 4.5, but not at pH 7.4. Ferrous iron was much more effective than ferric iron at oxidizing LDL when added after the oxidation was already underway. The iron chelators diethylenetriaminepentaacetic acid and, to a lesser extent, desferrioxamine inhibited LDL oxidation when added during its initial stages but were unable to prevent aggregation of LDL after it had been partially oxidized. Surprisingly, desferrioxamine increased the rate of LDL modification when added late in the oxidation process. α-Tocopherol enrichment of LDL initially increased the rate of oxidation of LDL but decreased it later. The presence of oxidized and highly aggregated lipid within lysosomes has the potential to perturb the function of these organelles and to promote atherosclerosis.
低密度脂蛋白（LDL）最近被证明可在巨噬细胞溶酶体中的铁的作用下被氧化，这是动脉粥样硬化中 LDL 氧化的一种新的潜在机制。我们的目的是描述在溶酶体 pH 值下铁诱导 LDL 发生的化学和物理变化，并研究铁螯合剂和α-生育酚对这一过程的影响。在 pH 4.5 和 37°C 下用铁使 LDL 氧化，并通过分光光度法和高效液相色谱法监测其氧化情况。FeSO4（5-50 μM）可有效地使 LDL 氧化，在 pH 4.5 时 LDL 高度聚集，但在 pH 7.4 时则不然。胆固醇酯的水平降低，在明显的滞后之后，7-酮胆固醇的水平大大增加。通过三碘化物测定法测量的总过氧化物水平在 24 小时内增加，然后仅缓慢减少。在 pH 4.5 和 37°C 下 12 小时后的脂质组成与在 pH 7.4 和 4°C 下用铜氧化的 LDL 相似，即富含过氧化物但低含量的氧化固醇。先前氧化的 LDL 在 pH 4.5 时迅速且自发地聚集，但在 pH 7.4 时则不然。亚铁比三价铁在氧化 LDL 时更有效，尤其是在氧化已经开始时添加亚铁。二乙三胺五乙酸和（在较小程度上）去铁胺在氧化初始阶段添加时可抑制 LDL 氧化，但不能防止部分氧化后的 LDL 聚集。令人惊讶的是，去铁胺在氧化后期添加时会增加 LDL 修饰的速度。最初，LDL 中α-生育酚的富集会增加 LDL 氧化的速度，但后来则会降低。在溶酶体中存在氧化和高度聚集的脂质有可能扰乱这些细胞器的功能并促进动脉粥样硬化的形成。
