Li Q, Tallant A, Cathcart M K
Research Institute, Cleveland Clinic Foundation, Ohio 44195.
J Clin Invest. 1993 Apr;91(4):1499-506. doi: 10.1172/JCI116355.
The oxidative modification of LDL seems a key event in atherogenesis and may participate in inflammatory tissue injury. Our previous studies suggested that the process of LDL oxidation by activated human monocytes/macrophages required O2- and activity of intracellular lipoxygenase. Herein, we studied the mechanisms involved in this oxidative modification of LDL. In this study, we used the human monocytoid cell line U937 to examine the role of Ca2+ in U937 cell-mediated lipid peroxidation of LDL. U937 cells were activated by opsonized zymosan. Removal of Ca2+ from cell culture medium by EGTA inhibited U937 cell-mediated peroxidation of LDL lipids. Therefore, Ca2+ influx and mobilization were examined for their influence on U937 cell-mediated LDL lipid peroxidation. Ca2+ channel blockers nifedipine and verapamil blocked both Ca2+ influx and LDL lipid peroxidation by activated U937 cells. The inhibitory effects of nifedipine and verapamil were dose dependent. TMB-8 and ryanodine, agents known to prevent Ca2+ release from intracellular stores, also caused a dose-dependent inhibition of LDL lipid peroxidation by activated U937 cells while exhibiting no effect on Ca2+ influx. Thus, both Ca2+ influx through functional calcium channels and Ca2+ mobilization from intracellular stores participate in the oxidative modification of LDL by activated U937 cells. 45Ca2+ uptake experiments revealed profound Ca2+ influx during the early stages of U937 cell activation, however, the Ca2+ ionophore 4-bromo A23187 was unable to induce activation of U937 cells and peroxidation of LDL lipids. Release of intracellular Ca2+ by thapsigargin only caused a suboptimal peroxidation of LDL lipids. Our results indicate that although increases in intracellular Ca2+ levels provided by both influx and intracellular Ca2+ mobilization are required, other intracellular signals may be involved for optimal peroxidation of LDL lipids by activated human monocytes.
低密度脂蛋白（LDL）的氧化修饰似乎是动脉粥样硬化发生过程中的关键事件，并且可能参与炎症性组织损伤。我们之前的研究表明，活化的人单核细胞/巨噬细胞对LDL的氧化过程需要超氧阴离子（O2-）和细胞内脂氧合酶的活性。在此，我们研究了参与LDL这种氧化修饰的机制。在本研究中，我们使用人单核细胞样细胞系U937来研究Ca2+在U937细胞介导的LDL脂质过氧化中的作用。U937细胞通过调理酵母聚糖被激活。用乙二醇双四乙酸（EGTA）从细胞培养基中去除Ca2+可抑制U937细胞介导的LDL脂质过氧化。因此，研究了Ca2+内流和动员对U937细胞介导的LDL脂质过氧化的影响。Ca2+通道阻滞剂硝苯地平和维拉帕米可阻断活化的U937细胞的Ca2+内流和LDL脂质过氧化。硝苯地平和维拉帕米的抑制作用呈剂量依赖性。已知可阻止Ca2+从细胞内储存释放的药物三甲基溴化铵（TMB-8）和ryanodine，也对活化的U937细胞介导的LDL脂质过氧化产生剂量依赖性抑制，而对Ca2+内流无影响。因此，通过功能性钙通道的Ca2+内流和从细胞内储存的Ca2+动员均参与活化的U937细胞对LDL的氧化修饰。45Ca2+摄取实验显示在U937细胞活化早期有大量Ca2+内流，然而，Ca2+离子载体4-溴-A23187无法诱导U937细胞活化和LDL脂质过氧化。毒胡萝卜素释放细胞内Ca2+仅引起LDL脂质的次优过氧化。我们的结果表明，尽管通过内流和细胞内Ca2+动员使细胞内Ca2+水平升高都是必需的，但其他细胞内信号可能参与活化的人单核细胞对LDL脂质的最佳过氧化。
