Khouw A S, Parthasarathy S, Witztum J L
Department of Medicine, University of California, San Diego, La Jolla 92093-0682.
J Lipid Res. 1993 Sep;34(9):1483-96.
It is now apparent that low density lipoprotein (LDL) is very susceptible to lipid peroxidation and that the resulting oxidized LDL has altered biological properties. Radiation, particularly of longer duration and lower intensities, initiates lipid peroxidation, yet radioiodination with 125I and 131I is a frequently used method to label LDL for biological studies. To test the possibility that this procedure alters the biological properties of LDL, native LDL was radioiodinated with 125I/131I using ICl to average specific activities of approximately 300 and approximately 100 cpm/ng protein, respectively. Lipid peroxidation was monitored by TBARS and conjugated diene formation. Biological properties were monitored by fibroblast and macrophage uptake of LDL as well as by rate of plasma clearance (FCR) in guinea pigs. 131I-labeled LDL showed enhanced indices of lipid peroxidation compared to 125I-labeled LDL and both were greater than native LDL. The FCR of 131I-labeled LDL was greater than that of 125I-labeled LDL (by 20-40%) and both increased progressively (by > 250%) when measured at 2, 6, and 13 days after iodination. The radioiodinated LDL samples were also more susceptible to pro-oxidant conditions. Thus, after exposure to Cu2+, 131I-labeled LDL showed greatly enhanced lipid peroxidation, decreased uptake by fibroblasts, increased uptake by macrophages and greatly accelerated FCR in guinea pigs. Exposure of LDL to 131I-labeled albumin produced similar changes. Protecting LDL with antioxidants such as BHT and ascorbate immediately after radioiodination generally ameliorated the adverse effects.
现在很明显，低密度脂蛋白（LDL）非常容易发生脂质过氧化，并且由此产生的氧化型LDL具有改变的生物学特性。辐射，尤其是较长时间和较低强度的辐射，会引发脂质过氧化，但用125I和131I进行放射性碘化是用于标记LDL以进行生物学研究的常用方法。为了测试该程序是否会改变LDL的生物学特性，使用ICl分别将天然LDL用125I/131I进行放射性碘化，使其平均比活度分别约为300和约100 cpm/ng蛋白质。通过硫代巴比妥酸反应物（TBARS）和共轭二烯的形成来监测脂质过氧化。通过成纤维细胞和巨噬细胞对LDL的摄取以及豚鼠血浆清除率（FCR）来监测生物学特性。与125I标记的LDL相比，131I标记的LDL显示出脂质过氧化指标增强，且两者均高于天然LDL。131I标记的LDL的FCR大于125I标记的LDL（高20 - 40%），并且在碘化后第2、6和13天测量时，两者均逐渐增加（超过250%）。放射性碘化的LDL样品也更容易受到促氧化条件的影响。因此，暴露于Cu2+后，131I标记的LDL显示出脂质过氧化大大增强，成纤维细胞摄取减少，巨噬细胞摄取增加，并且豚鼠的FCR大大加快。将LDL暴露于131I标记的白蛋白会产生类似的变化。放射性碘化后立即用抗氧化剂如丁基羟基甲苯（BHT）和抗坏血酸保护LDL通常会减轻不良反应。
