Mori Y, Watanabe R, Sakamoto S, Endo N, Nakano S, Kanaori K, Takashima H, Ohkawa M, Tajima K
Department of Radiology, Kagawa Medical University, 1750 Ikenobe Miki Kagawa, 761-0793 Japan.
J Med. 2004;35(1-6):49-61.
The OH radical scavenging activity of a series of Gd(III) MRI contrast media, such as Gd(III)DTPA, Gd(III)BMA and Gd(III)DO3A, were evaluated by means of EPR spin trapping measurements. The second order reaction rate constant (k2) occurring between Gd(III)DTPA and OH radical was estimated to be 3.26 x 10(10) (M(-1)s(-1)), which was ten times larger than that of the free ligand DTPA (3.86 x 10(9) M(-1)s(-1). The k2 values of Gd(III)BMA and Gd(III)DO3A were also determined to be 1.31 x 10(10) and 1.77 x 10(10) (M(-1)s(1)), respectively. The present results suggest that widely used Gd(III) containing MRI reagent exhibit OH radical scavenging activity, and these values of k2 are same order as that of ascorbic acid (1.16 x 10(10) M(-1)s(-1)) which has been well established to be the most powerful OH radical scavenger. Based on the EPR measurements performed for these Gd(III) complexes, a possible reaction mechanism of the OH radical scavenging action of these MRI contrast media will be discussed.
通过电子顺磁共振（EPR）自旋捕集测量法评估了一系列钆（III）磁共振成像（MRI）造影剂（如钆（III）二乙三胺五乙酸（Gd(III)DTPA）、钆（III）双甲脒（Gd(III)BMA）和钆（III）三乙醇胺（Gd(III)DO3A））的羟基自由基清除活性。据估计，Gd(III)DTPA与羟基自由基之间发生的二级反应速率常数（k2）为3.26×10¹⁰（M⁻¹s⁻¹），这比游离配体二乙三胺五乙酸（DTPA）的反应速率常数（3.86×10⁹ M⁻¹s⁻¹）大十倍。Gd(III)BMA和Gd(III)DO3A的k2值也分别确定为1.31×10¹⁰和1.77×10¹⁰（M⁻¹s⁻¹）。目前的结果表明，广泛使用的含钆（III）的MRI试剂具有羟基自由基清除活性，并且这些k2值与已被公认为最强有力的羟基自由基清除剂的抗坏血酸（1.16×10¹⁰ M⁻¹s⁻¹）处于同一数量级。基于对这些钆（III）配合物进行的EPR测量，将讨论这些MRI造影剂羟基自由基清除作用的可能反应机制。
