Hermes-Lima M, Ponka P, Schulman H M
Oxyradical Research Group, Departamento de Biologia Celular, Universidade de Brasília, Brasília, Brazil.
Biochim Biophys Acta. 2000 Oct 18;1523(2-3):154-60. doi: 10.1016/s0304-4165(00)00115-x.
Iron chelating agents are essential for treating iron overload in diseases such as beta-thalassemia and are potentially useful for therapy in non-iron overload conditions, including free radical mediated tissue injury. Deferoxamine (DFO), the only drug available for iron chelation therapy, has a number of disadvantages (e.g., lack of intestinal absorption and high cost). The tridentate chelator pyridoxal isonicotinoyl hydrazone (PIH) has high iron chelation efficacy in vitro and in vivo with high selectivity and affinity for iron. It is relatively non-toxic, economical to synthesize and orally effective. We previously demonstrated that submillimolar levels of PIH and some of its analogues inhibit lipid peroxidation, ascorbate oxidation, 2-deoxyribose degradation, plasmid DNA strand breaks and 5,5-dimethylpyrroline-N-oxide (DMPO) hydroxylation mediated by either Fe(II) plus H(2)O(2) or Fe(III)-EDTA plus ascorbate. To further characterize the mechanism of PIH action, we studied the effects of PIH and some of its analogues on the degradation of 2-deoxyribose induced by Fe(III)-EDTA plus ascorbate. Compared with hydroxyl radical scavengers (DMSO, salicylate and mannitol), PIH was about two orders of magnitude more active in protecting 2-deoxyribose from degradation, which was comparable with some of its analogues and DFO. Competition experiments using two different concentrations of 2-deoxyribose (15 vs. 1.5 mM) revealed that hydroxyl radical scavengers (at 20 or 60 mM) were significantly less effective in preventing degradation of 2-deoxyribose at 15 mM than 2-deoxyribose at 1.5 mM. In contrast, 400 microM PIH was equally effective in preventing degradation of both 15 mM and 1.5 mM 2-deoxyribose. At a fixed Fe(III) concentration, increasing the concentration of ligands (either EDTA or NTA) caused a significant reduction in the protective effect of PIH towards 2-deoxyribose degradation. We also observed that PIH and DFO prevent 2-deoxyribose degradation induced by hypoxanthine, xanthine oxidase and Fe(III)-EDTA. The efficacy of PIH or DFO was inversely related to the EDTA concentration. Taken together, these results indicate that PIH (and its analogues) works by a mechanism different than the hydroxyl radical scavengers. It is likely that PIH removes Fe(III) from the chelates (either Fe(III)-EDTA or Fe(III)-NTA) and forms a Fe(III)-PIH(2) complex that does not catalyze oxyradical formation.
铁螯合剂对于治疗β地中海贫血等疾病中的铁过载至关重要，并且在非铁过载病症（包括自由基介导的组织损伤）的治疗中可能有用。去铁胺（DFO）是唯一可用于铁螯合治疗的药物，有许多缺点（例如，缺乏肠道吸收且成本高）。三齿螯合剂吡啶醛异烟酰腙（PIH）在体外和体内具有高铁螯合效力，对铁具有高选择性和亲和力。它相对无毒，合成经济且口服有效。我们之前证明，亚毫摩尔水平的PIH及其一些类似物可抑制由Fe(II)加H(2)O(2)或Fe(III)-EDTA加抗坏血酸介导的脂质过氧化、抗坏血酸氧化、2-脱氧核糖降解、质粒DNA链断裂和5,5-二甲基吡咯啉-N-氧化物（DMPO）羟基化。为了进一步表征PIH的作用机制，我们研究了PIH及其一些类似物对Fe(III)-EDTA加抗坏血酸诱导的2-脱氧核糖降解的影响。与羟基自由基清除剂（二甲基亚砜、水杨酸盐和甘露醇）相比，PIH在保护2-脱氧核糖不被降解方面的活性高约两个数量级，这与其一些类似物和DFO相当。使用两种不同浓度的2-脱氧核糖（15 mM对1.5 mM）进行的竞争实验表明，羟基自由基清除剂（20或60 mM）在防止15 mM的2-脱氧核糖降解方面比1.5 mM的2-脱氧核糖明显效果更差。相比之下，400 μM的PIH在防止15 mM和1.5 mM的2-脱氧核糖降解方面同样有效。在固定的Fe(III)浓度下，增加配体（EDTA或NTA）的浓度会导致PIH对2-脱氧核糖降解的保护作用显著降低。我们还观察到PIH和DFO可防止次黄嘌呤、黄嘌呤氧化酶和Fe(III)-EDTA诱导的2-脱氧核糖降解。PIH或DFO的效力与EDTA浓度呈负相关。综上所述，这些结果表明PIH（及其类似物）的作用机制与羟基自由基清除剂不同。PIH可能从螯合物（Fe(III)-EDTA或Fe(III)-NTA）中去除Fe(III)并形成不催化氧自由基形成的Fe(III)-PIH(2)复合物。
