Role of ascorbic acid in transferrin-independent reduction and uptake of iron by U-937 cells.
Role of ascorbic acid in transferrin-independent reduction and uptake of iron by U-937 cells.
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DOI：
10.1016/s0006-2952(99)00040-4
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发表时间：
1999-06
影响因子：
5.8
通讯作者：
James M. May;Z. Qu;S. Mendiratta
中科院分区：
文献类型：
--
作者：
James M. May;Z. Qu;S. Mendiratta
抗坏血酸在转铁蛋白非依赖性三价铁还原和摄取中的作用在培养的U-937单核细胞中进行了评价。U-937细胞对55 Fe的摄取在100 μM细胞外抗坏血酸作用下加倍，在100 μM脱氢抗坏血酸（抗坏血酸的双电子氧化形式）作用下加倍。还原的细胞外柠檬酸铁也被加强负载细胞与脱氢抗坏血酸。脱氢抗坏血酸被细胞迅速吸收并还原为抗坏血酸盐，使后者达到细胞内浓度高达6 mM。然而，一些抗坏血酸盐确实逸出细胞，并可在孵育培养基中检测到浓度高达1 μM的抗坏血酸盐。此外，抗坏血酸氧化酶的加入几乎逆转了脱氢抗坏血酸对55 Fe吸收和柠檬酸铁还原的影响。因此，很可能细胞外抗坏血酸盐将三价铁还原为亚铁，然后被细胞吸收。这一假设也得到了以下发现的支持：在柠檬酸铁负载期间，只有细胞外抗坏血酸盐增加了细胞内亚铁的池，其可以与细胞渗透亚铁螯合剂螯合。与抗坏血酸氧化酶抑制抗坏血酸依赖的三价铁还原相反，抗坏血酸氧化酶对抗坏血酸依赖的细胞外铁氰化物还原没有影响。这表明细胞使用不同的机制来还原三价铁和铁氰化物。因此，来自细胞的细胞外抗坏血酸盐可以通过将三价铁还原为二价铁来增强不依赖于转铁蛋白的铁摄取，但细胞内抗坏血酸盐既不有助于这种还原，也不改变细胞内游离铁的氧化还原状态。
The role of ascorbic acid in transferrin-independent ferric iron reduction and uptake was evaluated in cultured U-937 monocytic cells. Uptake of55Fe by U-937 cells was doubled by 100 μM extracellular ascorbate, and by pre-incubation of cells with 100 μM dehydroascorbic acid, the two-electron-oxidized form of ascorbate. Reduction of extracellular ferric citrate also was enhanced by loading the cells with dehydroascorbic acid. Dehydroascorbic acid was taken up rapidly by the cells and reduced to ascorbate, such that the latter reached intracellular concentrations as high as 6 mM. However, some ascorbate did escape the cells and could be detected at concentrations of up to 1 μM in the incubation medium. Further, addition of ascorbate oxidase almost reversed the effects of dehydroascorbic acid on both55Fe uptake and ferric citrate reduction. Thus, it is likely that extracellular ascorbate reduced ferric to ferrous iron, which was then taken up by the cells. This hypothesis also was supported by the finding that during loading with ferric citrate, only extracellular ascorbate increased the pool of intracellular ferrous iron that could be chelated with cell-penetrant ferrous iron chelators. In contrast to its inhibition of ascorbate-dependent ferric iron reduction, ascorbate oxidase was without effect on ascorbate-dependent reduction of extracellular ferricyanide. This indicates that the cells use different mechanisms for reduction of ferric iron and ferricyanide. Therefore, extracellular ascorbate derived from cells can enhance transferrin-independent iron uptake by reducing ferric to ferrous iron, but intracellular ascorbate neither contributes to this reduction nor modifies the redox status of intracellular free iron.