Smith K R, Aust A E
Department of Chemistry and Biochemistry, Utah State University, Logan 84322-0300, USA.
Chem Res Toxicol. 1997 Jul;10(7):828-34. doi: 10.1021/tx960164m.
Many of the biochemical effects of asbestos in cultured cells have been shown to be due to iron, which can be as high as 27% by weight. Urban air particulates also contain iron, and some of the pathological effects after inhalation may be due to reactive oxygen species produced by iron-catalyzed reactions. Two standard reference material (SRM) urban air particulate samples were used for the studies described here. SRM 1648 (3.9% iron by weight) was collected in the St. Louis, MO, area, and SRM 1649 (3% iron by weight) was collected in the Washington, DC, area. To determine if iron associated with urban particulates could be mobilized, as it is from asbestos, SRMs 1648 and 1649 were incubated with 1 mM citrate or EDTA, in the presence or absence of ascorbate. Iron was mobilized from both particulates by either chelator, especially in the presence of ascorbate. Citrate, in the presence of ascorbate, mobilized 30.9 nmol of Fe/mg of SRM 1648 and 65.1 nmol of Fe/mg of SRM 1649 in 24 h. EDTA, in the presence of ascorbate, mobilized 53.8 nmol of Fe/mg of SRM 1648 and 98.8 nmol of Fe/mg of SRM 1649 in 24 h. To determine whether reactive oxygen species were being produced by the particulate iron, each particulate was incubated with phi X174 RFI DNA in the presence or absence of ascorbate. Single-strand breaks (SSBs) were produced by either particulate, but only in the presence of ascorbate. Incubation of SRM 1648 or 1649 (0.5 mg/mL) with DNA in the presence of ascorbate and citrate resulted in 20% or 34% DNA with SSBs, respectively. Incubation of SRM 1648 or 1649 (0.1 mg/mL) with DNA in the presence of ascorbate and EDTA resulted in 26% or 45% DNA with SSBs, respectively. To determine if iron associated with urban particulates could be mobilized by human lung epithelial cells (A549), cells were treated with particulates and the amount of the iron storage protein ferritin was determined at the end of treatment. The 6.4- or 8.4-fold increase in ferritin observed in cells treated with SRM 1648 or 1649, respectively, over that of control (untreated) cells strongly suggested that iron was mobilized in the cultured cells. If similar mobilization and reactivity of the iron occurs in the lung, this may explain some of the pathological effects of urban particulates.
在培养细胞中，石棉的许多生化效应已被证明是由铁引起的，铁含量按重量计可达27%。城市空气颗粒物中也含有铁，吸入后产生的一些病理效应可能归因于铁催化反应产生的活性氧。这里描述的研究使用了两种标准参考物质（SRM）城市空气颗粒物样本。SRM 1648（铁含量按重量计为3.9%）采集于密苏里州圣路易斯地区，SRM 1649（铁含量按重量计为3%）采集于华盛顿特区地区。为了确定与城市颗粒物结合的铁是否能像石棉中的铁那样被动员出来，将SRM 1648和1649在有或没有抗坏血酸存在的情况下与1 mM柠檬酸盐或乙二胺四乙酸（EDTA）一起孵育。两种螯合剂都能从两种颗粒物中动员出铁，尤其是在有抗坏血酸存在的情况下。在有抗坏血酸存在的情况下，柠檬酸盐在24小时内从SRM 1648中动员出30.9 nmol铁/毫克，从SRM 1649中动员出65.1 nmol铁/毫克。在有抗坏血酸存在的情况下，EDTA在24小时内从SRM 1648中动员出53.8 nmol铁/毫克，从SRM 1649中动员出98.8 nmol铁/毫克。为了确定颗粒物中的铁是否会产生活性氧，将每种颗粒物在有或没有抗坏血酸存在的情况下与φX174 RFI DNA一起孵育。单链断裂（SSB）由两种颗粒物产生，但仅在有抗坏血酸存在的情况下。在有抗坏血酸和柠檬酸盐存在的情况下，将SRM 1648或1649（0.5毫克/毫升）与DNA一起孵育，分别导致20%或34%的DNA出现单链断裂。在有抗坏血酸和EDTA存在的情况下，将SRM 1648或1649（0.1毫克/毫升）与DNA一起孵育，分别导致26%或45%的DNA出现单链断裂。为了确定与城市颗粒物结合的铁是否能被人肺上皮细胞（A549）动员出来，用颗粒物处理细胞，并在处理结束时测定铁储存蛋白铁蛋白的含量。与对照（未处理）细胞相比，用SRM 1648或SRM 1649处理的细胞中观察到的铁蛋白分别增加了6.4倍或8.4倍，这有力地表明铁在培养细胞中被动员出来了。如果肺部发生类似的铁动员和反应，这可能解释城市颗粒物的一些病理效应。
