MOBILIZATION OF IRON FROM URBAN PARTICULATES LEADS TO GENERATION OF REACTIVE OXYGEN SPECIES IN-VITRO AND INDUCTION OF FERRITIN SYNTHESIS INHUMAN LUNG EPITHELIAL-CELLS

Many of the biochemical effects of asbestos in cultured cells have bee n shown to be due to iron, which can be as high as 27% by weight. Urba n air particulates also contain iron, and some of the pathological eff ects after inhalation may be due to reactive oxygen species produced b y iron-catalyzed reactions. Two standard reference material (SRM) urba n air particulate samples were used for the studies described here. SR M 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 b e 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. I ron was mobilized from both particulates by either chelator, especiall y 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 SR M 1649 in 24 h. EDTA, in the presence of ascorbate, mobilized 53.8 nmo l 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 p articulate iron, each particulate was incubated with phi X174 RFI DNA in the presence or absence of ascorbate. Single-strand breaks (SSBs) w ere produced by either particulate, but only in the presence of ascorb ate. Incubation of SRM 1648 or 1649 (0.5 mg/mL) with DNA in the presen ce of ascorbate and citrate resulted in 20% or 34% DNA with SSBs, resp ectively. Incubation of SRM 1648 or 1649 (0.1 mg/mL) with DNA in the p resence of ascorbate and EDTA resulted in 26% or 45% DNA with SSBs, re spectively. To determine if iron associated with urban particulates co uld be mobilized by human lung epithelial cells (A549), cells were tre ated with particulates and the amount of the iron storage protein ferr itin was determined at the end of treatment. The 6.4- or 8.4-fold incr ease in ferritin observed in cells treated with SRM 1648 or 1649, resp ectively, over that of control (untreated) cells strongly suggested th at iron was mobilized in the cultured cells. If similar mobilization a nd reactivity of the iron occurs in the lung, this may explain some of the pathological effects of urban particulates.