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Particle complexation of mitochondrial iron produces superoxide generation and activates MAP kinases, NF-kappa B, nrf-2 in human respiratory epithelial cell
Citation:
GHIO, A. J., J. M. SOUKUP, L. A. DAILEY, H. TONG, H. TONG, W. Cheng, J. M. SAMET, M. Kesic, J. Turi, D. Upadhyay, D. Budinger, AND G. M. Mutlu. Particle complexation of mitochondrial iron produces superoxide generation and activates MAP kinases, NF-kappa B, nrf-2 in human respiratory epithelial cell. Presented at American Thoracic Society (ATS) Meeting, Denver, CO, May 13 - 18, 2011.
Impact/Purpose:
This is an abstract summarizing a presentation to be provided at the American Thoracic Society (20II ).
Description:
The biological effect of particles is associated with a disruption in cell iron homeostasis. We tested the postulate that complexation of cell iron by silica (Si02) results in both an oxidative stress and biological effect. BEAS-2B cells were exposed to either media or 100 ug/ml. Si02 (Minusil-5) for 4 hr. Exposure of BEAS-2B cells to Si02 increased iron import relative to media (0.32±0.02 and 0.22±0.01 ppm respectively) measured as non-heme iron by inductively coupled plasma (ICP) optical emission spectroscopy; co-exposure to 100 ug/ml. Si02 and 200 uM ferric ammonium citrate (FAC) further increased cell iron concentrations relative to incubations with FAC alone (0.50±0.03 and 0.38±0.03 ppm respectively). Si02 exposure was associated with an increased cell import of metal. Complexation of mitochondrial iron by Si02 was studied using BEAS-2B cells grown in 75 cm2 flasks and exposed to 1.0 uM 57Fe FAC and ICP mass spectroscopy. Incubation with 100 ug/ml. Si02 resulted in diminished mitochondrial 57Fe concentrations in the particle-exposed BEAS-2B cells (0.36±0.02 and 0.24±0.02 ppm in Si02 and PBS exposed cells respectively) as the silica complexed host metal from the organelle. Preincubation of respiratory epithelial cells with 200 uM FAC increased nuclear and mitochondrial metal concentrations and prevented significant iron loss from mitochondria exposed to Si02• Cell oxidant generation, measured as Amplex Red fluorescence at 3 hours, increased with various doses of Si02 exposure relative to PBS incubations. Some portion of this oxidant generation was inhibited by pre-exposures with 1 uM rotenone. In addition, pre-exposure of the BEAS-2B with 200 uM FAC diminished oxidant generation. Finally, exposure of BEAS-2B cells to 100 ug/ml. Si02 increased expression of nrf2 relative to incubations with PBS (RLU values of 806±250 and 140±25) and this elevation was inhibited by 4 hr pre-treatment with 200 uM FAC (l20±36 and 131±33). We conclude that oxidative stress and biological response following exposure to silica is associated with complexation of host mitochondrial iron; increasing available iron in the cell diminished both oxidative stress and biological response to Si02. The initiating event in the cell response to a particle appears to be a surface complexation of iron away from the cell. (Abstract does not reflect EPA policy)