title: Cytotoxicity and genotoxicity of size-fractionated iron oxide (magnetite) in A549 human lung epithelial cells: role of ROS, JNK, and NF-κB.
abstract: Airborne particulate matter (PM) of varying size and composition is known to cause health problems in humans. The iron oxide Fe(3)O(4) (magnetite) may be a major anthropogenic component in ambient PM and is derived mainly from industrial sources. In the present study, we have investigated the effects of four different size fractions of magnetite on signaling pathways, free radical generation, cytotoxicity, and genotoxicity in human alveolar epithelial-like type-II cells (A549). The magnetite particles used in the exposure experiments were characterized by mineralogical and chemical techniques. Four size fractions were investigated: bulk magnetite (0.2-10 μm), respirable fraction (2-3 μm), alveolar fraction (0.5-1.0 μm), and nanoparticles (20-60 nm). After 24 h of exposure, the A549 cells were investigated by transmission electron microscopy (TEM) to study particle uptake. TEM images showed an incorporation of magnetite particles in A549 cells by endocytosis. Particles were found as agglomerates in cytoplasm-bound vesicles, and few particles were detected in the cytoplasm but none in the nucleus. Increased production of reactive oxygen species (ROS), as determined by the 2',7'-dichlorfluorescein-diacetate assay (DCFH-DA), as well as genotoxic effects, as measured by the cytokinesis block-micronucleus test and the Comet assay, were observed for all of the studied fractions after 24 h of exposure. Moreover, activation of c-Jun N-terminal kinases (JNK) without increased nuclear factor kappa-B (NF-κB)-binding activity but delayed IκB-degradation was observed. Interestingly, pretreatment of cells with magnetite and subsequent stimulation with the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFα) led to a reduction of NF-κB DNA binding compared to that in stimulation with TNFα alone. Altogether, these experiments suggest that ROS formation may play an important role in the genotoxicity of magnetite in A549 cells but that activation of JNK seems to be ROS-independent.
authors.affiliation: Department of Environmental Health Sciences, University Medical Center Freiburg, Freiburg, Germany. mathias.koenczoel@uniklinik-freiburg.de
authors.forename: Mathias
authors.initials: M
authors.lastname: Könczöl
authors.forename: Sandra
authors.initials: S
authors.lastname: Ebeling
authors.forename: Ella
authors.initials: E
authors.lastname: Goldenberg
authors.forename: Fabian
authors.initials: F
authors.lastname: Treude
authors.forename: Richard
authors.initials: R
authors.lastname: Gminski
authors.forename: Reto
authors.initials: R
authors.lastname: Gieré
authors.forename: Bernard
authors.initials: B
authors.lastname: Grobéty
authors.forename: Barbara
authors.initials: B
authors.lastname: Rothen-Rutishauser
authors.forename: Irmgard
authors.initials: I
authors.lastname: Merfort
authors.forename: Volker
authors.initials: V
authors.lastname: Mersch-Sundermann
mesh_terms: D045744:Cell Line, Tumor; D004789:Enzyme Activation; D052203:Ferrosoferric Oxide / Q000633:toxicity*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008168:Lung / Q000166:cytology*; D009153:Mutagens / Q000633:toxicity*; D016328:NF-kappa B / Q000378:metabolism*; D052638:Particulate Matter / Q000633:toxicity; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D009153:Mutagens; D016328:NF-kappa B; D052638:Particulate Matter; D017382:Reactive Oxygen Species; D048031:JNK Mitogen-Activated Protein Kinases; D052203:Ferrosoferric Oxide