Abstract
BackgroundExperimental studies provide evidence that inhaled nanoparticles may translocate over the airspace epithelium and cause increased cellular inflammation. Little is known, however, about the dependence of particle size or material on translocation characteristics, inflammatory response and intracellular localization.ResultsUsing a triple cell co-culture model of the human airway wall composed of epithelial cells, macrophages and dendritic cells we quantified the entering of fine (1 μm) and nano-sized (0.078 μm) polystyrene particles by laser scanning microscopy. The number distribution of particles within the cell types was significantly different between fine and nano-sized particles suggesting different translocation characteristics. Analysis of the intracellular localization of gold (0.025 μm) and titanium dioxide (0.02–0.03 μm) nanoparticles by energy filtering transmission electron microscopy showed differences in intracellular localization depending on particle composition. Titanium dioxide nanoparticles were detected as single particles without membranes as well as in membrane-bound agglomerations. Gold nanoparticles were found inside the cells as free particles only. The potential of the different particle types (different sizes and different materials) to induce a cellular response was determined by measurements of the tumour necrosis factor-α in the supernatants. We measured a 2–3 fold increase of tumour necrosis factor-α in the supernatants after applying 1 μm polystyrene particles, gold nanoparticles, but not with polystyrene and titanium dioxide nanoparticles.ConclusionQuantitative laser scanning microscopy provided evidence that the translocation and entering characteristics of particles are size-dependent. Energy filtering transmission electron microscopy showed that the intracellular localization of nanoparticles depends on the particle material. Both particle size and material affect the cellular responses to particle exposure as measured by the generation of tumour necrosis factor-α.
Highlights
Experimental studies provide evidence that inhaled nanoparticles may translocate over the airspace epithelium and cause increased cellular inflammation
Translocation of polystyrene fine particles and nanoparticles In order to compare the entering and translocation of fine particles and NP into cells of the airway epithelial barrier the interaction of fluorescently labelled polystyrene particles of two different sizes (1 μm, and 0.078 μm) with the cells of the triple cell co-culture system was studied by laser scanning microscopy (LSM) in combination with immunofluorescence methods and digital image restoration
monocyte derived macrophages (MDM) and monocyte derived dendritic cells (MDDC) were filled with 1 μm particles, and only few of these particles were detected in epithelial cells (Fig. 1)
Summary
Experimental studies provide evidence that inhaled nanoparticles may translocate over the airspace epithelium and cause increased cellular inflammation. About the dependence of particle size or material on translocation characteristics, inflammatory response and intracellular localization. Besides the generation of ultrafine particles from combustion processes (UFP), an increasing number of manufactured nanoparticles (NP), defined as structures with a diameter of 1–100 nm, are released into air, water and soil [1,2]. Revealed penetration of NP into mitochondria of macrophages and epithelial cells, associated with oxidative stress and mitochondrial damage [26]. NP may cause several biological responses including the enhanced expression of pro-inflammatory cytokines [30], the generation of reactive oxygen species [31] and DNA strand breaks [32]. Further associations between oxidative stress and inflammation responses are described in the literature [19,33,34] and inflammation responses are associated again with adverse health effects [35,36]
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