Endocytosis of Ultrafine Particles by A549 Cells

Abstract

Alveolar epithelium's capacity to ingest inhaled ultrafine particles is not well characterized. The objectives of this study were to use an in vitro model of type II lung epithelium and evaluate the cells' ability to take up ultrafine particles (titanium dioxide [TiO(2)], 50 nm diameter). The human epithelial cell line A549 was grown on aclar substrates and exposed to 40 microg/ml TiO(2) particles for 3, 6, and 24 h before imaging with energy-filtering transmission electron microscopy. Elemental mapping and electron energy loss spectroscopy were used to colocalize Ti/O with electron-dense particles. Particle endocytosis was compared in A549 cells with and without pretreatment with cytochalasin D (cyto D) (2 microg/ml). After 3 h of TiO(2) exposure, cells internalized aggregates of the ultrafine particles which were observed in cytosolic, membrane-bound vacuoles. After 24 h of exposure there were considerably more intracellular aggregates of membrane-bound particles, and aggregated particles were also enmeshed in loosely and tightly packed lamellar bodies. Throughout 24 h of exposure a preponderance of particles remained associated with the free surface of the cells and were not internalized. The majority of membrane-bound vacuoles contained aggregates of particles and only occasionally did they contain as few as two or three particles, despite the use of several different approaches to assure the possibility for individual particles to be ingested and detected. There was morphologic evidence of microfilament disturbance, but no evidence of a decrease in internalized particles in cells pretreated with cyto D. Thus, this model of type II epithelium is able to internalize aggregates of ultrafine particles.

In vitro toxicity evaluation of single walled carbon nanotubes on human A549 lung cells

“…Interestingly, a very similar plasma membrane projection as that identiWed by us in Fig. 7F was shown by Stearns et al (2001), in an electron micrograph following exposure of A549 cells to 40 g/ml ultraWne titanium dioxide. Stearns et al (2001) also reported that aggregates of TiO 2 , which entered the A549 cells by ingestion, were later found in membrane-bound vacuoles and enmeshed within lamellar bodies.…”

“…More recently, the same group (Rouse et al, 2006) has reported that fullerene-based amino acid nanoparticles can also localize to intracytoplasmic vacuoles in HEK cells. The internalization of ultraWne titanium dioxide by A549 cells has also been reported (Stearns et al, 2001). In the concurrent spectroscopic study performed by our group (Casey et al, in press) Raman and Xuorescence emission analysis indicated that no debundling or reduction in aggregation state occurred upon the dispersion of SWCNT in the media over the concentration range studied.…”

“…7F was shown by Stearns et al (2001), in an electron micrograph following exposure of A549 cells to 40 g/ml ultraWne titanium dioxide. Stearns et al (2001) also reported that aggregates of TiO 2 , which entered the A549 cells by ingestion, were later found in membrane-bound vacuoles and enmeshed within lamellar bodies. Recently, in an in vivo study, Shvedova et al (2005) also observed increased numbers of AE2 cells expressing cytoplasmic lamellar bodies in TEM sections of mouse lung following SWCNT exposure via pharyngeal aspiration.…”

Multi-omics analysis of ten carbon nanomaterials effects highlights cell type specific patterns of molecular regulation and adaptation

“…Studying the uptake of different sized ultrafine particles of TiO 2 in A549, Singh and collaborators noted that the uptake was limited to aggregated particles, found inside the lamellar bodies and membrane bound vacuoles (Singh et al, 2007). Similar results were regained in another study by Stearns et al, where the uptake of TiO 2 particles was limited to aggregates found inside the lamellar bodies of the A549 cells after 24 h exposure (Stearns et al, 2001). They also postulated that single ultrafine particles are possibly not a target of phagocytosis by type II epithelium, but are internalized as aggregates, as also concluded by Churg et al (Churg et al, 1998) Type II alveolar cells, including A549 cells, are the main producers of pulmonary surfactants, such as phospholipids that reduce the surface tension.…”

Quantifying the characteristics of particulate matters captured by urban plants using an automatic approach

“…The morphological characteristics of the particles, however, have important implications. Firstly, the morphology of particles can affect deposition and transport properties (Stearns et al, 2001) by changing the drag force of individual particles. Secondly, particles can scatter or absorb both incoming solar radiation and thermal radiation emitted from the earth's surface to directly change the radiation balance (Bellouin et al, 2005;Gustafson et al, 2011).…”