The pro-inflammatory effects of low-toxicity low-solubility particles, nanoparticles and fine particles, on epithelial cells in vitro: the role of surface area.
OBJECTIVE
Rats exposed to high airborne mass concentrations of low-solubility low-toxicity particles (LSLTP) have been reported to develop lung disease such as fibrosis and lung cancer. These particles are regulated on a mass basis in occupational settings, but mass might not be the appropriate metric as animal studies have shown that nanoparticles (ultrafine particles) produce a stronger adverse effect than fine particles when delivered on an equal mass basis.


METHODS
This study investigated whether the surface area is a better descriptor than mass of LSLTP of their ability to stimulate pro-inflammatory responses in vitro. In a human alveolar epithelial type II-like cell line, A549, we measured interleukin (IL)-8 mRNA, IL8 protein release and glutathione (GSH) depletion as markers of pro-inflammatory effects and oxidative stress after treatment with a range of LSLTP (fine and nanoparticles) and DQ12 quartz, a particle with a highly reactive surface.


RESULTS
In all the assays, nanoparticle preparations of titanium dioxide (TiO2-np) and of carbon black (CB-np) produced much stronger pro-inflammatory responses than the same mass dose of fine TiO2 and CB. The results of the GSH assay confirmed that oxidative stress was involved in the response to all the particles, and two ultra-fine metal dusts (cobalt and nickel) produced GSH depletion similar to TiO2-np, for similar surface-area dose. As expected, DQ12 quartz was more inflammatory than the low toxicity dusts, on both a mass and surface-area basis.


CONCLUSIONS
Dose-response relationships observed in the in vitro assays appeared to be directly comparable with dose-response relationships in vivo when the doses were similarly standardised. Both sets of data suggested a threshold in dose measured as surface area of particles relative to the surface area of the exposed cells, at around 1-10 cm2/cm2. These findings are consistent with the hypothesis that surface area is a more appropriate dose metric than mass for the pro-inflammatory effects of LSLTP in vitro and in vivo, and consequently that the high surface area of nanoparticles is a key factor in their inflammogenicity.
Monteiller
Claire
C
Institute of Occupational Medicine, Research Park North, Edinburgh, UK.
Tran
Lang
L
MacNee
William
W
Faux
Steve
S
Jones
Alan
A
Miller
Brian
B
Donaldson
Ken
K
D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects* / Q000032:analysis; D016209:Interleukin-8 / Q000378:metabolism; D008175:Lung Neoplasms / Q000209:etiology*; D053758:Nanoparticles / Q000633:toxicity; D018384:Oxidative Stress; D010316:Particle Size; D052638:Particulate Matter / Q000633:toxicity*; D011658:Pulmonary Fibrosis / Q000209:etiology*; D011791:Quartz / Q000032:analysis; D012333:RNA, Messenger / Q000378:metabolism; D020545:Respiratory Mucosa / Q000187:drug effects; D014025:Titanium / Q000633:toxicity
D016209:Interleukin-8; D052638:Particulate Matter; D012333:RNA, Messenger; D011791:Quartz; C009495:titanium dioxide; D014025:Titanium; D005978:Glutathione