Atomic Layer Deposition Coating of Carbon Nanotubes with Aluminum Oxide Alters Pro-Fibrogenic Cytokine Expression by Human Mononuclear Phagocytes In Vitro and Reduces Lung Fibrosis in Mice In Vivo

Abstract

BackgroundMulti-walled carbon nanotubes (MWCNTs) pose a possible human health risk for lung disease as a result of inhalation exposure. Mice exposed to MWCNTs develop pulmonary fibrosis. Lung macrophages engulf MWCNTs and produce pro-fibrogenic cytokines including interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and osteopontin (OPN). Atomic layer deposition (ALD) is a novel process used to enhance functional properties of MWCNTs, yet the consequence of ALD-modified MWCNTs on macrophage biology and fibrosis is unknown.MethodsThe purpose of this study was to determine whether ALD coating with aluminum oxide (Al2O3) would alter the fibrogenic response to MWCNTs and whether cytokine expression in human macrophage/monocytes exposed to MWCNTs in vitro would predict the severity of lung fibrosis in mice. Uncoated (U)-MWCNTs or ALD-coated (A)-MWCNTs were incubated with THP-1 macrophages or human peripheral blood mononuclear cells (PBMC) and cell supernatants assayed for cytokines by ELISA. C57BL6 mice were exposed to a single dose of A- or U-MWCNTs by oropharyngeal aspiration (4 mg/kg) followed by evaluation of histopathology, lung inflammatory cell counts, and cytokine levels at day 1 and 28 post-exposure.ResultsALD coating of MWCNTs with Al2O3 enhanced IL-1β secretion by THP-1 and PBMC in vitro, yet reduced protein levels of IL-6, TNF-α, and OPN production by THP-1 cells. Moreover, Al2O3 nanoparticles, but not carbon black NPs, increased IL-1β but decreased OPN and IL-6 in THP-1 and PBMC. Mice exposed to U-MWCNT had increased levels of all four cytokines assayed and developed pulmonary fibrosis by 28 days, whereas ALD-coating significantly reduced fibrosis and cytokine levels at the mRNA or protein level.ConclusionThese findings indicate that ALD thin film coating of MWCNTs with Al2O3 reduces fibrosis in mice and that in vitro phagocyte expression of IL-6, TNF-α, and OPN, but not IL-1β, predict MWCNT-induced fibrosis in the lungs of mice in vivo.

Stromelysin-2 (MMP-10) facilitates clearance and moderates inflammation and cell death following lung exposure to long multiwalled carbon nanotubes

“…Macrophages are critical responders to MWCNT exposure, a finding that is consistent with other in vivo 30,52 and in vitro studies. 8 In addition, our group and others have shown that Mmp10 is a critical determinant of macrophage responses and differentiation status in models of acute colon injury, 22 skin wounds, 18 and lung infection with Pseudomonas aeruginosa.…”

“…This dose of MWCNT was based on exposures used on other studies. [28][29][30] Lungs were collected 24 h later and processed for mRNA isolation. In lungs from unchallenged wild-type mice (ie, no MWCNTs, no DM alone), we detected a Ct range for Mmp10 mRNA between 36 and 37 indicating essentially no or very low levels of expression.…”

“…48 Consistent with other studies, we found that oropharyngeal aspiration of 80 µg/mouse of MWCNTs initiated a robust damage response. 30,44,49 Compared to DM controls, MWCNT-treated mice exhibited enhanced pulmonary hemorrhage, edema, neutrophilia, and macrophage cell death, as well as accumulations of MWCNTs in BAL macrophages at 24 h postexposure. In addition, mRNA analyses revealed an upregulation of multiple pro-inflammatory transcripts including Il6, Nos2, and notably, Il1β, which is important in the initiation of MWCNT-induced pathology.…”

Myofibroblasts and lung fibrosis induced by carbon nanotube exposure

“…In other studies, the thin film coating of MWCNTs with Al 2 O 3 via atomic layer deposition reduced lung fibrosis in mice [55]; and the surface functionalization of MWCNTs with carboxylation or other covalent modifications demonstrates that strong cationic modifications induced significant lung fibrosis, whereas carboxylation significantly reduced the extent of lung fibrosis, compared with pristine CNTs [56]. Therefore, the surface reactivity and surface charge of CNTs play critical roles in determining their fibrogenicity and toxicity.…”

Surface modification of acetaminophen particles by atomic layer deposition

“…The coating may also provide chemical stabilization for the pharmaceutical (Wu et al, 2011) or control of the drug release (Chen et al, 2006). There are many biological interfaces, such as between nanoparticles and carbon nanotubes and APIs, where control of the surface characteristics of pharmaceutical powders can improve their therapeutic response and bioavailability (Terracciano et al, 2015;Taylor et al, 2014;Schäfer et al, 2013;Chow et al, 2007).…”