Alteration of deposition pattern and pulmonary response as a result of improved dispersion of aspirated single-walled carbon nanotubes in a mouse model

Abstract

Nanoparticles have a fundamental dimension of <100 nm. However, on suspension in media, agglomerates of nanoparticles are the more common structure. This is particularly evident in prior intratracheal instillation or aspiration studies of single-walled carbon nanotubes (SWCNT), in which granulomatous lesions encased by epithelioid macrophages were produced by large agglomerates. In this study, we tested the hypothesis of whether exposure to more dispersed SWCNT structures would alter pulmonary distribution and response. A dispersed preparation of single-walled carbon nanotubes (DSWCNT) with a mean diameter of 0.69 microm was given by pharyngeal aspiration to C57BL/6 mice. Electron microscopy demonstrated a highly dispersed, interstitial distribution of DSWCNT deposits by 1 day postexposure. Deposits were generally <1 microm. Macrophage phagocytosis of DSWCNT was rarely observed at any time point. Lung responses were studied by lavage and morphometry at 1 h, 1 day, 7 day, and 1 mo after a single DSWCNT exposure of 10 microg/mouse. Lung sections and lavage cells demonstrated an early, transient neutrophilic and inflammatory phase that rapidly resolved and was similar to that observed with large agglomerates. No granulomatous lesions or epithelioid macrophages were detected. Morphometric measurement of Sirius red staining was used to assess the connective tissue response. The average thickness of connective tissue in alveolar regions was 0.10 +/- 0.02, 0.09 +/- 0.02, 0.10 +/- 0.01, 0.48 +/- 0.04, and 0.88 +/- 0.19 microm for PBS and 1-h, 1-day, 7-day, and 1-mo postexposure groups, respectively. The results demonstrate that dispersed SWCNT are rapidly incorporated into the alveolar interstitium and that they produce an increase in collagen deposition.

Single-walled carbon nanotube-induced mitotic disruption

“…Secondary antibodies were Rhodamine Red goat anti-rabbit IgG and Alexa 488 goat anti-mouse IgG (Invitrogen, Carlsbad, CA). Small aggregates of SWCNT (carbon nanoropes) appeared as black structures in differential interference contrast (DIC) imaging due to absorbance of light [39][40][41]. The morphology of the mitotic spindle and centrosome, and the relationship with carbon nanoropes, was analyzed in the BEAS-2B cells using a laser scanning confocal microscope (LSM 510, Carl Zeiss MicroImaging Inc., Thornwood, NY) as previously described [25].…”

Occupational Nanosafety Considerations for Carbon Nanotubes and Carbon Nanofibers

“…Aspiration of a well-dispersed suspension of SWCNTs resulted in a less severe granulomatous response and a 4-fold greater interstitial fibrotic response than a poorly dispersed SWCNT suspension. 15 Furthermore, aspiration of gold-labeled SWCNTs demonstrated that agglomerates induced granulomatous lesions in the terminal bronchioles and proximal alveoli, while more dispersed SWCNT structures deposited in the distal lung, rapidly entered the alveolar interstitium, and caused progressive fibrosis. 15 Aspiration of purified MWCNTs in mice caused a similar spectrum of pulmonary responses as SWCNTs, that is, rapid but transient damage and inflammation, granulomatous lesions, and interstitial fibrosis.…”

“…15 Furthermore, aspiration of gold-labeled SWCNTs demonstrated that agglomerates induced granulomatous lesions in the terminal bronchioles and proximal alveoli, while more dispersed SWCNT structures deposited in the distal lung, rapidly entered the alveolar interstitium, and caused progressive fibrosis. 15 Aspiration of purified MWCNTs in mice caused a similar spectrum of pulmonary responses as SWCNTs, that is, rapid but transient damage and inflammation, granulomatous lesions, and interstitial fibrosis. 16 Short-term inhalation (4 days) of MWCNTs induced pulmonary responses in mice similar to those reported after aspiration.…”

“…[40][41][42] Aspiration of a welldispersed SWCNT preparation also caused more transient inflammation and persistent interstitial fibrosis than poorly dispersed SWCNTs. 15 In contrast, poorly dispersed SWCNTs caused a greater granulomatous response. Similarly, Li et al 47 reported a greater degree of inflammation following intratracheal instillation of agglomerated MWCNTs and greater alveolar wall thickening after inhalation of more dispersed MWCNTs.…”

Hazard Assessments of Manufactured Nanomaterials

“…In the results of the characterization of the MWCNT samples, the authors noted that the lengths of individual MWCNTs were greatly altered by grounding, from 5.9 µm to 0.7 µm, but the other main characteristics such as tube diameter and specific surface area were not changed by the operation. In addition, in a study by Mercer et al 61) , mice were subjected to pharyngeal aspiration exposure to dispersed SWCNTs (particle size, 0.69 µm) and non-dispersed SWCNTs (particle size, 1.52 µm), and it was reported that thickening of the alveolar wall was found only in the groups exposed to dispersed SWCNTs. The authors considered that the dispersed SWCNTs would more easily penetrate the interstitium.…”