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Multi-walled carbon nanotubes (MWCNTs), dispersed in suspensions consisting mainly of individual tubes, were used for intratracheal instillation and inhalation studies. Rats intratracheally received a dose of 0.2 mg, or 1 mg of MWCNTs and were sacrificed from 3 days to 6 months. MWCNTs induced a pulmonary inflammation, as evidenced by a transient neutrophil response in the low-dose groups, and presence of small granulomatous lesion and persistent neutrophil infiltration in the high-dose groups. In the inhalation study, rats were exposed to 0.37 mg/m(3) aerosols of well-dispersed MWCNTs (>70% of MWCNTs were individual fibers) for 4 weeks, and were sacrificed at 3 days, 1 month, and 3 months after the end of exposure. The inhalation exposures delivered less amounts of MWCNTs into the lungs, and therefore less pulmonary inflammation responses was observed, as compared to intratracheal instillation. The results of our study show that well-dispersed MWCNT can produce pulmonary lesions, including inflammation.

This paper describes a method for determination of multiwall carbon nanotubes (MWCNTs) in rat lungs after intratracheal instillation exposure. The MWCNTs were quantitatively decomposed to CO 2 by combustive oxidation and were then determined by non-dispersive infrared analysis. Samples were pretreated by acid digestion, muffle ashing and in situ preheating to remove interferences due to coexisting biological carbon from the lung tissue sample, while preserving the MWCNTs as in its their original form. The preservation was confirmed by transmission electron microscopic observation of the pretreated samples of exposed lung tissues and by the fact that the recoveries of MWCNTs spiked to the lung tissues were close to 100%. The detection limit for MWCNTs obtained by the proposed method was 0.30 μg and the repeatability as expressed by the relative standard deviation was 5.6% ( n = 4). The method was sufficiently sensitive and precise to apply to real samples of rat lung to investigate the in vivo persistence of intratracheally instilled MWCNTs. To our knowledge, this is the first report of this type of sample pretreatment and direct determination of pristine MWCNTs without modification or tagging. Conventional indirect methods use tagging with other compounds or metal impurities in the CNTs for detection, and the detachment of these tags can increase uncertainties in the determination of the CNTs. The tags can also change how the CNTs persist in vivo , which can lead to an incorrect understanding of the persistence of pristine CNTs in vivo .

In recent years, industrial or commercial products incorporating nanomaterials have triggered concerns for human health. Manufactured nanomaterials are unstable and tend to form secondary particles by agglomeration. Little is known about the cytotoxicity induced by nano-sized secondary particles dispersed in aqueous solution. In the present study, we have attempted to disperse ultrafine nickel oxide particles in water (Uf-NiO), characterize the physicochemical properties, and instill into the trachea of rat lungs. Analysis by inductively couple plasma mass spectrometry (ICP-MS) and transmission electron microscope (TEM) revealed that the Uf-NiO particles began to be cleared from the lungs immediately after treatment, and that low levels of the particles were present at 6 months post-instillation. Genome-wide expression analysis using DNA microarray revealed that intratracheal instillation of Uf-NiO particles led to a rapid increase in the expression of chemokines and genes involved in inflammation. These changes were most pronounced at 1 week post-instillation with Uf-NiO. The expression of Mmp12 mRNA, encoding macrophage metalloelastase 12, was strongly induced immediately following intratracheal instillation. However, expression returned to control levels by 6 months post-instillation expression of various other genes categorized into the detection of chemical stimulus were increased at this time point, at which time the inflammatory response had diminished. These results suggest that residual Uf-NiO in the lungs subacutely initiated distinct cellular events through signal transduction after resolution of the inflammatory response. We conclude that gene expression analysis using DNA microarrays can be extremely useful in assessing the influence of utrafine particles on biological systems.