Abstract
The pulmonary toxicity of multi-wall carbon nanotubes (MWCNT) were examined by intratracheal instillation. We prepared a well-dispersed MWCNT dispersion including MWCNTs of 3.71 µm geometric average length. The fiber length of most of the MWCNTs in the dispersion was 10 µm or less. The MWCNT dispersion was administered to rat lung by single intratracheal instillation at doses of 0.2 mg and 0.6 mg/rat. Bronchoalveolar lavage fluid (BALF) was collected at 3 days, 1 week, 1 month, 3 months, and 6 months after instillation. The influences of the longer MWCNTs on the induction of inflammation and oxidative stress were examined by the number of neutrophils, cytokine induced neutrophil chemoattractant-1 (CINC-1), CINC-2, CINC-3 and HO-1 in the BALF. Additionally, ho-1 gene expression in the lung was examined. The intratracheal instillation of MWCNT induced transient inflammation dose dependently in the lung. The number of neutrophils was highest at 3 days after instillation and then decreased. However, the neutrophils in the MWCNT administered animals tended to be higher than in the control group until 3 months after instillation. The CINC-1 and CINC-2 concentrations in the BALF increased at 1 month after instillation. There were no significant differences in CINC-3 and HO-1 between the MWCNT administered animals and the control animals. These results revealed that the MWCNTs of 1–10 µm in length induced persistent inflammation in rat lung. There were no remarkable differences between the MWCNTs in the present study and previously reported, shorter MWCNTs prepared from “the same” raw MWCNT material.
Highlights
A carbon nanotube (CNT) is a nanomaterial consisting of only carbon
The cytokine induced neutrophil chemoattractant (CINC) concentration in the BALF was measured in order to examine the inflammation response induced by the intratracheal instillation of multi-wall carbon nanotubes (MWCNT) (Figure 6)
Recent investigations suggest that fiber length is one of the important factors in the pulmonary toxicity of CNTs
Summary
A carbon nanotube (CNT) is a nanomaterial consisting of only carbon. CNT has many beneficial features for industry, such as its rigidity and flexibility. CNT is an important functional material for industry. Among the physical and chemical properties of CNT, it has recently been reported that the length of CNT fibers is related to its toxicity. In some in vivo and in vitro studies, long fibers (more than 10 μm in length) were pathogenic [3,4,5,6]. Short fibers (less than 1 μm) of CNT have been reported to be more toxic than long fibers [6]. It is inconclusive whether the toxicity of CNTs depends on the length of fiber. CNTs with a length from 1 to 5 μm (intermediate length) has recently been reported. It is important to estimate the pulmonary toxicity of intermediate length CNTs because of their direct exposure route. We prepared individual MWCNTs, approximately 60% of whose length was 1 to 5 μm and 40% of whose length was 5–10 μm, and the effect of the fiber length on pulmonary inflammation was examined in an intratracheal instillation study
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