Multi‐walled carbon nanotubes translocate into the pleural cavity and induce visceral mesothelial proliferation in rats

Abstract

Multi-walled carbon nanotubes have a fibrous structure similar to asbestos and induce mesothelioma when injected into the peritoneal cavity. In the present study, we investigated whether carbon nanotubes administered into the lung through the trachea induce mesothelial lesions. Male F344 rats were treated with 0.5 mL of 500 lg/mL suspensions of multi-walled carbon nanotubes or crocidolite five times over a 9-day period by intrapulmonary spraying. Pleural cavity lavage fluid, lung and chest wall were then collected. Multi-walled carbon nanotubes and crocidolite were found mainly in alveolar macrophages and mediastinal lymph nodes. Importantly, the fibers were also found in the cell pellets of the pleural cavity lavage, mostly in macrophages. Both multi-walled carbon nanotube and crocidolite treatment induced hyperplastic proliferative lesions of the visceral mesothelium, with their proliferating cell nuclear antigen indices approximately 10-fold that of the vehicle control. The hyperplastic lesions were associated with inflammatory cell infiltration and inflammationinduced fibrotic lesions of the pleural tissues. The fibers were not found in the mesothelial proliferative lesions themselves. In the pleural cavity, abundant inflammatory cell infiltration, mainly composed of macrophages, was observed. Conditioned cell culture media of macrophages treated with multi-walled carbon nanotubes and crocidolite and the supernatants of pleural cavity lavage fluid from the dosed rats increased mesothelial cell proliferation in vitro, suggesting that mesothelial proliferative lesions were induced by inflammatory events in the lung and pleural cavity and likely mediated by macrophages. In conclusion, intrapulmonary administration of multi-walled carbon nanotubes, like asbestos, induced mesothelial proliferation potentially associated with mesothelioma development. (Cancer Sci 2012; 103: 2045-2050 M ulti-walled carbon nanotubes (MWCNT) are structurally composed of cylinders rolled up from several layers of graphite sheets. They are several to tens of nanometers in diameter and several to tens of micrometers in length. This high length to diameter aspect ratio, a characteristic shared with asbestos fibers, has led to concern that exposure to MWCNT might cause asbestos-like lung diseases, such as lung fibrosis, lung cancer, pleural plaque and malignant mesothelioma.(1-6) Pleural plaque and malignant mesothelioma are characteristic lesions in asbestos-exposed humans. Although fiber dimensions, biopersistence, oxidative stress and inflammation have all been implicated, (7)(8)(9)(10)(11)(12) the exact mechanisms of pleural pathogenesis are unclear. According to a pathogenesis paradigm suggested by Donaldson et al.,asbestos fibers penetrate into the pleural cavity from the alveoli and deposit in the pleural tissue. Unlike spherical particles, fibrous materials such as asbestos are not cleared effectively from the pleural cavity, resulting in deposition of the fibers in the parietal pleura. This deposition, in turn, causes frustrated ...

Significance of Intratracheal Instillation Tests for the Screening of Pulmonary Toxicity of Nanomaterials

“…Fujita et al reported that intratracheal injection of short MWCNT using an aerosolizing microsprayer induced time-dependent pleural inflammation [20]. There are reports of the deposition of MWCNT in the pleura in the acute phase after intratracheal injection of MW-CNT using the spray type [20,21], and that same injection of MWCNT induced malignant mesothelioma in rat lung [22]. On the other hand, in a 24-month inhalation study MWCNT did not induce malignant mesothelioma but did induce pulmonary tumors [23].…”

Inflammation in the pleural cavity following injection of multi-walled carbon nanotubes is dependent on their characteristics and the presence of IL-1 genes

“…Likewise, several studies in vitro have shown that IL-1 signaling may also be important in cellular responses to nanomaterials in general, but the role of IL-1 in cellular responses of MWCNTs in the pleura has not been studied in vivo. It has been shown that MWCNTs can reach the subpleura and the pleural space in mice after a single and short time inhalation exposure (Ryman-Rasmussen et al, 2009;Xu et al, 2012;Porter et al, 2013), raising concerns that inhaled nanotubes may cause pleural fibrosis and/or mesothelioma. We therefore chose the i.pl.…”

“…Similarly, after intratracheal (i.tr.) instillation, long MWCNTs translocated more readily than the shorter ones from the lung to the pleural space, and only long fibers were associated with inflammatory responses and hyperplastic visceral mesothelial proliferation (Xu et al, 2012). Following intrapleural (i.pl.)…”

Lung toxicity assessment using bronchoalveolar lavage fluid and pleural lavage fluid cytology by intratracheal treatment in rats

“…The PLF was collected by modified method of Xu et al (2012) from Wistar rats after intratrachially treatment with PBS under anesthesia with isoflurane. One and seven days after the treatment, animals were euthanized with isoflurane.…”

“…Much attention is gathering to manufactured nanomaterials in terms of pulmonary (lung and plural cavity) toxicity in recent years. Multi wall carbon nanotubes moved from lung to thoracic cavity when intrapulmonary spraying in rats (Xu et al, 2012). The first contact surface encountered by inhaled materials is the epithelium of the respiratory tract and bronchial alveolar lavage fluid (BALF) can be used as a proper material for assessment of the volatile/mist chemical toxicity.…”