Carbon Nanotubes: A Summary of Beneficial and Dangerous Aspects of an Increasingly Popular Group of Nanomaterials

Abstract

Carbon nanotubes (CNTs) are nanomaterials with broad applications that are produced on a large scale. Animal experiments have shown that exposure to CNTs, especially one type of multi-walled carbon nanotube, MWCNT-7, can lead to malignant transformation. CNTs have characteristics similar to asbestos (size, shape, and biopersistence) and use the same molecular mechanisms and signaling pathways as those involved in asbestos tumorigenesis. Here, a comprehensive review of the characteristics of carbon nanotubes is provided, as well as insights that may assist in the design and production of safer nanomaterials to limit the hazards of currently used CNTs.

Keywords: asbestos; carbon nanotubes; carcinogen; malignant mesothelioma; nanomaterials.

Figure 1

Representative scheme of CNT drainage and pathological lesions induced by CNTs. CNT administered through airway exposure then penetrates the pulmonary alveoli and visceral pleura into the pleural cavity (A). CNT can also be administered to pleural cavity through intrapleural injection (B). Small-sized CNT or CNT aggregates lead to mild pathological lesions due to its engulfment by macrophages and lymphatic drainage. Long, rigid, and needlelike CNTs deposited in pleural cavity fail to negotiate with the stroma. It can induce pro-inflammatory cytokines and oxidants released by macrophages due to frustrated phagocytosis. Long CNTs are located in fibrotic parietal pleura, while a few CNTs could pierce and penetrate into the parietal mesothelium. [Modified from (58)].

Figure 2

Pathogenesis of MPM induced by CNT exposure. The characteristics of CNT, including length, diameter, surface modification, etc., can influence pathological lesions on pleura. Administrative route, exposure time, and dose also play critical roles in lesion development of the pleura. Macrophages are involved in the process of transformation of mesothelial cells. A hypothesis of DNA damage in mesothelial cells, ROS, pro-inflammatory cytokines, and perturbed signaling pathway may thus be proposed in the transformation of mesothelial cells.