Role of p53 in the chronic pulmonary immune response to tangled or rod-like multi-walled carbon nanotubes

Abstract

The fiber-like shape of multi-walled carbon nanotubes (MWCNTs) is reminiscent of asbestos, suggesting they pose similar health hazards when inhaled, including pulmonary fibrosis and mesothelioma. Mice deficient in the tumor suppressor p53 are susceptible to carcinogenesis. However, the chronic pathological effect of MWCNTs delivered to the lungs of p53 heterozygous (p53+/−) mice has not been investigated. We hypothesized that p53+/− mice would be susceptible to lung tumor development after exposure to either tangled (t-) or rod-like (r-) MWCNTs. Wild type (p53+/+) or p53+/− mice were exposed to MWCNTs (1 mg/kg) via oropharyngeal aspiration weekly over 4 consecutive weeks and evaluated for cellular and pathologic outcomes 11-months post initial exposure. No lung or pleural tumors were observed in p53+/+ or p53+/− mice exposed to either t- or rMWCNTs. In comparison to tMWCNTs, the rMWCNTs induced the formation of larger granulomas, a greater number of lymphoid aggregates and greater epithelial cell hyperplasia in terminal bronchioles in both p53+/− and p53+/+ mice. A constitutively larger area of CD45R+/CD3+ lymphoid tissue was observed in p53+/− mice compared to p53+/+ mice. Importantly, p53+/− mice had larger granulomas induced by rMWCNTs as compared to p53+/+ mice. These findings indicate that a combination of p53 deficiency and physicochemical characteristics including nanotube geometry are factors in susceptibility to MWCNT-induced lymphoid infiltration and granuloma formation.

Physicochemical characterization and genotoxicity of the broad class of carbon nanotubes and nanofibers used or produced in U.S. facilities

“…Previous studies have considered the role of CNT agglomeration as a determinant of toxicity outcome, particularly within the context of genotoxicity, macrophage recognition, the activation of downstream inflammatory cascades, and pulmonary fibrosis [5,18,33,[81][82][83]. Rod-like and less tangled particles, including singlets, were more likely to influence inflammation histopathology outcomes by inducing more pulmonary fibrosis, and impact extrapulmonary translocation [17,33,81].…”

Profiling of Sub-Lethal in Vitro Effects of Multi-Walled Carbon Nanotubes Reveals Changes in Chemokines and Chemokine Receptors

“…Indeed, previous investigations have shown that long and needle-like NM401, but not short and tangled NM400 or NM402, elicited a dose-dependent loss of cell viability [ 12 ]. Furthermore, in vivo studies have demonstrated that “rod-like” MWCNTs are prone to triggering pulmonary responses with fibrosis and granuloma formation [ 26 , 27 , 28 ]. However, other properties or features of MWCNTs in addition to their geometric characteristics may also play a role, including the presence of metallic impurities [ 29 , 30 , 31 ].…”

The pulmonary toxicity of carboxylated or aminated multi-walled carbon nanotubes in mice is determined by the prior purification method

“…Varying the physicochemical properties of CNT can influence toxicity [ 14 , 62 , 63 ]. In the present study, Mitsui-7 MWCNTs were used as a positive control, due to their rigidity and long length [ 64 , 65 ]. In the mice, exposure to Mitsui-7 induced greater lung infiltration with inflammatory cells, enhanced pro-inflammatory/pro-fibrotic cytokines and induced greater granulomatous lung lesions, when compared to the parent NC7000 MWCNTs.…”

“…Morphology is also a crucial parameter determining the biological activity of CNTs. While thin MWCNTs (≤ 20 nm diameter) tend to display a tangled morphology with low fiber-specific toxicity, thicker MWCNTs (≥ 30 to < 100 nm) show higher stability and rigidity characterized by a stronger potential to induce mesothelioma or fibrosis in rodents [ 65 , 70 , 71 ]. While rigidity is an important determinant of pulmonary toxicity, it appears that tangled MWCNTs, such as NC7000 used as the parent compound in the present study, are more representative of MWCNTs that are widely used in industry.…”