Inhaled Multiwalled Carbon Nanotubes Potentiate Airway Fibrosis in Murine Allergic Asthma

Abstract

Carbon nanotubes are gaining increasing attention due to possible health risks from occupational or environmental exposures. This study tested the hypothesis that inhaled multiwalled carbon nanotubes (MWCNT) would increase airway fibrosis in mice with allergic asthma. Normal and ovalbumin-sensitized mice were exposed to a MWCNT aerosol (100 mg/m(3)) or saline aerosol for 6 hours. Lung injury, inflammation, and fibrosis were examined by histopathology, clinical chemistry, ELISA, or RT-PCR for cytokines/chemokines, growth factors, and collagen at 1 and 14 days after inhalation. Inhaled MWCNT were distributed throughout the lung and found in macrophages by light microscopy, but were also evident in epithelial cells by electron microscopy. Quantitative morphometry showed significant airway fibrosis at 14 days in mice that received a combination of ovalbumin and MWCNT, but not in mice that received ovalbumin or MWCNT only. Ovalbumin-sensitized mice that did not inhale MWCNT had elevated levels IL-13 and transforming growth factor (TGF)-beta1 in lung lavage fluid, but not platelet-derived growth factor (PDGF)-AA. In contrast, unsensitized mice that inhaled MWCNT had elevated PDGF-AA, but not increased levels of TGF-beta1 and IL-13. This suggested that airway fibrosis resulting from combined ovalbumin sensitization and MWCNT inhalation requires PDGF, a potent fibroblast mitogen, and TGF-beta1, which stimulates collagen production. Combined ovalbumin sensitization and MWCNT inhalation also synergistically increased IL-5 mRNA levels, which could further contribute to airway fibrosis. These data indicate that inhaled MWCNT require pre-existing inflammation to cause airway fibrosis. Our findings suggest that individuals with pre-existing allergic inflammation may be susceptible to airway fibrosis from inhaled MWCNT.

Defect density in multiwalled carbon nanotubes influences ovalbumin adsorption and promotes macrophage activation and CD4^+ T-cell proliferation

“…For example, our earlier studies found that MWCNTs with a length of 10-100 μm impaired pulmonary function 22 and induced severe cardiac ischemic/ reperfusion injury after pulmonary instillation. 23 Similar results on MWCNT toxicity were also reported elsewhere, [24][25][26][27] such as subchronic toxicity, asbestos-like pathogenicity in mice, and airway fibrosis. In contrast, CNTs with a length shorter than 2 μm have been shown to exhibit minimal toxicity to various cell types, such as human promyelocytic leukemia (HL60) and human T-cells (Jurkat).…”

Aerosolization System for Experimental Inhalation Studies of Carbon-Based Nanomaterials

“…There are few studies that have developed aerosolization systems and delivered carbon-based nanomaterials via inhalation (Li et al 2007;Mitchell et al 2007;Ryman-Rasmussen et al 2008;Shvedova et al 2008). In the Mitchell et al (2007) study, MW-CNTs were aerosolized with a jet mill coupled to a dry chemical screw feeder and a 2-µm cut-point cyclone.…”

“…For example, a system encompassing an acoustic fluidization feeder, mill, and size separator was used to generate aerosolized single-walled carbon nanotubes (SW-CNTs; Baron et al 2008), whereas a jet mill coupled to a dry chemical screw feeder (Mitchell et al 2007) or a 6-jet collision nebulizer (Ryman-Rasmussen et al 2008) was utilized to aerosolize multiwalled carbon nanotubes (MW-CNTs). Other test systems employed for generating nanomaterials have included a brush dust generator for inhalation studies of nanotitanium dioxide (Ma-Hock et al 2009), as well as a direct delivery of aerosolized nanomaterials from an evaporation reactor (e.g., silicon dioxide; Ostraat et al 2008) or combustion with a laminar diffusion flame system (e.g., ultrafine iron; Yang et al 2001).…”

Functional consequences for primary human alveolar macrophages following treatment with long, but not short, multiwalled carbon nanotubes

“…[16][17][18] Such events result in protracted AM release of inflammatory cytokines, chemokines, interferons, and other soluble mediators; further recruitment of immune effector cells; increased production/release of free radicals (eg, reactive oxygen species [ROS]); and possible damage to the delicate underlying alveolar epithelium. These events may be a precursor to known MWCNT-induced pathologies such as pulmonary fibrosis 19 and granulomatous inflammation 20 in rodents following inhalation. Previous work in our laboratory showed that the length of MWCNTs is a critical determinant of their adverse bioreactivity with primary human AMs (in terms of proinflammatory mediator release and cell death); following an acute (24 hours) treatment, AMs displayed greatest reactivity toward long MWCNTs (~20 μm in length) than toward short MWCNTs (~0.6 μm in length).…”