mRNAs and miRNAs in whole blood associated with lung hyperplasia, fibrosis, and bronchiolo‐alveolar adenoma and adenocarcinoma after multi‐walled carbon nanotube inhalation exposure in mice

Abstract

Inhalation exposure to multi-walled carbon nanotubes (MWCNT) in mice results in inflammation, fibrosis, and the promotion of lung adenocarcinoma; however, the molecular basis behind these pathologies is unknown. This study determined global mRNA and miRNA profiles in whole blood from mice exposed by inhalation to MWCNT that correlated with the presence of lung hyperplasia, fibrosis, and bronchiolo-alveolar adenoma and adenocarcinoma. Six-week-old, male, B6C3F1 mice received a single intraperitoneal injection of either the DNA-damaging agent methylcholanthrene (MCA, 10 μg/g body weight) or vehicle (corn oil). One week after injections, mice were exposed by inhalation to MWCNT (5 mg/m³, 5 hours/day, 5 days/week) or filtered air (control) for a total of 15 days. At 17 months post-exposure, mice were euthanized and examined for the development of pathological changes in the lung, and whole blood was collected and analyzed using microarray analysis for global mRNA and miRNA expression. Numerous mRNAs and miRNAs in the blood were significantly up- or down-regulated in animals developing pathological changes in the lung after MCA/corn oil administration followed by MWCNT/air inhalation, including fcrl5 and miR-122-5p in the presence of hyperplasia, mthfd2 and miR-206-3p in the presence of fibrosis, fam178a and miR-130a-3p in the presence of bronchiolo-alveolar adenoma, and il7r and miR-210-3p in the presence of bronchiolo-alveolar adenocarcinoma, among others. The changes in miRNA and mRNA expression, and their respective regulatory networks, identified in this study may potentially serve as blood biomarkers for MWCNT-induced lung pathological changes.

Evaluating the mechanistic evidence and key data gaps in assessing the potential carcinogenicity of carbon nanotubes and nanofibers in humans

“…In a subsequent study of the same groups of mice studied in Sargent et al (2014), Snyder-Talkington et al (2016) observed increased expression of total mRNA and miRNA in the blood of the mice 17 months after exposure to MWCNT-7. In mice that developed pathological changes in the lungs – including hyperplasia, fibrosis, bronchiolo-alveolar adenoma, and bronchiolo-alveolar carcinoma – after the MCA/corn oil administration followed by MWCNT/air inhalation, numerous mRNAs and miRNAs in the blood were significantly up- or down-regulated (Snyder-Talkington et al 2016).…”

“…In mice that developed pathological changes in the lungs – including hyperplasia, fibrosis, bronchiolo-alveolar adenoma, and bronchiolo-alveolar carcinoma – after the MCA/corn oil administration followed by MWCNT/air inhalation, numerous mRNAs and miRNAs in the blood were significantly up- or down-regulated (Snyder-Talkington et al 2016). For a given pathology, the expression profile was different between the exposure groups, suggesting a specific response to the different exposures.…”

“…In the MWCNT exposed group, the observed pathways were: wound repair, fibrosis and tumorigenesis, cell growth, proliferation and invasion, and cell apoptosis owing to stress to the endoplasmic reticulum. In the MCA + MWCNT exposed group, the observed pathways were: lipid metabolism and glycolysis, inflammation, cell proliferation, invasion and tumor immune evasion, and leukocyte migration (Snyder-Talkington et al 2016). …”

Fibrosis biomarkers in workers exposed to MWCNTs

“…It should be emphasized that the MWCNT exposed workers investigated as a part of this study are all males, have various exposure regimes and have only spent about ~1–3 years working at the facility. In fact, the upregulation of TGF-β1 and OPN upon exposure to MWCNTs was not always consistent and depended on several experimental factors including CNT characteristics, animal gender, concentration, exposure type and time points employed in each study (Porter et al, 2010; Dymacek et al, 2015; Khaliullin et al, 2015; Poulsen et al, 2015; Snyder-Talkington et al, 2015; Snyder-Talkington et al, 2016). A larger cohort of workers exposed to MWCNTs during life-time employment would provide a more accurate validation of realistic markers by simultaneously comparing nasal lavage, sputum and serum.…”

“…Additionally, it was shown that exposure to MWCNT activated TGF-b/Smad signaling pathway in fibroblasts and myofibroblasts thus facilitating pulmonary fibrosis (Wang et al, 2015). Moreover, inhalation exposure to MWCNT promotes the growth and neoplastic progression of initiated lung cells in mice (Sargent et al, 2014; Snyder-Talkington et al, 2016). These effects were observed at a dose of 31.2 µg/mouse – that is achievable in human exposures in occupational settings (Erdely et al, 2013; Khaliullin et al, 2015).…”