Chronic nasal exposure to nanoparticulate TiO2 causes pulmonary tumorigenesis in male mice

Chronic inhalation bioassays in rodents are used to assess pulmonary carcinogenicity for purposes of hazard identification and potentially for risk characterization. Numerous studies have been confirmed that exposure to titanium dioxide nanoparticles (TiO₂ NPs) may result in chronic pulmonary inflammation in both mice and rats. However, very few studies have focused on the pulmonary tumorigenesis. In this study, to examine whether chronic TiO₂ NP exposure induce tumorigenesis in the lung, forty mice (each group) were nasally exposed to 1.25, 2.5, and 5 mg/kg body weight TiO₂ NPs for nine consecutive months, lung pathology was then evaluated, and the biochemical function parameters in bronchoalveolar lavage (BAL) and tumor markers in the serum were investigated using an ELISA method. We observed that nasal exposure to TiO₂ NPs caused infiltration of inflammatory cells, tumorigenesis in the lung, and accompanied by significant increases of lactate dehydrogenase, alkaline phosphatase, and total protein levels in BLAF, significant increases in tumor markers including cytokeratin 19, neuron-specific enolase, carcinoembryonic antigen, squamous cell carcinoma antigen, and cancer antigen-125 in the serum. It implies that chronic inhaled TiO₂ NPs may increase possibility of pulmonary tumor formation for human. Therefore, the production and application of TiO₂ NPs should be paid more attention. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1651-1657, 2017.

Lung tumorigenesis induced by human vascular endothelial growth factor (hVEGF)-A165 overexpression in transgenic mice and amelioration of tumor formation by miR-16

Many studies have shown that vascular endothelial growth factor (VEGF), especially the human VEGF-A₁₆₅ (hVEGF-A₁₆₅) isoform, is a key proangiogenic factor that is overexpressed in lung cancer. We generated transgenic mice that overexpresses hVEGF-A₁₆₅ in lung-specific Clara cells to investigate the development of pulmonary adenocarcinoma. In this study, three transgenic mouse strains were produced by pronuclear microinjection, and Southern blot analysis indicated similar patterns of the foreign gene within the genomes of the transgenic founder mice and their offspring. Accordingly, hVegf-A₁₆₅ mRNA was expressed specifically in the lung tissue of the transgenic mice. Histopathological examination of the lung tissues of the transgenic mice showed that hVEGF-A₁₆₅ overexpression induced bronchial inflammation, fibrosis, cysts, and adenoma. Pathological section and magnetic resonance imaging (MRI) analyses demonstrated a positive correlation between the development of pulmonary cancer and hVEGF expression levels, which were determined by immunohistochemistry, qRT-PCR, and western blot analyses. Gene expression profiling by cDNA microarray revealed a set of up-regulated genes (hvegf-A₁₆₅, cyclin b1, cdc2, egfr, mmp9, nrp-1, and kdr) in VEGF tumors compared with wild-type lung tissues. In addition, overexpressing hVEGF-A₁₆₅ in Clara cells increases CD105, fibrogenic genes (collagen α1, α-SMA, TGF-β1, and TIMP1), and inflammatory cytokines (IL-1, IL-6, and TNF-α) in the lungs of hVEGF-A₁₆₅-overexpressing transgenic mice as compared to wild-type mice. We further demonstrated that the intranasal administration of microRNA-16 (miR-16) inhibited lung tumor growth by suppressing VEGF expression via the intrinsic and extrinsic apoptotic pathways. In conclusion, hVEGF-A₁₆₅ transgenic mice exhibited complex alterations in gene expression and tumorigenesis and may be a relevant model for studying VEGF-targeted therapies in lung adenocarcinoma.