Pulmonary instillation of low doses of titanium dioxide nanoparticles in mice leads to particle retention and gene expression changes in the absence of inflammation

Abstract

We investigated gene expression, protein synthesis, and particle retention in mouse lungs following intratracheal instillation of varying doses of nano-sized titanium dioxide (nano-TiO2). Female C57BL/6 mice were exposed to rutile nano-TiO2 via single intratracheal instillations of 18, 54, and 162μg/mouse. Mice were sampled 1, 3, and 28days post-exposure. The deposition of nano-TiO2 in the lungs was assessed using nanoscale hyperspectral microscopy. Biological responses in the pulmonary system were analyzed using DNA microarrays, pathway-specific real-time RT-PCR (qPCR), gene-specific qPCR arrays, and tissue protein ELISA. Hyperspectral mapping showed dose-dependent retention of nano-TiO2 in the lungs up to 28days post-instillation. DNA microarray analysis revealed approximately 3000 genes that were altered across all treatment groups (±1.3 fold; p<0.1). Several inflammatory mediators changed in a dose- and time-dependent manner at both the mRNA and protein level. Although no influx of neutrophils was detected at the low dose, changes in the expression of several genes and proteins associated with inflammation were observed. Resolving inflammation at the medium dose, and lack of neutrophil influx in the lung fluid at the low dose, were associated with down-regulation of genes involved in ion homeostasis and muscle regulation. Our gene expression results imply that retention of nano-TiO2 in the absence of inflammation over time may potentially perturb calcium and ion homeostasis, and affect smooth muscle activities.

MWCNTs of different physicochemical properties cause similar inflammatory responses, but differences in transcriptional and histological markers of fibrosis in mouse lungs

“…The strong inflammatory and acute phase responses are not unique to MWCNT exposure. Similar responses have been observed following exposure to nano-titanium dioxide particles (nano-TiO 2 ) and nano-carbon black (nano-CB) particles via instillation or inhalation using experimental designs similar to that used in the present study (Bourdon et al, 2012a;Halappanavar et al, 2011;Husain et al, 2013;Jackson et al, 2011b). However, the number of differentially expressed genes was an order of magnitude greater following exposure to the two MWCNTs than following exposure to nano-TiO 2 and nano-CB, indicating stronger potency of MWCNT.…”

“…Doses and time points were selected based on the previous and ongoing studies in our group (Bourdon et al, 2012b;Husain et al, 2013;Jacobsen et al, 2009;Poulsen et al, 2013;Saber et al, 2012Saber et al, , 2013. The consistency in doses and time points across many studies enabled comparison of responses after exposure to different nanomaterials.…”

Identification of Metal Oxide Nanoparticles in Histological Samples by Enhanced Darkfield Microscopy and Hyperspectral Mapping

“…A wide variety of applications are being investigated for use in biomedical research 11 . This method could be utilized for assessment of different biological samples (such as various tissues types, bronchoalveolar lavage samples, and blood smears) that have been exposed to nanoparticles of a variety of elemental compositions [16][17][18][19] . Furthermore, this method is useful for studying nanoparticle biodistribution in vivo and in vitro, which is pertinent for nanoscale drug delivery studies 11 .…”

Comparative plasma proteomic studies of pulmonary TiO2 nanoparticle exposure in rats using liquid chromatography tandem mass spectrometry

“…It is interesting to note that there is a positive z score (up regulation) associated with acute phase response signaling, and a negative z score (down regulation) associated with LXR/RXR activation, but neither is considered significant. Others have observed an up regulation of the acute phase response signaling pathway in response to TiO 2 NP exposure via gene expression analysis of mouse lung tissue[35, 36]. Husian and coworkers examined differentially expressed genes from mouse lung tissue after intratracheal instillation of low, medium, and high concentrations of TiO 2 NPs at 1, 3, and 28 days post exposure.…”

“…Analyses of bronchoalveolar lavage fluid (BALF) from animal studies have demonstrated TiO 2 NP exposure increases inflammatory cells, such as neutrophils and lympohcytes; moreover, the observed increase of inflammatory cells was found to be dependent on days after exposure [30-33], dose [32-34], and method of introduction (whole body inhalation vs. intratracheal instillation) [33]. Furthermore, gene expression analyses of lung tissue have shown immune and inflammatory responses as a result of TiO 2 particle exposure [34-36]. Additionally, markers associated with oxidative and nitrosative stresses in the microcirculation increase [20-22, 25].…”