Long-term Pulmonary Responses to Quadweekly Intermittent Intratracheal Spray Instillations of Magnetite (Fe3O4) Nanoparticles for 52 Weeks in Fischer 344 Rats

Iron oxide nanoparticles exert inhibitory effects on N-Bis(2-hydroxypropyl)nitrosamine (DHPN)-induced lung tumorigenesis in rats

Iron oxide nanoparticles (magnetite) have been widely used in industry and medicine. However, the safety assessment of magnetite has not been fully completed. The present study was conducted to assess effects of magnetite on carcinogenic activity, using a medium-term bioassay protocol. A total of 100 male Fischer 344 rats, 6 weeks old, were randomly divided into 5 groups of 20 animals each, and given a basal diet and drinking water containing 0 or 0.1% of N-bis(2-hydroxypropyl)nitrosamine (DHPN) for 2 weeks. Two weeks later, the rats were intratracheally instilled magnetite 7 times at an interval of 4 weeks, at the doses of 0, 1.0 or 5.0 mg/kg body weight, and sacrificed at the end of the experimental period of 30 weeks. The multiplicities of macroscopic lung nodules and histopathologically diagnosed bronchiolo-alveolar hyperplasia, induced by DHPN, were both significantly decreased by the high dose of magnetite. The expression of minichromosome maintenance (MCM) protein 7 in non-tumoral alveolar epithelial cells, and the number of CD163-positive macrophages in tumor nodules were both significantly reduced by magnetite. It is suggested that magnetite exerts inhibitory effects against DHPN-induced lung tumorigenesis, by the reduction of alveolar epithelial proliferation and the M2 polarization of tumor-associated macrophages.

Contribution of toxicologic pathologists for the safety of human health in biomedical research-past, present, and future of the JSTP

The research field of “Toxicologic Pathology” evaluates potentially toxic chemical exposures and chemically mediated illnesses in humans and experimental animals. Comparative studies of chemical exposures between model organisms and humans are essential for the risk assessment of chemicals and human health. Here we review the development and activities of the Japanese Society of Toxicologic Pathology (JSTP) during its 37-year history. Toxicological pathology studies provide many interesting and valuable findings. Rodent cancer bioassay data demonstrate the importance of dose levels, times, and duration of exposures to chemicals that possibly cause human cancers. Studies of toxic injuries in the nasal cavity demonstrate that specific chemical compounds affect different target cells and tissues. These observations are relevant for current air pollution studies in the preventive medicine field. Future toxicological pathology studies will be enhanced by applying molecular pathology with advanced observation techniques. In addition to the nasal cavity, another sense organ such as the tongue should be a potential next program of our mission for risk assessment of inhaled and ingested chemicals. As a message to the younger members of the JSTP, interdisciplinary and global cooperation should be emphasized. Elucidating the mechanisms of toxicologic pathology with a combination of advanced expertise in genetics and molecular biology offers promise for future advances by JSTP members.

Comparison of the local pulmonary distribution of nanoparticles administered intratracheally to rats via gavage needle or microsprayer delivery devices

Intratracheal administration methods are used to conduct toxicological assessments of inhaled nanoparticles (NPs), and gavage needles or microsprayers are common intratracheal delivery devices. The NP suspension is delivered in a liquid state via gavage needle and as a liquid aerosol via microsprayer. The differences in local pulmonary NP distribution (called the microdistribution) arising from the different states of the NP suspension cause differential pulmonary responses; however, this has yet to be investigated. Herein, using microbeam X-ray fluorescence microscopy, we quantitatively evaluated the TiO₂ pulmonary microdistribution (per mesh: 100 μm × 100 μm) in lung sections from rats administered an intratracheal dose of TiO₂ NPs (6 mg kg^-1 ) via gavage needle or microsprayer. The results revealed that: (i) using a microsprayer appears to reduce the variations in TiO₂ content (ng mesh^-1 ) among rats (e.g., coefficients of variation, n = 3, microsprayer vs gavage needle: 13% vs 30%, for the entire lungs); (ii) TiO₂ appears to be deposited less in the right middle lobes than in the rest of the lung lobes, irrespective of the chosen intratracheal delivery device; and (iii) similar TiO₂ contents (ng mesh^-1 ) and frequencies are deposited in the lung lobes of rats administered TiO₂ NPs via gavage needle or microsprayer. This suggests that the physical state of the administered NP suspension does not markedly alter TiO₂ pulmonary microdistribution. The results of this investigation are important for the standardization of intratracheal administration methods. Copyright © 2016 John Wiley & Sons, Ltd.

Pulmonary distribution of nanoceria: comparison of intratracheal, microspray instillation and dry powder insufflation

Particles can be delivered to the respiratory tract of animals using various techniques. Inhalation mimics environmental exposure but requires large amounts of aerosolized NPs over a prolonged dosing time, varies in deposited dose among individual animals, and results in nasopharyngeal and fur particle deposition. Although less physiological, intratracheal (IT) instillation allows quick and precise dosing. Insufflation delivers particles in their dry form as an aerosol. We compared the distribution of neutron-activated ¹⁴¹CeO₂ nanoparticles (5 mg/kg) in rats after (1) IT instillation, (2) left intrabronchial instillation, (3) microspraying of nanoceria suspension and (4) insufflation of nanoceria dry powder. Blood, tracheobronchial lymph nodes, liver, gastrointestinal tract, feces and urine were collected at 5 min and 24 h post-dosing. Excised lungs from each rat were dried at room temperature while inflated at a constant 30 cm water pressure. Dried lungs were then sliced into 50 pieces. The radioactivity of each lung piece and other organs was measured. The evenness index (EI) of each lung piece was calculated [EI = (μCi/mg_piece)/(μCi/mg_lung)]. The degree of EI value departure from 1.0 is a measure of deposition heterogeneity. We showed that the pulmonary distribution of nanoceria differs among modes of administration. Dosing by IT or microspraying resulted in similar spatial distribution. Insufflation resulted in significant deposition in the trachea and in more heterogeneous lung distribution. Our left intrabronchial instillation technique yielded a concentrated deposition into the left lung. We conclude that animal dosing techniques and devices result in varying patterns of particle deposition that will impact biokinetic and toxicity studies.

Magnetite/dextran-functionalized graphene oxide nanosheets for in vivo positive contrast magnetic resonance imaging

In vivo positive contrast MRI by magnetite/dextran-functionalized graphene oxide (SPIO-Dex-FGO) as compared to Magnevist® (the right rat).

Autophagy as a Possible Underlying Mechanism of Nanomaterial Toxicity

The rapid development of nanotechnologies is raising safety concerns because of the potential effects of engineered nanomaterials on human health, particularly at the respiratory level. Since the last decades, many in vivo studies have been interested in the pulmonary effects of different classes of nanomaterials. It has been shown that some of them can induce toxic effects, essentially depending on their physico-chemical characteristics, but other studies did not identify such effects. Inflammation and oxidative stress are currently the two main mechanisms described to explain the observed toxicity. However, the exact underlying mechanism(s) still remain(s) unknown and autophagy could represent an interesting candidate. Autophagy is a physiological process in which cytoplasmic components are digested via a lysosomal pathway. It has been shown that autophagy is involved in the pathogenesis and the progression of human diseases, and is able to modulate the oxidative stress and pro-inflammatory responses. A growing amount of literature suggests that a link between nanomaterial toxicity and autophagy impairment could exist. In this review, we will first summarize what is known about the respiratory effects of nanomaterials and we will then discuss the possible involvement of autophagy in this toxicity. This review should help understand why autophagy impairment could be taken as a promising candidate to fully understand nanomaterials toxicity.