Toxic Effects of Low-Level Long-Term Inhalation Exposures of Rats to Nickel Oxide Nanoparticles

Rats were exposed to nickel oxide nanoparticles (NiO-NP) inhalation at 0.23 ± 0.01 mg/m³ for 4 h a day 5 times a week for up to 10 months. The rat organism responded to this impact with changes in cytological and some biochemical characteristics of the bronchoalveolar lavage fluid along with a paradoxically little pronounced pulmonary pathology associated with a rather low chronic retention of nanoparticles in the lungs. There were various manifestations of systemic toxicity, including damage to the liver and kidneys; a likely allergic syndrome as indicated by some cytological signs; transient stimulation of erythropoiesis; and penetration of nickel into the brain from the nasal mucous membrane along the olfactory pathway. Against a picture of mild to moderate chronic toxicity of nickel, its in vivo genotoxic effect assessed by the degree of DNA fragmentation in nucleated blood cells (the RAPD test) was pronounced, tending to increasing with the length of the exposure period. When rats were given orally, in parallel with the toxic exposure, a set of innocuous substances with differing mechanisms of expected bioprotective action, the genotoxic effect of NiO-NPs was found to be substantially attenuated.

Combined Subchronic Toxicity of Aluminum (III), Titanium (IV) and Silicon (IV) Oxide Nanoparticles and Its Alleviation with a Complex of Bioprotectors

Stable suspensions of metal/metalloid oxide nanoparticles (MeO-NPs) obtained by laser ablation of 99.99% pure elemental aluminum, titanium or silicon under a layer of deionized water were used separately, or in three binary combinations, or in a ternary combination to induce subchronic intoxications in rats. To this end, the MeO-NPs were repeatedly injected intraperitoneally (i.p.) 18 times during 6 weeks before measuring a large number of functional, biochemical, morphological and cytological indices for the organism’s status. In many respects, the Al₂O₃-NP was found to be the most toxic species alone and the most dangerous component of the combinations studied. Mathematical modeling with the help of the Response Surface Methodology showed that, as well as in the case of any other binary toxic combinations previously investigated by us, the organism’s response to a simultaneous exposure to any two of the MeO-NP species under study was characterized by a complex interaction between all possible types of combined toxicity (additivity, subadditivity or superadditivity of unidirectional action and different variants of opposite effects) depending on which outcome this type was estimated for and on effect and dose levels. With any third MeO-NP species acting in the background, the type of combined toxicity displayed by the other two remained virtually the same or changed significantly, becoming either more or less unfavorable. Various harmful effects produced by the (Al₂O₃-NP + TiO₂-NP + SiO₂-NP)-combination, including its genotoxicity, were substantially attenuated by giving the rats per os during the entire exposure period a complex of innocuous bioactive substances expected to increase the organism’s antitoxic resistance.

The most important inferences from the Ekaterinburg nanotoxicology team's animal experiments assessing adverse health effects of metallic and metal oxide nanoparticles

During 2009-2017 we have studied nanoparticles of elemental silver or gold and of iron, copper, nickel, manganese, lead, zinc, aluminium and titanium oxides (Me-NPs) using, in most cases, a single low-dose intratracheal instillation 24 h before the bronchoalveolar lavage to obtain a fluid for cytological and biochemical assessment and, in all cases, repeated intraperitoneal injections in non-lethal doses to induce subchronic intoxications assessed by a lot of toxicodynamic and toxicokinetic features. We have also studied the same effects for a number of relevant combinations of these Me-NPs and have revealed some important patterns of their combined toxicity. Besides, we have carried out long-term inhalation experiments with Fe2O3, NiO and amorphous SiO2 nano-aerosols. We have demonstrated that Me-NPs are much more noxious as compared with their fine micrometric counterparts although the physiological mechanisms of their elimination from the lungs proved to be highly active. Even if water-insoluble, Me-NPs are significantly solubilized in some biological milieus in vitro and in vivo, which may explain some important peculiarities of their toxicity. At the same time, the in situ cytotoxicity, organ-systemic toxicity and in vivo genotoxicity of Me-NPs strongly depends on specific mechanisms characteristic of a particular metal. For some of the Me-NPs studied, we have proposed standards of presumably safe concentrations in workplace air. Along with this, we have proved that the adverse effects of Me-NPs could be significantly alleviated by background or preliminary administration of adequately composed combinations of some bioprotectors.

Changes in the Dose-Response Relationship of One Toxicant Under Simultaneous Exposure to Another Toxicant

We considered, in general form for a 22 full factorial experiment, linear approximations of the organism's dose-response relationship for some factors operating alone and modification of this relationship by another factor operating in the background. A typological classification of such modifications is suggested. An analysis of the outcomes obtained in a number of subchronic animal experiments on rats in which this response was assessed by changes in a large number of biomedical indices revealed that all theoretically possible variants (types) of the modification under consideration are actually observed depending on a specific index and specific harmful exposure. Statistical significance estimation procedures are formulated for each of them.

On the contribution of the phagocytosis and the solubilization to the iron oxide nanoparticles retention in and elimination from lungs under long-term inhalation exposure

The aim of our study was to test a hypothesis according to which the pulmonary clearance vs. retention of metal oxide nanoparticles (NPs) is controlled not only by physiological mechanisms but also by their solubilization which in some cases may even prevail. Airborne Fe2O3 NPs with the mean diameter of 14±4nm produced by sparking from 99.99% pure iron rods were fed into a nose-only exposure tower. Rats were exposed to these NPs for 4h a day, 5days a week during 3, 6 or 10 months at the mean concentration of 1.14±0.01mg/m(3). NPs collected from the air exhausted from the exposure tower proved insoluble in water but dissolved markedly in the cell free broncho-alveolar lavage fluid supernatant and in the sterile bovine blood serum. The Fe2O3 content of the lungs and lung-associated lymph nodes was measured by the Electron Paramagnetic Resonance (EPR) spectroscopy. We found a relatively low but significant pulmonary accumulation of Fe2O3, gradually increasing with time. Besides, we obtained TEM-images of nanoparticles within alveolocytes and the myelin sheaths of brain fibers associated with ultrastructural damage. We have developed a multicompartmental system model describing the toxicokinetics of inhaled nanoparticles after their deposition in the lower airways as a process controlled by their (a) high ability to penetrate through the alveolar membrane; (b) active endocytosis; (c) in vivo dissolution. To conclude, both experimental data and the identification of the system model confirmed our initial hypothesis and demonstrated that, as concerns iron oxide NPs of the dimensions used, the dissolution-depending mechanisms proved to be dominant.

Attenuation of Combined Nickel(II) Oxide and Manganese(II, III) Oxide Nanoparticles' Adverse Effects with a Complex of Bioprotectors

Stable suspensions of NiO and Mn₃O₄ nanoparticles (NPs) with a mean (±s.d.) diameter of 16.7±8.2 and 18.4±5.4 nm, respectively, purposefully prepared by laser ablation of 99.99% pure nickel or manganese in de-ionized water, were repeatedly injected intraperitoneally (IP) to rats at a dose of 2.5 mg/kg 3 times a week up to 18 injections, either alone or in combination. A group of rats was injected with this combination with the background oral administration of a "bio-protective complex" (BPC) comprising pectin, vitamins A, C, E, glutamate, glycine, N-acetylcysteine, selenium, iodide and omega-3 PUFA, this composition having been chosen based on mechanistic considerations and previous experience. After the termination of injections, many functional and biochemical indices and histopathological features (with morphometric assessment) of the liver, spleen, kidneys and brain were evaluated for signs of toxicity. The Ni and Mn content of these organs was measured with the help of the atomic emission and electron paramagnetic resonance spectroscopies. We obtained blood leukocytes for performing the RAPD (Random Amplified Polymorphic DNA) test. Although both metallic NPs proved adversely bio-active in many respects considered in this study, Mn₃O₄-NPs were somewhat more noxious than NiO-NPs as concerns most of the non-specific toxicity manifestations and they induced more marked damage to neurons in the striatum and the hippocampus, which may be considered an experimental correlate of the manganese-induced Parkinsonism. The comparative solubility of the Mn₃O₄-NPs and NiO-NPs in a biological medium is discussed as one of the factors underlying the difference in their toxicokinetics and toxicities. The BPC has attenuated both the organ-systemic toxicity and the genotoxicity of Mn₃O₄-NPs in combination with NiO-NPs.