Quantitative biokinetics over a 28 day period of freshly generated, pristine, 20 nm titanium dioxide nanoparticle aerosols in healthy adult rats after a single two-hour inhalation exposure

Biokinetics of carbon black, multi-walled carbon nanotubes, cerium oxide, silica, and titanium dioxide nanoparticles after inhalation: a review

Understanding the biokinetics of nanoparticles will support the identification of target organs for toxicological endpoints. We investigated the biokinetics of poorly soluble nanomaterials carbon black, multi-walled carbon nanotubes (MWCNT), cerium oxide (CeO2), titanium dioxide (TiO2), crystalline silica (SiO2) in inhalation studies in rodents (the soluble amorphous silica was also included). By reviewing research papers on the inhalation of these substances, we collected physico-chemical data and elemental distribution to organs, urine, and feces. Carbon black, MWCNT, cerium, and titanium accumulated during exposure and persisted in the lung post-exposure (still present at >3000 h). For silica, the amorphous form resulted in silicon accumulation in the lungs. Silicon was increased in the blood. Lymph node accumulation was observed for MWCNT, cerium, and titanium. Liver accumulation was observed for cerium and titanium. Cerium and silicon were increased in the spleen. Titanium accumulated and remained in the spleen (>4000 h). MWCNT were increased in several organs, some of which had a persistent presence of this material. In conclusion, we collected data on the biodistribution of five nanomaterials that, except for amorphous silica, are poorly soluble. The poorly soluble materials or their elements were persistent in the lungs but also showed persistence in other organs. In addition, the data on lung content supports Haber's rule, with titanium being deposited to a greater extent at exposure end than the other materials. Lung deposition seems relatively linear for the collected MMAD values, indicating size may be less important than previously suggested regarding alveolar deposition of the sub-2-micrometer size.

Mechanistic Insights into Toxicity of Titanium Dioxide Nanoparticles at the Micro- and Macro-levels

Titanium oxide nanoparticles (TiO2 NPs) have been regarded as a legacy nanomaterial due to their widespread usage across multiple fields. The TiO2 NPs have been and are still extensively used as a food and cosmetic additive and in wastewater and sewage treatment, paints, and industrial catalysis as ultrafine TiO2. Recent developments in nanotechnology have catapulted it into a potent antibacterial and anticancer agent due to its excellent photocatalytic potential that generates substantial amounts of highly reactive oxygen radicals. The method of production, surface modifications, and especially size impact its toxicity in biological systems. The anatase form of TiO2 (<30 nm) has been found to exert better and more potent cytotoxicity in bacteria as well as cancer cells than other forms. However, owing to the very small size, anatase particles are able to penetrate deep tissue easily; hence, they have also been implicated in inflammatory reactions and even as a potent oncogenic substance. Additionally, TiO2 NPs have been investigated to assess their toxicity to large-scale ecosystems owing to their excellent reactive oxygen species (ROS)-generating potential compounded with widespread usage over decades. This review discusses in detail the mechanisms by which TiO2 NPs induce toxic effects on microorganisms, including bacteria and fungi, as well as in cancer cells. It also attempts to shed light on how and why it is so prevalent in our lives and by what mechanisms it could potentially affect the environment on a larger scale.

Biodistribution of cerium dioxide and titanium dioxide nanomaterials in rats after single and repeated inhalation exposures

BACKGROUND

Physiologically based kinetic models facilitate the safety assessment of inhaled engineered nanomaterials (ENMs). To develop these models, high quality datasets on well-characterized ENMs are needed. However, there are at present, several data gaps in the systemic availability of poorly soluble particles after inhalation. The aim of the present study was therefore to acquire two comparable datasets to parametrize a physiologically-based kinetic model.

METHOD

Rats were exposed to cerium dioxide (CeO2, 28.4 ± 10.4 nm) and titanium dioxide (TiO2, 21.6 ± 1.5 nm) ENMs in a single nose-only exposure to 20 mg/m3 or a repeated exposure of 2 × 5 days to 5 mg/m3. Different dose levels were obtained by varying the exposure time for 30 min, 2 or 6 h per day. The content of cerium or titanium in three compartments of the lung (tissue, epithelial lining fluid and freely moving cells), mediastinal lymph nodes, liver, spleen, kidney, blood and excreta was measured by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) at various time points post-exposure. As biodistribution is best studied at sub-toxic dose levels, lactate dehydrogenase (LDH), total protein, total cell numbers and differential cell counts were determined in bronchoalveolar lavage fluid (BALF).

RESULTS

Although similar lung deposited doses were obtained for both materials, exposure to CeO2 induced persistent inflammation indicated by neutrophil granulocytes influx and exhibited an increased lung elimination half-time, while exposure to TiO2 did not. The lavaged lung tissue contained the highest metal concentration compared to the lavage fluid and cells in the lavage fluid for both materials. Increased cerium concentrations above control levels in secondary organs such as lymph nodes, liver, spleen, kidney, urine and faeces were detected, while for titanium this was found in lymph nodes and liver after repeated exposure and in blood and faeces after a single exposure.

CONCLUSION

We have provided insight in the distribution kinetics of these two ENMs based on experimental data and modelling. The study design allows extrapolation at different dose-levels and study durations. Despite equal dose levels of both ENMs, we observed different distribution patterns, that, in part may be explained by subtle differences in biological responses in the lung.

Current research on ecotoxicity of metal-based nanoparticles: from exposure pathways, ecotoxicological effects to toxicity mechanisms

Metal-based nanoparticles have garnered significant usage across industries, spanning catalysis, optoelectronics, and drug delivery, owing to their diverse applications. However, their potential ecological toxicity remains a crucial area of research interest. This paper offers a comprehensive review of recent advancements in studying the ecotoxicity of these nanoparticles, encompassing exposure pathways, toxic effects, and toxicity mechanisms. Furthermore, it delves into the challenges and future prospects in this research domain. While some progress has been made in addressing this issue, there is still a need for more comprehensive assessments to fully understand the implications of metal-based nanoparticles on the environment and human well-being.

Oropharyngeal aspirated Ag/TiO2 nanohybrids: Transformation, distribution and toxicity

The wide application of Ag-loaded TiO2 nanohybrids photocatalysts on environment and energy increases the lung exposure risk to humans. Ag/TiO2 nanohybrids inhalation can cause pulmonary toxicity, and there are concerns about whether the loaded silver can be released and cause toxic effects on extrapulmonary organs. Therefore, in this study, the possible biotransformation, biodistribution, and toxicity of oropharyngeal aspirated Ag/TiO2 nanohybrids were investigated first time in vitro and in vivo to answer this question. Firstly, the results of biotransformation showed that the ultrafine silver nanoparticles (~3.5 nm, 2 w/w%) loaded on the surface of nano-TiO2 (~25 nm) could agglomerate and release in Gamble's solution, and the hydrodynamic diameter of the nanohybrids agglomerates increased from about 200 nm to 1 μm. Furthermore, after exposure 10 mg/kg Ag/TiO2 nanohybrids to C57BL/6 J male mice by oropharyngeal aspiration weekly, the biodistribution results showed that the released silver could result in blood, liver, and brain distribution within 28 d. Finally, body weight, organ coefficient, blood biochemical indicators of liver and kidney function, and pathological images demonstrated that although silver could release and lead to extrapulmonary organ distribution, it did not cause obvious extrapulmonary organ damage. The original lung was still the main toxicity and accumulation target organ of Ag/TiO2 nanohybrids, which mainly manifested as the pro-inflammatory and pro-fibrotic effects that should be focused on in the future. Therefore, this study is of great significance in evaluating the safety of Ag-loaded TiO2 nanoparticles and predicting their toxic mechanisms.

The bio-distribution, clearance pathways, and toxicity mechanisms of ambient ultrafine particles

Ambient particles severely threaten human health worldwide. Compared to larger particles, ultrafine particles (UFPs) are highly concentrated in ambient environments, have a larger specific surface area, and are retained for a longer time in the lung. Recent studies have found that they can be transported into various extra-pulmonary organs by crossing the air-blood barrier (ABB). Therefore, to understand the adverse effects of UFPs, it is crucial to thoroughly investigate their bio-distribution and clearance pathways in vivo after inhalation, as well as their toxicological mechanisms. This review highlights emerging evidence on the bio-distribution of UFPs in pulmonary and extra-pulmonary organs. It explores how UFPs penetrate the ABB, the blood-brain barrier (BBB), and the placental barrier (PB) and subsequently undergo clearance by the liver, kidney, or intestine. In addition, the potential underlying toxicological mechanisms of UFPs are summarized, providing fundamental insights into how UFPs induce adverse health effects.

The internal dose makes the poison: higher internalization of polystyrene particles induce increased perturbation of macrophages

Plastics are emerging pollutants of great concern. Macroplastics released in the environment degrade into microplastics and nanoplastics. Because of their small size, these micro and nano plastic particles can enter the food chain and contaminate humans with still unknown biological effects. Plastics being particulate pollutants, they are handled in the human body by scavenger cells such as macrophages, which are important players in the innate immune system. Using polystyrene as a model of micro and nanoplastics, with size ranging from under 100 nm to 6 microns, we have showed that although non-toxic, polystyrene nano and microbeads alter the normal functioning of macrophages in a size and dose-dependent manner. Alterations in the oxidative stress, lysosomal and mitochondrial functions were detected, as well as changes in the expression of various surface markers involved in the immune response such as CD11a/b, CD18, CD86, PD-L1, or CD204. For each beads size tested, the alterations were more pronounced for the cell subpopulation that had internalized the highest number of beads. Across beads sizes, the alterations were more pronounced for beads in the supra-micron range than for beads in the sub-micron range. Overall, this means that internalization of high doses of polystyrene favors the emergence of subpopulations of macrophages with an altered phenotype, which may not only be less efficient in their functions but also alter the fine balance of the innate immune system.

Titanium Dioxide Nanoparticles Modulate Systemic Immune Response and Increase Levels of Reduced Glutathione in Mice after Seven-Week Inhalation

Titanium dioxide nanoparticles (TiO₂ NPs) are used in a wide range of applications. Although inhalation of NPs is one of the most important toxicologically relevant routes, experimental studies on potential harmful effects of TiO₂ NPs using a whole-body inhalation chamber model are rare. In this study, the profile of lymphocyte markers, functional immunoassays, and antioxidant defense markers were analyzed to evaluate the potential adverse effects of seven-week inhalation exposure to two different concentrations of TiO₂ NPs (0.00167 and 0.1308 mg TiO₂/m³) in mice. A dose-dependent effect of TiO₂ NPs on innate immunity was evident in the form of stimulated phagocytic activity of monocytes in low-dose mice and suppressed secretory function of monocytes (IL-18) in high-dose animals. The effect of TiO₂ NPs on adaptive immunity, manifested in the spleen by a decrease in the percentage of T-cells, a reduction in T-helper cells, and a dose-dependent decrease in lymphocyte cytokine production, may indicate immunosuppression in exposed mice. The dose-dependent increase in GSH concentration and GSH/GSSG ratio in whole blood demonstrated stimulated antioxidant defense against oxidative stress induced by TiO₂ NP exposure.

Occupational Exposure to Metal Engineered Nanoparticles: A Human Biomonitoring Pilot Study Involving Italian Nanomaterial Workers

Advances in nanotechnology have led to an increased use of engineered nanoparticles (ENPs) and the likelihood for occupational exposures. However, how to assess such exposure remains a challenge. In this study, a methodology for human biomonitoring, based on Single Particle Inductively Coupled Plasma Mass Spectrometry (SP-ICP-MS), was developed as a tool to assess the ENPs exposure of workers involved in nanomaterial activities in two Italian Companies. The method was validated for size and number concentration determination of Ag, Au, In₂O₃, Ir, Pd, Pt, and TiO₂ NPs in urine and blood samples. The results showed the presence of In₂O₃ NPs in blood of exposed workers (mean, 38 nm and 10,371 particles/mL), but not in blood of controls. Silver, Au, and TiO₂ NPs were found in urine (mean, Ag 29 nm and 16,568 particles/mL) or blood (mean, Au 15 nm and 126,635 particles/mL; TiO₂ 84 nm and 27,705 particles/mL) of workers, though these NPs were found also in controls. The presence of ENPs in both workers and controls suggested that the extra-professional exposure is a source of ENPs that cannot be disregarded. Iridium, Pd, and Pt NPs were not detected neither in blood nor in urine. Overall, the findings provided a rational basis to evaluate the exposure assessment to ENPs in cohorts of workers as part of risk assessment and risk management processes in workplaces.

Imaging drug delivery to the lungs: Methods and applications in oncology

Direct delivery to the lung via inhalation is arguably one of the most logical approaches to treat lung cancer using drugs. However, despite significant efforts and investment in this area, this strategy has not progressed in clinical trials. Imaging drug delivery is a powerful tool to understand and develop novel drug delivery strategies. In this review we focus on imaging studies of drug delivery by the inhalation route, to provide a broad overview of the field to date and attempt to better understand the complexities of this route of administration and the significant barriers that it faces, as well as its advantages. We start with a discussion of the specific challenges for drug delivery to the lung via inhalation. We focus on the barriers that have prevented progress of this approach in oncology, as well as the most recent developments in this area. This is followed by a comprehensive overview of the different imaging modalities that are relevant to lung drug delivery, including nuclear imaging, X-ray imaging, magnetic resonance imaging, optical imaging and mass spectrometry imaging. For each of these modalities, examples from the literature where these techniques have been explored are provided. Finally the different applications of these technologies in oncology are discussed, focusing separately on small molecules and nanomedicines. We hope that this comprehensive review will be informative to the field and will guide the future preclinical and clinical development of this promising drug delivery strategy to maximise its therapeutic potential.

About the Transient Effects of Synthetic Amorphous Silica: An In Vitro Study on Macrophages

Silica (either crystalline or amorphous) is widely used for different applications and its toxicological assessment depends on its characteristics and intended use. As sustained inflammation induced by crystalline silica is at the root of silicosis, investigating the inflammatory effects induced by amorphous silicas and their persistence is needed. For the development of new grades of synthetic amorphous silicas, it is also desirable to be able to understand better the factors underlying potential adverse effects. Therefore, we used an optimized in vitro macrophage system to investigate the effects of amorphous silicas, and their persistence. By using different amorphous silicas, we demonstrated that the main driver for the adverse effects is a low size of the overall particle/agglomerate; the second driver being a low size of the primary particle. We also demonstrated that the effects were transient. By using silicon dosage in cells, we showed that the transient effects are coupled with a decrease of intracellular silicon levels over time after exposure. To further investigate this phenomenon, a mild enzymatic cell lysis allowed us to show that amorphous silicas are degraded in macrophages over time, explaining the decrease in silicon content and thus the transiency of the effects of amorphous silicas on macrophages.

Toxicokinetics, dose-response, and risk assessment of nanomaterials: Methodology, challenges, and future perspectives

The rapid growth of nanomaterial applications has raised safety concerns for human health. A number of studies have been conducted to assess the toxicokinetics, toxicology, dose-response, and risk assessment of different nanomaterials using in vitro and in vivo animal and human models. However, current studies cannot meet the demand for efficient assessment of toxicokinetics, dose-response relationships, or the toxicological risk arising from the rapidly increasing number of newly synthesized nanomaterials. In this article, we review the methods for conducting toxicokinetics, hazard identification, dose-response, exposure, and risk assessment studies of nanomaterials, identify the knowledge gaps, and discuss the challenges remaining. We provide the rationale behind the appropriate design of nanomaterial plasma toxicokinetic and tissue distribution studies, including caveats on the interpretation and correlation of in vitro and in vivo toxicology studies. The potential of using physiologically based pharmacokinetic (PBPK) models to extrapolate toxicokinetic and toxicity findings from in vitro to in vivo and from animals to humans is discussed, and the knowledge gaps of PBPK modeling for nanomaterials are identified. While challenges still exist, there has been progress in the toxicokinetics, hazard identification, and risk assessment of nanomaterials in the past two decades. Recent advancements in the field are highlighted with relevant examples. We also share latest guidelines as well as our perspectives on future studies needed to characterize the toxicokinetics, toxicity, and dose-response relationship in support of nanomaterial risk assessment. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

Passage of exogeneous fine particles from the lung into the brain in humans and animals

Addressing the knowledge gaps regarding the access to and harmful effects of airborne fine particles on the central nervous system is critical. Various exogenous fine particles were found in human cerebrospinal fluids, including commonly found particles and others that have not been reported previously. Animal experiments provided mechanistic explanations and verifications of the translocation of inhaled particles into the brain. Moreover, retention of particles in the brain for longer durations than in other organs was demonstrated through isotope labeling–based biodistribution studies in mice, suggesting possible long-term effects on the brain. This work unravels indications and associations between inhalation and particle transport and adds evidence on the relationship between air pollution and detrimental effects of exogenous particles on the brain.

There are still significant knowledge gaps in understanding the intrusion and retention of exogeneous particles into the central nervous system (CNS). Here, we uncovered various exogeneous fine particles in human cerebrospinal fluids (CSFs) and identified the ambient environmental or occupational exposure sources of these particles, including commonly found particles (e.g., Fe- and Ca-containing ones) and other compositions that have not been reported previously (such as malayaite and anatase TiO₂), by mapping their chemical and structural fingerprints. Furthermore, using mouse and in vitro models, we unveiled a possible translocation pathway of various inhaled fine particles from the lung to the brain through blood circulation (via dedicated biodistribution and mechanistic studies). Importantly, with the aid of isotope labeling, we obtained the retention kinetics of inhaled fine particles in mice, indicating a much slower clearance rate of localized exogenous particles from the brain than from other main metabolic organs. Collectively, our results provide a piece of evidence on the intrusion of exogeneous particles into the CNS and support the association between the inhalation of exogenous particles and their transport into the brain tissues. This work thus provides additional insights for the continued investigation of the adverse effects of air pollution on the brain.

Toxicokinetics of Nanoparticles Deposited in Lungs Using Occupational Exposure Scenarios

Various synthetic powders with primary particle sizes at the nanoscale and a high commercial impact have been studied using Wistar rats. The test materials were metal oxides, i.e., TiO₂, ZnO and amorphous silica, and carbon black (technical soot). Dosing schemes were in the regular ranges typically used in subacute rat studies to simulate occupational exposure scenarios (mg range). Nanoscaled particle agglomerates have the potential to disintegrate and translocate as individual nanoparticles to remote locations following deposition in the lungs. The toxicokinetic fate of metal oxides post-inhalation in lungs/organs was investigated (i) by chemical analysis of the retained particulate/dissolved matter and (ii) by visualization of particles in various remote organs using transmission electron microscopy (TEM). The three titanium dioxides (NM-103, NM-104, NM-105; JRC coding) showed a very slow dissolution in lung fluids. In contrast, the coated ZnO (NM-111) dissolved quickly and was eliminated from the body within approximately 1 day. The precipitated amorphous silica (NM-200) showed a partial dissolution. Chemical analysis in lungs (particulate and soluble TiO₂) and in remote organs (liver and brain) showed a small solubility effect under physiological conditions. The translocation to remote organs was negligible. This confirms that for poorly soluble TiO₂ particles there was no considerable translocation to the liver and brain. The chemical analysis of zinc demonstrated a very rapid dissolution of ZnO particles after deposition in the lungs. Statistically significant increases in Zn levels in the lungs were detectable only on day 1 post-exposure (NM-111). Overall, no relevant amounts of increased NM-111 in the ionic or particulate matter were detected in any body compartment. Amorphous silica (NM-200) particles were found in the cytoplasm of intraalveolar macrophages in the lung and the cytoplasm of macrophages in the lung associated lymph node. Interestingly, these particles were found in a few animals of all treatment groups (1, 2.5, and 5 mg/m³ NM-200) even after 91 days post-exposure. In all other organs of the NM-200 treated animals such as the nasal epithelium, trachea, larynx, liver, spleen, kidney, and mesenteric lymph node no particles were found at any time point investigated. Carbon black was tagged internally (“intrinsically”) with a γ tracer (⁷beryllium; half-time: 53.3 days). Due to limited amounts, the test item (0.3 mg per rat lung) was intratracheally instilled into the lungs. This dose avoided a particle overload effect, meaning that the toxicokinetic fate of carbon black could be followed under the approximated physiological conditions of lung clearance. Analysis of the γ labeled carbon black confirmed conclusively that there was no evidence for the translocation of carbon black beyond the lung into the blood or other body compartments. Very small amounts were only detected in lung-associated lymph nodes (LALN). On day 20 post-treatment, upon necropsy, both carbon black samples were practically exclusively found in lungs (75.1% and 91.0%, respectively) and in very small amounts in the lung-associated lymph nodes (LALN), i.e., ~0.5%. In the other organs/tissues, the test item was not significantly detectable. Separation of leukocytes and cell-free supernatant of a bronchoalveolar lavagate by centrifugation revealed that carbon black was completely located in the cell sediment, indicating total engulfment by alveolar macrophages. In conclusion, in occupational settings the nanomaterials titanium dioxide, zinc oxide, amorphous silica, and carbon black acted as microscaled agglomerates, not as individual nanoparticles. They displayed no potential to translocate beyond the lung into the blood compartment. Besides lungs, very small particulate amounts were detected only in LALN. This finding is consistent with the behavior of microscaled poorly soluble particles. Overall, there was no evidence of translocation of the nanomaterials following pulmonary exposures.

Biomimetic pulmonary surfactant modification on the in vivo fate of nanoparticles in the lung

Direct biomimetic modification of nanoparticles (NPs) with endogenous surfactants is helpful to improve the biocompatibility of NPs and avoid damage to the physiological function of the lung. Therefore, the objective of this study is to investigate the influence of biomimetic endogenous pulmonary surfactant phospholipid modification on the in vivo fate of NPs after lung delivery. Here, two neutral phospholipids (dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylamine (DPPE)) and two negatively charged phospholipids (dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylserine (DPPS)) were selected to modify paclitaxel (PTX)-loaded PLGA NPs with different molar ratio. DPPC, DPPE, and DPPG improved mucoadhesion, in contrast, DPPS improved the mucus permeability of the NPs. Neutral DPPC and DPPE reduced, but negatively charged DPPS and DPPG increased the uptake by alveolar macrophages, all types of phospholipid increased the uptake by lung epithelial cells and increased PTX retention in the whole lung. Whereas, DPPC, DPPE, and DPPG promoted PTX retention in bronchoalveolar lavage fluid (BALF), while DPPS promoted PTX absorption in the lung tissue. Only DPPS-PLGA (1:1) NPs remarkably increased PTX systemic exposure. A good correlation between PTX percentage in the supernatant of BALF and PTX concentration in plasma was established, implying PTX entered the system circulation mainly in molecular form. Phospholipid modification had no effect on extrapulmonary organ distribution of PTX. Taken together, our study disclosed that different phospholipid modification can endow the NPs mucoadhesive or mucus penetration and cellular uptake properties, with tunable retention in BALF and absorption in the lung tissue, providing the scientific background for translational nanocarrier design for inhalation as required. STATEMENT OF SIGNIFICANCE: Inhaled nanomedicines will inevitably interact with pulmonary surfactant and form "surfactant corona". However, the contribution of individual pulmonary surfactant phospholipid on the in vivo fate of nanomedicines is still unclear. In this regard, the most abundant pulmonary surfactant phospholipid dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylamine, and dipalmitoylphosphatidylglycerol and dipalmitoylphosphatidylserine were selected to modify the paclitaxel loaded PLGA nanoparticles and the effect of these pulmonary surfactant phospholipids on their in vivo fate was investigated. It was demonstrated that different phospholipid modification can endow the nanoparticles mucoadhesive or mucus penetration properties, with tunable retention in bronchoalveolar lavage fluid, alveolar macrophages uptake and absorption in the lung tissue. The present study provided a comprehensive understanding for the role of pulmonary surfactant phospholipid on inhaled nanomedicines.

Exploring the intrinsic micro-/nanoparticle size on their in vivo fate after lung delivery

Micro-/nanocarriers due to their significant advantages are widely investigated in pulmonary drug delivery. However, different size carriers have varied drug release rate, concealing the effect of particle size on the fate of drugs in vivo. Therefore, by keeping drug release rate comparable, the objective of this study is to elucidate the influence of particle size itself on drug in vivo fate after intratracheal instillation to mice. Here, using paclitaxel (PTX) as a drug model, 100 nm, 300 nm, 800 nm, and 2500 nm poly(lactide-co-glycolide) (PLGA) particles with the same release rate were prepared. It was demonstrated that the in vivo fate of particles after lung delivery was size-dependent. Consistent with most reports of model particles with neglected release kinetics, the mucus penetration capacity in airtifical mucus decreased with increasing particle size and there is no significant difference between 800 nm and 2500 nm particles. The in vivo airway distribution experiments confirmed the results of the in vitro mucus penetration study, that is, the smaller the particles, the more distributed in the airway. Both in vitro and in vivo macrophage uptake results confirmed that the larger particles were more readily taken up by macrophages. In contrast, the uptake of smaller particles in A549 cells was higher than that of larger particles. Some new findings were disclosed in lung retention, lung absorption and lung targeting. Different from previous reports, this study demonstrated that particles with smaller size had longer lung retention, AUC_(0-t) in bronchoalveolar lavage fluid (BALF) of 100 nm particles was 1.6, 1.9, 2.5 times higher than that of 300 nm, 800 nm, and 2500 nm particles and 11.7 times of the PTX solution group. The same trend was observed in lung tissue absorption, the AUC_(0-t) in the lavaged lung of 100 nm particles was 1.8, 2.2, 2.8, 8.6 times higher than that of 300 nm, 800 nm, 2500 nm particles and PTX solution groups, respectively. The lung targeting efficiency was particles size independent. In conclusion, the in vivo fate of particles with the same release kinetics after intratracheal instillation is size-dependent, smaller size particles are conducive for lung retention and lung absorption. Overall, our study provided scientific guidance for the rational design of particle based pulmonary drug delivery system.

The Road to Achieving the European Commission's Chemicals Strategy for Nanomaterial Sustainability-A PATROLS Perspective on New Approach Methodologies

The European Green Deal outlines ambitions to build a more sustainable, climate neutral, and circular economy by 2050. To achieve this, the European Commission has published the Chemicals Strategy for Sustainability: Towards a Toxic-Free Environment, which provides targets for innovation to better protect human and environmental health, including challenges posed by hazardous chemicals and animal testing. The European project PATROLS (Physiologically Anchored Tools for Realistic nanOmateriaL hazard aSsessment) has addressed multiple aspects of the Chemicals Strategy for Sustainability by establishing a battery of new approach methodologies, including physiologically anchored human and environmental hazard assessment tools to evaluate the safety of engineered nanomaterials. PATROLS has delivered and improved innovative tools to support regulatory decision-making processes. These tools also support the need for reducing regulated vertebrate animal testing; when used at an early stage of the innovation pipeline, the PATROLS tools facilitate the safe and sustainable development of new nano-enabled products before they reach the market.

Nanomaterials and hepatic disease: toxicokinetics, disease types, intrinsic mechanisms, liver susceptibility, and influencing factors

The widespread use of nanomaterials (NMs) has raised concerns that exposure to them may introduce potential risks to the human body and environment. The liver is the main target organ for NMs. Hepatotoxic effects caused by NMs have been observed in recent studies but have not been linked to liver disease, and the intrinsic mechanisms are poorly elucidated. Additionally, NMs exhibit varied toxicokinetics and induce enhanced toxic effects in susceptible livers; however, thus far, this issue has not been thoroughly reviewed. This review provides an overview of the toxicokinetics of NMs. We highlight the possibility that NMs induce hepatic diseases, including nonalcoholic steatohepatitis (NASH), fibrosis, liver cancer, and metabolic disorders, and explore the underlying intrinsic mechanisms. Additionally, NM toxicokinetics and the potential induced risks in the livers of susceptible individuals, including subjects with liver disease, obese individuals, aging individuals and individuals of both sexes, are summarized. To understand how NM type affect their toxicity, the influences of the physicochemical and morphological (PCM) properties of NMs on their toxicokinetics and toxicity are also explored. This review provides guidance for further toxicological studies on NMs and will be important for the further development of NMs for applications in various fields.

Chronic upper airway and systemic inflammation from copier emitted particles in healthy operators at six Singaporean workplaces

Toner-based printing equipment (TPE), including laser printers and photocopiers, utilize several engineered nanomaterials (ENMs) to improve toner performance. Operation of TPE, which rarely employ any exposure controls, generates high exposures to nanoparticles that contain ENMs and complex organics. Epidemiological literature in copier operators documents respiratory effects, including nasal blockage, cough, excessive sputum, and breathing difficulties, cardiovascular effects, oxidative stress, and inflammation. However, epidemiological studies in humans with adequate exposure assessment and dose-response analysis are lacking. We present herein the analysis of the upper airway and systemic inflammation in plasma of 19 healthy copier operators at six Singapore workplaces. We employed a repeated panel design (four biomarker measurements over two weeks) combined with a multi-marker approach (14 inflammatory cytokines in plasma and nasal lavage (NL)), and comprehensive exposure assessment using four distinct exposure metrics. We investigated spatial and temporal patterns of markers of upper airway and systemic inflammation and their association with various exposure metrics. Several inflammatory markers, namely fractalkine, IL-1β, and IL-1α in NL, and fractalkine, IL-1β, TNF-α, and IFN-γ in plasma, were strongly and positively associated with at least one exposure metric, whereas GM-CSF was negatively associated. The inflammation score was also strongly associated with TPE nanoparticle exposures. Exposure to TPE emissions induced moderate upper airway inflammation and stronger systemic inflammation in these healthy operators, characterized by upregulation of at least IL-1β, fractalkine, TNF-α and IFN-γ. Proinflammatory cytokines TNF-α, IFN-γ and IL-1β play an important role in orchestrating inflammatory responses in various clinical conditions, including cardiovascular and autoimmune disease, and likely trigger activation of endothelial cells, leading to overexpression of fractalkine, a chemokine that is involved in and associated with multiple disorders, including atherosclerosis and vascular disease. Future larger-scale epidemiological studies in these workers and consumers exposed chronically to TPE nanoparticle emissions and proactive interventions to reduce or eliminate TPE exposures are recommended.

Lung retention and particokinetics of silver and gold nanoparticles in rats following subacute inhalation co-exposure

Background

Inhalation exposure to nanomaterials in workplaces can include a mixture of multiple nanoparticles. Such ambient nanoparticles can be of high dissolution or low dissolution in vivo and we wished to determine whether co-exposure to particles with different dissolution rates affects their biokinetics.

Methods and Results

Rats were exposed to biosoluble silver nanoparticles (AgNPs, 10.86 nm) and to biopersistent gold nanoparticles (AuNPs, 10.82 nm) for 28 days (6-h/day, 5-days/week for 4 weeks) either with separate NP inhalation exposures or with combined co-exposure. The separate NPs mass concentrations estimated by the differential mobility analyzer system (DMAS) were determined to be 17.68 ± 1.69 μg/m³ for AuNP and 10.12 ± 0.71 μg/m³ for AgNP. In addition, mass concentrations analyzed by atomic absorption spectrometer (AAS) via filter sampling were for AuNP 19.34 ± 2.55 μg/m³ and AgNP 17.38 ± 1.88 μg/m³ for separate exposure and AuNP 8.20 ± 1.05 μg/m³ and AgNP 8.99 ± 1.77 μg/m³ for co-exposure. Lung retention and clearance were determined on day 1 (6-h) of exposure (E-1) and on post-exposure days 1, 7, and 28 (PEO-1, PEO-7, and PEO-28, respectively). While the AgNP and AuNP deposition rates were determined to be similar due to the similarity of NP size of both aerosols, the retention half-times and clearance rates differed due to the difference in dissolution rates. Thus, when comparing the lung burdens following separate exposures, the AgNP retention was 10 times less than the AuNP retention at 6-h (E-1), and 69, 89, and 121 times lower less than the AuNP retention at PEO-1, PEO-7, and PEO-28, respectively. In the case of AuNP+AgNP co-exposure, the retained AgNP lung burden was 14 times less than the retained AuNP lung burden at E-1, and 26, 43, and 55 times less than the retained AuNP lung burden at PEO-1, PEO-7, and PEO-28, respectively. The retention of AuNP was not affected by the presence of AgNP, but AgNP retention was influenced in the presence of AuNP starting at 24 h after the first day of post day of exposure. The clearance of AgNPs of the separate exposure showed 2 phases; fast (T_1/2 3.1 days) and slow (T_1/2 48.5 days), while the clearance of AuNPs only showed one phase (T_1/2 .81.5 days). For the co-exposure of AuNPs+AgNPs, the clearance of AgNPs also showed 2 phases; fast (T_1/2 2.2 days) and slow (T_1/2 28.4 days), while the clearance of AuNPs consistently showed one phase (T_1/2 54.2 days). The percentage of Ag lung burden in the fast and slow clearing lung compartment was different between separate and combined exposure. For the combined exposure, the slow and fast compartments were each 50% of the lung burden. For the single exposure, 1/3 of the lung burden was cleared by the fast rate and 2/3 of the lung burden by the slow rate.

Conclusions

The clearance of AgNPs follows a two- phase model of fast and slow dissolution rates while the clearance of AuNPs could be described by a one- phase model with a longer half-time. The co-exposure of AuNPs+AgNPs showed that the clearance of AgNPs was altered by the presence of AuNPs perhaps due to some interaction between AgNP and AuNP affecting dissolution and/or mechanical clearance of AgNP in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00397-z.

Uptake of Cerium Dioxide Nanoparticles and Impact on Viability, Differentiation and Functions of Primary Trophoblast Cells from Human Placenta

The human placenta is at the interface between maternal and fetal circulations, and is crucial for fetal development. The nanoparticles of cerium dioxide (CeO₂ NPs) from air pollution are an unevaluated risk during pregnancy. Assessing the consequences of placenta exposure to CeO₂ NPs could contribute to a better understanding of NPs’ effect on the development and functions of the placenta and pregnancy outcome. We used primary villous cytotrophoblasts purified from term human placenta, with a wide range of CeO₂ NPs concentrations (0.1–101 μg/cm²) and exposure time (24–72 h), to assess trophoblast uptake, toxicity and impact on trophoblast differentiation and endocrine function. We have shown the capacity of both cytotrophoblasts and syncytiotrophoblasts to internalize CeO₂ NPs. CeO₂ NPs affected trophoblast metabolic activity in a dose and time dependency, induced caspase activation and a LDH release in the absence of oxidative stress. CeO₂ NPs decreased the fusion capacity of cytotrophoblasts to form a syncytiotrophoblast and disturbed secretion of the pregnancy hormones hCG, hPL, PlGF, P4 and E2, in accordance with NPs concentration. This is the first study on the impact of CeO₂ NPs using human primary trophoblasts that decrypts their toxicity and impact on placental formation and functions.

Quantitative biokinetics over a 28 day period of freshly generated, pristine, 20 nm silver nanoparticle aerosols in healthy adult rats after a single 1½-hour inhalation exposure

Background

There is a steadily increasing quantity of silver nanoparticles (AgNP) produced for numerous industrial, medicinal and private purposes, leading to an increased risk of inhalation exposure for both professionals and consumers. Particle inhalation can result in inflammatory and allergic responses, and there are concerns about other negative health effects from either acute or chronic low-dose exposure.

Results

To study the fate of inhaled AgNP, healthy adult rats were exposed to 1½-hour intra-tracheal inhalations of pristine ¹⁰⁵Ag-radiolabeled, 20 nm AgNP aerosols (with mean doses across all rats of each exposure group of deposited NP-mass and NP-number being 13.5 ± 3.6 μg, 7.9 ± 3.2•10¹¹, respectively). At five time-points (0.75 h, 4 h, 24 h, 7d, 28d) post-exposure (p.e.), a complete balance of the [¹⁰⁵Ag]AgNP fate and its degradation products were quantified in organs, tissues, carcass, lavage and body fluids, including excretions.

Rapid dissolution of [¹⁰⁵Ag]Ag-ions from the [¹⁰⁵Ag]AgNP surface was apparent together with both fast particulate airway clearance and long-term particulate clearance from the alveolar region to the larynx. The results are compatible with evidence from the literature that the released [¹⁰⁵Ag]Ag-ions precipitate rapidly to low-solubility [¹⁰⁵Ag]Ag-salts in the ion-rich epithelial lining lung fluid (ELF) and blood. Based on the existing literature, the degradation products rapidly translocate across the air-blood-barrier (ABB) into the blood and are eliminated via the liver and gall-bladder into the small intestine for fecal excretion. The pathway of [¹⁰⁵Ag]Ag-salt precipitates was compatible with auxiliary biokinetics studies at 24 h and 7 days after either intravenous injection or intratracheal or oral instillation of [^110mAg]AgNO₃ solutions in sentinel groups of rats. However, dissolution of [¹⁰⁵Ag]Ag-ions appeared not to be complete after a few hours or days but continued over two weeks p.e. This was due to the additional formation of salt layers on the [¹⁰⁵Ag]AgNP surface that mediate and prolonge the dissolution process. The concurrent clearance of persistent cores of [¹⁰⁵Ag]AgNP and [¹⁰⁵Ag]Ag-salt precipitates results in the elimination of a fraction > 0.8 (per ILD) after one week, each particulate Ag-species accounting for about half of this. After 28 days p.e. the cleared fraction rises marginally to 0.94 while 2/3 of the remaining [¹⁰⁵Ag]AgNP are retained in the lungs and 1/3 in secondary organs and tissues with an unknown partition of the Ag species involved. However, making use of our previous biokinetics studies of poorly soluble [¹⁹⁵Au]AuNP of the same size and under identical experimental and exposure conditions (Kreyling et al., ACS Nano 2018), the kinetics of the ABB-translocation of [¹⁰⁵Ag]Ag-salt precipitates was estimated to reach a fractional maximum of 0.12 at day 3 p.e. and became undetectable 16 days p.e. Hence, persistent cores of [¹⁰⁵Ag]AgNP were cleared throughout the study period. Urinary [¹⁰⁵Ag]Ag excretion is minimal, finally accumulating to 0.016.

Conclusion

The biokinetics of inhaled [¹⁰⁵Ag]AgNP is relatively complex since the dissolving [¹⁰⁵Ag]Ag-ions (a) form salt layers on the [¹⁰⁵Ag]AgNP surface which retard dissolution and (b) the [¹⁰⁵Ag]Ag-ions released from the [¹⁰⁵Ag]AgNP surface form poorly-soluble precipitates of [¹⁰⁵Ag]Ag-salts in ELF. Therefore, hardly any [¹⁰⁵Ag]Ag-ion clearance occurs from the lungs but instead [¹⁰⁵Ag]AgNP and nano-sized precipitated [¹⁰⁵Ag]Ag-salt are cleared via the larynx into GIT and, in addition, via blood, liver, gall bladder into GIT with one common excretional pathway via feces out of the body.

Advanced In Vitro Testing Strategies and Models of the Intestine for Nanosafety Research

There is growing concern about the potential adverse effects of oral exposure to engineered nanomaterials (ENM). Recent years have witnessed major developments in and advancement of intestinal in vitro models for nanosafety evaluation. The present paper reviews the key factors that should be considered for inclusion in nonanimal alternative testing approaches to reliably reflect the in vivo dynamics of the physicochemical properties of ENM as well the intestinal physiology and morphology. Currently available models range from simple cell line-based monocultures to advanced 3D systems and organoids. In addition, in vitro approaches exist to replicate the mucous barrier, digestive processes, luminal flow, peristalsis, and interactions of ENM with the intestinal microbiota. However, while the inclusion of a multitude of individual factors/components of particle (pre)treatment, exposure approach, and cell model approximates in vivo-like conditions, such increasing complexity inevitably affects the system's robustness and reproducibility. The selection of the individual modules to build the in vitro testing strategy should be driven and justified by the specific purpose of the study and, not least, the intended or actual application of the investigated ENM. Studies that address health hazards of ingested ENM likely require different approaches than research efforts to unravel the fundamental interactions or toxicity mechanisms of ENM in the intestine. Advanced reliable and robust in vitro models of the intestine, especially when combined in an integrated testing approach, offer great potential to further improve the field of nanosafety research.