Comparing inhaled ultrafine versus fine zinc oxide particles in healthy adults: a human inhalation study

Evaluation of the effects of zinc oxide (ZnO NPs) nanoparticles synthesized by green synthesis on Caenorhabditis elegans

In recent years, the rapid development of nanotechnology has caused the products obtained with this technology to be used more daily. Information on the effects of these products, which provide great advantages in every respect, on human health and the environment is insufficient. It has been suggested that these nanoparticles may have toxic effects on living things, mostly in animal experiments and cell cultures. In this paper, the organism Caenorhabditis elegans (C. elegans), which contains a genome and biochemical ways highly similar to humans, is used to understand and reveal the metabolism of Zinc oxide nanoparticles (ZnO NPs) toxicological effects. The toxicological effects of ZnO NPs on C. elegans organisms were investigated and the results were evaluated in terms of environment and human health. C. elegans was exposed to commercial ZnO NPs and green synthesized ZnO NPs from Olea europaea (olive tree, OLE). LC50 values were determined by probit analysis (green synthesized ZnO NP LC5024h = 84.97 mg/L, LC5072h = 33.27 mg/L, commercial ZnO NPs LC5024h = 5.75 mg/L, LC5072h = 1.91 mg/L). When the survival times of C. elegans were evaluated by the Kaplan-Meier method, it was seen that commercial ZnO NPs were more toxic than green synthesized ZnO NPs. In MTT tests, it was clearly seen that commercial ZnO NPs and green synthesized ZnO NPs entered the cell and caused different cytotoxicity. While there was a difference between control and 0.5, 2.5, 5, 10, 25, and 50 mg/L doses in commercial ZnO NP applications, there were significant differences between control and 25, 50 mg/L concentrations in green synthesized ZnO NP applications.

Zinc oxide nanoparticles-induced testis damage at single-cell resolution: Depletion of spermatogonia reservoir and disorder of Sertoli cell homeostasis

The widespread application of zinc oxide nanoparticles (ZnO NPs) in our daily life has initiated an enhanced awareness of their biosafety concern. An incredible boom of evidence of organismal disorder has accumulated for ZnO NPs, yet there has been no relevant study at the single-cell level. Here, we profiled > 28,000 single-cell transcriptomes and assayed > 25,000 genes in testicular tissues from two healthy Sprague Dawley (SD) rats and two SD rats orally exposed to ZnO NPs. We identified 10 cell types in the rat testis. ZnO NPs had more deleterious effects on spermatogonia, Sertoli cells, and macrophages than on the other cell types. Cell-cell communication analysis indicated a sharp decrease of interaction intensity for all cell types except macrophages in the ZnO NPs group than in the control group. Interestingly, two distinct maturation states of spermatogonia were detected during pseudotime analysis, and ZnO NPs induced reservoir exhaustion of undifferentiated spermatogonia. Mechanically, ZnO NPs triggered fatty acid accumulation in GC-1 cells through protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling and peroxisome proliferator-activated receptor alpha (PPARα)/acyl-CoA oxidase 1 (Acox1) axis, contributing to cell apoptosis. In terms of Sertoli cells, downregulated genes were highly enriched for tight junction. In vitro and in vivo experiments verified that ZnO NPs disrupted blood-testis barrier formation and growth factors synthesis, which subsequently inhibited the proliferation and induced the apoptosis of spermatogonia. As for the macrophages, ZnO NPs activated oxidative stress of Raw264.7 cells through nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway and promoted cell apoptosis through extracellular signal-regulated kinase (ERK) 1/2 pathway. Collectively, our work reveals the cell type-specific and cellularly heterogenetic mechanism of ZnO NPs-induced testis damage and paves the path for identifying putative biomarkers and therapeutics against this disorder.

The effects of UV filters on health and the environment

Sunscreens are an important means of protection against sunburns, dyspigmentation, photoaging, and photocarcinogenesis. Sunscreens come in a variety of formulations that can protect against ultraviolet B (UVB) radiation, both UVB and ultraviolet A (UVA) radiation (broad-spectrum sunscreens), and UVB, UVA, and visible light (tinted broad-spectrum sunscreens). In the USA, there is currently a paucity of FDA-approved broad-spectrum filters on the market. Studies have identified the presence of multiple UV filters in water sources globally. Many laboratory studies have implicated the potential impact of UV filters on coral reef bleaching, the food chain, and human health. However, many of these studies are performed at concentrations that are much higher than those present in the natural environment. With increasing discussion surrounding the role of organic and inorganic UV filters as potential environmental pollutants over the past decade, approval of additional broad-spectrum filters would be an important means of alleviating the use of more controversial filters. The aim of this article is to review the effects of UV filters on health and the environment and explore potential adjunctive agents for photoprotection.

Systemic inflammatory effects of zinc oxide particles: is a re-evaluation of exposure limits needed?

Exposure to airborne substances such as gases, vapours, and particles remains a relevant health risk in many workplaces. A current topic and cause for discussion is the investigation of the health effects of particles containing zinc oxide (ZnO). Among other data, those collected from our study on human exposure data of ZnO in 2018 prompted the National Research Centre for the Working Environment 2021 to formulate a new, sharply lowered proposed occupational exposure limit (OEL) for zinc in workplaces. Since the publication of the Danish report, further studies have been conducted with ZnO. In the following text, all arguments for deriving this new limit value for zinc from the report are discussed, extended with the more recent data since 2018. It should be noted that especially the application of time extrapolation factors needs further discussion and harmonization between regulatory authorities. From our point of view, the data situation can justify a higher OEL for zinc than that proposed by the Danish National Research Centre for the Working Environment.

Disruption of the lung-gut-brain axis is responsible for cortex damage induced by pulmonary exposure to zinc oxide nanoparticles

Increasing evidence shows that gut microbiota is important for host health in response to metal nanomaterials exposure. However, the effect of gut microbiota on the cortex damage caused by pulmonary exposure to zinc oxide nanoparticles (ZnONPs) remains mainly unknown. In this study, a total of 48 adult C57BL/6J mice were intratracheally instilled with 0.6 mg/kg ZnONPs in the presence or absence of antibiotics (ABX) treatment. Besides, 24 mice were treated with or without fecal microbiota transplantation (FMT) after the intraperitoneal administration of ABX. Our results demonstrated for the first time that dysbiosis induced by ABX treatment significantly aggravated cortex damage induced by pulmonary exposure to ZnONPs. Such damage might highly occur through the induction of oxidative stress, manifested by the enhancement of antioxidative enzymes and products of lipid peroxidation. However, ferroptosis was not involved in this process. Interestingly, our data revealed that ABX treatment exacerbated the alterations of gut-brain peptides (including Sst, Sstr2, and Htr4) induced by ZnONPs in both gut and cortex tissues. Moreover, fecal microbiota transplantation (FMT) was able to alleviate cerebral cortex damage, oxidative stress, and alterations of gut-brain peptides induced by pulmonary exposure to ZnONPs. The results together indicate that pulmonary exposure to ZnONPs causes cerebral cortex damage possibly via the disruption of the lung-gut-brain axis. These findings not only propose valuable insights into the mechanism of ZnONPs neurotoxicity but also provide a potential therapeutic method against brain disorders induced by pulmonary exposure to ZnONPs. AVAILABILITY OF DATA AND MATERIALS: The datasets used and/or analyzed during the current study are available from the The corresponding author on reasonable request.

A proposed synergetic mechanism for metal fume fever involving ZnO and Fe3O4 nanoparticles

Metal fumes fever (MFF) is an inflammatory condition, whose mechanism is yet unclear, associated with the inhalation of metal fumes, particularly zinc. In this study we investigate experimentally the hypothesis of a two-step mechanism of MFF onset: (1) the photocatalytic production of airborne hydrogen peroxide (H₂O₂) via ZnO and (2) the production of hydroxyl radicals (HOׄ) through Fenton reaction via magnetite (Fe₃O₄) nanoparticles. Photocatalysis and Fenton reaction products were measured using a multiscattering-enhanced absorbance device and assessing the degradation of bromophenol blue with microplate photometry, respectively. We observed that in the presence of UV, ZnO produces 3 to 4-times more H₂O₂ than UV alone or that non-UV irradiated ZnO. In the presence of biologically-relevant ligands, we also measured a Fenton reaction at physiological pH with either Fe(II), Fe(III) or Fe₃O₄ nanoparticles. Our results support the hypothesis of a two-step mechanism of MFF onset, in which the prior presence of Fe in the lungs exacerbates the oxidative stress, triggered by the photocatalysis of ZnO, a situation that could occurs when welding galvanized steel. More broadly, this raises the question of the role of the Fenton mechanism in respiratory exposure to metal particles and its possible contribution to other lung diseases.

Unchanged pulmonary toxicity of ZnO nanoparticles formulated in a liquid matrix for glass coating

The inclusion of nanoparticles can increase the quality of certain products. One application is the inclusion of Zinc oxide (ZnO) nanoparticles in a glass coating matrix to produce a UV-absorbing coating for glass sheets. Yet, the question is whether the inclusion of ZnO in the matrix induces toxicity at low exposure levels. To test this, mice were given single intratracheal instillation of 1) ZnO powder (ZnO), 2) ZnO in a glass matrix coating in its liquid phase (ZnO-Matrix), and 3) the matrix with no ZnO (Matrix). Doses of ZnO were 0.23, 0.67, and 2 µg ZnO/mouse. ZnO Matrix doses had equal amounts of ZnO, while Matrix was adjusted to have an equal volume of matrix as ZnO Matrix. Post-exposure periods were 1, 3, or 28 d. Endpoints were pulmonary inflammation as bronchoalveolar lavage (BAL) fluid cellularity, genotoxicity in lung and liver, measured by comet assay, histopathology of lung and liver, and global gene expression in lung using microarrays. Neutrophil numbers were increased to a similar extent with ZnO and ZnO-Matrix at 1 and 3 d. Only weak genotoxicity without dose-response effects was observed in the lung. Lung histology showed an earlier onset of inflammation in material-exposed groups as compared to controls. Microarray analysis showed a stronger response in terms of the number of differentially regulated genes in ZnO-Matrix exposed mice as compared to Matrix only. Activated canonical pathways included inflammatory and cardiovascular ones. In conclusion, the pulmonary toxicity of ZnO was not changed by formulation in a liquid matrix for glass coating.

Zinc associated nanomaterials and their intervention in emerging respiratory viruses: Journey to the field of biomedicine and biomaterials

Respiratory viruses represent a severe public health risk worldwide, and the research contribution to tackle the current pandemic caused by the SARS-CoV-2 is one of the main targets among the scientific community. In this regard, experts from different fields have gathered to confront this catastrophic pandemic. This review illustrates how nanotechnology intervention could be valuable in solving this difficult situation, and the state of the art of Zn-based nanostructures are discussed in detail. For virus detection, learning from the experience of other respiratory viruses such as influenza, the potential use of Zn nanomaterials as suitable sensing platforms to recognize the S1 spike protein in SARS-CoV-2 are shown. Furthermore, a discussion about the antiviral mechanisms reported for ZnO nanostructures is included, which can help develop surface disinfectants and protective coatings. At the same time, the properties of Zn-based materials as supplements for reducing viral activity and the recovery of infected patients are illustrated. Within the scope of noble adjuvants to improve the immune response, the ZnO NPs properties as immunomodulators are explained, and potential prototypes of nanoengineered particles with metallic cations (like Zn2+) are suggested. Therefore, using Zn-associated nanomaterials from detection to disinfection, supplementation, and immunomodulation opens a wide area of opportunities to combat these emerging respiratory viruses. Finally, the attractive properties of these nanomaterials can be extrapolated to new clinical challenges.

Repeated intratracheal instillation of zinc oxide nanoparticles induced pulmonary damage and a systemic inflammatory response in cynomolgus monkeys

Recently, some researchers have demonstrated that inhaled zinc oxide nanoparticles (ZnONPs) induce an acute systemic inflammatory response in workers. Considering nonhuman primates are preferably considered an animal model for translational research due to their proven similarity with humans in terms of genetics and physiology, we intratracheally instilled ZnONPs to cynomolgus monkey for 14 days and identified the toxic mechanism and bioaccumulation. ZnONPs were rapidly ionized or aggregated in a simulated pulmonary fluid, and they attracted neutrophils to the lungs and increased the pulmonary level of inflammatory mediators. Additionally, thickened alveolar walls, fibrin clots, and hemorrhages were observed in the lungs of the monkeys instilled with the higher dose accompanied by cell debris in the alveolar ducts and alveoli. Dark-field microscopy images revealed translocation of ZnONPs into other tissues accompanied by an increase in the relative weight of livers to body weight. In addition, when instilled at the higher dose, the albumin/globulin ratio notably decreased compared to the control, whereas the C-reactive protein (CRP) level was significantly elevated. ZnONPs also clearly induced apoptotic cell death in a 24 h exposure to alveolar macrophages. Taken together, part of inhaled ZnONPs may be ionized in the lung, resulting in acute toxic effects, including cell death and tissue damage, and the rest may move to other tissues in the form of particles, causing a systemic inflammatory response. Based on the proven evidence among workers, we also suggest that the CRP level can be recommended as a biomarker for ZnONPs-induced adverse health effects.

Human Inhalation Study with Zinc Oxide: Analysis of Zinc Levels and Biomarkers in Exhaled Breath Condensate

Workers in the zinc processing, for example, welding or hot-dip galvanizing, are exposed to aerosols consisting of particles and gases, including zinc oxide (ZnO), which can affect human health. In this study, we addressed the effects of short-term controlled exposure to nano-sized ZnO on the airway inflammatory markers in healthy volunteers. To this end, we determined the influence of ZnO inhalation on the content of zinc and biomarkers (leukotriene B₄ (LTB₄), peptide leukotrienes (LTC₄/D₄/E₄), 8-iso-PGF_2α, pH, and prostaglandin E₂ (PGE₂)) in exhaled breath condensate (EBC). Sixteen non-smoking subjects (8 females, 8 men) were exposed to filtered air (sham) or ZnO nanoparticles (0.5, 1.0, and 2.0 mg/m³) for 4 h. EBC samples were collected according to specific study design. We found that the peptide leukotrienes were below the limit of quantification (LOQ) in all the EBC samples. ZnO exposure showed no detectable effect on any other parameters investigated when comparing the two groups. The content of Zn in EBC was unaffected by ZnO inhalation at any concentration used. Therefore, we conclude that the evaluation of Zn and biomarker content in EBC would not be a suitable way to assess the exposure to inhaled ZnO.

Associations between short term exposure to ambient particulate matter from dust storm and anthropogenic sources and inflammatory biomarkers in healthy young adults

This study examined the association between particulate matter from anthropogenic and natural sources and inflammatory biomarkers, including hs-CRP, IL-6, sTNF-RII, and WBCs, in two groups of healthy young subjects. We followed up subjects of two panels (16 to 22 years old), including 22 subjects selected from the urban area (Tehran city) with high-level pollution background and 22 subjects selected from the rural area (Ahmadabad) with low-level pollution background. In each group, we collected 4 times blood samples in various air pollution conditions, In the subjects of the urban group, there was a substantial difference (p < 0.05) between inversion days and cold season control days, and between dust storm days and warm season control days for concentrations of hs-CRP, IL-6, and WBCs biomarkers. In the subjects of the rural group, a significant difference could be detected in the concentration of hs-CRP, IL-6, and WBCs biomarkers (p < 0.05) between inversion days and cold season control days, and between dust storm and warm control days. We found that the difference in concentrations of hs-CRP, IL-6, and WBCs biomarkers between dust storm days and warm control conditions in the rural group were higher than the difference in inversion and cold control conditions, which can be attributed to low background air pollution in the rural area. In the urban area, the health effect of anthropogenic sources of PM is higher than the dust storm condition, which can be attributed to the stronger effect of anthropogenic pollution effect.

The Effects of Exposure Time on Systemic Inflammation in Subjects With Exposure to Zinc- and Copper-Containing Brazing Fumes

INTRODUCTION

Inhalation of copper and zinc containing brazing fumes (2.5 mg/m for 6 hours) is able to induce asymptomatic systemic inflammation which is supposed to be connected with an increased risk for cardiovascular disease. In this study it was investigated if inflammation can be prevented by reducing the exposure time.

METHODS

A total of 15 healthy male subjects were exposed to such brazing fumes in a crossover design for 3, 4, and 5 hours in randomized order. Before and 24 hours after exposure, blood samples were taken and c-reactive protein (CRP) as marker for an acute phase reaction was measured.

RESULTS

Five-hour exposure induced an increase of CRP, whereas the shorter exposure times did not result in a significant inflammatory reaction.

CONCLUSIONS

Reducing daily exposure times below 5 hours is able to prevent systemic inflammatory reactions.

Health effects after inhalation of micro- and nano-sized zinc oxide particles in human volunteers

Inhalation of ZnO particles can cause inflammation of the airways and metal fume fever. It is unclear if different sizes of the particles alter these effects. However, various studies report higher biological activity of other nano-sized particles compared to microparticles. No effects at all were observed after inhalation of micro- and nano-sized zinc oxide (ZnO) particle concentrations of 0.5 mg/m³. Studies with different particle sizes of ZnO at higher exposures are not available. Accordingly, we hypothesized that inhalation of nano-sized ZnO particles induces stronger health effects than the inhalation of the same airborne mass concentration of micro-sized ZnO particles. 16 healthy volunteers (eight men, eight women) were exposed to filtered air and ZnO particles (2.0 mg/m³) for 2 h (one session with nano- and one with micro-sized ZnO) including 1 h of cycling at moderate workload. Effect parameters were symptoms, body temperature, inflammatory markers in blood and in induced sputum. Induced sputum was obtained at baseline examination, 22 h after exposure and at the end of the final test. The effects were assessed before, immediately after, about 22 h after, as well as two and three days after each exposure. Neutrophils, monocytes and acute-phase proteins in blood increased 22 h after micro- and nano-sized ZnO exposure. Effects were generally stronger with micro-sized ZnO particles. Parameters in induced sputum showed partial increases on the next day, but the effect strengths were not clearly attributable to particle sizes. The hypothesis that nano-sized ZnO particles induce stronger health effects than micro-sized ZnO particles was not supported by our data. The stronger systemic inflammatory responses after inhalation of micro-sized ZnO particles can be explained by the higher deposition efficiency of micro-sized ZnO particles in the respiratory tract and a substance-specific mode of action, most likely caused by the formation of zinc ions.

No Observed Effect Level (NOEL) for Systemic Inflammation by Copper and Zinc in Welding Fumes

: Copper and zinc containing welding fumes are able to induce systemic inflammation in healthy subjects. In this study the no observed effect levels (NOEL) for welding fumes containing either copper or zinc were assessed.Fifteen healthy male volunteers participated in an exposure. Each subject was exposed to two different concentrations of both, copper and zinc containing welding fumes. Exposure was performed in the Aachen Workplace Simulation Lab.The NOEL was found at metal concentrations between 0.2 and 0.3 mg/m for copper and between 0.8 and 1.2 mg/m for zinc.The NOEL identified in this study was about a factor of 10 higher than the German workplace threshold limit values (TLV). However, TLV in other countries was in the same range or even higher than the NOEL indicating a considerable risk for workers.

Nanotoxicology: The Need for a Human Touch?

With the ever-expanding number of manufactured nanomaterials (MNMs) under development there is a vital need for nanotoxicology studies that test the potential for MNMs to cause harm to health. An extensive body of work in cell cultures and animal models is vital to understanding the physicochemical characteristics of MNMs and the biological mechanisms that underlie any detrimental actions to cells and organs. In human subjects, exposure monitoring is combined with measurement of selected health parameters in small panel studies, especially in occupational settings. However, the availability of further in vivo human data would greatly assist the risk assessment of MNMs. Here, the potential for controlled inhalation exposures of MNMs in human subjects is discussed. Controlled exposures to carbon, gold, aluminum, and zinc nanoparticles in humans have already set a precedence to demonstrate the feasibility of this approach. These studies have provided considerable insight into the potential (or not) of nanoparticles to induce inflammation, alter lung function, affect the vasculature, reach the systemic circulation, and accumulate in other organs. The need for further controlled exposures of MNMs in human volunteers - to establish no-effect limits, biological mechanisms, and provide vital data for the risk assessment of MNMs - is advocated.

Heart rate variability and cardiac repolarization after exposure to zinc oxide nanoparticles in healthy adults

Background

Exposure to airborne zinc oxide (ZnO) particles occurs in many industrial processes, especially in galvanizing and welding. Systemic inflammation after experimental inhalation of ZnO particles has been demonstrated previously, but little is known about the impact on the cardiovascular system, particularly on the autonomic cardiac system and the risk of arrhythmias. In this study we investigated the short-term effects of ZnO nanoparticles on heart rate variability (HRV) and repolarization in healthy adults in a concentration-dependent manner at rest and during exercise in a controlled experimental set-up.

Methods

Sixteen healthy subjects were exposed to filtered air and ZnO particles (0.5, 1.0 and 2.0 mg/m³) for 4 h, including 2 h of cycling at low workloads. Parameters were assessed before, during, immediately after, and about 24 h after each exposure. For each subject, a total number of 46 10-min-sections from electrocardiographic records were analyzed. Various parameters of HRV and QT interval were measured.

Results

Overall, no statistically significant effects of controlled ZnO inhalation on HRV parameters and QT interval were observed. Additionally, a concentration-response was absent.

Conclusion

Inhalation of ZnO nanoparticles up to 2.0 mg/m³ for 4 h does not affect HRV and cardiac repolarization in healthy adults at the chosen time points. This study supports the view that cardiac endpoints are insensitive for the assessment of adverse effects after short-term inhalation of ZnO nanoparticles.

Inhalation of Ultrafine Zinc Particles Impaired Cardiovascular Functions in Hypertension-Induced Heart Failure Rats With Preserved Ejection Fraction

Although it is possible for inhalation of ultrafine particles to impair human health, its effect is not clear in patients with HFpEF. This study investigated cardiac and hemodynamic changes in hypertension-induced rats of HFpEF after inhaling ultrafine zinc particles for a while. Multiple experimental measurements were carried out in DSS rats fed with high salt (HS) and low salt (LS) diets as well as HS diet with the inhalation of ultrafine zinc particles (defined as HP). Cardiac strain and strain rate were quantified by the speckle tracking echocardiography. The pressure and flow waves were recorded in the carotid artery and abdominal aorta and analyzed by the models of Windkessel and Womersley types. HS and HP rats were found to show lower strains on endocardium and epicardium than LS rats. The inhalation of ultrafine zinc particles further reduced the strain in the longitudinal direction on the endocardium of rats with HFpEF, but had relatively small effects on the epicardium. The inhalation of ultrafine zinc particles resulted in the increase of systemic resistance and the decrease of total vascular compliance as well as the increased PWV and induced more severe vascular stiffening in rats with HFpEF. In summary, the inhalation of ultrafine zinc particles deteriorated local myocardial dysfunctions in the LV and the hemodynamic environment in peripheral arteries in rats of HFpEF. This study is of importance to understand the mechanisms of cardiovascular impairments owing to air pollution.

Analysis of the Exposure of Organisms to the Action of Nanomaterials

The rapid development of the production of materials containing metal nanoparticles and metal oxides is a potential risk to the environment. The degree of exposure of organisms to nanoparticles increases from year to year, and its effects are not fully known. This is due to the fact that the range of nanoparticle interactions on cells, tissues and the environment requires careful analysis. It is necessary to develop methods for testing the properties of nanomaterials and the mechanisms of their impact on individual cells as well as on entire organisms. The particular need to raise public awareness of the main sources of exposure to nanoparticles should also be highlighted. This paper presents the main sources and possible routes of exposure to metal nanoparticles and metal oxides. Key elements of research on the impact of nanoparticles on organisms, that is, in vitro tests, in vivo tests and methods of detection of nanoparticles in organisms, are presented.

Airway inflammation after inhalation of nano-sized zinc oxide particles in human volunteers

Background

Workers in the zinc production and processing of galvanized sheet steel are exposed to a complex mixture of particles and gases, including zinc oxide (ZnO) that can affect human health. We aimed to study the effects of short-term controlled exposure to nano-sized ZnO on airway inflammatory markers in healthy volunteers.

Methods

Sixteen subjects (8 females, 8 men; age 19–42, non-smokers) were exposed to filtered air and ZnO nanoparticles (0.5, 1.0 and 2.0 mg/m³) for 4 h, including 2 h of cycling with a low workload. Induced sputum samples were collected during a medical baseline and a final examination and also about 24 h after each exposure. A number of inflammatory cellular and soluble markers were analyzed.

Results

Frequency and intensity of symptoms of airway irritation (throat irritation and cough) were increased in some subjects 24 h after ZnO exposures when compared to filtered air. The group comparison between filtered air and ZnO exposures showed statistically significant increases of neutrophils and interleukin-8 (IL-8), interleukin-6 (IL-6), matrix metalloproteinase (MMP-9) and tissue inhibitors of metalloproteinases (TIMP-1) in sputum starting at the lowest ZnO concentration of 0.5 mg/m³. However, a concentration-response relationship was absent. Effects were reversible. Strong correlations were found between neutrophil numbers and concentrations of total protein, IL-8, MMP-9, and TIMP-1.

Conclusions

Controlled exposures of healthy subjects to ZnO nanoparticles induce reversible airway inflammation which was observed at a concentration of 0.5 mg/m³ and higher. The lack of a concentration-response relationship warrants further studies.

The role of sex in particle-induced inflammation and injury

The use of engineered nanomaterials within various applications such as medicine, electronics, and cosmetics has been steadily increasing; therefore, the rate of occupational and environmental exposures has also increased. Inhalation is an important route of exposure to nanomaterials and has been shown to cause various respiratory diseases in animal models. Human lung disease frequently presents with a sex/gender-bias in prevalence or severity, but investigation of potential sex-differences in the adverse health outcomes associated with nanoparticle inhalation is greatly lacking. Only ~20% of basic research in the general sciences use both male and female animals and a substantial percentage of these do not address differences between sexes within their analyses. This has prevented researchers from fully understanding the impact of sex-based variables on health and disease, particularly the pathologies resulting from the inhalation of particles. The mechanisms responsible for sex-differences in respiratory disease remain unclear, but could be related to a number of variables including sex-differences in hormone signaling, lung physiology, or respiratory immune function. By incorporating sex-based analysis into respiratory nanotoxicology and utilizing human data from other relevant particles (e.g., asbestos, silica, particulate matter), we can improve our understanding of sex as a biological variable in nanoparticle exposures. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Application of ZnO-Based Nanocomposites for Vaccines and Cancer Immunotherapy

Engineering and application of nanomaterials have recently helped advance various biomedical fields. Zinc oxide (ZnO)-based nanocomposites have become one of the most promising candidates for biomedical applications due to their biocompatibility, unique physicochemical properties, and cost-effective mass production. In addition, recent advances in nano-engineering technologies enable the generation of ZnO nanocomposites with unique three-dimensional structures and surface characteristics that are optimally designed for in vivo applications. Here, we review recent advances in the application of diverse ZnO nanocomposites, with an especial focus on their development as vaccine adjuvant and cancer immunotherapeutics, as well as their intrinsic properties interacting with the immune system and potential toxic effect in vivo. Finally, we summarize promising proof-of-concept applications as prophylactic and therapeutic vaccines against infections and cancers. Understanding the nano-bio interfaces between ZnO-based nanocomposites and the immune system, together with bio-effective design of the nanomaterial using nano-architectonic technology, may open new avenues in expanding the biomedical application of ZnO nanocomposites as a novel vaccine platform.

Autophagy-dependent release of zinc ions is critical for acute lung injury triggered by zinc oxide nanoparticles

Pulmonary exposure to zinc oxide nanoparticles (ZnONPs) could cause acute lung injury (ALI), but the underlying molecular mechanism remains unclear. Herein, we established a ZnONPs-induced ALI mouse model, characterized by the histopathological changes (edema and infiltration of inflammatory cells in lung tissues), and the elevation of total protein and cytokine interleukin-6 in bronchoalveolar lavage fluid in time- and dose-dependent manners. This model also exhibited features like the disturbance of redox-state (reduced of glutathione to glutathione disulfide ratio, elevation of heme oxygenase-1 and superoxide dismutase 2), the decrease of adenosine triphosphate synthesis and the release of zinc ions in the lung tissues. Interestingly, we found that ZnONPs exposure caused the accumulation of autophagic vacuoles and the elevation of microtubule-associated proteins 1A/1B light chain (LC)3B-II and p62, indicating the impairment of autophagic flux. Our data indicated that the above process might be regulated by the activation of AMP-activated protein kinase but not the mammalian target of rapamycin pathway. The association between ZnONPs-induced ALI and autophagy was further verified by a classical autophagy inhibitor, 3-methyladenine (3-MA). 3-MA administration reduced the accumulation of autophagic vacuoles, the expression of LC3B-II and p62, followed by a significant attenuation of histopathological changes, inflammation, and oxidative stress. More importantly, 3-MA could directly decrease the release of zinc ions in lung tissues. Taken together, our study provides the evidence that ZnONPs-induced pulmonary toxicity is autophagy-dependent, suggests that limiting the release of zinc ions by inhibiting autophagy could be a feasible strategy for the prevention of ZnONPs-associated pulmonary toxicity.

Concentration-dependent systemic response after inhalation of nano-sized zinc oxide particles in human volunteers

Background

Inhalation of high concentrations of zinc oxide particles (ZnO) may cause metal fume fever. In an earlier human inhalation study, no effects were observed after exposure to ZnO concentrations of 0.5 mg/m³. Further data from experimental studies with pure ZnO in the concentration range between 0.5 and 2.5 mg/m³ are not available. It was the aim of this experimental study to establish the concentration-response relationship of pure nano-sized ZnO particles.

Methods

Sixteen healthy subjects were exposed to filtered air and ZnO particles (0.5, 1.0 and 2.0 mg/m³) for 4 h on 4 different days, including 2 h of cycling with a low workload. The effects were assessed before, immediately after, and about 24 h after each exposure. Effect parameters were symptoms, body temperature, inflammatory markers and clotting factors in blood, and lung function.

Results

Concentration-dependent increases in symptoms, body temperature, acute phase proteins and neutrophils in blood were detected after ZnO inhalation. Significant effects were detected with ZnO concentrations of 1.0 mg/m³ or higher, with the most sensitive parameters being inflammatory markers in blood.

Conclusion

A concentration-response relationship with nano-sized ZnO particles in a low concentration range was demonstrated. Systemic inflammatory effects of inhaled nano-sized ZnO particles were observed at concentrations well below the occpational exposure limit for ZnO in many countries. It is recommended to reassess the exposure limit for ZnO at workplaces.

Occupational exposure to ultrafine particles in police officers: no evidence for adverse respiratory effects

Background

Inhalation exposure to fine and ultrafine particles (UFPs) has been associated with respiratory diseases. However, little is known on the quality, threshold levels and concentration of these particles causing adverse health effects.

Methods

The impact of occupational exposure to submicrometer and UFPs was assessed in 30 healthy police shooting instructors by clinical investigation, self-assessment questionnaire, sputum and spirometry and compared to a control group. General laboratory chemistry parameters, circulating cytokines (interleukin [IL]-2, IL-4, IL-5, IL-6, IL-8, interferon-gamma [IFN-γ]), and granulocyte macrophage colony-stimulating factor (GM-CSF) in serum were measured. UFP exposure was recorded by Scanning Mobility Particle Sizer.

Results

Concentrations of submicrometer sized airborne particles (< 700 nm) measured between 3.34 × 10⁵/cm³ and 7.58 × 10⁵/cm³ at shooting sites, with highest concentrations found in the UFP range (< 100 nm). The size of the monodispersed particles ranged from 54.74 ± 16.25 nm to 98.19 ± 22.83 nm. Short term exposure (4 h) to high levels of UFPs caused an increase of IFN-γ in exposed subjects (p = 0.022). 24 h after exposure a significant decrease of IgG, albumin fibrinogen and factor VII was found. Neither directly after 4 h of high levels UFPs exposure nor 24 h after exposure subjective complaints or objective measurements indicating adverse respiratory effects in exposed subjects were found.

Conclusions

No consistent indications for adverse respiratory or inflammatory effects directly following exposure and 24 h after exposure to high levels of UFPs in our study group were detected. However we showed the assessment of short-term exposure effects at a genuine occupational setting, which might is relevant when a risk assessment of high level occupational exposures to UFPs is considered.

Evaluation of Long-Term Toxicity of Oral Zinc Oxide Nanoparticles and Zinc Sulfate in Mice

The toxicological effects of zinc oxide nanoparticles (nano-ZnOs) are related to their dissolution and interference with zinc ion homeostasis. High-soluble zinc sources may produce more severe and acute toxicity; however, the evaluation of potential toxicity of long-term exposure to nano-ZnOs and high-soluble sources of zinc remains obscure. This study aimed at evaluating effects of nano-ZnOs and zinc sulfate on development, serum and hematological parameters, and mineral concentrations in selected tissues and intestinal microbiota in mice via gastrointestinal administration for 7 weeks. Results indicated that 250 mg/kg nano-ZnOs reduced the body weight from weeks 8 to 11, increased serum glutamic-pyruvic transaminase activity, and increased the zinc concentrations of the serum, liver, and kidney while did not affect the relative organ weight, intestinal microbiota, and other mineral concentrations (Fe, Cu, and Mn) in the kidney, liver, and thigh muscle. Oral administration with 250 mg/kg zinc sulfate seemed to show more severe and acute toxicity since mice in zinc sulfate group exhibited reduced body weight from weeks 5 to 11, decreased relative pancreas weight, and increased serum glutamic-oxalacetic transaminase activity and intestinal enteric group.

Inhalation exposure during spray application and subsequent sanding of a wood sealant containing zinc oxide nanoparticles

Nano-enabled construction products have entered into commerce. There are concerns about the safety of manufactured nanomaterials, and exposure assessments are needed for a more complete understanding of risk. This study assessed potential inhalation exposure to ZnO nanoparticles during spray application and power sanding of a commercially available wood sealant and evaluated the effectiveness of local exhaust ventilation in reducing exposure. A tradesperson performed the spraying and sanding inside an environmentally-controlled chamber. Dust control methods during sanding were compared. Filter-based sampling, electron microscopy, and real-time particle counters provided measures of exposure. Airborne nanoparticles above background levels were detected by particle counters for all exposure scenarios. Nanoparticle number concentrations and particle size distributions were similar for sanding of treated versus untreated wood. Very few unbound nanoparticles were detected in aerosol samples via electron microscopy, rather nano-sized ZnO was contained within, or on the surface of larger airborne particles. Whether the presence of nanoscale ZnO in these aerosols affects toxicity merits further investigation. Mass-based exposure measurements were below the NIOSH Recommended Exposure Limit for Zn, although there are no established exposure limits for nanoscale ZnO. Local exhaust ventilation was effective, reducing airborne nanoparticle number concentrations by up to 92% and reducing personal exposure to total dust by at least 80% in terms of mass. Given the discrepancies between the particle count data and electron microscopy observations, the chemical identity of the airborne nanoparticles detected by the particle counters remains uncertain. Prior studies attributed the main source of nanoparticle emissions during sanding to copper nanoparticles generated from electric sander motors. Potentially contrary results are presented suggesting the sander motor may not have been the primary source of nanoparticle emissions in this study. Further research is needed to understand potential risks faced by construction workers exposed to mixed aerosols containing manufactured nanomaterials. Until these risks are better understood, this study demonstrates that engineering controls can reduce exposure to manufactured nanomaterials; doing so may be prudent for protecting worker health.

Effect of orally administered zinc oxide nanoparticles on albino rat thymus and spleen

This study aimed to evaluate the toxicological effects of oral intake of Zinc oxide nanoparticles (ZnO NPs) on the structure of thymus and spleen. Twenty-four young male Wistar albino rats were assigned into two groups: group I (control) and group II (ZnO NPs treated group).The thymus and spleen were analyzed biochemically, histopathologically and immunohistochemically. After ZnO NPs intake, hematologically, the total leucocytic count was significantly increased while the RBCs and platelets counts and Hb % were significantly decreased. Biochemically, a significant decrease in serum total antioxidant capacity and anti-inflammatory cytokines including interleukin 4 and 10 (IL-4 and IL-10) levels was noted. While a significant increase in splenic and thymic malondialdehyde (MDA) and DNA shearing, as well as the studied proinflammatory cytokines; IL-1β, tumor necrotic factor (TNF-α) and interferon (INF-γ) levels was detected. Notably, we noted upregulation of the immunomodulatory [CD3, CD11b, heme oxygenase (HO-1)] and the inflammatory [toll-like receptor 4 and 6 (TLR4 and TLR6)] genes. Histopathologically, degenerative changes were detected in thymus and spleen of ZnO NPs treated group. While the immunohistochemical analysis of the ZnO NPs treated group revealed a decrease in the number of cells expressed positive reactions of anti-PCNA and an increase in the number of cells expressed positive reaction of anti-p53 in the thymus and spleen. In conclusion, ZnO NPs induced obvious immunotoxicity in the thymus and spleen, where oxidative/inflammatory pathway may be the potential mechanism underlying this immunotoxicity. © 2017 IUBMB Life, 69(7):528-539, 2017.

Neurotoxic effect of active ingredients in sunscreen products, a contemporary review

Sunscreen application is the main strategy used to prevent the maladies inflicted by ultraviolet (UV) radiation. Despite the continuously increasing frequency of sunscreen use worldwide, the prevalence of certain sun exposure-related pathologies, mainly malignant melanoma, is also on the rise. In the past century, a variety of protective agents against UV exposure have been developed. Physical filters scatter and reflect UV rays and chemical filters absorb those rays. Alongside the evidence for increasing levels of these agents in the environment, which leads to indirect exposure of wildlife and humans, recent studies suggest a toxicological nature for some of these agents. Reviews on the role of these agents in developmental and endocrine impairments (both pathology and related mechanisms) are based on both animal and human studies, yet information regarding the potential neurotoxicity of these agents is scant. In this review, data regarding the neurotoxicity of several organic filters: octyl methoxycinnamate, benzophenone-3 and −4, 4-methylbenzylidene camphor, 3-benzylidene camphor and octocrylene, and two allowed inorganic filters: zinc oxide and titanium dioxide, is presented and discussed. Taken together, this review advocates revisiting the current safety and regulation of specific sunscreens and investing in alternative UV protection technologies.

Deep vein thrombosis related to environment (Review)

The first-time venous thromboembolism (VTE) is less frequent than other thrombotic events, however, both the pulmonary embolism (PE) and the deep vein thrombosis (DVT) show a frequent morbidity. Many factors play as risk situations in determining VTE, and the air exposure to the fine and ultrafine particulate matter (PM) as PM10, PM2.5, PM0.1 is considered. Epidemiological studies have supported this association although both the effective burden of the association and the mechanisms are to date unclear. The PM concentrations and the exposure time are notable as emerging factors. Interestingly, the seasonal climate variations resulted as effective risk factor for appearance of VTE or DVT. There is a need to ameliorate the environment by reducing the air pollution at global scale.

Zinc oxide nanoparticles exhibit cytotoxicity and genotoxicity through oxidative stress responses in human lung fibroblasts and Drosophila melanogaster

Background

Although zinc oxide nanoparticles (ZnO NPs) have been widely used, there has been an increasing number of reports on the toxicity of ZnO NPs. However, study on the underlying mechanisms under in vivo conditions is insufficient.

Methods

In this study, we investigated the toxicological profiles of ZnO NPs in MRC5 human lung fibroblasts in vitro and in an in vivo model using the fruit fly Drosophila melanogaster. A comprehensive study was conducted to evaluate the uptake, cytotoxicity, reactive oxygen species (ROS) formation, gene expression profiling and genotoxicity induced by ZnO NPs.

Results

For in vitro toxicity, the results showed that there was a significant release of extracellular lactate dehydrogenase and decreased cell viability in ZnO NP-treated MRC5 lung cells, indicating cellular damage and cytotoxicity. Generation of ROS was observed to be related to significant expression of DNA Damage Inducible Transcript (DDIT3) and endoplasmic reticulum (ER) to nucleus signaling 1 (ERN1) genes, which are ER stress-related genes. Oxidative stress induced DNA damage was further verified by a significant release of DNA oxidation product, 8-hydroxydeoxyguanosine (8-OHdG), as well as by the Comet assay. For the in vivo study using the fruit fly D. melanogaster as a model, significant toxicity was observed in F1 progenies upon ingestion of ZnO NPs. ZnO NPs induced significant decrease in the egg-to-adult viability of the flies. We further showed that the decreased viability is closely associated with ROS induction by ZnO NPs. Removal of one copy of the D. melanogaster Nrf2 alleles further decreased the ZnO NPs-induced lethality due to increased production of ROS, indicating that nuclear factor E2-related factor 2 (Nrf2) plays important role in ZnO NPs-mediated ROS production.

Conclusion

The present study suggests that ZnO NPs induced significant oxidative stress-related cytotoxicity and genotoxicity in human lung fibroblasts in vitro and in D. melanogaster in vivo. More extensive studies would be needed to verify the safety issues related to increased usage of ZnO NPs by consumers.

Toxic Effects of Engineered Nanoparticles on Living Cells

Measuring toxic effects of engineered nanoparticles on living cells would require a deep understanding of themselves by the mean of their composition, physical and chemical properties and exposure concentrations. Actually, high exposure concentrations are needed to generate quantifiable effects and to perceive accumulation above background. This chapter presents an overview on the assessment about the toxic effects of engineered nanoparticles on living cells. It consists of three main sections starting with a brief introduction, the current state of engineered nanoparticles in the environment, physical and chemical properties of some important engineered nanoparticles such as “Ag, Au, ZnO, TiO2” and the target organ toxicity of the engineered nanoparticles in several biological organisms.

Nanometer-sized emissions from municipal waste incinerators: A qualitative risk assessment

Municipal waste incinerators (MWI) are beneficial alternatives to landfills for waste management. A recent constituent of concern in emissions from these facilities is incidental nanometer-sized particles (INP_MWI), i.e., particles smaller than 1 micrometer in size that may deposit in the deepest parts of the lungs, cross into the bloodstream, and affect different regions of the body. With limited data, the public may fear INP_MWI due to uncertainty, which may affect public acceptance, regulatory permitting, and the increased lowering of air quality standards. Despite limited data, a qualitative risk assessment paradigm can be applied to determine the relative risk due to INP_MWI emissions. This review compiles existing data on nanometer-sized particle generation by MWIs, emissions control technologies used at MWIs, emission releases into the atmosphere, human population exposure, and adverse health effects of nanometer-sized particles to generate a qualitative risk assessment and identify data gaps. The qualitative risk assessment conservatively concludes that INP_MWI pose a low to moderate risk to individuals, primarily due to the lack of relevant toxicological data on INP_MWI mixtures in ambient particulate matter.

The role of hypoxia-inducible factor-1α in zinc oxide nanoparticle-induced nephrotoxicity in vitro and in vivo

Background

Zinc oxide nanoparticles (ZnO NPs) are used in an increasing number of products, including rubber manufacture, cosmetics, pigments, food additives, medicine, chemical fibers and electronics. However, the molecular mechanisms underlying ZnO NP nephrotoxicity remain unclear. In this study, we evaluated the potential toxicity of ZnO NPs in kidney cells in vitro and in vivo.

Results

We found that ZnO NPs were apparently engulfed by the HEK-293 human embryonic kidney cells and then induced reactive oxygen species (ROS) generation. Furthermore, exposure to ZnO NPs led to a reduction in cell viability and induction of apoptosis and autophagy. Interestingly, the ROS-induced hypoxia-inducible factor-1α (HIF-1α) signaling pathway was significantly increased following ZnO NPs exposure. Additionally, connective tissue growth factor (CTGF) and plasminogen activator inhibitor-1 (PAI-1), which are directly regulated by HIF-1 and are involved in the pathogenesis of kidney diseases, displayed significantly increased levels following ZnO NPs exposure in HEK-293 cells. HIF-1α knockdown resulted in significantly decreased levels of autophagy and increased cytotoxicity. Therefore, our results suggest that HIF-1α may have a protective role in adaptation to the toxicity of ZnO NPs in kidney cells. In an animal study, fluorescent ZnO NPs were clearly observed in the liver, lungs, kidneys, spleen and heart. ZnO NPs caused histopathological lesions in the kidney and increase in serum creatinine and blood urea nitrogen (BUN) which indicate possible renal possible damage. Moreover, ZnO NPs enhanced the HIF-1α signaling pathway, apoptosis and autophagy in mouse kidney tissues.

Conclusions

ZnO NPs may cause nephrotoxicity, and the results demonstrate the importance of considering the toxicological hazards of ZnO NP production and application, especially for medicinal use.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0163-3) contains supplementary material, which is available to authorized users.

Effects of zinc oxide nanoparticles on human coronary artery endothelial cells

Inhalation of zinc oxide (ZnO) metal fumes is known to cause metal fume fever and to have systemic effects; however, the effects of ZnO nanoparticles (ZnONPs) on the cardiovascular system remain unclear. The objective of this study was to investigate the cardiovascular toxicity of ZnONPs. Human coronary artery endothelial cells (HCAECs) were exposed to ZnONPs of different sizes to investigate the cell viability, 8-hydroxy-2'-deoxyguanosine (8-OHdG), interleukin (IL)-6, nitric oxide (NO), and regulation of cardiovascular disease-related genes. Exposure of HCAECs to ZnONPs resulted in decreased cell viability and increased levels of 8-OHdG, IL-6, and NO. Downregulation of cardiovascular-associated genes was observed in response to ZnONPs in HCAECs determined by qPCR, suggesting that the calcium signaling pathway, neuroactive ligand-receptor interaction, hypertrophic cardiomyopathy, dilated cardiomyopathy, and renin-angiotensin system are important affected pathways in response to ZnONPs. Furthermore, we observed a significant response of AGTR1 to ZnONP exposure in HCAECs. Our results suggest that ZnONPs cause toxicity to HCAECs, which could be associated with cardiovascular dysfunction.

Computational modeling of nanoscale and microscale particle deposition, retention and dosimetry in the mouse respiratory tract

Comparing effects of inhaled particles across rodent test systems and between rodent test systems and humans is a key obstacle to the interpretation of common toxicological test systems for human risk assessment. These comparisons, correlation with effects and prediction of effects, are best conducted using measures of tissue dose in the respiratory tract. Differences in lung geometry, physiology and the characteristics of ventilation can give rise to differences in the regional deposition of particles in the lung in these species. Differences in regional lung tissue doses cannot currently be measured experimentally. Regional lung tissue dosimetry can however be predicted using models developed for rats, monkeys, and humans. A computational model of particle respiratory tract deposition and clearance was developed for BALB/c and B6C3F1 mice, creating a cross-species suite of available models for particle dosimetry in the lung. Airflow and particle transport equations were solved throughout the respiratory tract of these mice strains to obtain temporal and spatial concentration of inhaled particles from which deposition fractions were determined. Particle inhalability (Inhalable fraction, IF) and upper respiratory tract (URT) deposition were directly related to particle diffusive and inertial properties. Measurements of the retained mass at several post-exposure times following exposure to iron oxide nanoparticles, micro- and nanoscale C60 fullerene, and nanoscale silver particles were used to calibrate and verify model predictions of total lung dose. Interstrain (mice) and interspecies (mouse, rat and human) differences in particle inhalability, fractional deposition and tissue dosimetry are described for ultrafine, fine and coarse particles.

Toll-like receptor 6 mediated inflammatory and functional responses of zinc oxide nanoparticles primed macrophages

Macrophages are among the most sensitive immune cells because of their phagocytic activity and are prone to become dysfunctional or not able to perform properly if nanoparticle load increases. We have previously reported that zinc oxide nanoparticles (ZNPs) induce inflammatory responses in macrophages that contribute to their death. Recognition of ZNPs by pattern recognition receptors such as toll-like receptors (TLRs) might be a factor in the initiation of these responses in macrophages. Therefore, in this study we explored the role played by TLR6 and mitogen-activated protein kinase (MAPKs) pathways in the inflammatory responses of macrophages during ZNPs exposure. ZNPs-activated macrophages showed enhanced expression of activation and maturation markers (CD1d, MHC-II, CD86 and CD71). Among various TLRs screened, TLR6 emerged as the most potent activator for ZNPs-induced inflammatory responses. Downstream signalling proteins myeloid differentiation 88, interleukin-1 receptor associated kinase and tumour necrosis factor receptor-associated factor were also enhanced. On inhibiting MAPKs pathways individually, the inflammatory responses such as interleukin-1β, interleukin-6, tumour necrosis factor-α, cyclooxygenase-2 and inducible nitric oxide synthase were suppressed. TLR6 silencing significantly inhibited the pro-inflammatory cytokine levels, reactive nitrogen species generation and inducible nitric oxide synthase expression. Also, inhibition of MAPKs in the absence of TLR6 signalling validated the link between TLR6 and MAPKs in ZNPs-induced inflammatory responses. TLR6 was found to be co-localized with autophagosomes. Macrophages lacking TLR6 inhibited the autophagosome marker protein-microtubule-associated protein1 light chain 3-isoform II formation and phagocytosis. These results demonstrate that inflammatory responses caused by ZNPs-activated macrophages strongly depend on TLR6-mediated MAPK signalling.

Bioavailability, distribution and clearance of tracheally-instilled and gavaged uncoated or silica-coated zinc oxide nanoparticles

BACKGROUND

Nanoparticle pharmacokinetics and biological effects are influenced by several factors. We assessed the effects of amorphous SiO2 coating on the pharmacokinetics of zinc oxide nanoparticles (ZnO NPs) following intratracheal (IT) instillation and gavage in rats.

METHODS

Uncoated and SiO2-coated ZnO NPs were neutron-activated and IT-instilled at 1 mg/kg or gavaged at 5 mg/kg. Rats were followed over 28 days post-IT, and over 7 days post-gavage. Tissue samples were analyzed for 65Zn radioactivity. Pulmonary responses to instilled NPs were also evaluated at 24 hours.

RESULTS

SiO2-coated ZnO elicited significantly higher inflammatory responses than uncoated NPs. Pulmonary clearance of both 65ZnO NPs was biphasic with a rapid initial t1/2 (0.2 - 0.3 hours), and a slower terminal t1/2 of 1.2 days (SiO2-coated ZnO) and 1.7 days (ZnO). Both NPs were almost completely cleared by day 7 (>98%). With IT-instilled 65ZnO NPs, significantly more 65Zn was found in skeletal muscle, liver, skin, kidneys, cecum and blood on day 2 in uncoated than SiO2-coated NPs. By 28 days, extrapulmonary levels of 65Zn from both NPs significantly decreased. However, 65Zn levels in skeletal muscle, skin and blood remained higher from uncoated NPs. Interestingly, 65Zn levels in bone marrow and thoracic lymph nodes were higher from coated 65ZnO NPs. More 65Zn was excreted in the urine from rats instilled with SiO2-coated 65ZnO NPs. After 7 days post-gavage, only 7.4% (uncoated) and 6.7% (coated) of 65Zn dose were measured in all tissues combined. As with instilled NPs, after gavage significantly more 65Zn was measured in skeletal muscle from uncoated NPs and less in thoracic lymph nodes. More 65Zn was excreted in the urine and feces with coated than uncoated 65ZnO NPs. However, over 95% of the total dose of both NPs was eliminated in the feces by day 7.

CONCLUSIONS

Although SiO2-coated ZnO NPs were more inflammogenic, the overall lung clearance rate was not affected. However, SiO2 coating altered the tissue distribution of 65Zn in some extrapulmonary tissues. For both IT instillation and gavage administration, SiO2 coating enhanced transport of 65Zn to thoracic lymph nodes and decreased transport to the skeletal muscle.

Engineering safer-by-design, transparent, silica-coated ZnO nanorods with reduced DNA damage potential

Zinc oxide (ZnO) nanoparticles absorb UV light efficiently while remaining transparent in the visible light spectrum rendering them attractive in cosmetics and polymer films. Their broad use, however, raises concerns regarding potential environmental health risks and it has been shown that ZnO nanoparticles can induce significant DNA damage and cytotoxicity. Even though research on ZnO nanoparticle synthesis has made great progress, efforts on developing safer ZnO nanoparticles that maintain their inherent optoelectronic properties while exhibiting minimal toxicity are limited. Here, a safer-by-design concept was pursued by hermetically encapsulating ZnO nanorods in a biologically inert, nanothin amorphous SiO2 coating during their gas-phase synthesis. It is demonstrated that the SiO2 nanothin layer hermetically encapsulates the core ZnO nanorods without altering their optoelectronic properties. Furthermore, the effect of SiO2 on the toxicological profile of the core ZnO nanorods was assessed using the Nano-Cometchip assay by monitoring DNA damage at a cellular level using human lymphoblastoid cells (TK6). Results indicate significantly lower DNA damage (>3 times) for the SiO2-coated ZnO nanorods compared to uncoated ones. Such an industry-relevant, scalable, safer-by-design formulation of nanostructured materials can liberate their employment in nano-enabled products and minimize risks to the environment and human health.