Toxicity of particles derived from combustion of Ethiopian traditional biomass fuels in human bronchial and macrophage-like cells

The combustion of traditional fuels in low-income countries, including those in sub-Saharan Africa, leads to extensive indoor particle exposure. Yet, the related health consequences in this context are understudied. This study aimed to evaluate the in vitro toxicity of combustion-derived particles relevant for Sub-Saharan household environments. Particles (< 2.5 µm) were collected using a high-volume sampler during combustion of traditional Ethiopian biomass fuels: cow dung, eucalyptus wood and eucalyptus charcoal. Diesel exhaust particles (DEP, NIST 2975) served as reference particles. The highest levels of particle-bound polycyclic aromatic hydrocarbons (PAHs) were found in wood (3219 ng/mg), followed by dung (618 ng/mg), charcoal (136 ng/mg) and DEP (118 ng/mg) (GC-MS). BEAS-2B bronchial epithelial cells and THP-1 derived macrophages were exposed to particle suspensions (1-150 µg/mL) for 24 h. All particles induced concentration-dependent genotoxicity (comet assay) but no pro-inflammatory cytokine release in epithelial cells, whereas dung and wood particles also induced concentration-dependent cytotoxicity (Alamar Blue). Only wood particles induced concentration-dependent cytotoxicity and genotoxicity in macrophage-like cells, while dung particles were unique at increasing secretion of pro-inflammatory cytokines (IL-6, IL-8, TNF-α). In summary, particles derived from combustion of less energy dense fuels like dung and wood had a higher PAH content and were more cytotoxic in epithelial cells. In addition, the least energy dense and cheapest fuel, dung, also induced pro-inflammatory effects in macrophage-like cells. These findings highlight the influence of fuel type on the toxic profile of the emitted particles and warrant further research to understand and mitigate health effects of indoor air pollution.

Modelled lung deposition and retention of welding fume particles in occupational scenarios: a comparison to doses used in vitro

Translating particle dose from in vitro systems to relevant human exposure remains a major challenge for the use of in vitro studies in assessing occupational hazard and risk of particle exposure. This study aimed to model the lung deposition and retention of welding fume particles following occupational scenarios and subsequently compare the lung doses to those used in vitro. We reviewed published welding fume concentrations and size distributions to identify input values simulating real-life exposure scenarios in the multiple path particle dosimetry (MPPD) model. The majority of the particles were reported to be below 0.1 μm and mass concentrations ranged between 0.05 and 45 mg/m³. Following 6-h exposure to 5 mg/m³ with a count median diameter of 50 nm, the tracheobronchial lung dose (0.89 µg/cm²) was found to exceed the in vitro cytotoxic cell dose (0.125 µg/cm²) previously assessed by us in human bronchial epithelial cells (HBEC-3kt). However, the tracheobronchial retention decreased rapidly when no exposure occurred, in contrast to the alveolar retention which builds-up over time and exceeded the in vitro cytotoxic cell dose after 1.5 working week. After 1 year, the tracheobronchial and alveolar retention was estimated to be 1.15 and 2.85 µg/cm², respectively. Exposure to low-end aerosol concentrations resulted in alveolar retention comparable to cytotoxic in vitro dose in HBEC-3kt after 15-20 years of welding. This study demonstrates the potential of combining real-life exposure data with particle deposition modelling to improve the understanding of in vitro concentrations in the context of human occupational exposure.

Gold Nanoparticles Dissolve Extracellularly in the Presence of Human Macrophages

INTRODUCTION

Gold nanoparticles (AuNPs) have the potential to be used in various biomedical applications, partly due to the inertness and stability of gold. Upon intravenous injection, the NPs interact with the mononuclear phagocyte system, first with monocytes in the blood and then with macrophages in tissue. The NP-macrophage interaction will likely affect the stability of the AuNPs, but this is seldom analyzed. This study aimed to elucidate the role of macrophages in the biodissolution of AuNPs and underlying mechanisms.

METHODS

With an in vitro dissolution assay, we used inductively coupled plasma mass spectrometry to quantitatively compare the dissolution of 5 and 20 nm AuNPs coated with citrate or PEG in cell medium alone or in the presence of THP1-derived macrophages at 24 hours. In addition, we analyzed the cell dose, compared extra- and intracellular dissolution, and explored the possible role of reactive nitrogen species.

RESULTS

The results showed a higher cellular dose of the citrate-coated AuNPs, but dissolution was mainly evident for those sized 5 nm, irrespective of coating. The macrophages clearly assisted the dissolution, which was approximately fivefold higher in the presence of macrophages. The dissolution, however, appeared to take place mainly extracellularly. Acellular experiments demonstrated that peroxynitrite can initiate oxidation of gold, but a ligand is required to keep the gold ions in solution.

CONCLUSION

This study suggests extracellular dissolution of AuNPs in the presence of macrophages, likely with the contribution of the release of reactive nitrogen species, and provides new insight into the fate of AuNPs in the body.

Welding fume nanoparticles from solid and flux-cored wires: Solubility, toxicity, and role of fluorides

Welding fume particles are hazardous. Their toxicity likely depends on their composition and reactivity. This study aimed at exploring the role of sodium or other fluorides (NaF), which are intentionally added to flux-cored wire electrodes for stainless steel welding, on the solubility (in phosphate buffered saline) and toxicity of the generated welding fume particles. A multi-analytical particle characterization approach along with in-vitro cell assays was undertaken. The release of Cr(VI) and Mn from the particles was tested as a function of fluoride solution concentration. The welding fume particles containing NaF released significantly higher amounts of Cr(VI) compared with solid wire reference fumes, which was associated with increased cytotoxicity and genotoxicity in-vitro. No crystalline Na or potassium (K) containing chromates were observed. Cr(VI) was incorporated in an amorphous mixed oxide. Solution-added fluorides did not increase the solubility of Cr(VI), but contributed to a reduced Mn release from both solid and flux-cored wire fume particles and the reduction of Cr(VI) release from solid wire fume particles. Chemical speciation modeling suggested that metal fluoride complexes were not formed. The presence of NaF in the welding electrodes did not have any direct, but possibly an indirect, role in the Cr(VI) solubility of welding fumes.

Adsorption of Horseradish Peroxidase on Metallic Nanoparticles: Effects on Reactive Oxygen Species Detection Using 2',7'-Dichlorofluorescin Diacetate

The fluorescent probe 2',7'-dichlorofluorescein diacetate (DCFH-DA) together with the enzyme horseradish peroxidase (HRP) is widely used in nanotoxicology to study acellular reactive oxygen species (ROS) production from nanoparticles (NPs). This study examined whether HRP adsorbs onto NPs of Mn, Ni, and Cu and if this surface process influences the extent of metal release and hence the ROS production measurements using the DCFH assay in phosphate buffered saline (PBS), saline, or Dulbecco's modified Eagle's medium (DMEM). Adsorption of HRP was evident onto all NPs and conditions, except for Mn NPs in PBS. The presence of HRP resulted in an increased release of copper from the Cu NPs in PBS and reduced levels of nickel from the Ni NPs in saline. Both metal ions in solution and the adsorption of HRP onto the NPs can change the activity of HRP and thus influence the ROS results. The effect of HRP on the NP reactivity was shown to be solution chemistry dependent. Most notable was the evident affinity/adsorption of phosphate toward the metal NPs, followed by a reduced adsorption of HRP, the concomitant reduction in released manganese from the Mn NPs, and increased levels of released metals from the Cu NPs in PBS. Minor effects were observed for the Ni NPs. The solution pH should be monitored since the release of metals can change the solution pH and the activity of HRP is known to be pH-dependent. It is furthermore essential that solution pH adjustments are made following the addition of NaOH during diacetyl removal of DCFH-DA. Even though not observed for the given exposure conditions of this study, released metal ions could possibly induce agglomeration or partial denaturation of HRP, which in turn could result in steric hindrance for H2O2 to reach the active site of HRP. This study further emphasizes the influence of HRP on the background kinetics, its solution dependence, and effects on measured ROS signals. Different ways of correcting for the background are highlighted, as this can result in different interpretations of generated results. The results show that adsorption of HRP onto the metal NPs influenced the extent of metal release and may, depending on the investigated system, result in either under- or overestimated ROS signals if used together with the DCFH assay. HRP should hence be used with caution when measuring ROS in the presence of reactive metallic NPs.

ToxTracker Reporter Cell Lines as a Tool for Mechanism-Based (geno)Toxicity Screening of Nanoparticles-Metals, Oxides and Quantum Dots

The increased use of nanoparticles (NPs) requires efficient testing of their potential toxic effects. A promising approach is to use reporter cell lines to quickly assess the activation of cellular stress response pathways. This study aimed to use the ToxTracker reporter cell lines to investigate (geno)toxicity of various metal- or metal oxide NPs and draw general conclusions on NP-induced effects, in combination with our previous findings. The NPs tested in this study (n = 18) also included quantum dots (QDs) in different sizes. The results showed a large variation in cytotoxicity of the NPs tested. Furthermore, whereas many induced oxidative stress only few activated reporters related to DNA damage. NPs of manganese (Mn and Mn₃O₄) induced the most remarkable ToxTracker response with activation of reporters for oxidative stress, DNA damage, protein unfolding and p53-related stress. The QDs (CdTe) were highly toxic showing clearly size-dependent effects and calculations suggest surface area as the most relevant dose metric. Of all NPs investigated in this and previous studies the following induce the DNA damage reporter; CuO, Co, CoO, CdTe QDs, Mn, Mn₃O₄, V₂O₅, and welding NPs. We suggest that these NPs are of particular concern when considering genotoxicity induced by metal- and metal oxide NPs.

High variability in toxicity of welding fume nanoparticles from stainless steel in lung cells and reporter cell lines: the role of particle reactivity and solubility

Millions of people in the world perform welding as their primary occupation resulting in exposure to metal-containing nanoparticles in the fumes generated. Even though health effects including airway diseases are well-known, there is currently a lack of studies investigating how different welding set-ups and conditions affect the toxicity of generated nanoparticles of the welding fume. The aim of this study was to investigate the toxicity of nine types of welding fume particles generated via active gas shielded metal arc welding (GMAW) of chromium-containing stainless steel under different conditions and, furthermore, to correlate the toxicity to the particle characteristics. Toxicological endpoints investigated were generation of reactive oxygen species (ROS), cytotoxicity, genotoxicity and activation of ToxTracker reporter cell lines. The results clearly underline that the choice of filler material has a large influence on the toxic potential. Fume particles generated by welding with the tested flux-cored wire (FCW) were found to be more cytotoxic compared to particles generated by welding with solid wire or metal-cored wire (MCW). FCW fume particles were also the most potent in causing ROS and DNA damage and they furthermore activated reporters related to DNA double- strand breaks and p53 signaling. Interestingly, the FCW fume particles were the most soluble in PBS, releasing more chromium in the hexavalent form and manganese compared to the other fumes. These results emphasize the importance of solubility of different metal constituents of the fume particles, rather than the total metal content, for their acute toxic potential.

Inflammation and (secondary) genotoxicity of Ni and NiO nanoparticles

Nanoparticle-induced genotoxicity can arise through different mechanisms, and generally, primary and secondary genotoxicity can be distinguished where the secondary is driven by an inflammatory response. It is, however, yet unclear how a secondary genotoxicity can be detected using in vitro methods. The aim of this study was to investigate inflammation and genotoxicity caused by agglomerated nickel (Ni) and nickel oxide (NiO) nanoparticles and, furthermore, to explore the possibility to test secondary (inflammation-driven) genotoxicity in vitro. As a benchmark particle to compare with, we used crystalline silica (quartz). A proteome profiler antibody array was used to screen for changes in release of 105 different cytokines and the results showed an increased secretion of various cytokines including vascular endothelial growth factor (VEGF) following exposure of macrophages (differentiated THP-1 cells). Both Ni and NiO caused DNA damage (comet assay) following exposure of human bronchial epithelial cells (HBEC) and interestingly conditioned media (CM) from exposed macrophages also resulted in DNA damage (2- and 3-fold increase for Ni and NiO, respectively). Similar results were also found when using a co-culture system of macrophages and epithelial cells. In conclusion, this study shows that it is possible to detect a secondary genotoxicity in lung epithelial cells by using in vitro methods based on conditioned media or co-cultures. Further investigation is needed in order to find out what factors that are causing this secondary genotoxicity and whether such effects are caused by numerous nanoparticles.

In vitro and in vivo genotoxicity of oxygenated polycyclic aromatic hydrocarbons

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are a group of environmental pollutants found in complex mixtures together with PAHs. In contrast to the extensively studied PAHs, which have been established to have mutagenic and carcinogenic properties, much less is known about the effects of oxy-PAHs. The present work aimed to investigate the genotoxic potency of a set of environmentally relevant oxy-PAHs along with environmental soil samples in human bronchial epithelial cells (HBEC). We found that all oxy-PAHs tested induced DNA strand breaks in a dose-dependent manner and some of the oxy-PAHs further induced micronuclei formation. Our results showed weak effects in response to the oxy-PAH containing subfraction of the soil sample. The genotoxic potency was confirmed in both HBEC and HepG2 cells following exposure to oxy-PAHs by an increased level of phospho-Chk1, a biomarker used to estimate the carcinogenic potency of PAHs in vitro. We further exposed zebrafish embryos to single oxy-PAHs or a binary mixture with PAH benzo[a]pyrene (B[a]P) and found the mixture to induce comparable or greater effects on the induction of DNA strand breaks compared to the sum of that induced by B[a]P and oxy-PAHs alone. In conclusion, oxy-PAHs were found to elicit genotoxic effects at similar or higher levels to that of B[a]P which indicates that oxy-PAHs may contribute significantly to the total carcinogenic potency of environmental PAH mixtures. This emphasizes further investigations of these compounds as well as the need to include oxy-PAHs in environmental monitoring programs in order to improve health risk assessment.

Bold zebrafish (Danio rerio) express higher levels of delta opioid and dopamine D2 receptors in the brain compared to shy fish

Individual variation in coping with environmental challenges is a well-known phenomenon across vertebrates, including teleost fish. Dopamine is the major transmitter in the brain reward networks, and important for motivational processes and stress coping. Functions of the endogenous opioid system are not well studied in teleosts. However, in mammals the activity in the brain reward networks is regulated by the endogenous opioid system. This study aimed at investigating if there was a correlation between risk-taking behavior and the expression of dopamine and opioid receptors in the zebrafish (Danio rerio) brain. Risk-taking behavior was assessed in a novel tank diving test, and the most extreme high risk taking, i.e. bold, and low risk taking, i.e. shy, fish were sampled for qPCR analysis of whole brain gene expression. The expression analysis showed a significantly higher expression of the dopamine D2 receptors (drd2a and drd2b) and the delta opioid receptor (DOR; oprd1b) in bold compared to shy fish. Besides reward and reinforcing properties, DORs are also involved in emotional responses. Dopamine D2 receptors are believed to be important for active stress coping in rodents, and taken together the results of the current study suggest similar functions in zebrafish. However, additional experiments are required to clarify how dopamine and opioid receptor activation affect behavior and stress coping in this species.