Relationship between Cytotoxicity and Surface Oxidation of Artificial Black Carbon

Review of in vitro studies evaluating respiratory toxicity of aerosols: impact of cell types, chemical composition, and atmospheric processing

In recent decades, several cell-based and acellular methods have been developed to evaluate ambient particulate matter (PM) toxicity. Although cell-based methods provide a more comprehensive assessment of PM toxicity, their results are difficult to comprehend due to the diversity in cellular endpoints, cell types, and assays and the interference of PM chemical components with some of the assays' techniques. In this review, we attempt to clarify some of these issues. We first discuss the morphological and immunological differences among various macrophage and epithelial cells, belonging to the respiratory systems of human and murine species, used in the in vitro studies evaluating PM toxicity. Then, we review the current state of knowledge on the role of different PM chemical components and the relevance of atmospheric processing and aging of aerosols in the respiratory toxicity of PM. Our review demonstrates the need to adopt more physiologically relevant cellular models such as epithelial (or endothelial) cells instead of macrophages for oxidative stress measurement. We suggest limiting macrophages for investigating other cellular responses (e.g., phagocytosis, inflammation, and DNA damage). Unlike monocultures (of macrophages and epithelial cells), which are generally used to study the direct effects of PM on a given cell type, the use of co-culture systems should be encouraged to investigate a more comprehensive effect of PM in the presence of other cells. Our review has identified two major groups of toxic PM chemical species from the existing literature, i.e., metals (Fe, Cu, Mn, Cr, Ni, and Zn) and organic compounds (PAHs, ketones, aliphatic and chlorinated hydrocarbons, and quinones). However, the relative toxicities of these species are still a matter of debate. Finally, the results of the existing studies investigating the effect of aging on PM toxicity are ambiguous, with varying results due to different cell types, different aging conditions, and the presence/absence of specific oxidants. More systematic studies are necessary to understand the role of different SOA precursors, interactions between different PM components, and aging conditions in the overall toxicity of PM. We anticipate that our review will guide future investigations by helping researchers choose appropriate cell models, resulting in a more meaningful interpretation of cell-based assays and thus ultimately leading to a better understanding of the health effects of PM exposure.

Disruption of phosphofructokinase activity and aerobic glycolysis in human bronchial epithelial cells by atmospheric ultrafine particulate matter

Exposure to ambient ultrafine particulate matter (UPM) causes respiratory disorders; however, the underlying molecular mechanisms remain unclear. In this study, we synthesized simulated UPM (sUPM) with controlled physicochemical properties using the spark-discharge method. Subsequently, we investigated the biological effects of sUPM using BEAS-2B human bronchial epithelial cells (HBECs) and a mouse intratracheal instillation model. High throughput RNA-sequencing and bioinformatics analyses revealed that dysregulation of the glycolytic metabolism is involved in the inhibited proliferation and survival of HBECs by sUPM treatment. Furthermore, signaling pathway and enzymatic analyses showed that the treatment of BEAS-2B cells with sUPM induces the inactivation of extracellular signal-regulated kinase (ERK) and protein kinase B (PKB, also known as AKT), resulting in the downregulation of phosphofructokinase 2 (PFK2) S483 phosphorylation, PFK enzyme activity, and aerobic glycolysis in HBECs in an oxidative stress-independent manner. Additionally, intratracheal instillation of sUPM reduced the phosphorylation of ERK, AKT, and PFK2, decreased proliferation, and increased the apoptosis of bronchial epithelial cells in mice. The findings of this study imply that UPM induces pulmonary toxicity by disrupting aerobic glycolytic metabolism in lung epithelial cells, which can provide novel insights into the toxicity mechanisms of UPM and strategies to prevent their toxic effects.

Tracing the plasma kallikrein-kinin system-activating component in the atmospheric particulate matter with different origins

Atmospheric particulate matter (PM) perturbs hematological homeostasis by targeting the plasma kallikrein-kinin system (KKS), causing a cascade of zymogen activation events. However, the causative components involved in PM-induced hematological effects are largely unknown. Herein, the standard reference materials (SRMs) of atmospheric PM, including emissions from the diesel (2975), urban (1648a), and bituminous coal (2693), were screened for their effects on plasma KKS activation, and the effective constituent contributing to PM-induced KKS activation was further explored by fraction isolation and chemical analysis. The effects of three SRMs on KKS activation followed the order of 2975 > 1648a > 2693, wherein the fractions of 2975 isolated by acetone and water, together with the insoluble particulate residues, exerted significant perturbations in the hematological homeostasis. The soot contents in the SRMs and corresponding isolated fractions matched well with their hematological effects, and the KKS activation could be dependent on the soot surface oxidation degree. This study, for the first time, uncovered the soot content in atmospheric PM with different origins contributed to the distinct effects on plasma KKS activation. The finding would be of utmost importance for the health risk assessment on inhaled airborne fine PM, given its inevitable contact with human circulatory system.

Establishment of an artificial particulate matter-induced lung disease model through analyzing pathological changes and transcriptomic profiles in mice

Particulate matter (PM), an environmental risk factor, is linked with health risks such as respiratory diseases. This study aimed to establish an animal model of PM-induced lung injury with artificial PM (APM) and identify the potential of APM for toxicological research. APM was generated from graphite at 600 °C and combined with ethylene. We analyzed diesel exhaust particulate (DEP) and APM compositions and compared toxicity and transcriptomic profiling in lungs according to the exposure. For the animal study, C57BL/6 male mice were intratracheally administered vehicle, DEP, or APM. DEP or APM increased relative lung weight, inflammatory cell numbers, and inflammatory protein levels compared with the vehicle control. Histological assessments showed an increase in particle-pigment alveolar macrophages and slight inflammation in the lungs of DEP and APM mice. In the only APM group, granulomatous inflammation, pulmonary fibrosis, and mucous hyperplasia were observed in the lungs of some individuals. This is the first study to compare pulmonary toxicity between DEP and APM in an animal model. Our results suggest that the APM-treated animal model may contribute to understanding the harmful effects of PM in toxicological studies showing that APM can induce various lung diseases according to different doses of APM.

Nanoparticles in the Environment and Nanotoxicology

Nanomaterials, including engineered nanoparticles and microplastics/nanoplastics, have attracted increasing concern as they might potentially release into the environment, leading to potential risks to ecosystems [...].

Hydrophobic soot nanoparticles as a non-cytotoxic motility activator of human spermatozoa

Sperm cryopreservation is vital in combating the human infertility, but regrettably, the toxicity of cryoprotectants and the occurrence of intracellular icing, osmotic shocks or shrinkage of the cells below a given threshold volume greatly affects the success rate of this technique. Using the virtue of nanotechnologies and depositing water-repellent soot nanoparticles on the inner walls of cryovials may outline new directions in the development of cryobiology, but doubts related to the soot's venomosity question its practical implementability. The scientific content of this article eliminates the existing apprehensions by analyzing the cytotoxicity of three types of rapeseed oil soot, differing in morphology, surface chemistry and zeta potential, towards human spermatozoa. Upon intermittent evaluations of the sperm motility within 270 min of incubation in vials comprising carbon nanoparticles, we reveal that this soot category is non-cytotoxic or at worst, faintly toxic to the gametes provided by twenty individuals. Enhanced progressive sperm motility is observed at ∼50-60% of patients following the soot treatments, which is attributed to electrostatic repulsions and biochemical alterations in the seminal plasma. These fascinating results open new horizons for incorporation of the rapeseed oil soot as a tool for functional preparation and activation of human spermatozoa preceding in vitro fertilization.

Coconut Oil Alleviates the Oxidative Stress-Mediated Inflammatory Response via Regulating the MAPK Pathway in Particulate Matter-Stimulated Alveolar Macrophages

Exposure to particulate matter (PM) is related to various respiratory diseases, and this affects the respiratory immune system. Alveolar macrophages (AMs), which are defenders against pathogens, play a key role in respiratory inflammation through cytokine production and cellular interactions. Coconut oil demonstrates antioxidant and anti-inflammatory properties, and it is consumed worldwide for improved health. However, reports on the protective effects of coconut oil on the PM-induced respiratory immune system, especially in AMs, are limited. In this study, we generated artificial PM (APM) with a diameter approximately of 30 nm by controlling the temperature, and compared its cytotoxicity with diesel exhaust particles (DEP). We also investigated the antioxidant and anti-inflammatory effects of coconut oil in APM− and DEP−stimulated AMs, and the underlying molecular mechanisms. Our results showed that APM and DEP had high cytotoxicity in a dose-dependent manner in AMs. In particular, APM or DEP at 100 μg/mL significantly decreased cell viability (p < 0.05) and significantly increased oxidative stress markers such as reactive oxygen species (p < 0.01); the GSSH/GSH ratio (p < 0.01); and cytokine production, such as tumor necrosis factor-α (p < 0.001), interleukin (IL)-1β (p < 0.001), and IL-6 (p < 0.001). The expression of the genes for chemokine (C-X-C motif) ligand-1 (p < 0.05) and monocyte chemoattractant protein-1 (p < 0.001); and the proteins toll-like receptor (TLR) 4 (p < 0.01), mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (p < 0.001), p38 (p < 0.001); and extracellular receptor-activated kinase (p < 0.001), were also upregulated by PM. These parameters were reversed upon treatment with coconut oil in APM− or DEP−stimulated AMs. In conclusion, coconut oil can reduce APM− or DEP−induced inflammation by regulating the TLR4/MAPK pathway in AMs, and it may protect against adverse respiratory effects caused by PM exposure.