Cytotoxicity of emerging halophenylacetamide disinfection byproducts in drinking water: Mechanism and prediction.

Halophenylacetamides (HPAcAms) have been identified as a new group of nitrogenous aromatic disinfection byproducts (DBPs) in drinking water, but the toxicity mechanisms associated with HPAcAms remain almost completely unknown. In this work, the cytotoxicity of HPAcAms in human hepatoma (HepG2) cells was evaluated, intracellular oxidative stress/damage levels were analyzed, their binding interactions with antioxidative enzyme were explored, and a quantitative structure-activity relationship (QSAR) model was established. Results indicated that the EC50 values of HPAcAms ranged from 2353 µM to 9780 µM, and the isomeric structure as well as the type and number of halogen substitutions could obviously induce the change in the cytotoxicity of HPAcAms. Upon exposure to 2-(3,4-dichlorophenyl)acetamide (3,4-DCPAcAm), various important biomarkers linked to oxidative stress and damage, such as reactive oxygen species, 8­hydroxy-2-deoxyguanosine, and cell apoptosis, exhibited a significant increase in a dose-dependent manner. Moreover, 3,4-DCPAcAm could directly bind with Cu/Zn-superoxide dismutase and induce the alterations in the structure and activity, and the formation of complexes was predominantly influenced by the van der Waals force and hydrogen bonding. The QSAR model supported that the nucleophilic reactivity as well as the molecular compactness might be highly important in their cytotoxicity mechanisms in HepG2 cells, and 2-(2,4-dibromophenyl)acetamide and 2-(3,4-dibromophenyl)acetamide deserved particular attention in future studies due to the relatively higher predicted cytotoxicity. This study provided the first comprehensive investigation on the cytotoxicity mechanisms of HPAcAm DBPs.

Operando Mobile Catalysis for Reverse Water Gas Shift Reaction.

Metal atoms on the support serve as active sites for many heterogeneous catalysts. However, the active metal sites on the support are conventionally described as static, and the intermediates adsorbed on the support far away from the active metal sites cannot be transformed. Herein, we report the first example of operando mobile catalysis to promote catalytic efficiency by enhancing the collision probability between active sites and reactants or reaction intermediates. Specifically, ligand-coordinated Pt single atoms (isolated MeCpPt- species) are bonded on CeO2 and transformed into mobile MeCpPt(H)CO complexes during the reverse water gas shift reaction for operando mobile catalysis. This strategy enables the conversion of inert carbonate intermediates on the CeO2 support. A turnover frequency (TOF) of 6358 mol CO2 molPt -1 ⋅ h-1 and 99 % CO selectivity at 300 °C is obtained for reverse water gas shift reaction, dramatically higher than those of Pt catalysts reported in the literature. Operando mobile catalysis presents a promising strategy for designing high-efficiency heterogeneous catalysts for various chemical reactions and applications.

Tailoring the Brønsted acidity of Ti-OH species by regulating Pt-TiO2 interaction.

Bifunctional catalysts comprising metal and acid sites are commonly used for many reactions. Interfacial acid sites impact intermediate reactions more than other sites. However, controlling the type and amounts of interfacial acid sites by regulating metal-support interaction (MSI) via traditional methods is difficult. Thus, the influence of MSI on interfacial acid sites remains unclear. We prepared Pt-mTiO2/α-Al2O3 (m represents the cycle number of TiO2) catalysts via atomic layer deposition (ALD). New Brønsted acid sites were generated via Pt-TiO2 interaction, and the acidity was precisely regulated by regulating Pt-TiO2 interaction by changing the TiO2 nanolayer thickness. We chose levulinic acid (LA) hydrogenation as a model reaction. The catalytic activity varied with the TiO2 nanolayer thickness and was linearly correlated with the Ti-OH species (Brønsted acid) content. Pt-40TiO2/α-Al2O3, with the highest acid site content of 0.486 mmol/g, exhibited the best catalytic activity. Hydrogen spillover and water dissociation at the Pt-TiO2 interface promoted Ti-OH species generation.

Environmental relevant concentrations of polystyrene nanoplastics and lead co-exposure triggered cellular cytotoxicity responses and underlying mechanisms in Eisenia fetida.

Heavy metal pollution of soils and the widespread use of plastics have caused environmental problems worldwide. Nanoplastics (NPs) contaminants in water and soil environments can adsorb heavy metals, thereby affecting the bioavailability and toxicity of heavy metals. In this paper, the effect of co-exposure of polystyrene microspheres with 100 nm particle size and lead acetate (Pb) on the Eisenia fetida coelomocytes was investigated. The environmental concentration of NPs used was 0.01 mg/L and the concentration of Pb ranged from 0.01 to 1 mg/L, and the exposed cells were incubated at 298 k for 24 h. Our study demonstrated that exposure of cells to environmental relevant concentrations of NPs did not significantly affect the cytotoxicity of Pb exposure. It was shown that co-exposure induced cellular production of reactive oxygen species (ROS, increased to 134.4 %) disrupted the antioxidant system of earthworm body cavity cells, activated superoxide dismutase and catalase (CAT), produced reduced glutathione, and inhibited glutathione-dependent enzyme (GST) activity (Reduced to 64 %). Total antioxidant capacity (T-AOC) is first enhanced against ROS due to the stress of NPs and Pb. When the antioxidant reserves of cells are exhausted, the antioxidant capacity will decrease. The level of malondialdehyde, a biomarker of eventual lipid peroxidation, increased to 231.7 %. At the molecular level, due to co-exposure to NPs and Pb, CAT was loosely structured and the secondary structure is misfolded, which was responsible for exacerbating oxidative damage in E. fetida coelomocytes. The findings of this study have significant implications for the toxicological interaction and future risk assessment of co-contamination of NPs and Pb in the environment.

Decoding the biological toxicity of phenanthrene on intestinal cells of Eisenia fetida: Effects, toxicity pathways and corresponding mechanisms.

Phenanthrene is frequently detected and exists extensively in the soil environment, and its residues inevitably impose a significant threat to soil organisms. Exposure to and toxicity of phenanthrene on earthworms has been extensively studied before, however, the possible mechanisms and related pathways associated with phenanthrene-triggered toxicity at the intestinal cell level remain unclear. Herein, primary intestinal cells isolated from Eisenia fetida (Annelida, Oligochaeta) intestine were used as targeted receptors to probe the molecular mechanisms involved in ROS-mediated damaging effects and the potential pathways of phenanthrene-induced toxicity at cellular and sub-cellular levels. Results indicated that phenanthrene exposure induced oxidative stress by activating intracellular ROS (elevated O2-, H2O2, and OH- content) bursts in E. fetida intestinal cells, causing various oxidative damage effects, including lipid peroxidation (increased MDA content), protein oxidation (enhanced PCO levels), and DNA damage (enhanced 8-OHdG levels). The enzymatic and non-enzymatic strategies in earthworm cells were activated to mitigate these detrimental effects by regulating ROS-mediated pathways involving defense regulation. Also, phenanthrene stress destroyed the cell membrane of E. fetida intestinal cells, resulting in cellular calcium homeostasis disruption and cellular energetic alteration, ultimately causing cytotoxicity and cell apoptosis/death. More importantly, the mitochondrial dysfunction in E. fetida cells was induced by phenanthrene-caused mitochondrial membrane depolarization, which in turn caused un-controlled ROS burst and induced apoptosis through mitochondria-mediated caspase-3 activation and ROS-mediated mitochondrial-dependent pathway. Furthermore, exposure to phenanthrene activated an abnormal mRNA expression profile associated with defense regulation (e.g., Hsp70, MT, CRT, SOD, CAT, and GST genes) in E. fetida intestinal cells, resulting in various cellular dysfunctions and pathological conditions, eventually, apoptotic cell death. Taken together, this study offers valuable insights for probing the toxic effects and underlying mechanisms posed by phenanthrene at the intestinal cell level, and is of great significance to estimate the detrimental side effects of phenanthrene on soil ecological health.

Randomly-shaped nanoplastics induced stronger biotoxicity targeted to earthworm Eisenia fetida species: Differential effects and the underlying mechanisms of realistic and commercial polystyrene nanoplastics.

Nanoplastics (NPs) are widely distributed in various environments, including soil, and have been known to adversely affect soil organisms. Currently, most of the obtained studies were principally focused on the ecological risks of commercial sphere-type microbeads (SNPs), while ignoring that they might be different from randomly-shaped nanoplastics (RNPs) in a real environment. Thus, this study was undertaken to probe the shape-dependent effects of NPs on the earthworm Eisenia fetida and the corresponding poisoning mechanisms, and discriminate the toxicity differences between SNPs and RNPs at the molecule, cell, tissue, and animal levels. The results showed SNPs and RNPs exhibited lethal effects to earthworms with the LC50 determined to be 27.42 g/kg and 21.69 g/kg, respectively after a 28-day exposure. SNPs and RNPs exposure can cause ROS-induced ROS release in worm, inducing oxidative stress through mitochondria-mediated pathway, leading to lipid peroxidation, DNA damage, and histopathological changes, thereby contributing to decreased stress resistance against exogenous stressors. To reduce ROS-mediated oxidative damage, the antioxidant defense system in E. fetida can be activated, which scavenges unwanted ROS. High doses of SNPs and RNPs inhibited the AChE activity in worms, causing excess acetylcholine accumulation in the synaptic space, which finally lead to neurotoxicity. Also, two kinds of NPs can induce the abnormal expression of genes relevant to oxidative stress, reproduction, growth, and tight junction protein in E. fetida, which ultimately contribute to various detrimental effects, tissue damage and dysfunction, reproductive and developmental toxicity. The results obtained from the Integrated Biological Response (IBR) suggested that long-term exposure to high-dose SNPs and RNPs can induce the stronger toxicity effects to E. fetida worms, and RNPs-induced toxicity can be different and stronger than that of SNPs. Our results provide insights for revealing the environmental effects posed by randomly-shaped NPs-contaminated soil, and are of importance for assessing the contribution of NPs with different physical characteristics to soil eco-safety.

Ecotoxicological evaluation of oxidative stress-mediated neurotoxic effects, genetic toxicity, behavioral disorders, and the corresponding mechanisms induced by fluorene-contaminated soil targeted to earthworm (Eisenia fetida) brain.

Fluorene is a commonly identified PAH pollutant in soil and exhibits various worrisome hazardous effects to soil organisms. Currently, the toxicity profiles of fluorene on earthworm brain are rare, and the mechanisms and their corresponding pathways involved in fluorene-triggered neurotoxicity, genotoxicity, and behavior changes have not been reported hitherto. Herein, earthworm (Eisenia fetida) brain was chosen as targeted receptor to explore the neurotoxic effects, genetic toxicity, behavioral disorders, and related mechanisms caused by fluorene-induced oxidative stress pathways. The results showed excess fluorene initiated the release of excessive quantities of ROS in earthworm brain, which have caused oxidative stress and accompanied by serious oxidative effects, including LPO (lipid peroxidation) and DNA injury. To minimize the damage effects, the antioxidant defense mechanisms (antioxidant enzymes and non-enzymatic antioxidants) were activated, and entailed a decrease of the antioxidant capacity in E. fetida brain, which, in turn, causes further ROS-induced ROS release. Exposure of fluorene induced the abnormal mRNA expression of genes relevant to oxidative stress (e.g., GST, SOD, CAT, GPx, MT, and Hsp70) and neurotoxicity (e.g., H02, C04, D06, and E08) in E. fetida brain. Specifically, fluorene can bind directly to AChE, destroying the conformation of this protein, and even affecting its physiological functions. This occurrence caused the inhibition of AChE activity and excess ACh accumulation at the nicotinic post-synaptic membrane, finally triggering neurotoxicity by activation of pathways related to oxidative stress. Moreover, the avoidance responses and burrowing behavior were obviously disturbed by oxidative stress-induced neurotoxicity after exposure to fluorene. The results form IBR suggested more severe poisoning effects to E. fetida brain initiated by high-dose and long-term exposure of fluorene. Among, oxidative stress injury and genotoxic potential are more sensitive endpoint than others. Collectively, fluorene stress can provoke potential neurotoxicity, genotoxicity, and behavioral disturbances targeted to E. fetida brain through the ROS-mediated pathways involving oxidative stress. These findings are of great significance to estimate the detrimental effects of fluorene and the corresponding mechanisms on soil eco-safety.

Response pathways of superoxide dismutase and catalase under the regulation of triclocarban-triggered oxidative stress in Eisenia foetida: Comprehensive mechanism analysis based on cytotoxicity and binding model.

Triclocarban (TCC) is an emerging environmental contaminant, posing potential ecological risks. Displaying a high accumulation effect and 120-day half-life in the soil environment, the toxic effects of TCC to soil organisms have been widely reported. Previous studies have confirmed that TCC can induce the oxidative stress and changes in superoxide dismutase (SOD) and catalase (CAT) activities in earthworms, but the underlying mechanisms of oxidative stress and disorder in antioxidant enzyme activities induced by TCC have not yet been elucidated. Here, we explored the multiple response mechanisms of SOD and CAT under the regulation of oxidative stress induced by TCC. Results indicated that higher-dose (0-2.0 mg/L) TCC exposure triggered the overproduction of ROS in Eisenia foetida coelomocytes, causing oxidative damage and a decrease in cell viability that was response to ROS accumulation. The TCC-induced inhibition of intracellular SOD/CAT activity was found under the regulation of oxidative stress (SOD: 29.2 %; CAT: 18.5 %), and this effect was blunted by antioxidant melatonin. At the same time, the interaction between antioxidative enzymes and TCC driven by various forces (SOD: electrostatic interactions; CAT: van der Waals forces and hydrogen bonding) led to inhibited SOD activity (9.84 %) and enhanced CAT activity (17.5 %). Then, to elucidate the binding mode of TCC, we explored the changes in SOD and CAT structure (protein backbone and secondary structure), the microenvironment of aromatic amino acids, and aggregation behavior through multispectral techniques. Molecular docking results showed that TCC inhibited SOD activity in a substrate competitive manner and enhanced CAT activity by the stabilizing effects of TCC on the heme groups. Collectively, this study reveals the response mechanisms of SOD/CAT under the regulation of TCC-triggered oxidative stress and shed a new light on revealing the toxic pathways of exogenous pollutants on antioxidant-related proteins function.

Size-dependent effects of nanoplastics on structure and function of superoxide dismutase.

The ubiquitous existence of nano-plastics (NPs) has attracted widespread concern. Currently, the uptake of NPs by organisms and cells has been reported. However, knowledge about the interaction between NPs and protein is still limited, and there is a gap in research on the size-dependent toxicity of NPs toward protein. In this study, multi-spectroscopic techniques and enzyme activity determination were used to explore the structure and function changes of the main antioxidant enzyme superoxide dismutase (SOD), caused by the binding of NPs with different particle sizes. Results indicated NPs with different sizes can directly interact with SOD. NPs with smaller sizes result in looser skeletons of SOD, while the larger lead to tighter peptide chains. In addition, NPs can bind with SOD to form complexes, and the smaller the NPs are easier to be induced to coalesce by SOD. The surface curvature of 100 nm NPs was more conducive to varying the secondary structure of SOD. NPs of 100 nm and 500 nm can cause greater sensitization of SOD endogenous fluorescence, and increase the polarity around tyrosine residue. The enzyme activity assay further revealed the functional differences caused by the size-dependent effects of NPs. NPs of 100 nm and 20 nm induced a more significant change in SOD activity (increased by 20% and 8%, respectively), while NPs of 500 nm and 1000 nm had a little impact on it. Together, smaller NPs have a greater impact on the structure and function of SOD. This study revealed the size-dependent toxicity of NPs to protein, which provided a rationale for the necessary avoidance and substitution of NPs in engineering applications.