Competitive Inhibition Mechanism of Acetylcholinesterase without Catalytic Active Site Interaction: Study on Functionalized C₆₀ Nanoparticles via in Vitro and in Silico Assays

Acetylcholinesterase (AChE) activity regulation by chemical agents or, potentially, nanomaterials is important for both toxicology and pharmacology. Competitive inhibition via direct catalytic active sites (CAS) binding or noncompetitive inhibition through interference with substrate and product entering and exiting has been recognized previously as an AChE-inhibition mechanism for bespoke nanomaterials. The competitive inhibition by peripheral anionic site (PAS) interaction without CAS binding remains unexplored. Here, we proposed and verified the occurrence of a presumed competitive inhibition of AChE without CAS binding for hydrophobically functionalized C₆₀ nanoparticles (NPs) by employing both experimental and computational methods. The kinetic inhibition analysis distinguished six competitive inhibitors, probably targeting the PAS, from the pristine and hydrophilically modified C₆₀ NPs. A simple quantitative nanostructure–activity relationship (QNAR) model relating the pocket accessible length of substituent to inhibition capacity was then established to reveal how the geometry of the surface group decides the NP difference in AChE inhibition. Molecular docking identified the PAS as the potential binding site interacting with the NPs via a T-shaped plug-in mode. Specifically, the fullerene core covered the enzyme gorge as a lid through π–π stacking with Tyr72 and Trp286 in the PAS, while the hydrophobic ligands on the fullerene surface inserted into the AChE active site to provide further stability for the complexes. The modeling predicted that inhibition would be severely compromised by Tyr72 and Trp286 deletions, and the subsequent site-directed mutagenesis experiments proved this prediction. Our results demonstrate AChE competitive inhibition of NPs without CAS participation to gain further understanding of both the neurotoxicity and the curative effect of NPs

Thermal Degradation of Octachloronaphthalene over As-Prepared Fe₃O₄ Micro/Nanomaterial and Its Hypothesized Mechanism

Decomposition of octachloronaphthalene (CN-75) featuring fully substituted chlorines was investigated over as-prepared Fe₃O₄ micro/nanomaterial at 300 °C. It conforms to pseudo-first-order kinetics with <i>k</i>_obs = 0.10 min^–1 as comparable to that of hexachlorobenzene and decachlorobiphenyl. Analysis of the products indicates that the degradation of CN-75 proceeds via two competitive hydrodechlorination and oxidation pathways. The onset of hydrodechlorination producing lower chlorinated naphthalenes (CNs) is more favored on α-position than β-position. Higher amounts of CN-73, CN-66/67, CN-52/60, and CN-8/11 isomers were found, while small content difference was detected within the tetrachloronaphthalene and trichloronaphthalene homologues, which might be attributed to lower energy principle and steric effects. The important hydrodechlorination steps, leading to CN-73 ≫ CN-74 in two heptachloronaphthalene isomers contrary to that in technical PCN-mixtures, were specified by calculating the charge of natural bond orbitals in CN-75 and the energy of two heptachloronaphthalene radicals. On the basis of the molecular electrostatic potential of CN-75, the nucleophilic O^2–, and eletrophilic O₂^– and O^–, present on the Fe₃O₄ surface, might attack the carbon atom and π electron cloud of naphthalene ring, producing naphthol species with Mars–van Krevelen mechanism, and formic and acetic acids

Influence of E‑Waste Dismantling and Its Regulations: Temporal Trend, Spatial Distribution of Heavy Metals in Rice Grains, and Its Potential Health Risk

Enhanced regulations, centralized dismantling processes, and sophisticated recycling technologies have been implemented in some e-waste dismantling areas in China with regard to environmental and economic aspects since 2005. In this study, rice grain samples were collected from 2006 to 2010 in an e-waste dismantling area to investigate the temporal trends and spatial distribution of As, Cd, Cu, and Pb. Geometric means of As, Cd, Cu, and Pb in rice samples from the e-waste dismantling area were 111, 217, 4676, and 237 ng g^–1, respectively. Levels of Pb showed a significant decreasing trend during the sampling period, whereas the other three elements remained relatively constant or even increased. Concentrations of Cd, Cu, and Pb in the e-waste dismantling area were significantly higher than those in the non-e-waste dismantling area (<i>p</i> < 0.05), which showed a close connection between e-waste dismantling activities and elevated Pb, Cu, and Cd contents. Risk assessment for human via rice consumption indicated that over 60% of the hazard quotient of Cd exceeded 1 in the e-waste dismantling area. Our study implied that stricter implementation of regulatory measures might lead to positive effects in controlling the release of some heavy metals to the environment. However, environmental behaviors differed with geochemical characteristics of individual elements. Further remediation actions to reduce heavy metal pollution to the surrounding environment might still be needed

Differential Accumulation and Elimination Behavior of Perfluoroalkyl Acid Isomers in Occupational Workers in a Manufactory in China

In this study, serum and urine samples were collected from 36 occupational workers in a fluorochemical manufacturing plant in China from 2008 to 2012 to evaluate the body burden and possible elimination of linear and branched perfluoroalkyl acids (PFAAs). Indoor dust, total suspended particles (TSP), diet, and drinking water samples were also collected to trace the occupational exposure pathway to PFAA isomers. The geometric mean concentrations of perfluorooctanesulfonate (PFOS), perfluorooctanoate (PFOA), and perfluorohexanesulfonate (PFHxS) isomers in the serum were 1386, 371, and 863 ng mL^–1, respectively. The linear isomer of PFOS, PFOA, and PFHxS was the most predominant PFAA in the serum, with mean proportions of 63.3, 91.1, and 92.7% respectively, which were higher than the proportions in urine. The most important exposure routes to PFAA isomers in the occupational workers were considered to be the intake of indoor dust and TSP. A renal clearance estimation indicated that branched PFAA isomers had a higher renal clearance rate than did the corresponding linear isomers. Molecular docking modeling implied that linear PFOS (<i>n</i>-PFOS) had a stronger interaction with human serum albumin (HSA) than branched isomers did, which could decrease the proportion of <i>n</i>-PFOS in the blood of humans via the transport of HSA

Structure-Dependent Hematological Effects of Per- and Polyfluoroalkyl Substances on Activation of Plasma Kallikrein–Kinin System Cascade

Per- and polyfluoroalkyl substances (PFASs) are a global concern because of their ubiquitous occurrence and high persistence in human blood, and increasing amounts of unidentified fluorinated compounds are now becoming new exposure issues. This study aims to investigate the structure-related effects of PFASs on the activation of the plasma kallikrein-kinin system (KKS). The effects of 20 PFASs and the related long-chain aliphatic compounds were screened, and their binding affinities for the initial zymogen, Hagmen factor XII (FXII) in the KKS, were evaluated by molecular docking analysis. PFASs were demonstrated to activate the KKS in a structure-dependent mode. More specifically, PFASs with longer carbon chain length, higher fluorine atom substitution degree, and terminal acid group exhibited relatively higher activities in activating the KKS. The binding affinities of PFASs with FXII determined their capabilities for inducing KKS activation. The alternative binding modes of PFASs with FXII, together with van der Waals and hydrogen bonds, specifically accommodated the distinctive chemical structures. To our knowledge, PFASs, for the first time, were found to induce the activation of the KKS in plasma, and their chemical structure-related effects would be extremely important for risk assessment on emerging PFASs in addition to the listing in Stockholm Convention

Remarkable Contamination of Short- and Medium-Chain Chlorinated Paraffins in Free-Range Chicken Eggs from Rural Tibetan Plateau

Rapid social-economic development introduces modern lifestyles into rural areas, not only bringing numerous modern products but also new pollutants, such as chlorinated paraffins (CPs). The rural Tibetan Plateau has limited industrial activities and is a unique place to investigate this issue. Herein we collected 90 free-range chicken egg pool samples across the rural Tibetan Plateau to evaluate the pollution status of CPs. Meanwhile, CPs in related soils, free-range chicken eggs from Jiangxi, and farmed eggs from markets were also analyzed. The median concentrations of SCCPs (159 ng g–1 wet weight (ww)) and MCCPs (1390 ng g–1 ww) in Tibetan free-range chicken eggs were comparable to those from Jiangxi (259 and 938 ng g–1 ww) and significantly higher than those in farmed eggs (22.0 and 81.7 ng g–1 ww). In the rural Tibetan Plateau, the median EDI of CPs via egg consumption by adults and children were estimated to be 81.6 and 220.2 ng kg–1 bw day–1 for SCCPs and 483.4 and 1291 ng kg–1 bw day–1 for MCCPs, respectively. MCCPs might pose potential health risks for both adults and children in the worst scenario. Our study demonstrates that new pollutants should not be ignored and need further attention in remote rural areas

Endogenous gene CYP1A1 expression in mouse hepatoma cells.

<p>Hepa1c1c7 cells were incubated with DMSO (1%, final concentration), TCDD (1 nM), or ginsenosides (10 µM) for 4 h at 37°C, mRNA was extracted, subjected to RT-PCR and amplification. The asterisk indicated that the gene expression was significantly induced compared to DMSO-treated sample at p<0.05 (*).</p

Structures of ginsenosides examined in this study.

<p>Abbreviations for carbohydrates are as follows: Glc, glucopyranoside; Ara, arabinopyranoside; Rha, rhamnopyranoside; Xyl, xylopyranoside; TG, total ginsenosides (mixed compounds). Superscripts indicated the carbon in the glucose ring that linked the two carbohydrates.</p

Dose-dependent induction of luciferase activity by TCDD and Rc in AHR-responsive recombinant guinea pig (G16L1.1c8), rat (H4L1.1c4), mouse (H1L1.1c2) and human (HG2L6.1c3) cells.

<p>Cells were incubated with the indicated concentration of Rc for 4 h and luciferase activity was determined as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066258#s2" target="_blank">Materials and Methods</a> section. Dose-dependent induction of luciferase activity by TCDD and Rc in (A) G16L1.1c8, (B) H4L1.1c4, (C) H1L1.1c2 and (D) HG2L6.1c3 cells were shown. Values were expressed in the figure as the percentage of maximal TCDD induction and represented the mean ± SD of triplicate determinations. All concentrations of TCDD ≥10⁻¹¹ M and of Rc ≥10⁻⁵ M were significantly greater than DMSO-treated sample at p<0.01 as determined by Student's <i>t</i>-test.</p

Induction of luciferase activity by ginsenosides in AHR-responsive recombinant guinea pig G16L1.1c8 cells.

<p>(A) G16L1.1c8 cells were treated with 1 µM or 10 µM ginsenosides for 4 h. (B) G16L1.1c8 cells were treated with 1 µM/10 µM ginsenosides + 1 nM TCDD for 4 h and luciferase activity was determined as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066258#s2" target="_blank">Materials and Methods</a> section. Values were expressed in the figure as the percentage of maximal TCDD induction and represented the mean ± SD of triplicate determinations. The asterisk indicated that the values of induction or inhibition was significantly increased compared to DMSO-treated sample at p<0.05 (*).</p