Characterization of mercury-binding proteins in human neuroblastoma SK-N-SH cells with immobilized metal affinity chromatography

Nano mercury selenide as a source of mercury for rice

Mercury (Hg) is a persistent and toxic metal while mercury selenide (HgSe) is generally considered as the environmental sink of Hg in its biogeochemical cycle. Recent studies found nano-sized HgSe (nano-HgSe) could be transformed by certain bacteria. This raises safety concerns about the application of selenium (Se) to curb Hg contamination in farmlands. Therefore, hydroponic experiments were performed in which rice plants were cultured with different concentrations of nano-HgSe and micro-sized HgSe (micro-HgSe) to explore their bioavailability and toxicity. It was found that both nano-HgSe and micro-HgSe did not affect the germination of rice seeds but affected the growth of rice seedlings. However, nano-HgSe could be more readily absorbed by roots and transferred to the aboveground parts compared to micro-HgSe. The highest Hg and Se levels were found to be 5255.67 ± 2496.14 μg/g and 1743.75 ± 61.87 μg/g, respectively in roots when exposed to 5000 mg/L nano-HgSe. Besides, small portion (1.2%) of methylmercury (MeHg) to total Hg was found accumulated in rice stem when exposed to 100 mg/L nano-HgSe, suggesting that nano-HgSe could be decomposed. Furthermore, nano-HgSe exposure brought oxidative damage to rice with decreased chlorophyll content and GSH-Px activity. In all, nano-HgSe was found to be more absorbable, transportable and methylated in rice plant compared to micro-HgSe. This suggests that although Se application in Hg contaminated farmland is an effective way to reduce the bioavailability of Hg, the risk of the possible remobilization of HgSe should not be neglected. Besides, the finding that nano-HgSe can act as an environmental source of Hg for plants deepens the understanding of biogeochemical cycle of Hg. More works are required to study the factors affecting the formation of nano-HgSe in the environment and the mechanisms of Hg methylation in rice plants after exposure to nano-HgSe.

Infrared microspectroscopy studies on the protective effect of curcumin coated gold nanoparticles against H2O2-induced oxidative stress in human neuroblastoma SK-N-SH cells

The contribution of oxidative stress in several chronic and degenerative diseases suggests that antioxidant therapy can be a promising therapeutic strategy. However, in the case of many antioxidants, their biodistribution and bioactivity are restricted due to low water solubility. Curcumin is a powerful free radical scavenger that upon conjugation to gold nanoparticles results in the formation of stable gold nanoparticles that act as highly water-soluble carriers for the curcumin molecules. In the present study, the effect of curcumin-coated gold nanoparticles (Cur-GNPs) on the H₂O₂-treated human neuroblastoma (SK-N-SH) cell line was evaluated by using Fourier transform infrared (FTIR) microspectroscopy. Biochemical changes in cells resulting from exposure to reactive oxygen species (ROS) and antioxidant treatment on cells were investigated. Analyzing changes in PO₂^- bands and amide bands in the fingerprint region and also changes in the ratio of CH_2(asym) to CH_3(asym) bands in the lipid region revealed that post-treatment with Cur-GNPs could effectively decrease the damage on DNA caused by H₂O₂ treatment, whereas pre-treatment of cells with Cur-GNPs was found to be more effective at preventing lipid peroxidation than post-treatment. Further analysis of the CH_2(asym) to CH_3(asym) ratio provided information on not only the lipid peroxidation level in cells, but also the interaction of nanoparticles with the plasma membrane, as confirmed by lactate dehydrogenase assay.

Molecular Mechanisms of Environmental Metal Neurotoxicity: A Focus on the Interactions of Metals with Synapse Structure and Function

Environmental exposure to neurotoxic metals and metalloids such as arsenic, cadmium, lead, mercury, or manganese is a global health concern affecting millions of people worldwide. Depending on the period of exposure over a lifetime, environmental metals can alter neurodevelopment, neurobehavior, and cognition and cause neurodegeneration. There is increasing evidence linking environmental exposure to metal contaminants to the etiology of neurological diseases in early life (e.g., autism spectrum disorder) or late life (e.g., Alzheimer’s disease). The known main molecular mechanisms of metal-induced toxicity in cells are the generation of reactive oxygen species, the interaction with sulfhydryl chemical groups in proteins (e.g., cysteine), and the competition of toxic metals with binding sites of essential metals (e.g., Fe, Cu, Zn). In neurons, these molecular interactions can alter the functions of neurotransmitter receptors, the cytoskeleton and scaffolding synaptic proteins, thereby disrupting synaptic structure and function. Loss of synaptic connectivity may precede more drastic alterations such as neurodegeneration. In this article, we will review the molecular mechanisms of metal-induced synaptic neurotoxicity.

DNA repair and cholesterol-mediated drug efflux induce dose-dependent chemoresistance in nutrient-deprived neuroblastoma cells

Neuroblastoma is a solid, heterogeneous pediatric tumor. Chemotherapy is widely used to treat neuroblastoma. However, dose-dependent responses and chemoresistance mechanisms of neuroblastoma cells to anticancer drugs remain challenging. Here, we investigated the dose-dependent effects of topotecan on human neuroblastoma cells (SK-N-SH, SH-SY5Y, and SK-N-BE) under various nutrient supply conditions. Serum-starved human neuroblastoma cells showed reduced toxicity. Their survival rate increased upon treatment with a high concentration (1 μM) of topotecan. Quantitative profiling of global and phosphoproteome identified 12,959 proteins and 48,812 phosphosites, respectively, from SK-N-SH cells. Network analysis revealed that topotecan upregulated DNA repair and cholesterol-mediated topotecan efflux, resulting in topotecan resistance. Results of DNA damage assay, cell cycle, and quantitative analyses of membrane cholesterol supported the validity of these resistance factors and their applicability to all neuroblastoma cells. Our results provide a model for high dose-dependent chemoresistance in neuroblastoma cells that could enable a patient-dependent chemotherapy screening strategy.

Sulfhydryl groups as targets of mercury toxicity

The present study addresses existing data on the affinity and conjugation of sulfhydryl (thiol; -SH) groups of low- and high-molecular-weight biological ligands with mercury (Hg). The consequences of these interactions with special emphasis on pathways of Hg toxicity are highlighted. Cysteine (Cys) is considered the primary target of Hg, and link its sensitivity with thiol groups and cellular damage. In vivo, Hg complexes play a key role in Hg metabolism. Due to the increased affinity of Hg to SH groups in Cys residues, glutathione (GSH) is reactive. The geometry of Hg(II) glutathionates is less understood than that with Cys. Both Cys and GSH Hg-conjugates are important in Hg transport. The binding of Hg to Cys mediates multiple toxic effects of Hg, especially inhibitory effects on enzymes and other proteins that contain free Cys residues. In blood plasma, albumin is the main Hg-binding (Hg2+, CH3Hg+, C2H5Hg+, C6H5Hg+) protein. At the Cys34 residue, Hg2+ binds to albumin, whereas other metals likely are bound at the N-terminal site and multi-metal binding sites. In addition to albumin, Hg binds to multiple Cys-containing enzymes (including manganese-superoxide dismutase (Mn-SOD), arginase I, sorbitol dehydrogenase, and δ-aminolevulinate dehydratase, etc.) involved in multiple processes. The affinity of Hg for thiol groups may also underlie the pathways of Hg toxicity. In particular, Hg-SH may contribute to apoptosis modulation by interfering with Akt/CREB, Keap1/Nrf2, NF-κB, and mitochondrial pathways. Mercury-induced oxidative stress may ensue from Cys-Hg binding and inhibition of Mn-SOD (Cys196), thioredoxin reductase (TrxR) (Cys497) activity, as well as limiting GSH (GS-HgCH3) and Trx (Cys32, 35, 62, 65, 73) availability. Moreover, Hg-thiol interaction also is crucial in the neurotoxicity of Hg by modulating the cytoskeleton and neuronal receptors, to name a few. However, existing data on the role of Hg-SH binding in the Hg toxicity remains poorly defined. Therefore, more research is needed to understand better the role of Hg-thiol binding in the molecular pathways of Hg toxicology and the critical role of thiols to counteract negative effects of Hg overload.

Mercury and Atherosclerosis: Cell Biology, Pathophysiology, and Epidemiological Studies

Today atherosclerosis is considered as a main cause of death in the worldwide. There is a significant association between heavy metal exposure and atherosclerosis. In this study, we discussed the scientific literature about the effect of mercury on the pathogenesis of atherosclerosis. We also considered the epidemiological studies on mercury as a risk factor for atherosclerosis. Web of Science, Google Scholar, Medline, PubMed, and Scopus were searched by using the following keywords to 2019: (cardiovascular diseases OR atherosclerosis OR endothelial dysfunction) AND (mercury). Mercury has the potential to act as one of the novel risk factors for atherosclerosis development. The findings have indicated the role of mercury in the pathogenesis of atherosclerosis, vascular endothelial dysfunction, oxidative stress, inflammation, and dyslipidemia. Mercury can induce atherosclerosis indirectly via increasing the total cholesterol, triglycerides, and LDL-C levels as well as decreasing the HDL-C level. Mercury can be considered as a risk factor in the atherosclerosis progression. However, more studies are required to find the exact mechanisms involved in the pathogenesis of atherosclerosis induced by mercury.

Bioaccumulation of Hg in Rice Leaf Facilitates Selenium Bioaccumulation in Rice (Oryza sativa L.) Leaf in the Wanshan Mercury Mine

Mercury (Hg) bioaccumulation in rice poses a health issue for rice consumers. In rice paddies, selenium (Se) can decrease the bioavailability of Hg through forming the less bioavailable Hg selenides (HgSe) in soil. Rice leaves can directly uptake a substantial amount of elemental Hg from the atmosphere, however, whether the bioaccumulation of Hg in rice leaves can affect the bioaccumulation of Se in rice plants is not known. Here, we conducted field and controlled studies to investigate the bioaccumulation of Hg and Se in the rice-soil system. In the field study, we observed a significantly positive correlation between Hg concentrations and BAFs of Se in rice leaves (r² = 0.60, p < 0.01) collected from the Wanshan Mercury Mine, SW China, suggesting that the bioaccumulation of atmospheric Hg in rice leaves can facilitate the uptake of soil Se, perhaps through the formation of Hg-Se complex in rice leaves. This conclusion was supported by the controlled study, which observed significantly higher concentrations and BAFs of Se in rice leaf at a high atmospheric Hg site at WMM, compared to a low atmospheric Hg site in Guiyang, SW China.

Cadmium-binding proteins in human blood plasma

Blood is the transmission medium for metal contaminants to and from bodily organs; as such, it can provide useful and reliable information about their bio-kinetics as they're distributed throughout the body. Metals can interact with endogenous proteins present in the blood, and these metal-protein complexes often dictate the fates of the introduced metals. The aim of this study was to investigate cadmium-binding protein characteristics in normal human plasma. Cadmium-binding plasma proteins in two different groups: normal human plasma (n = 29), and normal paired maternal and fetal umbilical cord plasmas (n = 3), were analyzed. In order to detect cadmium-binding plasma proteins present in low concentrations, blood plasma samples were first depleted of their two most abundant proteins - albumin and immunoglobulin G. Both the crude and depleted plasma samples were analyzed using column gel electrophoresis in conjunction with Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). One cadmium-binding protein was detected in 11 of 29 normal plasma samples and all three paired maternal and cord plasma samples. This protein was further identified as apolipoprotein A-I by high-resolution mass spectrometry. To the best of our knowledge, this is the first study to reveal cadmium-binding proteins in real human blood plasma, which is extremely critical to our understanding of cadmium transportation and accumulation in human blood.

Analysis of silver-associated proteins in pathogen via combination of native SDS-PAGE, fluorescent staining, and inductively coupled plasma mass spectrometry

Characterization of silver-associated proteins is important to elucidate underlined mechanisms of silver-containing materials against microbes. Gel electrophoresis based methods are the most popular and basic strategy for the analysis of biomolecules, i.e., proteins and nucleic acids. It solely provides molecular weights of analytes. Extending the method from molecular weight to elemental composition is highly desired when investigating metal-containing molecules. Herein, a gel electrophoresis based method combining native sodium dodecyl sulfate-polyacrylamide gel electrophoresis (native SDS-PAGE), fluorescent staining, and inductively coupled plasma mass spectrometry (ICP-MS) strategy was developed for separation and detection of silver-associated proteins. Two home-made silver-labeled proteins, carbonic anhydrase and ovalbumin, were used for validation of the strategy performance. Silver-associated proteins in Pseudomonas aeruginosa and Staphylococcus aureus treated with silver nanoparticles were further characterized by this method. Some well-known and new proteins were identified to associate to silver in both P. aeruginosa and S. aureus, demonstrating the feasibility of the developed strategy. In conclusion, the current study provides a convenient method for readily identification of silver-associated proteins in biological samples.

Interactions between an amphipathic di-histidine peptide and a metal affinity chromatographic resin derived from a bis(tacn)butane chelating ligand

The interactive behavior of an amphipathic peptide with the Cu²⁺ , Ni²⁺ , and Zn²⁺ complexes of 1,4-bis(triazacyclonon-1-yl)butane), bis(tacn)^but , immobilized onto Sepharose CL-4B, has been investigated. The effects of incubation time, as well as the incubation buffer pH and ionic strength, have been examined. The binding data have been interrogated using Langmuir, Langmuir-Freundlich, bi-Langmuir, and Temkin isothermal models and Scatchard plots. These results confirm that this amphipathic peptide binds with relatively high capacities to the immobilized Cu²⁺ - and Ni²⁺ -1,4-bis(triazacyclonon-1-yl)butane)-Sepharose CL-4B sorbents via at least two discrete sites. However, the corresponding immobilized Zn²⁺ -sorbent had low binding capacity. Moreover, the magnitude of the binding capacities of these sorbents was dependent on the pH and ionic strength of the incubation buffer. These results are relevant to the isolation of E. coli expressed recombinant proteins that incorporate this and related amphipathic peptide tags, containing two or more histidine residues, located at the N- or C-terminus of the recombinant protein, and the co-purification of low abundance host cell proteins of diverse structure, by immobilized metal ion affinity chromatographic methods.

In vivo oral bioavailability of fish mercury and comparison with in vitro bioaccessibility

Fish consumption is considered to be a major human exposure route for mercury (Hg), but assessing the actual Hg bioavailability from consumed fish is challenging. In this study, we conducted both in vivo bioavailability (using a mouse model) and in vitro bioaccessibility (using various gastrointestinal digestion methods) assessments of Hg from consumed fish. Lyophilized fish muscles which already absorbed Hg through natural incorporation were introduced to mice by active feeding. Assimilation efficiency (AE) was measured as a short-term kinetic parameter, while a 7-day accumulation of Hg in mice blood, liver and kidney was determined. The AEs of Hg in mice ranged between 82 and 96% and showed a positive relationship with MeHg in fish independent of the fish species. For long-term bioavailability tests in which the Hg retention in organs was measured after a 7-day exposure, most Hg was found to be accumulated in liver and kidney, resulting in a strong correlation between Hg dosage and accumulation in mice organs. The long-term absolute bioavailability of mice was comparable between the liver and kidney, but much lower in the blood. The calculated absolute total Hg bioavailability ranged between 38% and 99% and decreased as the Hg dosage increased. Results of bioaccessibility tests varied considerably among different methods, illustrating that there were limitations for the in vitro bioaccessibility assay to predict the digestive dynamics of Hg in mammalian gastrointestinal tract. Our study strongly demonstrated the expediency of direct determination of Hg bioavailability, but more bioaccessibility assessments should be explored and optimized as an alternative to traditional animal experimentation.

Au@gap@AuAg Nanorod Side-by-Side Assemblies for Ultrasensitive SERS Detection of Mercury and its Transformation

As one of the most toxic heavy metal elements, mercury ion (Hg²⁺ ) and its methylated product, methylmercury (MeHg) can pose a threat to human health and the environment. Herein, a novel Raman biosensor with cascade sensitivity is developed for Hg²⁺ detection through Au@gap@AuAg nanorod side-by-side assemblies. Due to the strong electromagnetic coupling from the assemblies and core-shell structure, the Raman sensor possesses high sensitivity with the limit of detection (LOD) of 0.001 ng mL^-1 , which is about one order lower than traditional atomic fluorescence spectrometer (AFS) methods. Moreover, the fabricated biosensor is used to measure residual mercury levels in tissues and eggs of hens fed high-mercury diets, and the results show total mercury in collected egg yolks is 20 times higher than whites. Furthermore, the form of mercury in the eggs is also analyzed by high-performance liquid chromatography coupled with AFS, and, unexpectedly, the methylated product MeHg tends to only be found in egg whites. These interesting differences may indicate a new research direction for the toxicity of mercury in living organisms, and the developed ultrasensitive Surface Enhanced Raman Scattering (SERS) method could pave a broad way for the application of biosensors in Hg detection.

Methylmercury exposure alters RNA splicing in human neuroblastoma SK-N-SH cells: Implications from proteomic and post-transcriptional responses

The neurotoxic effects of methylmercury (MeHg) have been intensively studied. However, the molecular mechanisms responsible for the neurotoxicity of MeHg are not fully understood. To decipher these mechanisms, proteomic and high-throughput mRNA sequencing (RNA-seq) technique were utilized, comprehensively evaluating the cellular responses of human neuroblastoma SK-N-SH cells to MeHg exposure. Proteomic results revealed that MeHg exposure interfered with RNA splicing via splicesome, along with the known molecular mechanisms of mercury-related neurotoxicity (e.g. oxidative stress, protein folding, immune system processes, and cytoskeletal organization). The effects of MeHg on RNA splicing were further verified using RNA-seq. Compared to control, a total of 658 aberrant RNA alternative splicing (AS) events were observed after MeHg exposure. Proteomics and RNA-seq results also demonstrated that mercury chloride (HgCl₂) influenced the expression levels of several RNA splicing related proteins and 676 AS events compared to control. These results suggested that RNA splicing could be a new molecular mechanism involved in MeHg and HgCl₂ neurotoxicity.

Thermophoresis for characterizing biomolecular interaction

The study of biomolecular interactions is crucial to get more insight into the biological system. The interactions of protein-protein, protein-nucleic acids, protein-sugars, nucleic acid-nucleic acids and protein-small molecules are supporting therapeutics and technological developments. Recently, the development in a large number of analytical techniques for characterizing biomolecular interactions reflect the promising research investments in this field. In this review, microscale thermophoresis technology (MST) is presented as an analytical technique for characterizing biomolecular interactions. Recent years have seen much progress and several applications established. MST is a powerful technique in quantitation of binding events based on the movement of molecules in microscopic temperature gradient. Simplicity, free solutions analysis, low sample volume, short analysis time, and immobilization free are the MST advantages over other competitive techniques. A wide range of studies in biomolecular interactions have been successfully carried out using MST, which tend to the versatility of the technique to use in screening binding events in order to save time, cost and obtained high data quality.

Characterization of mercury-binding proteins in rat blood plasma

Mercury-binding protein profiles in plasma in vitro and in vivo, which were unclear previously, were systematically investigated.

Electrochemical Hg2+ detection at tannic acid-gold nanoparticle modified electrodes by square wave voltammetry

We report the electrochemical sensing of Hg²⁺ based on tannic acid capped gold nanoparticle (AuNP@TA) complexes.

Tri-pillar[5]arene-based multi-stimuli-responsive supramolecular polymers for fluorescence detection and separation of Hg2+

A novel tri-pillar[5]arene based supramolecular polymer (JP5G) shows multiple stimuli-response properties and could detect and remove Hg²⁺ from aqueous solution.