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Inorganic Nanoparticles as Enzyme Mimics
Published in Grunwald Peter, Biocatalysis and Nanotechnology, 2017
Ruben Ragg, Karsten Korschelt, Karoline Herget, Filipe Natalio, Muhammad Nawaz Tahir, Wolfgang Tremel
Based on the reported intrinsic peroxidase and haloperoxidase activity, V2O5 nanowires were recently used to mimic the enzymatic activity of glutathione peroxidase (GPx) (Vernekar et al., 2014). Glutathione (GSH), a tripeptide consisting of glutamate, glycine and cysteine, contains a free sulfhydryl residue in its reduced form and is therefore able to act as an intracellular antioxidant by reducing potentially toxic reactive oxygen species (ROS), while being oxidized to glutathione disulfide dimer (GSSG) (Masella et al., 2005). Native glutathione peroxidase and V2O5 nanowires use H2O2 as co-substrate to oxidize GSH to GSSG leading to reduced intracellular H2O2 levels. V2O5 nanowires readily enter into mammalian cells, which are therefore protected when challenged with intrinsic or extrinsic oxidative stress by scavenging ROS (Vernekar et al., 2014).
Lead Toxicity
Published in Debasis Bagchi, Manashi Bagchi, Metal Toxicology Handbook, 2020
Rokeya Pervin, Md. Akil Hossain, Dipti Debnath, Mohiuddin Ahmed Bhuiyan
Lead toxicity is usually occurred by generating an increased amount of reactive oxygen species (ROS) and by interfering with an antioxidant generation [13]. Lead is not a redox-active element and it cannot directly play a role in those reactions which initiate the ROS formation. It was found that the generation of ROS in erythrocytes is increased by the interaction of lead with oxyhemoglobin [14]. The most significant contribution of lead in the initiation and expansion of oxidative stress is arisen by its interference with the enzymes and other cellular components/mechanisms of the defensive system which are responsible for preventing oxidative damage [15]. Glutathione (GSH), a tri-peptide of cysteine, histidine, and glutamate, is one of the most significant elements that protects cell components from ROS damage [2]. In healthy cells and tissues, 90% of GSH exists in reduced form and 10% in oxidized form, and it usually functions as an antioxidant defense mechanism. GSH after being converted (oxidized) to glutathione disulfide is reduced back to GSH by glutathione reductase [16]. Lead inactivates glutathione by binding to GSH’s sulphydryl group, which inhibits sulphydryl-dependent enzymes (e.g., glutathione reductase, superoxide dismutase, catalase, etc.) and causes GSH replenishment to become inefficient. Inhibition of these enzymes leads to the production of reactive oxygen species with resultant oxidative stress. The increase in oxidative stress leads to the damage of the cell membrane because of lipid peroxidation. Lead obstructs the activities of 5-aminolevulinic acid dehydratase and directs to hemoglobin oxidation, which together with the lipid peroxidation can cause hemolysis [17].
Mechanisms of Nanotoxicity to Cells, Animals, and Humans
Published in Vineet Kumar, Nandita Dasgupta, Shivendu Ranjan, Nanotoxicology, 2018
Belinda Wong Shu Ee, Puja Khanna, Ng Cheng Teng, Baeg Gyeong Hun
Nanoparticles can generate ROS not only through their reactive surfaces, but also through their interaction with cellular mechanisms such as mitochondria, which are the major source of ROS production. For instance, nanoparticles impaired ETC in mitochondria which led to the depolarization of the inner mitochondrial membrane, thus promoting ROS production (Manke et al. 2013). In support of this, cationic polystyrene nanospheres have been shown to target mitochondria and induce ROS-initiated apoptosis in murine macrophages (Xia et al. 2006). Similarly, multi-walled carbon nanotubes (MWCNT) were also reported to cause oxidative stress via mitochondrial damage (He et al. 2011). Antioxidant enzymes such as SOD, CAT, and NADPH-dependent flavoenzyme are important defenses against oxidative stress in a cell. GSH, a potent ROS scavenger, is equally important in combating oxidative stress by reacting with nanoparticle-generated free radicals (Manke et al. 2013). The oxidation of GSH to glutathione disulphide (GSSG) and cysteine-SH residues in antioxidant enzymes cripples the antioxidant defense system and subsequently induces oxidative stress (Figure 11.1) (Rahman et al. 2005). Studies have shown that single-walled carbon nanotubes (SWCNT) produce ROS by reducing mitochondrial membrane potential and the activities of antioxidant enzymes such as SOD and CAT in neuronal PC12 cells (Wang et al. 2011). Interestingly, exposure of the lung fibroblast MRC-5 cells to hematite nanoparticles has been shown to lead to a significant decrease in GSH levels along with a dramatic increase in the activity of antioxidant enzymes such as SOD, CAT, GPx, and glutathione reductase. However, the oxidative stress induced by hematite nanoparticles was not efficiently countered by the cells’ antioxidant enzymes as the GSH levels remained low over 72 h, suggesting that the antioxidant defense system of MRC-5 cells was crippled by hematite nanoparticles (Radu et al. 2010). Oxidative stress in cells can lead to severe repercussions in other cellular components.
A critical review of uranium in the soil-plant system: Distribution, bioavailability, toxicity, and bioremediation strategies
Published in Critical Reviews in Environmental Science and Technology, 2023
Qingliang Cui, Zhiqin Zhang, Jingzi Beiyuan, Yongxing Cui, Li Chen, Hansong Chen, Linchuan Fang
In addition to antioxidant enzymes, the antioxidant glutathione plays an important role in plant resistance to U toxicity. Glutathione occurs as oxidized glutathione disulfide (GSSG) and reduced GSH (Vanhoudt et al., 2011b). GSH is transformed into GSSG under U stress conditions, and their ratio (GSH/GSSG) is an important indicator of oxidative stress (Gupta et al., 2020). In addition, the reduced GSH is not only an important antioxidant but also a precursor for the synthesis of metal-bound peptides such as phytochelatins, which could reduce their toxicity by chelating directly with U (Jozefczak et al., 2012). The increased GSH concentrations and the increased GR activity after U exposure at low pH indicate an increased capacity to produce phytochelatins (Saenen et al., 2013). This may also indirectly provide a theoretical basis for the detoxification process of plant synthesis of phytochelatins under U stress.
Assessment of antioxidant and DPPH free radical scavenging activity of 1,2-dithiole-3-thione derivatives by using cyclic voltammetry, spectroscopic, and molecular docking studies
Published in Journal of Sulfur Chemistry, 2023
Elhafnaoui Lanez, Mokhtar Saidi, Touhami Lanez
The so-called enzyme ‘glutathione reductase’ is an important antioxidant enzyme, it catalyzes the reduction of the oxidized form of glutathione disulfide (GSSG) with NADPH to produce the reduced glutathione form (GSH), as shown in the reaction below. The above reaction is responsible for maintaining a high intracellular GSH/GSSG ratio in red blood cells. The ratio of reduced glutathione form (GSH) to the oxidized form of glutathione disulfide (GSSG) is an indicator of cellular health. Increased GSH/GSSG ratio levels resulted in intracellular signal transmission, free radical and reactive oxygen species removal, and intracellular redox state preservation [36].
Detoxifying effects of optimal hyperoxia (40% oxygenation) exposure on benzo[a]pyrene-induced toxicity in human keratinocytes
Published in Journal of Toxicology and Environmental Health, Part A, 2020
Yong Chan Kwon, Hyung Sik Kim, Byung-Mu Lee
Glutathione (GSH) and glutathione disulfide (GSSG) were determined using the GSH + GSSG/GSH Assay Kit (Abcam, Cambridge, MA) according to the manufacturer’s instructions. HaCat cells were harvested and lysates collected using ice-cold GSH buffer and sulfosalicylic acid. The samples were loaded onto 96-well plates and glutathione substrate (DTNB) and reductase were added to initiate the GSH recycling system. Absorbance at 405 or 415 nm was measured using the VERSA Max Microplate Reader.