Assesment of metal inhibition of antioxidant enzyme glutathione reductase from rainbow trout liver

Purification and characterisation of glutathione reductase from scorpionfish (scorpaena porcus) and investigation of heavy metal ions inhibition

In the current study, glutathione reductase was purified from Scorpion fish (Scorpaena porcus) liver tissue and the effects of heavy metal ions on the enzyme activity were determined. The purification process consisted of three stages; preparation of the homogenate, ammonium sulphate precipitation and affinity chromatography purification. At the end of these steps, the enzyme was purified 25.9-fold with a specific activity of 10.479 EU/mg and a yield of 28.3%. The optimum pH was found to be 6.5, optimum substrate concentration was 2 mM NADPH and optimum buffer was 300 mM KH₂PO_4. After purification, inhibition effects of Mn⁺², Cd⁺², Ni⁺², and Cr³⁺, as heavy metal ions were investigated. IC₅₀ values of the heavy metals were calculated as 2.4 µM, 30 µM, 135 µM and 206 µM, respectively.

Gene knockout of glutathione reductase results in increased sensitivity to heavy metals in Acidithiobacillus caldus

Acidithiobacillus caldus plays an important role in bioleaching of low-grade metal ore. It can promote the release of heavy metals in mining-associated habitats and survive in high concentrations of heavy metals. Functions of glutathione reductase (GR) in cell defense against reactive oxygen species caused by heavy metals have been elucidated in some eukaryotic cells and bacteria; however, no information is available in A. caldus. In this research, the methods of bioinformatics, gene expression, GR activity assays were used to detect and characterize the glutathione reductase gene from the A. caldus MTH-04 strain. Then, A. caldus gr knockout mutant and gr overexpression strain were constructed, and the heavy metal tolerant properties and transcriptional levels of ROS related genes of them were compared to study the function of GR. The results showed that, a putative gr gene F0726_RS04210 was detected in the genome of A. caldus MTH-04. The purified recombinant protein of F0726_RS04210 showed remarkable GR activity at optimal pH 7.0 and 30°C using in vitro assay. The evolutionary relationship of GR from A. caldus MTH-04 was close to that from Escherichia coli K12. Gene knockout or overexpression of gr in A. caldus did not affect the growth rate on S0 medium, suggesting that GR did not play a key role in the activation of sulfur. Deletion of gr resulted in increased sensitivity to heavy metals (Cu2+ and Zn2+) in A. caldus, and the gr overexpression strain showed enhanced tolerance to heavy metals. Furthermore, transcription analysis also revealed strong correlations between GR and the antioxidant pathway. The above results suggest that GR can play an important role in heavy metal tolerance in A. caldus.

Study of the inhibition effects on glutathione peroxidase immobilized on MNPs using a stopped-flow microfluidic system

A stopped-flow microfluidic system to monitor glutathione peroxidase (GPx) activity and evaluate potential inhibitors of the enzyme has been developed based on the integration of the microfluidic chip in the reaction/detection zone. This integration supposes the physical alignment at the optimal location of the microfluidic channel, both the magnetically retained enzyme microreactor (MREµR) and the remote luminescence detection using a focused bifurcated fiber optic bundle (BFOB) connected to a conventional spectrofluorometer detector. The method is based on the coupling of two competitive oxidative chemical reactions, in which glutathione (GSH) and homovanillic acid (HVA) competed for their interaction with hydrogen peroxide in the presence of the magnetically retained GPx-MNPs. The biocatalytic reaction was followed by monitoring the fluorescence of the biphenyl-HVA dimer formed. The dynamic range of the calibration graph was 0.45-10 µmol L^-1, expressed as GSH concentration with a detection limit of 0.1 µmol L^-1 (r² = 0.9954, n = 10, r = 3). The precision expressed as the relative standard deviation (RSD%) was between 0.5 and 3.9%. The stopped-flow microfluidic system showed a sampling frequency of 25 h^-1. The method was applied to the study of GPx inhibition provided by three inhibitory compounds, two metallic ions Hg(II) and Cu(II) and t-butyl hydroperoxide, and their presence in liquid samples, as water, milk, and edible oil. Recovery values between 88.7 and 99.4% were achieved in all instances.

Impact of Nickel Oxide Nanoparticles (NiO) on Oxidative Stress Biomarkers and Hemocyte Counts of Mytilus galloprovincialis

In this study, the toxic effects of nickel oxide nanoparticles (NiO-NPs) on the model organism Mediterranean mussel (Mytilus galloprovincialis) gill, digestive gland, and hemolymph tissues for 96 h were investigated. Lipid peroxidation (MDA) determination was performed to reveal the oxidative stress generation potential of nanoparticles, and superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione-S-transferase (GST) enzyme levels were measured to determine antioxidant responses. Lysosomal membrane stability and total hemocyte counts were performed to determine cytotoxic effects. All parameters were altered in different concentrations of NiO-NPs (2, 20, and 200 mg L^-1). The SOD levels increased depending on the concentration (p < 0.05), and the increases in CAT, GPx, and GST levels were lower at 20 mg L^-1 concentration (p < 0.05). There was a slight difference between the exposure and the control groups in terms of GR enzyme. The MDA level increased in parallel with the concentration (p < 0.05), the stability of the cell membrane (p < 0.05), and the number of hemocyte cells decreased as a result of exposure (p < 0.05). The results emphasize that NiO-NPs may have negative effects on the aquatic environment.

Characterization of glutathione S-transferase enzyme from brown meagre (Sciaena umbra) and inhibitory effects of heavy metals

Glutathione S-transferase (GST) detoxifies a broad spectrum of xenobiotics, especially in chemotherapeutic drugs, endogenous molecules, and environmental pollutants. Since the enzyme metabolizes toxic compounds, it has been extensively studied in many living things including aquatic organisms. In the current study, the GST enzyme was purified from brown meagre (Sciaena umbra) muscle tissue for the first time. Then, kinetic parameters of the enzyme were determined as optimum ionic strength: 20 mM Tris/HCl, optimum pH: 7.0 (Tris/HCl), and optimum substrate concentration: 3.125 mM. Eventually, inhibitory effects of the heavy metals were evaluated. IC₅₀ values of the tested metal ions were calculated to be 0.1112, 0.6113, 0.727, and 0.7774 mM for Cd²⁺ , Fe³⁺ , Ag⁺ , and Cu²⁺ , respectively. Our results show that these heavy metals inhibit GST at very low concentrations which could cause dangerous results for aquatic systems.

Vacuolar H+ -ATPase is involved in preventing heavy metal-induced oxidative stress in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, vacuolar H⁺ -ATPase (V-ATPase) involved in the regulation of intracellular pH homeostasis has been shown to be important for tolerances to cadmium, cobalt and nickel. However, the molecular mechanism underlying the protective role of V-ATPase against these metals remains unclear. In this study, we show that cadmium, cobalt and nickel disturbed intracellular pH balance by triggering cytosolic acidification and vacuolar alkalinization, likely via their membrane permeabilizing effects. Since V-ATPase plays a crucial role in pumping excessive cytosolic protons into the vacuole, the metal-sensitive phenotypes of the Δvma2 and Δvma3 mutants lacking V-ATPase activity were supposed to result from highly acidified cytosol. However, we found that the metal-sensitive phenotypes of these mutants were caused by increased production of reactive oxygen species, likely as a result of decreased expression and activities of manganese superoxide dismutase and catalase. In addition, the loss of V-ATPase function led to aberrant vacuolar morphology and defective endocytic trafficking. Furthermore, the sensitivities of the Δvma mutants to other chemical compounds (i.e. acetic acid, H₂ O₂ , menadione, tunicamycin and cycloheximide) were a consequence of increased endogenous oxidative stress. These findings, therefore, suggest the important role of V-ATPase in preventing endogenous oxidative stress induced by metals and other chemical compounds.

In vitro thrombolytic activity of a purified fibrinolytic enzyme from Chlorella vulgaris

A fibrinolytic enzyme was produced by microalga Chlorella vulgaris cultivated in autotrophic and mixotrophic conditions added corn steep liquor, purified by a single chromatographic step, then biochemical characterization and in vitro thrombolytic activity was performed. Maximum cell concentration (1637.45 ± 15 mg L^-1) and productivity (181.93 mg L^-1 day^-1) was obtained in mixotrophic culture using 1% corn steep liquor. Enzyme-extracted microalgal biomass was purified by acetone precipitation and DEAE Sephadex anion exchange chromatography up to 2 fold with recovery of 4.0%. After purification, fibrinolytic activity was 1834.6 U mg^-1 and 226.86 mm² by spectrophotometry and fibrin plate assays, respectively. SDS-PAGE results exhibited a protein band of about 45 kDa and fibrinolytic band was detected by fibrin zymography. Enzyme activity was enhanced in the presence of Fe²⁺ and inhibited by phenylmethane sulfonyl fluoride (PMSF) and ethylenediamine tetracetic acid (EDTA), which suggest it to be a metal-dependent serine protease. The extract also showed a red blood cell lysis <4% and in vitro thrombolytic activity of 25.6% in 90 min of reaction. These results indicate that the fibrinolytic enzyme from C. vulgaris may have potential applications in the prevention and treatment of thrombosis.

Goose fat, a promising nutrient for fish feeding, activates antioxidant enzymes in rainbow trout, Oncorhynchus mykiss

The objective of this experiment was to test effects of different dietary lipids in rainbow trout feeding on the activity and expression of antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S-transferase (GST). Four iso-nitrogenous and iso-lipidic casein-gelatin based experimental diets were formulated. The sources of dietary lipids were cod liver oil (CO, rich in polyunsaturated fatty acids), goose fat (GF, rich in saturated fatty acids and monounsaturated fatty acids), soybean oil (SO, rich in linoleic acid), and a blend of CO, GF and SO. Dietary treatments had no significant effect on growth performance and survival was not affected. SOD, GPx and GST enzymes had the maximum activity in GF diet. However qPCR data showed that SOD and GPx mRNA levels were minimum in GF group. Overall data showed that rainbow trout liver enzymes were activated upon GF diet probably activating the enzyme structure itself without stimulating gene expression.