Search

The glutathione (GSH) system is one of the most powerful intracellular antioxidant systems for the elimination of reactive oxygen species (ROS) and maintaining cellular redox homeostasis. However, the rapid kinetics information (at the millisecond to the second level) during the dynamic antioxidation process of the GSH system remains unclear. As such, we specifically developed a novel dual‐wire nanosensor (DWNS) that can selectively and synchronously measure the levels of GSH and ROS with high temporal resolution, and applied it to monitor the transient ROS generation as well as the rapid antioxidation process of the GSH system in individual cancer cells. These measurements revealed that the glutathione peroxidase (GPx) in the GSH system is rapidly initiated against ROS burst in a sub‐second time scale, but the elimination process is short‐lived, ending after a few seconds, while some ROS are still present in the cells. This study is expected to open new perspectives for understanding the GSH antioxidant system and studying some redox imbalance‐related physiological. [ABSTRACT FROM AUTHOR]

Selenocysteine (Sec)‐derived cyclic selenenyl amides, formed by the intramolecular cyclization of Sec selenenic acids (Sec–SeOHs), have been postulated to function as protective forms in the bypass mechanism of glutathione peroxidase (GPx). However, their chemical properties have not been experimentally elucidated in proteins or small‐molecule systems. Recently, we reported the first nuclear magnetic resonance observation of Sec–SeOHs and their cyclization to the corresponding cyclic selenenyl amides by using selenopeptide model systems incorporated in a molecular cradle. Herein, we elucidate the structures and reactivities of Sec‐derived cyclic selenenyl amides. The crystal structures and reactions toward a cysteine thiol or a 1,3‐diketone‐type chemical probe indicated the highly electrophilic character of cyclic selenenyl amides. This suggests that they can serve not only as protective forms to suppress the inactivation of Sec–SeOHs in GPx but also as highly electrophilic intermediates in the reactions of selenoproteins. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) play essential roles in plant development and environmental stress responses. In this study, ROS dynamics, the glutathione redox status, the expression and subcellular localization of glutathione peroxidases (GPXs), and the effects of inhibitors of ROS-mediated metabolism were investigated along with fertilization and early zygotic embryogenesis in rice (Oryza sativa). Zygotes and early embryos exhibited developmental arrest upon inhibition of ROS production. Egg cells accumulated high ROS levels, and, after fertilization, intracellular ROS levels progressively declined in zygotes in which de novo expression of GPX1 and 3 was observed through upregulation of the genes. In addition to inhibition of GPX activity, depletion of glutathione impeded early embryonic development and led to failure of the zygote to appropriately decrease H2O2 levels. Moreover, through monitoring of the glutathione redox status, the developing zygotes exhibited a progressive glutathione oxidation, which became extremely delayed under inhibited GPX activity. Our results provide insights into the importance of ROS dynamics, GPX antioxidant activity, and glutathione redox metabolism during zygotic/embryonic development. [ABSTRACT FROM AUTHOR]

This article, titled "Cover Feature: Highly Electrophilic Intermediates in the Bypass Mechanism of Glutathione Peroxidase: Synthesis, Reactivity, and Structures of Selenocysteine-Derived Cyclic Selenenyl Amides," explores the role of selenocysteine cyclic selenenyl amides in the catalytic cycle of the antioxidant enzyme glutathione peroxidase (GPx). The study reveals that these intermediates, previously overlooked, have dual functionality. They not only prevent the inactivation of GPx but also act as highly electrophilic intermediates in selenoprotein reactions. The researchers compare the roles of these intermediates to a chess king, dynamically adapting to their application. [Extracted from the article]

Abstract: The objectives of the present study were to investigate the effects of selenium (Se) supplementation during in vitro maturation (IVM) on the developmental capacity of yak (Bos grunniens) oocytes. Nuclear maturation, DNA integrity, glutathione peroxidase (GSH‐Px) activity, subsequent embryonic development, and gene expression after in vitro fertilization (IVF) were evaluated. The Se concentrations in yak plasma and follicular fluid were 0.142 and 0.069 μg/mL, respectively. The DNA damage in cumulus cells decreased significantly with 2 and 4 μg/mL supplementation of sodium selenite to IVM medium (P < 0.05). Total GSH‐Px activity in oocytes increased in all Se supplementation groups, and the 2 and 4 μg/mL groups were significantly higher than the control group (0 μg/mL). However, the cleavage rate was not significantly different after Se supplementation (P > 0.05). The IVF blastocyst formation rates of 0, 1 and 4 μg/mL sodium selenite groups were 47.7%, 51.2% and 58.9%, respectively. The 2 μg/mL sodium selenite group had the highest blastocyst formation rate (60.5%). Gene expression analysis revealed that the quantity of transcripts associated with selenoprotein and protein synthesis were high in the 2 and 4 μg/mL groups. In conclusion, both GSH‐Px activity of oocytes and DNA integrity of cumulus cells significantly increased with supplemental Se during oocyte IVM. Considering that embryonic development is responsive to Se supplementation, we inferred that appropriate Se concentrations during IVM were beneficial for yak oocyte maturation and subsequent development. [ABSTRACT FROM AUTHOR]

Hepoxilins are biologically relevant epoxy-hydroxy eicosanoids synthesized through the 12 S-lipoxygenase (12 S-LOX) pathway of the arachidonic acid (AA) metabolism. The pathway is bifurcated at the level of 12 S-hydroperoxy-eicosatetraenoic acid (12 S-HpETE), which can either be reduced to 12 S-hydro-eicosatetraenoic acid (12 S-HETE) or converted to hepoxilins. The present review gives an update on the biochemistry, biology and clinical aspects of hepoxilin-based drug development. The isolation, cloning and characterization of a rat leukocyte-type 12 S-LOX from rat insulinoma RINm5F cells revealed a 12 S-LOX possessing an intrinsic 8 S/ R-hydroxy-11,12-epoxyeicosa-5 Z,9 E,14 Z-trienoic acid (HXA3) synthase activity. Site-directed mutagenesis studies on rat 12 S-LOX showed that the HXA3 synthase activity was impaired when the positional specificity of AA was altered. Interestingly, amino acid Leu353, and not conventional sequence determinants Met419 and Ile418, was found to be a crucial sequence determinant for AA oxygenation. The regulation of HXA3 formation is dependent on the cellular overall peroxide tone. Cellular glutathione peroxidases (cGPxs) compete with HXA3 synthase for 12 S-HpETE as substrate either to reduce to 12 S-HETE or to convert to HXA3, respectively. Therefore, RINm5F cells, which are devoid of GPxs, are capable of converting AA or 12 S-HpETE to HXA3 under basal conditions, whereas cells overexpressing cGPx are unable to do so. HXA3 exhibits a myriad of biological effects, most of which are associated with the stimulation of intracellular calcium or the transport of calcium across the membrane. The activation of HXA3–G-protein-coupled receptors explains many of the extracellular effects of HXA3, including AA- and diacylglycerol (DAG) release in human neutrophils, insulin secretion in rat pancreatic β-cells or islets, and synaptic actions in the brain. The availability of stable analogs of HXA3, termed 10-hydroxy-11,12-cyclopropyl-eicosa-5 Z,8 Z,14 Z-trienoic acid derivatives (PBTs), recently made several animal studies possible and explored the role of HXA3 as a therapeutic in treatment of diseases. Thus, PBT-3 induced apoptosis in K562 tumour cells and inhibited growth of K562 CML solid tumours in nude mice. HXA3 inhibited bleomycin-evoked lung fibrosis and inflammation in mice and the raised insulin level in the circulation of rats. At low glucose concentrations (0–3 mm), HXA3 also stimulated insulin secretion in RINm5F cells through the activation of IRE1α, an endoplasmic reticulum-resident kinase. The latter regulates the protein folding for insulin biosynthesis. In conclusion, HXA3-mediated signaling may be involved in normal physiological functions, and hepoxilin-based drugs may serve as therapeutics in diseases such as type II diabetes and idiopathic lung fibrosis. [ABSTRACT FROM AUTHOR]

The glutathione peroxidase Gpx3 from the yeast Saccharomyces cerevisiae has been overexpressed, purified and crystallized. Both gel-filtration and dynamic light-scattering (DLS) results indicate that Gpx3 is a monomer in solution at a concentration of about 2 mg ml−1, whereas glutathione peroxidases are normally tetrameric or dimeric. X-ray diffraction data from a single crystal of Gpx3 have been collected to 2.6 Å resolution. The crystals are triclinic and belong to space group P1, with unit-cell parameters a = 38.187, b = 43.372, c = 56.870 Å, α = 71.405, β = 73.376, γ = 89.633°. There are two Gpx3 monomers in a crystallographic asymmetric unit. Preliminary analyses show that the yeast Gpx3 is quite different from those of mammals. [ABSTRACT FROM AUTHOR]