Reduction Of Hydroperoxides Research Articles

Mutations Selectively Evolving Peroxidase Activity Among Alternative Catalytic Functions of Human Glutathione Transferase P1-1

Glutathione transferases are detoxication enzymes with broad catalytic diversity, and small alterations to the protein’s primary structure can have considerable effects on the enzyme’s substrate selectivity profile. We demonstrate that two point mutations in glutathione transferase P1-1 suffice to generate 20-fold enhanced non-selenium-dependent peroxidase activity indicating a facile evolutionary trajectory. Designed mutant libraries of the enzyme were screened for catalytic activities with alternative substrates representing four divergent chemistries. The chemical reactions comprised aromatic substitution, Michael addition, thiocarbamoylation, and hydroperoxide reduction. Two mutants, R1 (Y109H) and an R1-based mutant V2 (Q40M-E41Q-A46S-Y109H-V200L), were discovered with 16.3- and 30-foldincreased peroxidase activity with cumene hydroperoxide (CuOOH) compared to the wildtype enzyme, respectively. The basis of the improved peroxidase activity of the mutant V2 was elucidated by constructing double-point mutants. The mutants V501 (Q40M-Y109H) and V503 (E41Q-Y109H) were found to have 20- and 21-fold improvements in peroxidase activity relative to the wildtype enzyme, respectively. The steady-state kinetic profiles of mutants R1 and V2 in the reduction of CuOOH were compared to the wildtype parameters. The kcat values for R1 and V2 were 34- and 57-fold higher, respectively, than that of the wildtype enzyme, whereas the mutant Km values were increased approximately 3-fold. A 10-fold increased catalytic efficiency (kcat/Km) in CuOOH reduction is accomplished by the Tyr109His point mutation in R1. The 23-fold increase of the efficiency obtained in V2 was caused by adding further mutations primarily enhancing kcat. In all mutants with elevated peroxidase activity, His109 played a pivotal role.

Unraveling the Peroxidase Activity in Peroxiredoxins: A Comprehensive Review of Mechanisms, Functions, and Biological Significance.

Peroxiredoxins (Prxs) are members of the antioxidant enzymes necessary for every living object in the three domains of life and play critical roles in controlling peroxide levels in cells. This comprehensive literature review aims to elucidate the peroxidase activity of Prxs, examining their roles and significance for organisms across various taxa. Ironically, the primary role of the Prxs is the peroxidase activity, which comprises the reduction of hydrogen peroxide and other organic hydroperoxides and decreases the risk of oxidative damage in the cells. The above enzymatic activity occurs through the reversible oxidation-reduction catalyzed by cysteine residues in the active site by forming sulfenic acid and reduction by intracellular reductants. Structurally and functionally, Prxs function as dimers or decamers and show different catalytic patterns according to their subfamilies or cellular compartments. Compared to the mechanisms of the other two subgroups of Prxs, including 2-Cys Prxs and atypical Prxs, the 1-Cys Prxs have monomer-dimer switch folding coupled with catalytic activity. In addition to their peroxidase activity, which is widely known, Prxs are becoming acknowledged to be involved in other signaling processes, including redox signaling and apoptosis. This aversion to oxidative stress and regulation by the cellular redox state places them at the heart of adaptive cellular responses to changes in the environment or manifestations of diseases. In conclusion, based on the data obtained and on furthering the knowledge of Prxs' structure and function, these enzymes may be classified as a diverse yet essential family of proteins that can effectively protect cells from the adverse effects of oxidative stress due to peroxidase activity. This indicates secondary interactions, summarized as peroxide detoxification or regulatory signaling, and identifies their applicability in multiple biological pathways. Such knowledge is valuable for enhancing the general comprehension of essential cellular functions and disclosing further therapeutic approaches to the diseases caused by the increased production of reactive oxygen species.

Abstract PS12-04: Inhibition of GPX4 enhances CDK4/6 inhibitor activity in breast cancer

Abstract Background: Cyclin D-dependent kinases 4 and 6 (CDK4/6) inhibitors (CDK4/6i) including palbociclib, ribociclib and abemaciclib in combination with endocrine therapy are the standard of care for patients with estrogen receptor-positive (ER+). Despite the success of these treatments, cytostasis is frequently observed, and novel strategies that enhance efficacy are required to eradicate residual cancer in the clinic. Methods: In the search of an effective drug combinations to enhance the efficacy of CDK4/6 inhibitors in breast cancer, we performed a whole genome CRISPR-Cas9 suppressor screen in MCF-7, an ER+ model. We also carried out transcriptomics, proteomics, and functional molecular biology analysis of breast cancer models treated with palbociclib to identify resistant mechanisms. Results: The whole genome CRISPR-Cas9 screen revealed that multiple genes involved in oxidative stress and ferroptosis modulated palbociclib sensitivity, being GPX4 the top sensitizing hit. GPX4 is a key glutathione peroxidase that protects again ferroptosis by catalysing the reduction of phospholipid and cholesterol hydroperoxides. CRISPR-depletion or drug inhibition of GPX4 increased sensitivity to palbociclib in ER+ breast cancer models, and in addition sensitised triple negative breast cancer models to palbociclib. Moreover, GPX4 null xenografts were highly sensitive to palbociclib in vivo. Transcriptomics and proteomics analysis showed that palbociclib upregulate pathways involved in oxidative stress and lipid metabolism promoting a redox-lipid imbalance. Palbociclib induced lipid peroxidation leading to a ferroptosis vulnerable state with GPX4 preventing cell death. Polyunsaturated fatty acids (PUFAs) are highly susceptible of lipid peroxidation, and pathways that regulate their abundance in membrane phospholipids were explored. Interestedly, in ER+ breast cancer models, lipid peroxidation relied on a peroxisome AGPAT3-dependent pathway rather than the classical ACSL4 pathway. Conclusion: Our studies demonstrate that quiescence induced by palbociclib results in a ferroptosis-vulnerable state that could be exploited through combination with GPX4 inhibitors to enhance sensitivity to CDK4/6 inhibition in breast cancer. Citation Format: Maria Teresa Herrera Abreu, Uzma Khalid, Jian Ning, Rosalind Cutts, Gemma Wilson, Christopher Lord, Amanda Swain, Nicholas Turner. Inhibition of GPX4 enhances CDK4/6 inhibitor activity in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS12-04.

Redox dual-responsive diaryl ditelluride-containing nanoparticles as peroxidase mimetics

Polymeric nanoparticles with peroxidase-like enzyme mimetic activity were developed by incorporating catalytically active tellurium (Te) functionalities into cross-linked block copolymers. Bis(2-aminophenyl) ditelluride was used as a cross-linker to react with a diblock copolymer bearing pendent activated ester groups to generate of core-cross-linked nanoparticles (DiTe-NP) containing diaryl ditelluride bonds. DiTe-NP nanoparticles exhibit dual redox-responsiveness inherited from the sensitivity of ditelluride to both oxidants and reductants. When DiTe-NP nanoparticles were treated with H2O2, the oxidation of the ditellurides triggered the cleavage of Te-Te bonds to form Te(IV)-associated species. The oxidation-responsiveness endows DiTe-NP nanoparticles with haloperoxidase (HPO)-mimic activity. With NaBr and hydrogen peroxide, they catalyzed the oxidative bromination of phenol red, bromolactonization of 4-pentenoic acid, and bromination of 1,3,5-trimethoxybenzene due to the in-situ generation of hypobromous acid (HOBr) for halogenations. These ditelluride-containing nanoparticles also exhibited glutathione peroxidase (GPx)-like activity and accelerated the reduction of hydroperoxide by a thiol substrate. The cleavage of ditelluride bonds by a thiol substrate leads to the formation of key intermediates in the catalytic cycle of DiTe-NP nanoparticles. DiTe-NP nanoparticles showed enhanced activity for the reduction of hydrophobic cumene peroxide by 4-nitrothiophenol. These dual redox-responsive ditelluride-containing nanoparticles are promising candidates as peroxidase mimetics to apply as catalysts for green halogenation reactions and decompositions of toxic peroxides.

What is the Initiating Reaction for the Lipid Radical Chain Reaction System That Can Induce Ferroptotic Cell Death at the Lower Oxygen Content?

The neural cell death in cerebral infarction is suggested to be ferroptosis-like cell death, involving the participation of 15-lipoxygenase (15-LOx). Ferroptosis is induced by lipid radical species generated through the one-electron reduction of lipid hydroperoxides, and it has been shown to propagate intracellularly and intercellularly. At lower oxygen concentration, it appeared that both regiospecificity and stereospecificity of conjugated diene moiety in lipoxygenase-catalysed lipid hydroperoxidation are drastically lost. As a result, in the reaction with linoleic acid, the linoleate 9-peroxyl radical-ferrous lipoxygenase complex dissolves into the linoleate 9-peroxyl radical and ferrous 15-lipoxygenase. Subsequently, the ferrous 15-lipoxygenase then undergoes one-electron reduction of 13-hydroperoxy octadecadienoic acid, generating an alkoxyl radical (pseudoperoxidase reaction). A part of the produced lipid alkoxyl radicals undergoes cleavage of C-C bonds, liberating small molecular hydrocarbon radicals. Particularly, in ω-3 polyunsaturated fatty acids, which are abundant in the vascular and nervous systems, the liberation of small molecular hydrocarbon radicals was more pronounced compared to ω-6 polyunsaturated fatty acids. The involvement of these small molecular hydrocarbon radicals in the propagation of membrane lipid damage is suggested.

NADPH-dependent peroxidase activity of antibodies in patients with schizophrenia

IntroductionThe development of oxidative stress in patients with schizophrenia is associated with changes in the level of activity of antioxidant enzymes. It is likely that catalytically active antibodies (abzymes) can take on these functions. Abzymes are antibodies with enzymatic activity. Catalase and SOD activity of abzymes was previously detected in patients with schizophrenia. But NADPH-dependent peroxidase activity has not been studied. The present work discusses the protective role of abzymes against reactive oxygen species within the pathogenesis of schizophrenia.ObjectivesThe aim of the study was to investigate the NADPH-dependent peroxidase activity of IgG in patients with paranoid schizophrenia in the exacerbation phase and in the remission phase.MethodsA total of 124 patients were examined during the work. Of them, 82 patients with paranoid schizophrenia (F20.0) had a mean age of 33.6±5.12 years (52 males, 30 females), disease duration averaged 8.9± 4.62 years. Patients with schizophrenia included 42 patients with acute schizophrenia and 40 patients with schizophrenia in therapeutic remission. The control group included 42 sex- and age-matched patients. IgG was purified by affinity chromatography on columns with proteinsepharose on an AKTA purifier chromatograph (GE). The homogeneity of isolated IgG preparations was checked by Lemilly electrophoresis in a gradient of 4-18% PAAG. Gel filtration under pH-shock conditions was performed on a Superdex-200 HR 10/30 column. NADPH-dependent peroxidase activity of IgG was determined on a SPECORD M-40 spectrophotometer (Carl Zeiss) at 340 nm by NADPH oxidation in the conjugated glutathione reductase reaction of tertiary butyl hydroperoxide reduction. Statistical processing of data was performed in Statistica 12.0 program.ResultsIt was proved that IgG from patients with schizophrenia had NADPH-dependent peroxidase activity, and this activity is an intrinsic property of the investigated antibodies. The NADPH-dependent peroxidase activity in IgG patients in the exacerbation stage was increased 3-fold (p=0.0001) compared to the studied activity in the group of healthy individuals, and it was increased 2-fold (p=0.017) in the group of patients in therapeutic remission compared to the activity in healthy individuals. Also NADPH-dependent IgG peroxidase activity in patients in remission was 1.7 times lower than in patients during the exacerbation period (p=0.012).ConclusionsIt was established for the first time that abzymes from patients with schizophrenia and healthy individuals have NADPH-dependent peroxidase activity and can decompose lipo and hydroperoxides. We hypothesize that these abzymes help cope with generalized oxidative stress. Under the influence of neuroleptic therapy in patients in remission, the level of oxidative stress and NADPH-dependent peroxidase activity of abzymes decrease.Disclosure of InterestNone Declared

Protection of Membrane Contact Protein by the Methionine Sulfoxide Reductases.

In this News and Views, I discuss our recent publication that established how steroidogenic acute regulatory-related lipid transfer domain-3 (STARD3), a membrane contact protein situated at lysosomal membranes, plays a role in the detoxification of cholesterol hydroperoxide. STARD3's methionine residues can be oxidized to methionine sulfoxide by cholesterol hydroperoxide, after which methionine sulfoxide reductases reduce the methionine sulfoxide residues back to methionine. The reaction also results in the reduction of the cholesterol hydroperoxide to an alcohol. The cyclic oxidation and reduction of methionine residues in STARD3 at membrane contact sites creates a catalytically efficient mechanism for detoxification of cholesterol hydroperoxide during cholesterol transport, thus protecting membrane contact sites and the entire cell against the toxicity of cholesterol hydroperoxide.

Repurposing Glutathione Transferases: Directed Evolution Combined with Chemical Modification for the Creation of a Semisynthetic Enzyme with High Hydroperoxidase Activity.

Glutathione peroxidases (GPXs) are antioxidant selenoenzymes, which catalyze the reduction of hydroperoxides via glutathione (GSH), providing protection to cells against oxidative stress metabolites. The present study aims to create an efficient semisynthetic GPX based on the scaffold of tau class glutathione transferase (GSTU). A library of GSTs was constructed via DNA shuffling, using three homologue GSTUs from Glycine max as parent sequences. The DNA library of the shuffled genes was expressed in E. coli and the catalytic activity of the shuffled enzymes was screened using cumene hydroperoxide (CuOOH) as substrate. A chimeric enzyme variant (named Sh14) with 4-fold enhanced GPX activity, compared to the wild-type enzyme, was identified and selected for further study. Selenocysteine (Sec) was substituted for the active-site Ser13 residue of the Sh14 variant via chemical modification. The GPX activity (kcat) and the specificity constant (kcat/Κm) of the evolved seleno-Sh14 enzyme (SeSh14) was increased 177- and 2746-fold, respectively, compared to that of the wild-type enzyme for CuOOH. Furthermore, SeSh14 effectively catalyzed the reduction of hydrogen peroxide, an activity that is completely undetectable in all GSTs. Such an engineered GPX-like biocatalyst based on the GSTU scaffold might serve as a catalytic bioscavenger for the detoxification of hazardous hydroperoxides. Furthermore, our results shed light on the evolution of GPXs and their structural and functional link with GSTs.

Endogenous chemicals guard health through inhibiting ferroptotic cell death.

Ferroptosis is a new form of regulated cell death caused by iron-dependent accumulation of lethal polyunsaturated phospholipids peroxidation. It has received considerable attention owing to its putative involvement in a wide range of pathophysiological processes such as organ injury, cardiac ischemia/reperfusion, degenerative disease and its prevalence in plants, invertebrates, yeasts, bacteria, and archaea. To counter ferroptosis, living organisms have evolved a myriad of intrinsic efficient defense systems, such as cyst(e)ine-glutathione-glutathione peroxidase 4 system (cyst(e)ine-GPX4 system), guanosine triphosphate cyclohydrolase 1/tetrahydrobiopterin (BH4) system (GCH1/BH4 system), ferroptosis suppressor protein 1/coenzyme Q10 system (FSP1/CoQ10 system), and so forth. Among these, GPX4 serves as the only enzymatic protection system through the reduction of lipid hydroperoxides, while other defense systems ultimately rely on small compounds to scavenge lipid radicals and prevent ferroptotic cell death. In this article, we systematically summarize the chemical biology of lipid radical trapping process by endogenous chemicals, such as coenzyme Q10 (CoQ10), BH4, hydropersulfides, vitamin K, vitamin E, 7-dehydrocholesterol, with the aim of guiding the discovery of novel ferroptosis inhibitors.

Modulation of sarcopenia phenotypes by glutathione peroxidase 4 overexpression in mice.

Our laboratory previously showed lipid hydroperoxides and oxylipin levels are elevated in response to loss of skeletal muscle innervation and are associated with muscle pathologies. To elucidate the pathological impact of lipid hydroperoxides, we overexpressed glutathione peroxidase 4 (GPx4), an enzyme that targets reduction of lipid hydroperoxides in membranes, in adult CuZn superoxide dismutase knockout (Sod1KO) mice that show accelerated muscle atrophy associated with loss of innervation. The gastrocnemius muscle from Sod1KO mice shows reduced mitochondrial respiration and elevated oxidative stress (F2 -isoprostanes and hydroperoxides) compared to wild-type (WT) mice. Overexpression of GPx4 improved mitochondrial respiration and reduced hydroperoxide generation in Sod1KO mice, but did not attenuate the muscle loss that occurs in Sod1KO mice. In contrast, contractile force generation is reduced in EDL muscle in Sod1KO mice relative to WT mice, and overexpression of GPx4 restored force generation to WT levels in Sod1KO mice. GPx4 overexpression also prevented loss of muscle contractility at the single fibre level in fast-twitch fibres from Sod1KO mice. Muscle fibres from Sod1KO mice were less sensitive to both depolarization and calcium at the single fibre level and exhibited a reduced activation by S-glutathionylation. GPx4 overexpression in Sod1KO mice rescued the deficits in both membrane excitability and calcium sensitivity of fast-twitch muscle fibres. Overexpression of GPx4 also restored the sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO gastrocnemius muscles. These data suggest that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and in maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia. KEY POINTS: Knockout of CuZn superoxide dismutase (Sod1KO) induces elevated oxidative stress with accelerated muscle atrophy and weakness. Glutathione peroxidase 4 (GPx4) plays a fundamental role in the reduction of lipid hydroperoxides in membranes, and overexpression of GPx4 improves mitochondrial respiration and reduces hydroperoxide generation in Sod1KO mice. Muscle contractile function deficits in Sod1KO mice are alleviated by the overexpression of GPx4. GPx4 overexpression in Sod1KO mice rescues the impaired muscle membrane excitability of fast-twitch muscle fibres and improves their calcium sensitivity. Sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO muscles is decreased, and it is restored by the overexpression of GPx4. Our results confirm that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia.

TaGPX1-D overexpression provides salinity and osmotic stress tolerance in Arabidopsis

Glutathione peroxidases (GPXs) are known to play an essential role in guarding cells against oxidative stress by catalyzing the reduction of hydrogen peroxide and organic hydroperoxides. The current study aims functional characterization of the TaGPX1-D gene of bread wheat (Triticum aestivum) for salinity and osmotic stress tolerance. To achieve this, we initially performed the spot assays of TaGPX1-D expressing yeast cells. The growth of recombinant TaGPX1-D expressing yeast cells was notably higher than the control cells under stress conditions. Later, we generated transgenic Arabidopsis plants expressing the TaGPX1-D gene and investigated their tolerance to various stress conditions. The transgenic plants exhibited improved tolerance to both salinity and osmotic stresses compared to the wild-type plants. The higher germination rates, increased antioxidant enzymes activities, improved chlorophyll, carotenoid, proline and relative water contents, and reduced hydrogen peroxide and MDA levels in the transgenic lines supported the stress tolerance mechanism. Overall, this study demonstrated the role of TaGPX1-D in abiotic stress tolerance, and it can be used for improving the tolerance of crops to environmental stressors, such as salinity and osmotic stress in future research.

Intramolecular H-Atom Transfers in Alkoxyl Radical Intermediates Underlie the Apparent Oxidation of Lipid Hydroperoxides by Fe(II).

The one-electron reduction of lipid hydroperoxides by low-valent iron species is believed to be a driver of cellular lipid peroxidation and associated ferroptotic cell death. We investigated reactions of cholesterol 7α-OOH, the primary cholesterol autoxidation product, with Fe2+ to find that 7-ketocholesterol (7-KC, an oxidation product) is the major product under these (reducing) conditions. Mechanistic studies reveal the intervention of a 1,2-H-atom shift upon formation of the 7-alkoxyl radical to yield a ketyl radical that can be oxidized by either Fe3+ or O2 to give 7-KC, the most abundant oxysterol in vivo. We also investigated the corresponding reduction of the isomeric cholesterol 5α-OOH and again found that an oxidation product (5-hydroxycholesten-3-one) predominates under reducing conditions. An intramolecular H-atom shift (this time 1,4-) in the initially formed 5-alkoxyl radical is suggested to yield a ketyl radical that is oxidized to give the observed product. It would appear that a 1,2-H shift also accounts for the predominance of ketones over alcohols when unsaturated fatty acid hydroperoxides are exposed to iron-based reductants, which had previously been reported with hematin and demonstrated here with Fe2+. The predominance of 7-KC over the corresponding alcohol is maintained when cholesterol 7α-OOH embedded in phospholipid liposomes is treated with Fe2+ or when ferroptosis is induced in mouse embryonic fibroblasts. Our observation that 7-KC accumulates in ferroptotic cells suggests that it may be a good biomarker for ferroptosis.

THE INFLUENCE OF PROLONGED STRESS ON THE ACTIVITY OF BLOOD ENZYMES IN THE CONDITIONS OF WAR IN UKRAINE

The article presents an analysis of scientific works on the effect of long-term stress on blood enzymes. It has been determined that enzymopathies include a wide range of diseases, the cause of which is a malfunction of enzymes. Understanding the mechanisms of the occurrence of such disorders is necessary for the search for new, effective methods of their treatment. In the course of the work, twenty scientific works in English, published in the period 2000-2021, were analyzed, which investigated the mechanisms of human enzyme disorders. It has been established that non-genetic factors, such as injuries or stress, can lead to enzyme malfunctions. Stress factors, such as physical injuries, can affect enzyme dysfunction. One of the ways in which stress affects the functioning of enzymes is a change in their activity in biochemical mechanisms. Mutations in the three-dimensional structure of enzymes are one of the main mechanisms underlying the disruption of enzyme activity under the influence of stress. Since enzymes are large proteins that often have a complex tertiary structure that is important for their functioning, mutations that affect this structure can change their catalytic activity, substrate specificity, and stability, leading to enzymopathies. The stress factor of war is not similar to everyday stress factors, because it exceeds a person's ability to adapt to the action of the stress factor. The results of the research and analysis of research indicate the significant role of stress in disrupting the work of antioxidant blood enzymes. As a result of the analysis of scientific research, it was established that these enzymes include superoxidedismutase, catalase, glutathioneperoxidase, and glutathionetransferase.
 Superoxidedismutase is an antioxidant enzyme that plays a crucial role in protecting cells from the harmful effects of reactive oxygen species. ROS are produced during normal cellular metabolism and can also be produced in response to stressful conditions. A decrease in the activity of superoxidedismutase in the erythrocytes of combatants may occur due to epigenetic changes in the regulation of this enzyme, which were caused by long-term stressful conditions.
 Catalase is another antioxidant enzyme that plays an important role in protecting cells from oxidative stress. Another possible cause may be a change in the expression of the genes that code for catalase, which leads to a decrease in the level of the enzyme.
 Glutathioneperoxidase is an antioxidant enzyme that helps protect cells from oxidative stress by catalyzing the reduction of hydrogen peroxide and organic hydroperoxides to less harmful compounds. Stressful conditions, in particular combat operations, can lead to an increase in the formation of reactive oxygen species and a decrease in antioxidant defense mechanisms, including glutathioneperoxidase.
 Glutathionetransferase catalyzes the conjugation of glutathione, a tripeptide consisting of glutamate, cysteine, and glycine, with electrophilic substrates, resulting in the formation of less reactive and more water-soluble products that are suitable for excretion. Prolonged exposure to stress can lead to depletion of glutathione and a decrease in the activity of this enzyme.
 The obtained results indicate that wartime conditions can be a significant factor in the development of disorders of these enzymes.

Atypical network topologies enhance the reductive capacity of pathogen thiol antioxidant defense networks

Infectious diseases are a significant health burden for developing countries, particularly with the rise of multidrug resistance. There is an urgent need to elucidate the factors underlying the persistence of pathogens such as Mycobacterium tuberculosis, Plasmodium falciparum and Trypanosoma brucei. In contrast to host cells, these pathogens traverse multiple and varied redox environments during their infectious cycles, including exposure to high levels of host-derived reactive oxygen species. Pathogen antioxidant defenses such as the peroxiredoxin and thioredoxin systems play critical roles in the redox stress tolerance of these cells. However, many of the kinetic rate constants obtained for the pathogen peroxiredoxins are broadly similar to their mammalian homologs and therefore, their contributions to the redox tolerances within these cells are enigmatic. Using graph theoretical analysis, we show that compared to a canonical Escherichia coli redoxin network, pathogen redoxin networks contain unique network connections (motifs) between their thioredoxins and peroxiredoxins. Analysis of these motifs reveals that they increase the hydroperoxide reduction capacity of these networks and, in response to an oxidative insult, can distribute fluxes into specific thioredoxin-dependent pathways. Our results emphasize that the high oxidative stress tolerance of these pathogens depends on both the kinetic parameters for hydroperoxide reduction and the connectivity within their thioredoxin/peroxiredoxin systems.

CHARACTERISTICS OF FERROPTOSE INDUCTORS (REVIEW)

Ferroptosis is an iron-dependent non-apoptotic form of regulated cell death. In 2012, the anti-cancer activity of erastin was shown, based on the induc-tion of a new type of cell death, which is prevented by iron chelators and lipophilic antioxidants. The term "ferroptosis" has been proposed to character-ize this iron-dependent, non-apoptotic form of cell death. The purpose of this work is to evaluate and classify the range of compounds capable of in-ducing ferroptosis in various cell types. Glutathione (GSH), a common intracellular antioxidant, is required for the activity of various antioxidant enzymes (eg, GPX4). Erastine inhibits the uptake of cystine by the cystine/glutamate antiporter, creating a defect in the cell's antioxidant defenses and leading to iron-dependent oxidative death. GPX4 is a selenium-containing enzyme that catalyzes the reduction of organic hydroperoxides and lipid peroxides by reduced glutathione. The study re-vealed two promising compounds, named RSL3 and RSL5 by the authors. Tert-butyl hydroperoxide (t-BuOOH) is such a lipid peroxide analog and is widely regarded as a lipid peroxidation stimulant. Exposure to t-BuOOH resulted in a ferrostatin-1 and liprostatin-1 sensitive increase in lipid peroxidation. An excess of non-heme iron (Fe2+ and Fe3+) causes ferroptosis. Live/dead cell viability analysis showed that Fe(III)-citrate, erastin and RSL3 induce cell death. Co-treatment with ferrostatin-1, an inhibitor of ferroptosis, inhibited cell death. Other materials can cause ferroptosis by inducing lipid peroxidation. Mitochondrial DNA damaging drugs such as zalcitabine induce autophagy-dependent ferroptosis in human pancreatic cancer cells. The implementation of the model of cell death in the form of ferroptosis is highly dependent on the state of cellular metabolism and degradation systems, such as autophagy, which form a complex network for the formation of oxidative stress. Pharmacological induction of ferroptosis is a promising direction in cancer chemotherapy.

One-step highly selective catalytic oxidation of cyclohexane to KA-oil over functional CeMn0.5Co0.5Ox composite oxide: Synergistic effects between Mn and Co species with different valences and metal ion ratios

Presently, one-step highly selective oxidation of cyclohexane to KA-oil, which is a crucial organic chemical intermediate for the production of ε-caprolactam and adipic acid, is still a tremendous challenge. In this work, the functional CeMn0.5Co0.5Ox composite oxide catalysts were successfully prepared by glycine-nitrate combustion method. The results showed that 93.0% of selectivity to KA-oil with 4.6% of cyclohexane conversion was achieved over CeMn0.5Co0.5Ox under the optimal reaction conditions. The experimental and characterization results showed that the excellent catalytic performance of CeMn0.5Co0.5Ox is attributed to the synergistic effects between Mn and Co species with different valences and metal ion ratios, which efficiently promote the directional decomposition or reduction of cyclohexyl hydroperoxide (CHHP) intermediate to KA-oil. The density functional theory (DFT) calculations further confirmed the synergistic catalysis of CeMn0.5Co0.5Ox in the selective oxidation. This work affords the new insights into the design of efficient catalyst for the selective oxidation of alkanes.

Research progress of glutathione peroxidase family (GPX) in redoxidation.

Maintaining the balance of a cell's redox function is key to determining cell fate. In the critical redox system of mammalian cells, glutathione peroxidase (GPX) is the most prominent family of proteins with a multifaceted function that affects almost all cellular processes. A total of eight members of the GPX family are currently found, namely GPX1-GPX8. They have long been used as antioxidant enzymes to play an important role in combating oxidative stress and maintaining redox balance. However, each member of the GPX family has a different mechanism of action and site of action in maintaining redox balance. GPX1-4 and GPX6 use selenocysteine as the active center to catalyze the reduction of H2O2 or organic hydroperoxides to water or corresponding alcohols, thereby reducing their toxicity and maintaining redox balance. In addition to reducing H2O2 and small molecule hydroperoxides, GPX4 is also capable of reducing complex lipid compounds. It is the only enzyme in the GPX family that directly reduces and destroys lipid hydroperoxides. The active sites of GPX5 and GPX7-GPX8 do not contain selenium cysteine (Secys), but instead, have cysteine residues (Cys) as their active sites. GPX5 is mainly expressed in epididymal tissue and plays a role in protecting sperm from oxidative stress. Both enzymes, GPX7 and GPX8, are located in the endoplasmic reticulum and are necessary enzymes involved in the oxidative folding of endoplasmic reticulum proteins, and GPX8 also plays an important role in the regulation of Ca2+ in the endoplasmic reticulum. With an in-depth understanding of the role of the GPX family members in health and disease development, redox balance has become the functional core of GPX family, in order to further clarify the expression and regulatory mechanism of each member in the redox process, we reviewed GPX family members separately.

Substrate Promiscuity and Hyperoxidation Susceptibility as Potential Driving Forces for the Co-evolution of Prx5-Type and Prx6-Type 1-Cys Peroxiredoxin Mechanisms

So-called 1-Cys peroxiredoxins (Prx) employ only one cysteine residue for the reduction of hydroperoxides and require an external thiol for the reduction of a reactive sulfenic acid during the catalytic cycle. Hence, 1-Cys Prx, which often belong to the structural Prx5- or the Prx6-type subfamily, are potentially promiscuous enzymes that could react with a variety of thiols. Furthermore, the dependence on an external thiol could affect the susceptibility of 1-Cys Prx to hyperoxidation, i.e., the formation of a sulfinic or sulfonic acid. Here, we compared the reaction mechanisms and kinetics of the Prx5- and Prx6-type enzymes PfAOP and PfPrx6 from the malaria parasite Plasmodium falciparum to address the hyperoxidation susceptibility and potential substrate promiscuity of 1-Cys Prx. While PfAOP did not react with common thiol-disulfide oxidoreductases, the enzyme turned out to be promiscuous regarding the reduction by synthesized glutathione analogues and other low-molecular-weight thiols. Furthermore, we established a complete single turnover experiment for PfAOP with glutathione and the glutaredoxin PfGrx and identified the rapid H2O2-dependent hyperoxidation of PfAOP as the cause for the apparent preference of this Prx5-type enzyme for alkylhydroperoxides in vitro. Unlike promiscuous PfAOP, PfPrx6 was inactive with ascorbate, the physiological low-molecular-weight thiols glutathione, cysteine, cysteamine, coenzyme A, and dihydrolipoamide, as well as physiological protein thiols, including PfTrx1, PfGrx, and the resolving cysteine of the Prx1-type enzyme PfPrx1a in potential hetero-oligomers. Reduction of PfPrx6 was only observed with dithiothreitol and required the presence of a histidine residue, which protects the enzyme from hyperoxidation and is the major structural difference between the active sites of Prx5- and Prx6-type enzymes. We propose two alternative evolutionary adaptations of the 1-Cys Prx mechanism to hyperoxidation and the formation of alternative mixed disulfides that could explain the co-existence of promiscuous Prx5- and protected Prx6-type enzymes in a variety of organisms and subcellular compartments.

Plant Glutathione Peroxidases: Non-Heme Peroxidases with Large Functional Flexibility as a Core Component of ROS-Processing Mechanisms and Signalling.

Glutathione peroxidases (GPXs) are non-heme peroxidases catalyzing the reduction of H2O2 or organic hydroperoxides to water or corresponding alcohols using glutathione (GSH) or thioredoxin (TRX) as a reducing agent. In contrast to animal GPXs, the plant enzymes are non-seleno monomeric proteins that generally utilize TRX more effectively than GSH but can be a putative link between the two main redox systems. Because of the substantial differences compared to non-plant GPXs, use of the GPX-like (GPXL) name was suggested for Arabidopsis enzymes. GPX(L)s not only can protect cells from stress-induced oxidative damages but are crucial components of plant development and growth. Due to fine-tuning the H2O2 metabolism and redox homeostasis, they are involved in the whole life cycle even under normal growth conditions. Significantly new mechanisms were discovered related to their transcriptional, post-transcriptional and post-translational modifications by describing gene regulatory networks, interacting microRNA families, or identifying Lys decrotonylation in enzyme activation. Their involvement in epigenetic mechanisms was evidenced. Detailed genetic, evolutionary, and bio-chemical characterization, and comparison of the main functions of GPXs, demonstrated their species-specific roles. The multisided involvement of GPX(L)s in the regulation of the entire plant life ensure that their significance will be more widely recognized and applied in the future.

2D Nanomaterial—Based Electrocatalyst for Water Soluble Hydroperoxide Reduction

Hydroperoxides generated on lipid peroxidation are highly reactive compounds, tend to form free radicals, and their elevated levels indicate the deterioration of lipid samples. A good alternative to the classical methods for hydroperoxide monitoring are the electroanalytical methods (e.g., a catalytic electrode for their redox-transformation). For this purpose, a series of metal oxides—doped graphitic carbon nitride 2D nanomaterials—have been examined under mild conditions (pH = 7, room temperature) as catalysts for the electrochemical reduction of two water-soluble hydroperoxides: hydrogen peroxide and tert-butyl hydroperoxide. Composition of the electrode modifying phase has been optimized with respect to the catalyst load and binding polymer concentration. The resulting catalytic electrode has been characterized by impedance studies, cyclic voltammetry and chronoamperometry. Electrocatalytic effect of the Co-g-C3N4/Nafion modified electrode on the electrochemical reduction of both hydroperoxides has been proved by comparative studies. An optimal range of operating potentials from −0.215 V to −0.415 V (vs. RHE) was selected with the highest sensitivity achieved at −0.415 V (vs. RHE). At this operating potential, a linear dynamic range from 0.4 to 14 mM has been established by means of constant-potential chronoamperometry with a sensitivity, which is two orders of magnitude higher than that obtained with polymer-covered electrode.