Redox Biochemistry and Chemistry最新文献

Nitrogen dioxide (^•NO₂) is a radical gas that forms part of air pollution and is produced chemically, photochemically and by ionizing radiation in aqueous and non-aqueous solutions as well as by various endogenous pathways in biological systems. This review describes the: (i) sources of ^•NO₂; (ii) kinetics and mechanism of ^•NO₂ reactions; (iii) ^•NO₂ as a key player in cellular oxidative and nitrosative stress leading to pathological conditions, and (iv) use of diverse antioxidants to reduce ^•NO₂ toxic effects.

Interest in the molecular actions of acrolein has increased in light of growing knowledge that implicates this reactive aldehyde in a wide range of pathophysiologies including neurodegenerative diseases, various lung disorders including chronic obstructive pulmonary disease, atherosclerosis, and certain cancers. This is rendered complex because acrolein exists in mixtures of environmental pollutants. Reactive α,β-unsaturated aldehydes like acrolein are major components of common environmental pollutants like cigarettes, automobile exhaust, and smoke from wood, coal, forest and house fires. It is a natural constituent of several foods and is generated in the human body during inflammation or oxidation of unsaturated lipids. Acrolein is also a toxic metabolic product of the widely used anticancer drug cyclophosphamide and is generated from the enzymatic oxidation of polyamines. It is a toxic by-product of lipid peroxidation and has been implicated as a mediator of oxidative damage in cells and tissues. The purpose of this review is to assess the literature about the activation of cell signalling pathways and transcription factors, and cell survival and cell death pathways by acrolein. Several reports show that anti-apoptosis processes dominate at lower dose exposures to acrolein, whereas pro-apoptotic processes and necrosis dominate at higher dose exposures. There has been improved understanding about the deleterious molecular and cellular mechanisms that are triggered in cells in response to acrolein injury. However, more progress is required to define the contributions of acrolein to human diseases and to design efficient therapeutic strategies based on the biochemical modulation of acrolein activity.

The leukocyte-derived enzyme myeloperoxidase (MPO) is a key component of the innate immune response and mediates the killing of pathogens via the generation of the powerful oxidant hypochlorous acid (HOCl). Unintended or excessive formation of this species can however result in damage to host tissues, and this is linked with multiple pathologies associated with acute or chronic inflammation. The active (Compound I) form of MPO is promiscuous and can oxidize multiple alternative anions, in addition to the Cl⁻ used to generate HOCl. These alternative substrates may therefore modulate MPO-mediated HOCl damage. In the current study we examined the hypothesis that selenocyanate (SeCN⁻), the selenium analogue of thiocyanate (SCN⁻, a well-established competitive MPO substrate) would inhibit HOCl-mediated damage to human plasma fibronectin (hpFN) or the extracellular matrix laid down by human coronary artery smooth muscle cells. SeCN⁻ modulated HOCl and MPO-mediated damage, in a dose-dependent manner. These data are consistent with SeCN⁻ acting as both a competitive substrate for Compound I of MPO (with IC₅₀ ∼23 μM), and as a direct scavenger of HOCl. Inhibition of protein damage by SeCN⁻ was also detected in the presence of the physiological anions Br⁻, I⁻ and SCN⁻ at the concentrations typically present in human plasma, consistent with a high affinity of SeCN⁻ for MPO Compound I. In addition, the protective effects of SeCN⁻ and SCN⁻, as competitive MPO substrates, were additive. Together these data indicate that modest concentrations of SeCN⁻ can, like its sulfur analogue SCN⁻, act as an effective modulator of inflammation-induced damage.

Toxic metal contaminants present in food and water have widespread effects on health and disease. Chalcophiles, such as arsenic, cadmium, and mercury, show a high affinity to selenium and exposure to these metals could have a modulating effect on enzymes dependent on selenocysteine in their active sites. The aim of this study was to assess the influence of these metals on the activity of the selenoprotein glutathione peroxidase 1 (GPX1) in erythrocytes of 100 children residing in rural Bangladesh, where drinking water often contains arsenic. GPX1 expression, as measured using high-throughput immunoblotting, showed little correlation with GPX activity (r_s = 0.02, p = 0.87) in blood samples. Toxic metals and selenium measured in erythrocytes using inductively coupled plasma mass spectrometry (ICP-MS) and C-reactive protein (CRP) measured in plasma, were all considered as effectors of this divergence in GPX enzymatic activity. Arsenic concentrations in erythrocytes were most influential for GPX1 activity (r_s = −0.395, p < 0.0001), and CRP levels also negatively impacted GPX1 activity (r_s = −0.443, p < 0.0001). These effects appear independent of each other as arsenic concentrations and CRP showed no correlation (r_s = 0.124, p = 0.2204). Erythrocyte selenium, cadmium, and mercury did not show any correlation with GPX1 activity, nor with CRP or arsenic. Our findings suggest that childhood exposure to inorganic arsenic, as well as inflammation triggering the release of CRP, may negatively affect GPX1 activity in erythrocytes.

Mitochondria are main sources of biological hydroperoxides, including hydrogen peroxide, peroxynitrite and various organic hydroperoxides. Most of these species are involved in the regulation of cellular functions when formed at low, physiological levels. Additionally, they can cause oxidative damage when formed at higher rates, eventually leading to mitochondrial disfunction and cytotoxicity. Different peroxidases sense the levels and catalyze the reduction of mitochondrial hydroperoxides. Among them, peroxiredoxin 3 and peroxiredoxin 5 decompose most hydrogen peroxide, peroxynitrite and free fatty acid hydroperoxides formed in the mitochondrial matrix. Kinetic considerations indicate that the role of selenol-dependent glutathione peroxidases in the reduction of these soluble hydroperoxides in mitochondria would be secondary. Glutathione peroxidase 4, which has a unique phospholipid hydroperoxide peroxidase activity, is only expressed in the mitochondria of selected tissues. Peroxiredoxin 3 catalyzes the reduction of hydroperoxides, but is also hyperoxidized and inactivated by them, in particular by free fatty acid hydroperoxides which react at high rate constants. Indeed, computer-assisted simulations support that free fatty acid hydroperoxides significantly contribute to Prdx3 hyperoxidation under biologically-relevant conditions. In addition, kinetic data indicate that hydroperoxides may partially diffuse to the cytosol. Several open questions regarding the oxidizing substrate specificities of mitochondrial peroxiredoxins and their modulation by CO₂ are presented. Thus, peroxiredoxins 3 and 5 are the main sensors of mitochondrial hydroperoxides, provide protection from their excess and also determine the ability of these reactive species to diffuse through mitochondria; these combined actions of the mitochondrial peroxiredoxins impact redox regulation and outcomes of physiological or pathological processes.

Cellular respiration is highly regulated, changes dynamically in response to the microenvironment of individual cells and during differentiation and differs between cell and tissue types. Too little cell respiration can cause an accumulation of reductants, leading to reductive stress, while inefficient respiration, that causes a build-up of reactive oxygen species (ROS), can result in oxidative stress. Most of the discussion of this central redox dichotomy has centred around oxidative stress because the damaging effects of cellular oxidants on DNA, lipids and proteins are well-established, and have been shown to contribute to health issues including, mitochondrial and cardiovascular diseases, tumorigenesis, and to the effects of ageing. Much less attention has been paid to cellular reductive stress. Nevertheless, excessive levels of key cellular reductants including NADH, NADPH and glutathione, as well as an imbalance in protein thiols, and insufficient levels of ROS to maintain cell signalling pathways, can be harmful to cells and result in poor health outcomes. Recently, cellular mechanisms that sense and regulate cellular reductive stress associated with low ROS levels have been identified. In addition, plasma membrane electron transport has been shown to be a key player in cellular redox homeostasis involving NAD(P)H/NAD(P)⁺ ratios. It is now well-established that the plasma membrane contains coenzyme Q-mediated electron transport pathways capable of oxidizing intracellular NAD(P)H and reducing extracellular electron acceptors such as molecular oxygen. A better understanding of the origins, cellular and subcellular compartmentalization and regulation of cellular reductants could lead to the development of new anticancer strategies.

Mycoredoxins (Mrxs) are a group of small dithiol oxidoreductases that share a conserved CXXC active site sequence motif resembling glutaredoxins. They are commonly found in saprophytic microorganisms, including Actinobacteria such as Mycobacterium tuberculosis. Among the known mycoredoxins, Corynebacterium glutamicum (Cg) Mrx1, featuring a conserved CVQC active site, functions as a mycothiol-dependent monothiol oxidoreductase. On the other hand, Mrx2, also known as NrdH-redoxin and containing the same CVQC motif, exhibits dithiol oxidoreductase properties and receives electrons from thioredoxin reductase (TrxR). Recently, it has been reported that CgMrx3, featuring a CGSC motif, acts as a thioredoxin, although its structural and biophysical characteristics remain unexplored.

In this study, we successfully determined the X-ray structure of CgMrx3 at a resolution of 1.7 Å, revealing a swapped dimer arrangement. We compared the structure of CgMrx3 with those of CgMrx1 and CgMrx2 and with the AlphaFold2 predicted structure of Mrx3 from Mycobaterium tuberculosis (MtMrx3). We correlated the number of hydrogen bonds accepted by the nucleophilic cysteines with the relatively low pKa's determined for MtMrx3 and CgMrx3. Finally, we showed that CgMrx3 has DsbA-like oxidase activity. Taken together, our results provide valuable insights into the structural and functional characteristics of Mrx3, thereby enhancing our understanding of mycoredoxin-dependent redox biology.

Fenamic acids are a group of non-steroidal anti-inflammatory drugs (NSAIDs) that are among the most common drugs prescribed globally. However, they have been associated with many adverse effects, such as agranulocytosis, neutropenia, hepatotoxicity, and nephrotoxicity. The interactions between peroxidase enzymes and fenamic acid-like NSAIDs cause the formation of reactive species, potentially involved in side effects. The aim of this study was to investigate the neutrophil myeloperoxidase (MPO)-mediated bioactivation of fenamic acids based on N-phenylanthranilic acid (NPA) and its four drug analogues: flufenamic acid (FFA), mefenamic acid (MFA), meclofenamic acid (MCFA), and tolfenamic acid (TFA). We hypothesized that the enzymatic oxidation of fenamic acids by MPO/hydrogen peroxide (H₂O₂) would produce reactive metabolites, cause oxidative damage and induce cytotoxicity. We utilized UV–Vis spectrophotometry, liquid chromatography-mass spectrometry (LC-MS), and electron paramagnetic spin resonance (EPR) spectroscopy using purified MPO from human neutrophils. In addition, in vitro studies were performed with MPO-containing human promyelocytic leukemia (HL-60) cells for cytotoxicity and immuno-spin trapping to detect protein-free radicals. UV–Vis spectrophotometry revealed that MPO oxidized the fenamic acids. LC-MS analyses revealed the formation of dimers, hydroxylated, and quinoneimine species, and glutathione (GSH) conjugates. EPR spin trapping with DMPO using GSH revealed that fenamic acids produced glutathionyl radicals in a concentration-dependent manner. We also detected the formation of protein-free radicals in HL-60 cells, which correlated with cytotoxicity. Despite the minor structural differences between the fenamic acids, there were variations in their oxidation potential. These findings revealed a correlation between pro-oxidant metabolite reactivity and cytotoxicity caused by fenamic acid NSAIDs.

In mammals, heme peroxidases are well known to generate oxidized (pseudo)halide products such as hypochlorous acid, hypobromous acid, oxidized iodine species, and hypothiocyanite. In addition, inter(pseudo)halogens are also oxidized (pseudo)halide compounds where two or more different (pseudo)halides are combined within a molecule without participation of other atoms. However, the information of this group of chemicals as potential products of peroxidases is limited and very fragmentary. In this review, we summarize current knowledge about chemical properties of inter(pseudo)halogens, their role as products of peroxidase-mediated conversions, and possible applications of these compounds in antimicrobial defense. The major focus is directed on bromyl chloride, cyanogen halides, and some products derived from interaction of oxidized iodine with thiocyanate.

Myeloperoxidase and eosinophil peroxidase exert their antimicrobial functions through the oxidative actions of their hypohalous acid products. Plasmalogen phospholipids are particularly susceptible to oxidation of their vinyl ether functional group by hypohalous acids. This produces a family of halogenated lipid products with pro-inflammatory roles and potential biomarker utility. The initial product of plasmalogen oxidation by HOCl is 2-chlorofatty aldehyde, which has been shown to play a key role at the blood-endothelium interface. In vitro and in vivo studies indicate increased endothelial barrier permeability, neutrophil chemotaxis, neutrophil and platelet adherence to endothelium, and promotion of erythrocyte lysis as some of its effects. These effects may be due to protein modification by 2-chlorofatty aldehyde. 2-Chlorofatty aldehyde is metabolized by host dehydrogenases to 2-chlorofatty acid. While it is less chemically reactive, 2-chlorofatty acid has partial overlap of pro-inflammatory effects with 2-chlorofatty aldehyde and unique actions such as induction of neutrophil extracellular trap formation. The stability of 2-chlorofatty acid in plasma also makes it well-suited as a biomarker of HOCl generation, and its plasma levels may be predictive of disease outcomes. 2-Bromofatty aldehydes and acids are produced analogously from HOBr reaction with plasmalogens. Their functions have yet to be well-elucidated, though similarities with chlorolipids have been observed, and increased reactivity with proteins is expected through enhanced electrophilicity of the alpha carbon. Altogether, these halogenated lipids represent underexplored mediators of diseases involving excess hypohalous acid production.