ARTICLE | doi:10.20944/preprints202007.0136.v1
Subject: Life Sciences, Biochemistry Keywords: thioredoxin reductase; oxidative stress; nitrosative stress; theta burst stimulation; experimental autoimmune encephalomyelitis; rats
Online: 7 July 2020 (17:30:22 CEST)
Cortical theta burst stimulation (TBS) structured as intermittent (iTBS) and continuous (cTBS) could prevent the progression of the experimental autoimmune encephalomyelitis (EAE). The interplay of brain antioxidant defense systems against overproduction of reactive oxygen, nitrogen, and thiol species induced by EAE has not been entirely investigated, just as the effect of iTBS or cTBS on oxidative-nitrogen stress (ONS) in EAE rats. Dark Agouti strain female rats were tested for the effects of EAE and TBS. The rats were randomly divided into the following groups: C - control, EAE - rats immunized for EAE, CFA - rats immunized with Complete Freund's adjuvant; iTBS and cTBS groups, and EAE+iTBS and EAE+cTBS - health and EAE rats exposed to iTBS and cTBS, respectively; EAE+iTBSsh and EAE+cTBSsh - sham stimulated EAE rats with the same noise artifacts of iTBS and cTBS, respectively. Superoxide dismutase activity, levels of superoxide anion (O2•-), lipid peroxidation, glutathione (GSH), nicotinamide adenine dinucleotide phosphate (NADPH) and thioredoxin reductase (TrxR) activity were analyzed in rat spinal cords homogenates. The severity of EAE clinical coincided with the climax of ONS, based on the increase of superoxide anion and lipid peroxidation; depletion of total thiols, GSH and NADPH; and decrease of SOD activity. The TrxR imposed the most sensitive response against the applied central nervous system (CNS) stressors to rats. We concluded that the TrxR upregulation meritoriously compensates decreased ROS sequestrating and GSH systems in EAE. Both iTBS and cTBS modulate the biochemical environment at a distance from the area of stimulation against ONS, accomplish a similar effect on TrxR activity to EAE and healthy rats, and alleviate symptoms of EAE.
ARTICLE | doi:10.20944/preprints202006.0069.v1
Subject: Medicine & Pharmacology, Nutrition Keywords: RNA virus; DNA synthesis; selenium; thioredoxin reductase; SARS-coronavirus-2
Online: 7 June 2020 (09:04:57 CEST)
The biosynthesis of DNA inherently competes with RNA synthesis because it depends on the reduction of ribonucleotides (RNA precursors) to 2’-deoxyribonucleotides by ribonucleotide reductase (RNR). Hence, RNA viruses can increase viral RNA production in cells by partially blocking the synthesis of DNA, e.g. by downregulating the mammalian selenoprotein thioredoxin reductase (TR), which normally acts to sustain DNA synthesis by regenerating reduced thioredoxin, a hydrogen donor for RNR. Computational and preliminary experimental evidence supports the hypothesis that a number of pathogenic RNA viruses, including HIV-1, Ebola, Zika, some flu viruses, and SARS-CoV-2, target TR isoforms by antisense. TR knockdown would create a host antioxidant defect that could be partially rectified by increased selenium intake, or be exacerbated by selenium deficiency, contributing to viral pathogenesis. There are several non-selenium-dependent means that viruses might also exploit to slow DNA synthesis, such as targeting RNR itself, or components of the glutaredoxin system, which serves as a backup redox system for RNR. HIV-1 substantially downregulates glutathione synthesis, so it interferes with both the thioredoxin and glutaredoxin systems. Computational results suggest that, like Ebola, SARS-CoV-2 targets TR3 by antisense. TR3 is the only TR isoform that includes an N-terminal glutaredoxin domain, so antisense knockdown of TR3 may also affect both redox systems, favoring RNA synthesis. In contrast, some DNA viruses encode their own glutaredoxins, thioredoxin-like proteins and even RNR homologues – so they are doing just the opposite, favoring DNA synthesis. This is clear evidence that viruses can benefit from shifting the RNA:DNA balance to their advantage.
ARTICLE | doi:10.20944/preprints202005.0432.v1
Subject: Medicine & Pharmacology, Nutrition Keywords: antisense; HIV-1 nef; stop codon readthrough; selenium; thioredoxin reductase
Online: 26 May 2020 (13:16:09 CEST)
The HIV-1 nef gene terminates in a 3’-UGA stop codon, which is highly conserved in the main group of HIV-1 subtypes, along with a downstream potential coding region that could extend the nef protein by 33 amino acids, if readthrough of the stop codon occurs. Antisense tethering interactions (ATIs) between a viral mRNA and a host selenoprotein mRNA are a potential viral strategy for the capture of a host selenocysteine insertion sequence (SECIS) element (Taylor et al, 2016) . This mRNA hijacking mechanism could enable the expression of virally encoded selenoprotein modules, via translation of in-frame UGA stop codons as selenocysteine (SeC). Here we show that readthrough of the 3’-terminal UGA codon of nef occurs during translation of HIV-1 nef expression constructs in transfected cells. This was accomplished via fluorescence microscopy image analysis and flow cytometry of HEK 293 cells, transfected with engineered GFP reporter gene plasmid constructs, in which GFP can only be expressed by translational recoding of the UGA codon. SiRNA knockdown of thioredoxin reductase 1 (TR1) mRNA resulted in a 67% decrease in GFP expression, presumably due to reduced availability of the components involved in selenocysteine incorporation for the stop codon readthrough, thus supporting the proposed ATI. Addition of 20 nM sodium selenite to the media significantly enhanced stop codon readthrough in the pNefATI1 plasmid construct, by >100%, supporting the hypothesis that selenium is involved in the UGA readthrough mechanism.
REVIEW | doi:10.20944/preprints202010.0511.v1
Subject: Life Sciences, Biochemistry Keywords: Ferroptosis; glutathione peroxidases; heme peroxidases; hydrogen peroxide; lipid peroxidation; nitrogen monoxide radical; superoxide dismutase; superoxide radical; thioredoxin
Online: 26 October 2020 (10:43:02 CET)
The beginnings of redox biology are recalled with special emphasis on formation, metabolism and function of reactive oxygen and nitrogen species in mammalian systems. The review covers the early history of heme peroxidases and the metabolism of hydrogen peroxide, the discovery of selenium as integral part of glutathione peroxidases, which expanded the scope of the field to other hydroperoxides including lipid hydroperoxide, the discovery of superoxide dismutases and superoxide radicals in biological systems and their role in host defense, tissue damage, metabolic regulation and signaling, the identification of the endothelial-derived relaxing factor as the nitrogen monoxide radical and its physiological and pathological implications. The article highlights the perception of hydrogen peroxide and other hydroperoxides as signaling molecules, which marks the beginning of the flourishing fields of redox regulation and redox signaling. Final comments describe the development of the redox language. In the 18th and 19th century, it was highly individualized and hard to translate into modern terminology. In the 20th century, the redox language co-developed with the chemical terminology and became clearer. More recently, the introduction and inflationary use of poorly defined terms has unfortunately impaired the understanding of redox events in biological systems.