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Initiation and Prevention of Biological Damage by Radiation-Generated Protein Radicals.
Gebicki, JM, Nauser, T
International journal of molecular sciences. 2021;(1)
Abstract
Ionizing radiations cause chemical damage to proteins. In aerobic aqueous solutions, the damage is commonly mediated by the hydroxyl free radicals generated from water, resulting in formation of protein radicals. Protein damage is especially significant in biological systems, because proteins are the most abundant targets of the radiation-generated radicals, the hydroxyl radical-protein reaction is fast, and the damage usually results in loss of their biological function. Under physiological conditions, proteins are initially oxidized to carbon-centered radicals, which can propagate the damage to other molecules. The most effective endogenous antioxidants, ascorbate, GSH, and urate, are unable to prevent all of the damage under the common condition of oxidative stress. In a promising development, recent work demonstrates the potential of polyphenols, their metabolites, and other aromatic compounds to repair protein radicals by the fast formation of less damaging radical adducts, thus potentially preventing the formation of a cascade of new reactive species.
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2.
Mechanism of Reduction of an Aminyl Radical Intermediate in the Radical SAM GTP 3',8-Cyclase MoaA.
Pang, H, Walker, LM, Silakov, A, Zhang, P, Yang, W, Elliott, SJ, Yokoyama, K
Journal of the American Chemical Society. 2021;(34):13835-13844
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Abstract
The diversity of the reactions catalyzed by radical S-adenosyl-l-methionine (SAM) enzymes is achieved at least in part through the variety of mechanisms to quench their radical intermediates. In the SPASM-twitch family, the largest family of radical SAM enzymes, the radical quenching step is thought to involve an electron transfer to or from an auxiliary 4Fe-4S cluster in or adjacent to the active site. However, experimental demonstration of such functions remains limited. As a representative member of this family, MoaA has one radical SAM cluster ([4Fe-4S]RS) and one auxiliary cluster ([4Fe-4S]AUX), and catalyzes a unique 3',8-cyclization of GTP into 3',8-cyclo-7,8-dihydro-GTP (3',8-cH2GTP) in the molybdenum cofactor (Moco) biosynthesis. Here, we report a mechanistic investigation of the radical quenching step in MoaA, a chemically challenging reduction of 3',8-cyclo-GTP-N7 aminyl radical. We first determined the reduction potentials of [4Fe-4S]RS and [4Fe-4S]AUX as -510 mV and -455 mV, respectively, using a combination of protein film voltammogram (PFV) and electron paramagnetic resonance (EPR) spectroscopy. Subsequent Q-band EPR characterization of 5'-deoxyadenosine C4' radical (5'-dA-C4'•) trapped in the active site revealed isotropic exchange interaction (∼260 MHz) between 5'-dA-C4'• and [4Fe-4S]AUX1+, suggesting that [4Fe-4S]AUX is in the reduced (1+) state during the catalysis. Together with density functional theory (DFT) calculation, we propose that the aminyl radical reduction proceeds through a proton-coupled electron transfer (PCET), where [4Fe-4S]AUX serves as an electron donor and R17 residue acts as a proton donor. These results provide detailed mechanistic insights into the radical quenching step of radical SAM enzyme catalysis.
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New potential biomarker for stratification of patients for pharmacological vitamin C in adjuvant settings of cancer therapy.
Bakalova, R, Zhelev, Z, Miller, T, Aoki, I, Higashi, T
Redox biology. 2020;:101357
Abstract
Our graphical review expands the analysis of cancer vulnerabilities for high dose vitamin C, based on several facts, illustrating the cytotoxic potential of the ascorbate free radical (AFR) via impairment of mitochondrial respiration and the mechanisms of its elimination in mammals by the membrane-bound NADHcytochrome b5 oxidoreductase 3 (Cyb5R3). We propose that vitamin C can function in "protective mode" or "destructive mode" affecting cellular homeostasis, depending on the intracellular "steady-state" concentration of AFR and differential expression/activity of Cyb5R3 in cancerous and normal cells. Thus, a specific anti-cancer effect can be achieved at high doses of vitamin C therapy. The review is intended for a wide audience of readers - from students to specialists in the field.
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4.
A Review on Free Radicals and Antioxidants.
Alkadi, H
Infectious disorders drug targets. 2020;(1):16-26
Abstract
Free radicals are generated in our body by several systems. A balance among free radicals and antioxidants is an important matter for appropriate physiological function. If free radicals become greater than the ability of the body to control them, a case known as oxidative stress appears, as a result of that, a number of human diseases spread in the body. Antioxidants can contribute to facingthis oxidative stress. The present review provides a brief overview of free radicals, oxidative stress, some natural antioxidants and the relationship between them.
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Carotenoid research: History and new perspectives for chemistry in biological systems.
Britton, G
Biochimica et biophysica acta. Molecular and cell biology of lipids. 2020;(11):158699
Abstract
The history of carotenoid research as this progressed from chemistry to biochemistry and biology is outlined. Proposed roles of carotenoids in eye health, as antioxidants, and in protection against cancer and other degenerative diseases, as well as stimulatory effects on the immune system and metabolism are covered. Proposed biological actions must be consistent with the chemistry of carotenoids in the largely aqueous biological systems, which may differ from the known chemistry of carotenoids in organic solvents. In particular, carotenoids tend to form aggregates. The effects of this aggregation and of other molecular interactions in vivo are likely to be crucial to biological activity. These perspectives of the chemistry of carotenoids and carotenoid free radicals are examined and the need for carotenoid samples used in experimental work to be pure and free from breakdown products and pro-oxidant peroxides is emphasised. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.
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6.
Adenosylation reactions catalyzed by the radical S-adenosylmethionine superfamily enzymes.
Ding, W, Ji, X, Zhong, Y, Xu, K, Zhang, Q
Current opinion in chemical biology. 2020;:86-95
Abstract
The radical S-adenosylmethionine (SAM) superfamily enzymes reductively cleave SAM to produce a highly reactive 5'-deoxyadenosyl (dAdo) radical, which in most cases abstracts a hydrogen from the substrate and initiates highly diverse reactions. In rare cases, the dAdo radical can add to a sp2 carbon to result in the production an adenosylated product. These radical SAM-dependent adenosylation reactions are present in natural product biosynthetic pathways and can be achieved by using unnatural substrate analogs containing olefin or aryl moieties. This Opinion provides a focused perspective on this emerging type of biochemistry and discusses its potential use in bioengineering and biocatalysis.
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Pulse Radiolysis Studies for Mechanism in Biochemical Redox Reactions.
Kobayashi, K
Chemical reviews. 2019;(6):4413-4462
Abstract
Pulse radiolysis is a powerful method for generating highly reduced or oxidized species and free radicals. Combined with fast time-resolved spectroscopic measurement, we can monitor the reactions of intermediate species on time scales ranging from picoseconds to seconds. The application of pulse radiolysis to water generates hydrated electrons (eaq-) and specific radicals, rendering this technique useful for investigating a number of biological redox processes. The first pulse radiolysis redox investigations explored in this review involved intramolecular electron transfer processes in protein with multiple electron-accepting sites. Pulse radiolysis enabled direct monitoring of the internal electron transfer rates and the distribution of electrons within proteins. Structural information from X-ray data has allowed analysis of the rate constants and their activation parameters in relation to the mechanisms with current theoretical treatments. The second set of pulse radiolysis redox investigations explored here concerned the intermediates of enzyme reactions after redox reactions. Pulse radiolysis allowed the extremely rapid donation of electrons to a redox center in a protein. It makes it possible to observe the unstable intermediates after the reduction and the following subsequent steps. For example, the intermediates generated through the one-electron reduction of oxygenated hemoproteins, such as cytochrome P450 and nitric oxide synthase, were characterized. Interestingly, ligand exchange can occur upon the reduction of heme iron, in which different amino acid residues bind to heme in the ferrous and ferric states, respectively. We directly observed the ligand-switching intermediates of bacterial CooA, a CO sensor, and bacterial iron response regulator protein. These ligand exchange processes are physiologically important for regulating the electrode potential and effective formation of superoxide anion or HO•. The third set of pulse radiolysis redox investigations explored in this review concerns free-radical processes in biological systems. Free radicals are produced in cells and organisms in a variety of processes. The cell has developed special and very effective machinery for controlling and detoxifying reactive radicals. Radiation-generated radicals allow studies of the reactions between specific radicals and solutes, often revealing the mechanisms underlying the initial and subsequent reactions. The crucial contribution was made using pulse radiolysis techniques and knowledge of the identities, properties, and reactions of radicals. These radicals include superoxide (O2•-), nitric monoxide (NO•), ascorbate, urate, and protein radicals. This review focuses on the reactions of these radicals and their physiological functions.
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8.
Radicals, Oxidative/Nitrosative Stress and Preeclampsia.
Taysi, S, Tascan, AS, Ugur, MG, Demir, M
Mini reviews in medicinal chemistry. 2019;(3):178-193
Abstract
Preeclampsia (PE) has a profound effect in increasing both maternal and fetal morbidity and mortality especially in third World. Disturbances of extravillous trophoblast migration toward uterine spiral arteries is characteristic feature of PE, which, in turn, leads to increased uteroplacental vascular resistance and by vascular dysfunction resulting in reduced systemic vasodilatory properties. Underlying pathogenesis appeared to be an altered bioavailability of nitric oxide (NO•) and tissue damage caused by increased levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS). The increase in ROS and RNS production or the decrease in antioxidant mechanisms generates a condition called oxidative and nitrosative stress, respectively, defined as the imbalance between pro- and antioxidants in favor of the oxidants. Additionally, ROS might trigger platelet adhesion and aggregation leading to intravascular coagulopathy. ROS-induced coagulopathy causes placental infarction and impairs the uteroplacental blood flow in PE. As a consequence of these disorders could result in deficiencies in oxygen and nutrients required for normal fetal development resulting in fetal growth restriction. On the one hand, enzymatic and nonenzymatic antioxidants scavenge ROS and protect tissues against oxidative damage. More specifically, placental antioxidant enzymes including catalase, superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) protect the vasculature from ROS, maintaining the vascular function. On the other hand, ischemia in placenta in PE reduces the antioxidant activity. Collectively, the extent of oxidative stress would increase and therefore leads to the development of the pathological findings of PE including hypertension and proteinuria. Our goal in this article is to review current literature about researches demonstrating the interplay between oxidative, nitrosative stresses and PE, about their roles in the pathophysiology of PE and also about the outcomes of current clinical trials aiming to prevent PE with antioxidant supplementation.
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9.
Fast reaction of carbon free radicals with flavonoids and other aromatic compounds.
Nauser, T, Gebicki, JM
Archives of biochemistry and biophysics. 2019;:108107
Abstract
Many theoretical and experimental studies have shown that the principal initial biological targets of free radicals are nucleic acids, lipids and proteins. The reaction normally generates carbon-centered radicals which can propagate molecular damage either directly or after formation of new reactive species following reaction with oxygen. Overall damage prevention is therefore best achieved by repair of the carbon radicals before they initiate further reactions. Recent studies have shown that the repair cannot be achieved by normal levels of the endogenous antioxidants glutathione, ascorbate or urate. Since their concentrations are well regulated and cannot be enhanced by oral intake, we have investigated the effectiveness of flavonoids and other polyphenols as potential carbon radical repair agents, because their levels in vivo can be significantly enhanced by diet. Pulse radiolysis measurements of the rate constants of repair of amino acid radicals by several polyphenols showed reversible formation of radical-polyphenol adducts 100-1000 times faster than previously reported for the bimolecular stoichiometric reactions of flavonoids i.e. with rate constants in the order of 1010 M-1s-1. Adduct formation depended only on the presence of a carbon-centered radical and an aromatic moiety in the reactants, without the involvement of redox reactions at the phenolic groups. Formation of adducts lowered the reactivity of the radicals. Our results suggest that flavonoids, polyphenols and many of their metabolites can effectively reduce the damaging potential of carbon radicals at concentrations achievable in vivo by diets rich in fruits and vegetables.
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10.
The effects of ketamine and lidocaine on free radical production after tourniquet-induced ischemia-reperfusion injury in adults.
Peker, K, Ökesli, S, Kıyıcı, A, Deyişli, C
Ulusal travma ve acil cerrahi dergisi = Turkish journal of trauma & emergency surgery : TJTES. 2019;(2):111-117
Abstract
BACKGROUND The primary aim of this study was to compare the effects of a small-dose infusion of 2 antioxidant agents, ketamine and lidocaine, on ischemia-reperfusion injury (IRI) in patients undergoing elective lower limb surgery. Ischemia-modified albumin (IMA), lactate, and blood gas levels were all measured and assessed. METHODS A total of 100 patients who underwent lower extremity surgery were randomized into 3 groups. After spinal anesthesia, the ketamine group (Group K, n=33) was given a ketamine infusion, a lidocaine infusion was administered to the lidocaine group (Group L, n=33), and in the control group (Group C), 0.9% a sodium chloride infusion was performed. Blood samples were obtained for IMA analysis before anesthetic administration (baseline), at 30 minutes of tourniquet inflation (ischemia), and 15 minutes after tourniquet deflation (reperfusion). Arterial blood gas measurements were determined before anesthetic administration and 15 minutes after tourniquet deflation. RESULTS The lactate and IMA levels at reperfusion were significantly lower in both the ketamine group and the lidocaine group when compared with the control group. CONCLUSION The administration of both ketamine and lidocaine infusions significantly decreased skeletal muscle IRI-related high lactate and IMA levels. These results suggest the possibility of the clinical application of ketamine or lidocaine infusions in cases of skeletal muscle-related IRI.