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Chemical Basis of Reactive Oxygen Species Reactivity and Involvement in Neurodegenerative Diseases

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Chemical Basis of Reactive Oxygen Species Reactivity and Involvement in Neurodegenerative Diseases International Journal of Molecular Sciences Review Chemical Basis of Reactive Oxygen Species Reactivity and Involvement in Neurodegenerative Diseases Fabrice Collin Laboratoire des IMRCP, Université de Toulouse, CNRS UMR 5623, Université Toulouse III-Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse CEDEX 09, France; [email protected] Received: 26 April 2019; Accepted: 13 May 2019; Published: 15 May 2019 Abstract: Increasing numbers of individuals suffer from neurodegenerative diseases, which are characterized by progressive loss of neurons. Oxidative stress, in particular, the overproduction of Reactive Oxygen Species (ROS), play an important role in the development of these diseases, as evidenced by the detection of products of lipid, protein and DNA oxidation in vivo. Even if they participate in cell signaling and metabolism regulation, ROS are also formidable weapons against most of the biological materials because of their intrinsic nature. By nature too, neurons are particularly sensitive to oxidation because of their high polyunsaturated fatty acid content, weak antioxidant defense and high oxygen consumption. Thus, the overproduction of ROS in neurons appears as particularly deleterious and the mechanisms involved in oxidative degradation of biomolecules are numerous and complexes. This review highlights the production and regulation of ROS, their chemical properties, both from kinetic and thermodynamic points of view, the links between them, and their implication in neurodegenerative diseases. Keywords: reactive oxygen species; superoxide anion; hydroxyl radical; hydrogen peroxide; hydroperoxides; neurodegenerative diseases; NADPH oxidase; superoxide dismutase 1. Introduction Reactive Oxygen Species (ROS) are radical or molecular species whose physical-chemical properties are well-known both on thermodynamic and kinetic points of view. They are produced from molecular oxygen, during the successive 4 steps of 1-electron reduction (reaction (1)). The reaction occurs in particular in the mitochondrial respiratory chain, where 85% of O2 is metabolized and where partially reduced O2 intermediates are produced in low quantity [1]. + + +e− +e−(+2H ) +e− +e−(+2H ) O O•− H O HO•(+HO−) 2H O (1) 2 −! 2 −! 2 2 −! −! 2 The three primary species, i.e., the superoxide anion (O2•−), hydrogen peroxide (H2O2) and the hydroxyl radical (HO•), are called reactive oxygen species because they are oxygen-containing compounds with reactive properties. O2•− and HO• are commonly referred to as “free radicals”. They can react with organic substrates and lead to intermediate species able to further produce other ROS. For instance, H atom abstraction by HO• free radicals on a C-H bond leads to a carbon-centered radical, that further reacts rapidly with O2 to give a peroxyl radical RO2• (Figure1)[ 2]. The latter may react with another substrate to give a new carbon-centered radical and a hydroperoxide ROOH, which may decompose into alkoxyl radical RO• in a reaction catalyzed by redox competent metal cations such as iron or copper (as occurring with heme proteins [3]). These “secondary” species are all ROS and share a similarity in structure and reactivity with the three primary species O2•−,H2O2 and HO•. Among them, H2O2 (and hydroperoxides) is a molecular species and is supposed to be less reactive than the other radical short-lived species that are able to react with a range of targets (an Int. J. Mol. Sci. 2019, 20, 2407; doi:10.3390/ijms20102407 www.mdpi.com/journal/ijms Int. J. Mol. Sci. 2019, 20, 2407 2 of 17 Int. J. Mol. Sci. 2019, 20, x FOR PEER REVIEW 2 of 17 exception may apply for O2•−). However, its toxicity can be exerted via Fenton reaction in the presence exception may apply for O2•‒). However, its toxicity can be exerted via Fenton reaction in the presence of redox metal ions such as iron or copper (Figure1), or via Haber–Weiss reaction in the presence of of redox metal ions such as iron or copper (Figure 1), or via Haber–Weiss reaction in the presence of O •‒[4]. 2O•−2 [4]. Fenton reaction 2+ 3+ 2+ • ‒ 3+ Fe Fe H2O2 + Fe HO + HO + Fe Haber-Weiss reaction e‒ H+ 3+ 2+ •‒ • •‒ Fe /Fe • ‒ O2 O2 HO2 O2 + H2O2 HO + HO + O2 pKa = 4.8 Superoxide Perhydroxyl anion Alkoxyl radical radical e‒ (+ 2H+) • 3+ Fe • RO O2 HO 2 Hydrogen peroxide Fe2+ Peroxyl H2O2 O 2+ + 2+ 2 Fe3+ Fe , H radical Carbon-centered Fe O2 • • radical ‒ RO2H RO2 R RH e (- HO‒) Fenton reaction • HO2 Hydroperoxide • RH e‒ (+ H+) R • Fe3+ H2O HO Hydroxyl radical Figure 1. The chemical basis of Reactive Oxygen Species (ROS) generation—primary radical and molecularFigure 1. The species chemical are produced basis of Reactive by incomplete Oxygen reductionSpecies (ROS) of moleculargeneration—primary oxygen and radical can furtherand react molecular species are produced by incomplete reduction of molecular oxygen and can further react with an organic substrate to generate substrate-derived ROS. Metal ions are engaged in electron transfer with an organic substrate to generate substrate-derived ROS. Metal ions are engaged in electron (through metalloenzymes in vivo), but also involved in both Fenton and Haber-Weiss reactions, and in transfer (through metalloenzymes in vivo), but also involved in both Fenton and Haber-Weiss thereactions, reduction and of in hydroperoxidethe reduction of hydroperoxide into alkoxyl radical. into alkoxyl radical. 2. Production of ROS 2. Production of ROS 2.1. Production of ROS In Vivo, Regulation and Oxidative Stress 2.1. Production of ROS In Vivo, Regulation and Oxidative Stress ROSROS cancan bebe deleteriousdeleterious for for biomolecules biomolecules and and lead lead to oxidative to oxidative damages damages involved involved in several in several pathologiespathologies (neurodegenerative diseases, diseases, atherosclero atherosclerosis,sis, cancer and cancer other and disorders). other disorders). However, they However, theyplay, play, above above all, an all, important an important role in role homeostasis, in homeostasis, cell signalization, cell signalization, regulation regulation of metabolism, of metabolism, or ormemory memory formation formation via via DNA DNA methylation methylation [5,6]. [ 5As,6 ].recently As recently reviewed, reviewed, oxidative oxidative stress may stress be a may key be a key modulatormodulator inin neurodegenerativeneurodegenerative diseases diseases [7]. [ 7In]. mammalian In mammalian cells, cells,ROS are ROS essentially are essentially produced produced by by enzymesenzymes andand areare from different different origins: origins: mainly mainly from from the thecytoplasmic cytoplasmic membrane membrane NADPH NADPH oxidase oxidase andand from from the the enzymeenzyme complex complex of of the the mitochondrial mitochondrial respiratory respiratory chain, chain, but also but from also sources from sourcesof other of other organellesorganelles such such asas xanthine oxidase oxidase (XO), (XO), lipo- lipo- and and cyclo-oxygenase, cyclo-oxygenase, cytochromes cytochromes P450 (endoplasmic P450 (endoplasmic reticulum) and peroxisomes. NADPH oxidase catalyzes the monoelectronic reduction of molecular reticulum) and peroxisomes. NADPH oxidase catalyzes the monoelectronic reduction of molecular oxygen, thus producing O2•‒ [8,9] that is released either outside the cell (for phagocytic cells) or inside oxygen,the cell thus(for non-phagocytic producing O2•− cells)[8,9 [10].] that Inis mitoch releasedondria, either ROS outside are produced the cell during (for phagocytic ATP biosynthesis cells) or inside thewhich cell (foris accompanied non-phagocytic by electron cells) and [10]. proton In mitochondria, transfers, with ROS molecular are produced oxygen duringas the final ATP target. biosynthesis whichElectron is accompaniedleaks, which represent by electron around and 1–3% proton of the transfers, total electron with production, molecular may oxygen occur in as complex the final target. ElectronI (NADH-ubiquinone leaks, which representoxidoreductase) around and 1–3% complex of the III total(ubiquinol-cytochrome electron production, c oxidoreductase) may occur in of complex I (NADH-ubiquinonethe electron transport chain oxidoreductase) and leads to andthe production complex IIIof (ubiquinol-cytochromeO2•‒ [11]. Because of the high c oxidoreductase) activity of of thethe electron mitochondrial transport respiratory chain andchain leads in aerobic to the organisms, production such of a O leak2•− [is11 the]. Becausemajor source of the of highROS activity ofproduction the mitochondrial in cells, more respiratory important chain than NAPDH in aerobic oxidase organisms, (except during such athe leak activation is themajor of phagocytic source of ROS productioncells) and XO in cells,[1]. The more latter important is a molybdenum than NAPDH enzyme,oxidase essentially (except located during in the cytosol, the activation that catalyzes of phagocytic the oxidation of hypoxanthine into xanthine and produces O2•‒, which might be further converted cells) and XO [1]. The latter is a molybdenum enzyme, essentially located in the cytosol, that catalyzes into H2O2 by XO (and oxidation of xanthine into uric acid) or by cytosolic Superoxide Dismutase the(SOD) oxidation [12]. Xanthine of hypoxanthine oxidase is also into able xanthine to convert and nitrite produces into Onitric2•−, oxide, which and might is thus be furthera potential converted into H2O2 by XO (and oxidation of xanthine into uric acid) or by cytosolic Superoxide Dismutase (SOD) [12]. Xanthine oxidase is also able to convert nitrite into nitric oxide, and
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