Free radicals and antioxidants PowerPoint Presentation

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Free radicals and antioxidants What is „free radical“? Reactive oxygen and nitrogen species (RONS) Are the RONS always dangerous? Well known term „oxidative stress“ - what is it? Antioxidants - types and appearance Markers of oxidative stress Disorders Associated with Oxidative stress

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Free radical - what is it? Atom: proton, neutron, electronic shell (orbital) Free radical particles with an unpaired electron spinning around the nucleus. (can be atom, ions, molecule). tend to reach equilibrium, plucks an electron from the nearest intact molecule. most of biomoleculs are not radicals

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Free radical and „science“ chemist during the thirties - there is superoxide biochemist during the sixties - make a discovery of superoxid dismutase (SOD) doctor free radicals are associated with many disorders

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Mechanism of radical reactions Radicals are highly reactive species Three distinc steps initiation (homolytic covalent bonds cleavage) propagation (chain propagation) termination

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ROS (reactive oxygen species) Free radicals superoxide, O2 · - hydroxyl radical, OH · peroxyl, ROO · alkoxyl, RO · hydroperoxyl, HO2 · Particals, which are not free radicals hydrogen peroxide, H2O2 (Fenton´s reaction) hypochlorous acid, HClO ozone, O3 singlet oxygen, 1O2

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RNS (reactive nitrogen species) Free radicals nitrogen(II) oxide, NO . nitrogen(IV) oxide, NO2 . Particals, which are not free radicals nitrosyl, NO+ nitrous acid, HONO nitogen(III) oxide, N2O3 peroxynitrite, ONOO - alkylperoxinitrite, ROONO

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The main sources of free radicals membranes enzymes and/or coenzymes with flavine structures, hem coenzymes, enzymes containing Cu atom in an active site 1. respiratory chain mitochondria : mainly superoxide and then H2O2 approx 1- 4% O2 entres into resp. chain (mainly complexes I a III)

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The main sources of free radicals II 2. Endoplasmic reticulum superoxide creation (by cytochrome P- 450) 3. special cells (leukocytes) superoxide creation by NADP-oxidas 4. hemoglobin to methemoglobin oxidation (erytrocyte is „full“ of antioxidants)

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Free radicals physiological function Used by oxides a oxygenes cytochromoxidase (toxic intermediates, H2O2 and superoxide, are bound to an enzymu) monoxygenases - activate O2 in liver ER or in adrenal gland mitochondria ; hydroxylation

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Free radicals physiological function II ROS a RNS against bacteria enzyme complex NADPH-oxidase of leukocytes myeloperoxidase - catalysis of the following reaction H2O2 + Cl- + H+ = HClO + H2O

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Free radicals physiological function III Signal molecules first messenger  second messenger  information net This info net function is affected by the redox state of cells redox state : antioxidant capacity, reduction equivalent availlability, RONS rate  ROS: second messenger

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Immunity vs. regulation a massive production of ROS as immunity instrument x an induction of the changes low concentration ROS, which are probably regulation mechanism

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Antioxidant defence system 3 levels inhibition of production the abundance of RONS capture of radicals (scavengers, trappers, quenchers) correction mechanism of destroyed biomoleculs

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Antioxidants and scavengers review 1. Endogennous antioxidants enzymes (cytochrome c,SOD, GSHPx, catalase) nonenzymatic - fixed in membranes ( -tocopherol, -caroten, coenzym Q 10) - out of membranes (ascorbate, transferrin, bilirubin)

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Antioxidants and scavengers review II 2. Exogennous antioxidants FR scavengers trace elements drugs and compounds influence to FR metabolism

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Enzymes defence mechanism

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Superoxid dismutase (EC 1.15.1.1, SOD) 2O2. - + 2H+  H2O2 + O2 SOD - is present in all oxygen-metabolizing cells, different cofactors (metals) an inducible in case of superoxide overproduction

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Superoxid dismutase Mn 2+ SOD (SOD1) tetramer matrix mitochondria lower stability then Cu, Zn - SOD

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Superoxid dismutase Cu 2+/Zn 2+ SOD (SOD 2) dimer, Cu = redox centr cytosol, intermitochondrial space hepatocyt, brain, erytrocyte high stability, catalysation at pH 4,5-9,5

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Glutathion peroxidases elimination of intracellular hydroperoxides and H2O2 2 GSH + ROOH  GSSH + H2O + ROH cytosolic GSH - glutathionperoxidasa (EC 1.11.1.9, cGPx) extracelullar GSH - glutathionperoxidasa (eGSHPx) phospholipidhydroperoxide GSH - peroxidase (EC 1.11.1.12, PHGPx)

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Catalasa (EC 1.11.1.6, KAT) 2 H2O2  2 H2O + O2 high affinity to H2O2 : peroxisomes hepatocytes mitochondria, cytoplasm of erytrocytes tetramer with Fe, needs NADPH

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High-molecula endogennous antioxidants transferrin ferritin haptoglobin hemopexin albumin

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Low-molecule endogennous antioxidats I Ascorbate (vitamin C) collagen synthesis dopamine to epinephrine conversion reduction agent Fe absorption antioxidant = reduction O2 · - OH ·, ROO·, HO2 · tocopheryl radical regeneration prooxidant Alfa-tocopherol a vitamin E localise in membranes produces hydroperoxides, which are changes by GSHPx

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Ascorbic acid and its metabolites

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Low-molecule endogennous antioxidats II ubiquinone (coenzyme Q) electron carrier in respisratory chain co-operates with tocopheryl carotenoides, -caroten, vitamin A removing the radicals from lipids

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Low-molecule endogennous antioxidats III glutathione (GSH, GSSG) in all mammalian cells (1-10 mmol/l) important redox buffer 2 GSH  GSSG + 2e- + 2H+ ROS elimination, stabilisation in reduction form ( SH- groups, tocopheryl and ascorbate regeneration) substrate of glutathione peroxidases

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Low-molecule endogennous antioxidats IV Lipoic acid (lipoate) PDH cofactor tocopheryl and ascorbate regeneration melatonin lipophilic ; hydroxyl radicals scavenger

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Low-molecule endogennous antioxidats V uric acid (urates) bilirubin flavonoids

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Trace elements influence to FR metabolism Selenium influence to vitamin E resorption, part of selenoproteins  of Se = insufficient immun. respons, erytrocytes hemolysis, methemoglobin synthesis Zinc cell membrane stabilisation Fe antagonist

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Oxidative stress Equilibrium failure between creation and a elimination of RONS leads to oxidative stress Be carefull - this equilibrium can be disbalance in both sides

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Oxidative damage to lipid Damage unsaturated bonds loss arising of reactive metabolites (aldehydes) Sequel changes in fluidity and permeability of membranes membranes integral enzymes are influenced

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The peroxidation of linoleic acid

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Oxidative damage to proteins Damage agregation, fragmentation and cleveage reaction with hem iron ion functional group modification Sequel changes in: enzymes activity, ions transport proteolysis

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Oxidative damage to DNA Damage saccharide ring cleveage bases modification chain breakeage Sequal mutation translation mistakes protoesynthesis inhibition

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Oxidative stress markers Free radicals detection very difficult, because of chem-phys. properties Oxidative stress products detection more simple, a wide range of techniques

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Oxidative stress markers II Lipoperoxidation markers: malondialdehyde (MDA), conjugated diens, isoprostanes Oxidative damage to protein markers : protein hydroperoxides Oxidative damage to DNA : modified nucleosides

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Antioxidants determination ascorbate tocopheryl SOD GSHPx glutathion

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Disorders Associated with Oxidative stress Neurological Alzheimers Disease Parkinson‘s Disease Endocrine Diabetes Gastrointestinal Acute Pancreatitis

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Disorders Associated with Oxidative stress Others conditions Obesity Air Pollution Toxicity Inflammation

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