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Free radicals and antioxidants

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 radicals and antioxidants

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  1. 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

  2. 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

  3. Free radical and „science“ • chemistduring the thirties - there is superoxide • biochemistduring the sixties - make a discovery of superoxid dismutase (SOD) • doctorfree radicals are associated with many disorders

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

  5. 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 ROS (reactive oxygen species)

  6. 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 RNS (reactive nitrogen species)

  7. 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)

  8. 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 methemoglobinoxidation (erytrocyte is „full“ of antioxidants)

  9. 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

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

  11. Free radicals physiological function III • Signal moleculesfirst 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

  12. 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

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

  14. 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)

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

  16. Enzymes defence mechanism

  17. 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

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

  19. 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

  20. 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)

  21. 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

  22. High-molecula endogennous antioxidants transferrin ferritin haptoglobin hemopexin albumin

  23. 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 Low-molecule endogennous antioxidats I

  24. Ascorbic acid and its metabolites

  25. 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

  26. 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

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

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

  29. 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

  30. 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

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

  32. The peroxidation of linoleic acid

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

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

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

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

  37. Antioxidants determination ascorbate tocopheryl SOD GSHPx glutathion

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

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

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