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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 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
free radical what is it
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
free radical and science
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
mechanism of radical reactions
Mechanism of radical reactions

Radicals are highly reactive species

Three distinc steps

  • initiation (homolytic covalent bonds cleavage)
  • propagation (chain propagation)
  • termination
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

ROS (reactive oxygen species)
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

RNS (reactive nitrogen species)
the main sources of free radicals
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)
the main sources of free radicals ii
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)

free radicals physiological function
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
free radicals physiological function ii
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

free radicals physiological function iii
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

immunity vs regulation
Immunity vs. regulation

a massive production of ROS as immunity instrument


an induction of the changes low concentration ROS, which are probably regulation mechanism

antioxidant defence system
Antioxidant defence system

3 levels

inhibition of production the abundance of RONS

capture ofradicals (scavengers, trappers, quenchers)

correction mechanism of destroyed biomoleculs

antioxidants and scavengers review
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)
antioxidants and scavengers review ii
Antioxidants and scavengers review II

2. Exogennous antioxidants

  • FR scavengers
  • trace elements
  • drugs and compounds influence to FR metabolism
superoxid dismutase
Superoxid dismutase


2O2. - + 2H+ H2O2 + O2

SOD - is present in all oxygen-metabolizing cells, different cofactors (metals)

an inducible in case of superoxide overproduction

superoxid dismutase1
Superoxid dismutase

Mn 2+ SOD (SOD1)


matrix mitochondria

lower stability then Cu, Zn - SOD

superoxid dismutase2
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

glutathion peroxidases
Glutathion peroxidases

elimination of intracellular hydroperoxides and H2O2


  • cytosolic GSH - glutathionperoxidasa(EC, cGPx)
  • extracelullar GSH- glutathionperoxidasa (eGSHPx)
  • phospholipidhydroperoxide GSH - peroxidase (EC, PHGPx)


2 H2O2 2 H2O + O2

high affinity to H2O2 : peroxisomes hepatocytes mitochondria, cytoplasm of erytrocytes

tetramer with Fe, needs NADPH

high molecula endogennous antioxidants

High-molecula endogennous antioxidants






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


Alfa-tocopherol a vitamin E

localise in membranes

produces hydroperoxides, which are changes by GSHPx

Low-molecule endogennous antioxidats I
low molecule endogennous antioxidats ii
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

low molecule endogennous antioxidats iii
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

low molecule endogennous antioxidats iv
Low-molecule endogennous antioxidats IV
  • Lipoic acid (lipoate)

PDH cofactor tocopheryl and ascorbate regeneration

  • melatonin

lipophilic ; hydroxyl radicals scavenger

low molecule endogennous antioxidats v
Low-molecule endogennous antioxidats V
  • uric acid (urates)
  • bilirubin
  • flavonoids
trace elements influence to fr metabolism
Trace elements influence to FR metabolism


influence to vitamin E resorption, part of selenoproteins of Se = insufficient immun. respons, erytrocytes hemolysis, methemoglobin synthesis


cell membrane stabilisation Fe antagonist

oxidative stress
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

oxidative damage to lipid

unsaturated bonds loss

arising of reactive metabolites (aldehydes)


changes in fluidity and permeability of membranes

membranes integral enzymes are influenced

Oxidative damage to lipid
oxidative damage to proteins

agregation, fragmentation and cleveage

reaction with hem iron ion

functional group modification


changes in: enzymes activity, ions transport


Oxidative damage to proteins
oxidative damage to dna

saccharide ring cleveage

bases modification

chain breakeage



translation mistakes

protoesynthesis inhibition

Oxidative damage to DNA
oxidative stress markers
Oxidative stress markers

Free radicals detection

  • very difficult, because of chem-phys. properties

Oxidative stress products detection

  • more simple, a wide range of techniques
oxidative stress markers ii
Oxidative stress markers II

Lipoperoxidation markers:

malondialdehyde (MDA), conjugated diens, isoprostanes

Oxidative damage to protein markers :

protein hydroperoxides

Oxidative damage to DNA :

modified nucleosides

antioxidants determination
Antioxidants determination






disorders associated with oxidative stress
Disorders Associated with Oxidative stress


Alzheimers Disease

Parkinson‘s Disease




Acute Pancreatitis

disorders associated with oxidative stress1
Disorders Associated with Oxidative stress

Others conditions


Air Pollution