free radical injury lecture part 1 from ROBIN

1. Free Radical Injury

2. • Free radicals are chemical species that have
single unpaired electron in their outer orbit.
• Examples of pathological conditions due to
free radical:
1. Chemical and radiation injury
2. Ischemic reperfusion injury
3. Cellular aging
4. Microbial killing by phagocytes

3. • Free radicals usually attacks:
Proteins , Lipids, Carbohydrate, Nucleic acids
Characteristic of free radicals:
1. they initiate autocatalytic reaction.
2. Molecules with which they reacts are
themselves converted into free radicals.
3. They propagate chain damage reactive oxygen
species are a type of oxygen derived free
radicals.

4. • Normally free radicals(ROS) are produced
normally in all cells during mitochondrial
respiration.
• Which are degraded by cellular defense system.
• So Ros are presents in low concentration and do
not damage the cell.
• Oxidative stress:
• when production of ROS increase or
scavenging system are ineffective leads to excess
of free radicals  called Oxidative stress which
play role in cell injury.

5. 1. Cancer.
2. Aging.
3. some degenerative disease like Alzheimer.
4. Ros also produced in large amount by neutrophil
and macrophages for destroying microbes, dead
tissue and other un wanted substances.
5. Injury caused by free radicals often accompanies
inflammatory reaction.

6. Generation of free radical
1. Reduction oxidative reaction:
• During normal metabolic process normally O2
reduced by four electron to H2 to generate water
molecule during this process small amount of
physically reduced intermediate product are
produced.
• These include :
1. O2 ( one electron)
2. H2O2 (two electron)
3. OH (three electron)

7. 2. Absorption of radiant energy:
• Ultraviolet rays , X-rays( ionizing radiation  can hydrolyze
water into H and OH free radical.
3. Rapid burst of ROS:
• Produced in activated leukocytes during inflammation .
uses NAPDPH oxidase for redox reaction – in addition in some
xanthine oxidase generate O2.
4. Enzymatic metabolism of chemical drugs:
• Generate free radicals e.g. from CCL4 –> CCL3 are
produced.

8. 5. Transition metals:
• As iron and copper donates or accept free
electron during intracellular reactions and
catalyze free radicals formations.
As in Fenton reaction
H202 + Fe (2+)Fe(3+)+OH+OH-
As most of intracellular free iron in ferric(Fe3+)
must be reduced to ferrous form for Fenton
reaction  this reduction enhanced by O2.
So O2 and iron co operate in oxidative cell damage.

9. 6. Nitric Oxide (NO):
• Important chemical meditator generalised by
– Endothelial cells, macrophages, neuron.
• Act as free radical
• Can also be converted to reactions
peroxynitrate(ONOO-)as well NO2 and NO3+

10. Pathological effects of free radicals
• Three reactions relevant to cell iryus.
1. Lipid peroxidation in membrane:
• Free radicals cause peroxidadtion of lipids in
membrane .
• Lipids are attacked by O2 derivatives
particularly off to double bond-- yields lipid
peroxide as they are unstable and reactive so
autocatalytic reaction ensues causes extensive
membrane damage.

11. 2. Oxidative modification of protein:
Free radical promote oxidation of amino acids.
Formation of protein – protein ion kafe(disulphide
bond) and oxidation protein backbone.
Oxidative modification:
• Damage the active site of enzyme.
• Disrupt the structural protein
• Enhance proteo somal degradation of unfolded
protein.
Raising havoc throughout cell.

12. • Lesion in DNA:
• Free radical react with thymine in nuclear and
mitochondrial DNA .
• Produced single and double strands breaks in
DNA and then cross linking of DNA and
formation of adduce implicated in
1. Cell aging
2. Malignant transformation

13. • Removal of free radicals:
1. Free radicals are there and unstable so decay spontaneous .
2. Cells have developed – Non enzymatic & enzymatic
mechanism to remove free radicals.
Antioxidants:
Either block the initiation of free radical formation or inactive
them.
Vitamin E,A and ascorbic acid and glutathione in cytoplasm act
as auto oxidant.
Transport protein like:
Transferrin ,ferritin lacto ferritin and ceruplasmin– binds with
iron and copper and minimizing free radical formation .

14. • Scavenging system:
• Series of enzyme breakdown free radicals into H2O2,
O2.
1. Catalase:
Present in peroxisomes decompose H2O2.
2. Superoxide dismutase(SOD)
Convert O2 to H2O2
2O2+2HH2O2+O2
This group include magnese SOD localised in
mitochondria and copper zinc SOD found in cytosol.

15. • Glutathione peroxidase:
Catalyse free radicals breakdown.
• H2O2+2GSHGSSG + 2H2O
• 2OH + 2GSHGSSG + 2H2O
Ratio of oxidised glutathione GSSG to reduced
glutathione GSH is important.

16. Clinico pathological correlation of cell
injury and Necrosis
• More cell injury and inflammation
Chemical Toxic injury
• Chemical injury remained as frequent problem in clinical
medicine is major limitation to drug therapy.
• Drugs are metabolised in liver so the organ is frequent
target of drug toxicity .
• Toxic liver injury the most frequent reason for terminating
the therapeutic use or development of a drug.
Two general mechanism of chemical injury are:
• Direct Toxicity
• Cyanide poisoning

17. Cellular response to stress and toxic
insult
Direct Toxicity:
Mercury chloride poisoning --- mercury binds to
sulphidial groups of cell membrane .protein causing
increased membrane permeability and inhibition of ion
transport.
The poison cells that absorb, excrete or concentrate the
chemicals so cells of GIT & Kidneys .
Cyanide poisoning:
Mitochondrial cytochrome oxidase is poisoned by
Cyanide.
It inhibits oxidation phosphorylation

18. • Conversion to toxic metabolic :
• Most toxic chemicals are not biologically toxic