Chp. 1 Free Radical Injury

Question 1

What is a free radical?

Answer 1

It is a chemical species with an unpaired e- in its outer orbit. Its this e- that causes the damage

Question 2

When does physiological generation of free radicals occur?

Answer 2

Physiological generation of free radicals occur during Ox/Phos.

Cyto C oxidase (complex 4) transfers e-‘s to O2. O2 can accept a max of 4 e-‘s. If O2 is partially reduced, then free radicals will be formed.

If given 1e- then O2-
If given 2e-: H2O2
If given 3e-: OH- (most damaging)
If given 4e-: H2O2

Question 3

When does pathological generation of free radicals occur?

Hint: 4 ways

Answer 3

1. They occur with ionizing radiation i.e. chemotherapy. The radiation oxidizes water in tissues into OH- (the most damaging free radical)
2. Occur during inflammation. When neutrophils carry out O2 dependent killing, they use an enzyme called NADPH oxidase. This enzyme creates SuperOxide free radical (O2-)
3. Metals - Cu and Fe. Fe2+ is oxidized to Fe3+ but makes 2OH- free radicals in the process. Fenton reaction
   Fe2+ + H2O2–>Fe3+ + 2OH-
   Could see this in hemochromatosis (too much Fe)
4. Drugs and chemicals: P450 system clears drugs i.e. acetaminophen and create free radicals in the process. Also CCL4 which causes fatty liver by creating CCl3- free radicals

Question 4

What is NADPH oxidase and what does it create?

Answer 4

It is an enzyme used in O2 dependent killing by neutrophils that turns O2 into O2-

A deficiency in this enzyme can be X-Linked or AR. Leads to Chronic Granulomatous Disease which is recurrent infection and granuloma formation with catalase+ species such as:
S. Aureas, 
Pseudomonas Cepacia
Serratia Marcessans
Nocardia
Aspergillus

NBT test remains colorless if enzyme is deficient

Question 5

How do free radicals cause cellular injury?

Answer 5

Create injury via per oxidation of lipids and oxidation of DNA and proteins. DNA damage is implicated in aging and oncogenesis

Question 6

How are free radicals eliminated?

Answer 6

4 ways:

1. Anti-oxidants - Vitamins A, C, E
2. Spontaneous Decay
3. Enzymes:
   - Superoxide Dismutase in mitochondria takes O2- into H2O2

• Catalase in peroxisome takes H2O2 to H20 and O2
• Glutathione Peroxidase in mitochondria takes H2O2 to form 2H2O and 2GS-SG
  4. Metal Carrier Proteins: ie transferrin and ceruloplasmin. They tightly bind Fe and Cu so that they can’t generate free radicals in the first place

Question 7

How is CCl4 an example of free radical injury?

Answer 7

It is an organic solvent used in dry cleaning industry that is converted to CCl3 by the P450 system.

CCl3 causes cellular swelling (hallmark of reversible cell injury) so the RER membrane swells. Ribosomes pop off and protein synthesis is decreased.

Fat continues to enter the liver, but no apolipoproteins can be made (decreased protein syn) to transport the fat out of the liver. –>FATTY LIVER

Question 8

How does repercussion injury cause free radical injury?

Answer 8

In this type of injury there is return of blood to ischemic tissue. This results in the production of O2- free radicals which causes even more damage than was there before.

So in a case of MI, if the occluded vessel is cleared and blood flow is restored to the infarcted tissue in Cath lab, if the troponin continues to rise, it could be due to reperfusion injury.

But, with the return of blood, what else would you get??Neutrophils because the area is infarcted, so you have necrosis. Necrosis is always followed by acute inflammation (neutrophils) and O2 dependent killing which creates O2- free radicals