Reactive oxygen, antioxidants, oxidative stress & Vitamin E

Question 1

Define reactive oxygen species giving examples.

Answer 1

-Highly reactive chemical formed from oxygen
* Consist of:
(1) Free radical, which contains one or more unpaired electrons.
E.g: superoxide (O2), hydroxyl radical (OH-), peroxyl radical (ROO-). (2) Nonradical derivatives of 02 which do not contain unpaired
electrons. E.g: hydrogen peroxide (H2O2), singlet oxygen.

Question 2

List the classes of antioxidants with examples for each group.

Answer 2

nature and action-enzymatic inactivation of ROS,non-enzymatic antioxidants
location
lipid peroxidation

Question 3

Define oxidative stress.

Answer 3

Disturbance of balance between the production of ROS and the levels of antioxidants in the body.

Question 4

List some common conditions of oxidative stress.

Answer 4

1. Protein- oxidation of sulfhydryl groups, modification of certain amino acids. Loss of biological activity of proteins.
2. Lipids- PUFA are highly susceptible to damage.
3. Carbohydrates: Linkage of CHOs to proteins (glycation) increases the susceptibility of proteins by attack of free radicals.
4. Nucleic acids-DNA strand breaks, fragmentation of bases and deoxyribose

Question 5

Describe lipid peroxidation with reactions.

Answer 5

-self-propagating chain-reaction, the initial oxidation of only a few lipid molecules can result in significant tissue damage.
-in atherosclerosis, asthma, Parkinson’s disease, kidney damage

1. Initiation – Hydroxyl radical begins the chain reaction. It remove a hydrogen atom from PUFA to produce a lipid free radical. Production of radical.
2. Propagation – Lipid free radical interact with oxygen and produce peroxyl radical. Attack another PUFA molecule. This can cause chain reaction.
3. Termination –The radical reaction stops when 2 radicals react and produce a non-radical species. Peroxyl radical reacts with another peroxyl radical to form inactive products.

Question 6

List the chemical names and most active form of V.E

Answer 6

-alpha-tocopherol (most active)
-beta-tocopherol
-gamma-tocopherol
delta-tocopherol
a- tocotrienol
b-tocotrienol
g-tocotrienol
d-tocotrienol

Question 7

V.E ,Mention its RDA

Answer 7

15 mg/day (a- tocopherol)
*Dietary intake of PUFA increases the need for Vit E

Question 8

List the dietary sources.V.E

Answer 8

✓Vegetable oils.
✓liver
✓Egg
✓Whole grains
✓Leafy vegetables
✓legumes

Question 9

List the functions. V.E

Answer 9

• Most powerful antioxidant
• Inhibit lipid peroxidation.
• It has synergistic antioxidant action with Selenium.
• Protect the plasma membrane from the attack of free radicals.
• Protect RBC from hemolysis by preventing the peroxidation.
• Boosts immune response.
• Reduces the risk of atherosclerosis by reducing the oxidation of LDL.

Question 10

Mention the deficiency manifestations. V.E

Answer 10

• Newborns have low reserves of vitamin E, but breast milk (and formulas) contain the vitamin E.
• Very-low-birth-weight infants may be given supplements to prevent the hemolysis and retinopathy associated with deficiency of vitamin E.
• In adults, deficiency is usually associated with defective lipid absorption or transport.
• It is characterized by sensitivity of RBCs to peroxides. Hence during deficiency patients can present with hemolytic anemia.

Question 11

Why non-radicals are reactive?

Answer 11

They are containing oxygen.
-H2O2
Presence of the extra oxygen atom in the hydrogen peroxide molecule that makes it so reactive.
-Singlet oxygen
Contain oxygen (in excited state)

Question 12

Sources of free radicals

Answer 12

1. Normal biological processes (cellular metabolism)/Endogenous
2. Environmental effects/Exogenous

Question 13

According to their nature & action

Answer 13

➢Enzymatic antioxidants- Enzymic inactivation
SOD(1st line of defense), catalase, glutathione peroxidase, glutathione reductase
➢Non-enzymatic antioxidants-chemical inactivation
(a) nutrient (beta-carotene, ascorbic acid,selenium, alpha-tocopherol)
(b) metabolic (glutathione ,transferrin, albumin,

Question 14

According to their location

Answer 14

➢Plasma antioxidants
beta-carotene, ascorbic acid, bilirubin, etc ➢Cell membrane antioxidants
alpha-tocopherol
➢Intracellular antioxidants
SOD, catalase, glutathione peroxidase

Question 15

In relation to lipid peroxidation

Answer 15

In relation to lipid peroxidation
➢Preventive antioxidants- CG.P
Block initial production of free radicals (catalase, glutathione peroxidase).
➢Chain breaking antioxidants SUV.E
Inhibit propagative phase of lipid peroxidation (SOD, Vit E, Uric acid).

Question 16

Why PUFA is prone to peroxidation ?

Answer 16

Because of its chemical structure:
Methylene bridge in between 2 double bonds
Contain 2H→highly reactive
Free radicals attack H on methylene bridge & stabilize itself & form H2O
* ROS attack the PUFA of the fatty acid membrane, initiating a self- propagating chain reaction.

Question 16

Why PUFA is prone to peroxidation ?

Answer 16

Because of its chemical structure:
Methylene bridge in between 2 double bonds
Contain 2H→highly reactive
Free radicals attack H on methylene bridge & stabilize itself & form H2O
* ROS attack the PUFA of the fatty acid membrane, initiating a self- propagating chain reaction.