16 – Antioxidants

Question 1

What are some examples of ROS?

Answer 1

• Superoxide (O2-)
• Hydrogen peroxide (H2O2)
• Hydroxyl radical
• Singlet oxygen
• Peroxynitririte

Question 2

Where do ROS come from?

Answer 2

• Exogenous (cigarette smoke, radiation, UV, heavy metals)
• Endogenous (ETC, ER, peroxisomes)

Question 3

What is oxidative stress?

Answer 3

• When antioxidant defenses are INSUFFICIENT to neutralize all ROS

Question 4

What are antioxidants?

Answer 4

• ‘free radical scavengers’
• Chemicals that prevent the transfer of electron from O2 to organic molecules
• Preferentially accepts UNPAIRED electron from free radicals
• Terminates free radical reactions

Question 5

What are the 2 categories of antioxidants?

Answer 5

1. Enzymatic antioxidants
2. Non-enzymatic antioxidants
   a. Organocellular compounds
   b. Vitamins and minerals

Question 6

What are some antioxidant enzymes?

Answer 6

• Superoxide dismutase (SOD)
• Glutathione peroxidase (Selenium) and catalase (Fe)

Question 7

Superoxide dismutase (SOD)

Answer 7

• Converts superoxide produced from ETC to hydrogen peroxide
• Mn SOD: mitochondria
• Cu and Zn SOD: cytosol

Question 8

Glutathione peroxidase (Selenium) and catalase (Fe)

Answer 8

• Convert hydrogen peroxide to H2O + O2

Question 9

Selenium

Answer 9

• Recognized as a toxic mineral before its essentiality for animals
• Narrow range from therapeutic to developmental toxicity doses in oviparous vertebrates

Question 10

Selenium metabolism

Answer 10

• Se-methionine is actively absorbed (same as Met)
• SeO4 -2 (selenate): resembles sulphate
• Absorbed in small intestine; no absorption in rumen
• Control of SE levels mainly be excretion in urine
• *stored as SeMet and SeCys

Question 11

What are the functions of selenium?

Answer 11

• Component of a single enzyme=glutathione peroxidase
  o Enzyme degrades peroxides formed during tissue fat oxidation
• Closely associated with Vit E
• *deficiencies of either cause similar diseases

Question 12

Selenium or Vit E deficiencies

Answer 12

• White muscle disease: calves and lambs
• Mulberry heart disease: pigs
• Stiff lamb disease
• Exudative diathesis
  o Young chicks develop severe edema due to poor capillary integrity

Question 13

Selenium toxicity in oviparous vertebrates (fish and birds)

Answer 13

• Se-Met and Se-Cys incorporated into egg yolk protein
  o maternal Se burden concentrated in egg then absorbed by embryo
  o causes spinal, skeletal and cardiac deformities and cataracts

Question 14

Selenium toxicity in non-oviparous vertebrates

Answer 14

• hoof problems
• hair loss

Question 15

Vitamin E

Answer 15

• antioxidant that helps to protect cell membranes from damage by radicals
  o *chain breaking antioxidant
  o Scavenges free radicals for excretion in the urine
• *oxidation reactions: accelerate cellular aging
  o Vit E claimed to retard the aging process
• Refers to family of 8 compounds called tocopherols
• *stored in adipose tissue

Question 16

Vit E deficiency

Answer 16

• Leads to fragile RBCs and reduced fertility

Question 17

Vit E and lipid peroxidation

Answer 17

• *stops propagation of lipid peroxidation

Question 18

Interaction between Vit E and selenium deficiencies

Answer 18

• Deficiency in Vit E causes greater NEED for selenium and vice versa

Question 19

Vitamin C

Answer 19

• Ascorbic acid
• Act as a free radical scavenger
• Can be endogenously synthesized from glucose in animals or obtained from green/citrus plants
• *high doses claimed to extend life in humans
• *necessary cofactor for several hydroxylase enzymes that synthesize or aid in
  o Collagen
  o Carnitine
• Co-administration of Vit C aids iron absorption

Question 20

Vitamin C deficiencies and toxicities

Answer 20

• Scurvy in humans
• Uncommon in animals due to endogenous synthetic capacity
• Toxicities uncommon