Chapter 14: Free Radicals and Anti-Oxidants

Question 1

Why is the lens susceptible to oxidative damage?

Answer 1

Susceptibility is due to challenge by active O2 species related to its low levels of molecular 02 and trace amounts of transition metals

Question 2

What are the anti-oxidant defense mechanisms of the lens epithelium and superficial cortex?

Answer 2

• Glutathione peroxidase
• catalase
• Superoxide Dismutase

Question 3

Which enzyme acts as the major scavenger of active 02 species in the lens?

Answer 3

glutathione peroxidase, which is synthesized in the lens epithelium and migrates deeper

Question 4

What trials found high dose supplementation of carotenoids, vitamin c, and vitamin a did not have any affect on the progression or rate of development of age-related cataracts?

Answer 4

AREDS and VECAT trials

Question 5

What are the mechanisms of retinal vulnerability to lipid peroxidation?

Answer 5

1- Outer rod segments susceptible to 02 damage due to increased concentration of polyunsaturated FA’s
2- Rod inner segment is rich in mitochondria, which may leak active 02 species
3- Increased 02 consumption of the retina
4- Light exposure may trigger photo-oxidative processes

Question 6

What happens to the photoreceptors if their RPE cells die?

Answer 6

the photoreceptors may supported by it may suffer severe death or damage

Question 7

What color light are the photoreceptors susceptible to? How do carotenoids help prevent this?

Answer 7

Blue light, due to the formation of the compound A2E, which is phototoxic and induces RPE DNA damage and apoptosis
Carotenoids (lutein and zeaxanthin) act as blue light filters, thus preventing the damage from occurring.