Session 1 - oxidative stress and antioxidants

Question 1

How do free radicals cause damage?

Answer 1

They taken an electron from protein/lipid/DNA

for their unpaired one(s)

Question 2

How does hydrogen peroxide (H2O2) produce free radicals?

Answer 2

Reacts with other molecules (like Fe2+) to produce free radicals

Question 3

Superoxide radicals react with nitric oxide radicals to make what?

Answer 3

ONOO-
peroxynitrite
highly reactive and can oxidise more molecules

Question 4

Which herbicide produces superoxide radicals?

Answer 4

paraquat

Question 5

Which type of DNA is especially sensitive to ROS damage?

Why?

Answer 5

mitochondrial DNA (mtDNA)

• Near the inner mitochondrial membrane where ROS are formed
• not protected by histones

Question 6

What are Heinz bodies?

Answer 6

Inclusions in Red blood cells made of denatured haemoglobin due to ROS damage

Question 7

How do ROS cause inappropriate crosslinking?

Answer 7

Takes an electron from a cysteine residue (thiol group; S-H) converting it to a disulphide bond

S-H > S-S

Question 8

How can ROS damage lead to atherosclerosis?

Answer 8

Lipid peroxidation of the membrane lipids disrupts the integrity and hydrophobicty of the membrane
(it damages the endothelium which leads to plaque formation)

Question 9

Which enzymes can break superoxide radicals down?

Answer 9

• Superoxide dismutase
  (converts to hydrogen peroxide and water)
• Catalase
  (converts H2O2 to water and oxygen)

Question 10

How does Glutathione protect from ROS damage?

Answer 10

The reduced form of glutathione (GSH) is continuously recycled so that it can reduce hydrogen peroxide to water.
(Usually abundant so a first line defense against ROS)

Question 11

What type of molecule is glutathione?

Answer 11

anti-oxidant

Question 12

Which enzyme catalyses oxidation of glutathione?

What co-factor does it require?

How does this protect from ROS?

Answer 12

Glutathione peroxidase

selenium

glutathione donates an electron from a cysteine residue which reduces H2O2 to water.

Question 13

How is the oxidised form of glutathione (GSSG) converted back to the protective form?
What is the reducing agent?

Answer 13

glutathione reductase reduces GSSG back to 2GSH

NADPH > NADP

Question 14

Which form of glutathione is protective against ROS?

Answer 14

The reduced form; 2GSH

Question 15

How does eating your 5 a day contribute to ROS protection?

Answer 15

Vitamin C
Vitamin E (nuts/seeds)
Carotenoids (carrots, oranges)
Melatonin (bananas)

are all antioxdiants/ free radical scavengers

Question 16

Which are the lipid soluble vitamins?

What type of ROS damage can Vitamin E protect against?

Answer 16

ADEK

lipid peroxidation
lipid soluble

Question 17

What is oxidative stress?

Answer 17

Too many free radicals

Question 18

How can inflammation lead to ROS damage?

Answer 18

• INOS, inducible NO synthase activated in inflammation
• Produces nitric oxide radicals
• React with superoxide radicals to to form ONOO- (peroxynitrite)

Question 19

Which enzyme facilitates the respiratory burst of neutrophils & monocytes?

Answer 19

NADPH oxidase

- oxidises NADPH and reduces oxygen to superoxide molecules which are released at the pathogen

Question 20

Why is a sufficient store of NADPH important in ROS protection?

Answer 20

need it to recycle oxidised glutathione (GSSG) back to the protective reduced form (2GSH)

(glutathione is an antoxidant)

Question 21

Patients with galactosaemia can’t meatbolise ____?

Which enzyme is overactive and how does this affect oxidative damage?

Answer 21

galactose

aldose reductase

consumes excess NADPH which is needed to maintain a store of reduced glutathione (GSH) to neutralise radicals
- less protectrion from ROS

Question 22

In which pathway is NADPH produced?

Which enzyme is first in this pathway and what happens in a deficiency?

Answer 22

pentose phosphate pathway

Glucose 6 phosphate dehydrogenase

G6PDH deficiency limits the amount of NADPH produce which reduces protection form oxidative damage

Question 23

How much paracetamol is a toxic dose?

Which drug should be given in an overdose?
Within what time period?

Answer 23

10g +

N-acetylcysteine
within 8 hours to prevent liver failure

Question 24

How does a paracetamol overdose kill you?

Answer 24

• Paracetamol at a toxic dose (10g) saturates the usual pathways of metabolism
• Metabolised to NAPQI;
  Extremely hepatotoxic
  Oxidises glutathione (GSH)
• Liver damage due to hepatotoxicity and increased susceptibility to oxidative stress
• Progress to liver failure and death

Question 25

How does N-acetylcysteine prevent death in a paracetamol overdose

Answer 25

(Given within 8 hours)

Replenishes stores of reduced glutathione (GSH) so the liver can safely metabolise NAPQI (hepatotoxic)