Oxidative Stress/Antioxidants

Question 1

Oxidative Stress: oxidative status, pro-oxidants, examples of ROS, where ROS come from

Answer 1

• Oxidative Status: balance between anti-oxidants and pro-oxidants
• Pro-oxidants: ROS, RNS,
  
  • Radicals/oxidizing agents/easily converted to radical
• Example ROS: superoxide anion (O₂^-), Hydroxyl radical, hydrogen peroxide
• ROS come from: futile cycling (quinones)

Question 2

Haber-Weiss Reaction

Answer 2

• Hydroxyl radical from superoxide and hydrogen peroxide in two steps with iron
• Fe3+ + superoxide→Fe2+ +O₂
• Fe2+ + H2O2→Fe3+ + OH^-+hydroxyl radical

Question 3

Reaction of reducing O2 into bad ju-ju

Answer 3

• O2→superoxide anion→hyrogen peroxide→hydroxyl radical→water
• 4 single electron reducing steps
• hydroxyl radical is the most damaging ROS

Question 4

Futile cycling with quinone

Answer 4

• Semiquinone radical that is a discrete intermediate
• Quinone→Semiquinone→Hydroquinone

Question 5

Origin of electrons for reduction; Why are ROS so bad

Answer 5

• electrons from UV, flavin, thiol, reduction of nitroaromatics, oxidation hydroquinone, mitochondrial respiration
• ROS cause tissue damage by lipid peroxidation
  
  • ADE

Question 6

Targets of ROS

Answer 6

• Draw lipid peroxidation diagram
• Target of ROS: DNA, thiol, membrane, enzyme, unsaturated lipids
• hydrozxyl radical pulls hydrogen off unsaturated lipid→lipid radical
• lipid radical react with O2→lipid peroxyl radical
• lipid peroxyl radical pulls hydrogen atom from another unsaturated lipid and propogates lipid radical an makes lipid peroxide
• Terminated at propgation step with ROO radical reacting with VitE instead of oxygen

Question 7

Vitamin E soaking up lipid peroxyl radiacal

Answer 7

• donates hydrogen atom to lipid peroxyl radical and makes O radical at phenol group

Question 8

Regeneration of Vitamin E by Ascorbate

Answer 8

• Gets hydrogen atom from Vitamin C
  
  • glutathione needed to regenerate vitamin C
• Phenol group of E sticks into cytosol so it can meet C

Question 9

Reasons antioxidant clinical trials with E have been disappointing (3)

Answer 9

• Inadequate monitoring of intake
• Too low dose/duration
• Lack vitamin C

Question 10

Superoxide Dismutase and Catalase

Answer 10

• SOD:
  
  • 2 O₂^-·→(+H⁺)→H2O2+O₂
  • Mito: Mn cofactor
  • Cyto: Cu and Zn cofactor
• Catalase
  
  • 2 H2O2→2H2O +O₂
  • Heme needing Fe

Question 11

Glutathione Pathway

Answer 11

• Gets rid of lipid hydroperoxides by reducing to alcohols
• Need NADPH from G6PD and reduced glutathione (GSH)
• ROOH→ROH with glutathione peroxidase (Se)
  
  • Uses GSH→GSSG
• GSSG→GSH
  
  • Glutathione reductase (yellow, riboflavin, B2)
  • Uses NADP+→NADPH
• G6P→6PG with G6PDH
  
  • (niacin, B3) to maintain NADP(H)
  • Deficency in G6PDH oxidative stress/hemolytic anermia because only way RBC get NADPH