NBC- Radicals

• What are some oxygen containing radicals we are discussing in lecture?

  • superoxide
  • Hydroxyl
  • Lipid carbon centered and peroxyl radicals
  • Hydrogen peroxide
  • Singlet oxygen
• What are some nitrogen-containing radicals?

  Nitric oxide and nitrogen dioxide
• Who is responsible for generating superoxide radicals?

  • Electron transport chain (coQ10: converting from ubiquinone who is oxidized to semiquinone to O2-)
  • Cytochrome P450 enzymes in liver
  • When oxygen is used in hydroxylation reactions: decarboxylase and hydrocarboxylase enzymes generate superoxides
  • Respiratory burst from phagocytes: NADPH oxidase (particularly NOX2)
• What enzyme reacting with hypochlorus acid produces hydroxyl radicals?

  Myeloperoxidase
• How does H202 diffuse through cell membranes?

  Aquaporins
• How is hydrogen peroxide produced??

  1. superoxide dismutase (SOD);Extracellular and cystolic (SOD) requires zinc and copper; Mitochondrial SOD requires manganese
  2. Generated in peroxisomes upon oxidation of very long chain FA: acyl coA dehydrogenase
  3. Ascorbate generates H202 (non-enzymatic)
  4. Xanthine oxidase
  5. H202 produced from monoamine oxidase for catabolism of monoamines such as dopamine, serotonin, melatonin, norepinephrine, and epinephrine
• How are hydroxyl radicals produced? (All non-enzymatic)?


  1. When body exposed to x-rays/gamma rays: radiolysis cuts water in body forming hydroxyl radicals
  2. Haber-Weiss reaction: hydrogen peroxide+superoxide = OH
  3. Fenton reaction: hydrogen peroxide+ Fe2+ or Cu+= OH
• What is precursor for nitric oxide?

  Arginine
• What enzyme does nitric oxide stimulate to initiate vasodilation, and inhibit platelet aggregation?

  Guanylate cyclase
• What is the function of peroxynitrite and how is it produced?

  Function: causes increase in BP and is damaging to cell

  Production: superoxide coupled with nitrix oxide produces peroxynitrite
• How are lipid carbon centered/lipid peroxyl radicals radicals formed? Why is this an issue and what are the products formed from this lipid peroxidation reaction?

  By the generation of polyunsaturated FA (double bond) in plasma membranes. Lipid carbon centered radicals are produced when OH oxidize the pi bond which destabilizes the cell's membrane (free radical chain reaction) producing malondialdehyde (MDA) and 4-hydroxyl-2-nonenal (HNE) which are reactive aldehydes that bind are toxic to cells and can bind to DNA. MDA and HND can be measured in urine/plasma to test for oxidative stress.
• Why shouldn't you give a unhealthy person fish oil supplement?

  Because fish oil has unsaturated FA in them, if the patient has an unhealthy diet you would be overloading them with polyunsaturated fats leading to increase oxidative stress.
• Free radicals are capable of stealing electrons from not only double bonds of polyunsaturated FA, but also amino acids with pi bonds. What amino acids are most likely to be oxidized by OH?

  Tryptophan, phenylalanine, arginine, and histidine

  
• How are singlet molecular oxygen formed? Provide an example.

  Created via photochemical reaction where on of oxygen's unshared electron absorbs energetic photon. This excited oxygen molecule then oxidizes double bonds, etc damaging cell membranes and nucleic acids.

  Ex: Sunburn
• How to eliminate/scavenge superoxide radicals?

  1. Ascorbate (vitamin C) takes superoxide and converts it to H202
  2. Superoxide dismutase
• How to eliminate/scavenge hydrogen peroxide radicals ?

  1. Ascobrate
  2. Glutathione peroxidase (selenium is cofactor)
  3. Catalase
  4. Peroxiredoxins aka thioredoxin peroxidase
  5. Myeloperoxidase (part of respiratory burst) and requires iron as cofactor
• What does the enzyme myeloperoxidase produce? what common houselhold agent contains this?

  hypochlorous acid (HOCL), bleach
• How to eliminate/scavenge hydroxyl radicals?

  1. Ascorbate
  2. glutathione
  3. Dihydrolipoic acid (DHLA): DHLA is the reduced form and lipoic acid is the oxidized form. Lipoic acid can chelate iron and copper ions to inhibit Fenton reactions which reduce OH production
  4. CoQ10
• How to eliminate lipid carbon centered and peroxyl radicals?

  1. Vitamin E= tocopherol
  2. alpha-tocopherol is most effective in electron donating
  3. Tocotrienols are more effective in scavenging free radicals
  4. Carotenoids: lycopenes
  5. Coq10
  6. Ascorbate
  7. Glutathione through glutathione peroxidase
• How to eliminate singlet oxygen?

  1. Carotenoids: lycopene; carotenoids absorb energy from singlet oxygen therefore returning oxygen to its ground state (inactivated)
  2. Vitamin E: has free hydroxyl group on position 6 of vitamin E's chromanol ring
• What regenerates Vitamin E (antioxidant)?

  1. Vitamin C (ascorbate)
  2. Glutathione
  3. CoQ10
• Because Vitamin C is used to regenerate Vitamin E, this produces a ascorbate radical. How do we regenerate the ascorbate radical?

  1. NADH (niacin): monodehydroascorbate reductase
  2. Dihydrolipoic acid (DHLA)
  3. Glutathione: dehydroascorbate reductase
  4. Thioredoxin
  5. Interaction between Vit C molecules: dismutation
• Because CoQ10 is used to regenerate Vitamin E, this produces a ubquinone radical. How do we regenerate ubiquionone radical?

  1. DHLA
  2. Thioredoxin
• Because glutathione is used to regenerate Vitamin E, this produces a glutathiyl radical. How do we regenerate the glutathiyl radical?

  1. Glutathione reductase
  2. Dihydrolipoic acid (DHLA)