ROS - Free Radicals

Question 0

Oxygen toxicity results from what?

Answer 0

It results from reactive oxygen species and free radicals.

Question 1

What are the two faces of oxygen

Answer 1

It supports life, but also bears toxicity

Question 2

What are free radicals and why are they harmful?

Answer 2

Free radicals are atomic or molecular species which are extremely reactive because they have an unpaired electron.

Question 3

What do ROS and free radicals initiate?

Answer 3

Cell injury

Question 4

Detoxification mechanisms overlap with what system?

Answer 4

The antioxidant system. Detoxification is one of the biggest generators of ROS.

Question 5

How are ROS generated?

Answer 5

One-electron transfers generate ROS

Question 6

Why don’t we want free iron floating around in the blood?

Answer 6

Iron (Fe2+) and also copper (Cu1+) combine with H2O2 to create OH* (hydroxyl radical: the “bad actor”) and OH-. This is the Fenton reaction.

Question 7

Where is the superoxide anion (O2-)produced?

Answer 7

It is produced in the electron transport chain, among other sites. It generates other ROS, but CAN NOT diffuse far from the site of origin.

Question 8

Hydrogen peroxide (H2O2) is NOT a free radical, so how is harmful?

Answer 8

It can generate free radicals by reaction with a transitional metal (i.e. Fe3+ or Cu1+). It can also diffuse into and through cell membranes.

Question 9

What is the most reactive species in attacking biological molecules and how is produced?

Answer 9

OH* (Hydroxyl radicals). They are produced by H2O2 in the presence of Fe2+

Question 10

What is produced by bacteria during the respiratory burst to destroy invading organisms?

Answer 10

HOCl (Hypochlorous acid)

Question 11

What are endogenous sources of free radicals in the body?

Answer 11

COX, LOX, Cytochrome P450, desaturases, xanthine oxidase - from enzyme activity, electron transport chain, and phagocytic respiratory burst.

Question 12

What are exogenous sources of free radicals?

Answer 12

UV radiation, drugs (doxorubin), and air pollutants

Question 13

Why is CoQ10 the biggest offender of free radical formation?

Answer 13

It is abundant, it is small, and unprotected.

Question 14

What other area of the ETC is a potential source of interaction for ROS?

Answer 14

The complexes that utilize metals (Fe, Cu)

Question 15

What is the key enzyme that creates HOCl, and causes destruction of the surface of bacteria through the respiratory burst? And which phagocytic cell secretes this enzyme?

Answer 15

Myeloperoxidase; neutrophil

Question 16

Lipids are susceptible to free radical damage. Oxidation involves the removal of _________ _________ from a/an _____________ fatty acid.

Answer 16

hydrogen radicals; unsaturated

Question 17

Which type of unsaturated fatty acids are the MOST susceptible to oxidative damage and why?

Answer 17

Polyunsaturated fatty acids (PUFA); because they have more double bonds

Question 18

Oxidation products form with what two other biosynthetic products?

Answer 18

amino acid residues and DNA

Question 19

Free radical damage to PUFA can involve what two reactions?

Answer 19

1. ) decomposition to bifunctional aldehydes and/or a,B-unsaturated aldehydes which can form adducts or crosslink other biomolucules (this gives more binding sites).
2. ) reacting with sulfhydryl groups on enzymes

Question 20

What are the four stages of the mechanisms for free radical damage of lipids?

Answer 20

Initiation, propagation, degradation, and termination

Question 21

What is the reaction taking place during initiation?

Answer 21

LH reacts with OH* (the bad actor) and creates a L* and H2O

Question 22

What is the reaction taking place during propagation and where will it go next?

Answer 22

The L* reacts with O2 to create LOO* which can continue on to either termination or propagation/degradation.

Question 23

If the LOO* interacts with antioxidants, it will follow which path and ultimately become what?

Answer 23

It will follow the termination pathway to become non-radical products or stable radicals.

Question 24

If the LOO* follows the propagation pathway, what other pathway will it interact with and what will be the outcomes?

Answer 24

LOO* will interact with LH leaving the L* to continue back through the cycle of propagation, and the LOOH will degrade to 4-HNE, malondialdehyde, ethane/pentane and other products.

Question 25

How do cells protect themselves against free radical damage/oxygen toxicity (the first line of defense).

Answer 25

Antioxidant enzymes: glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT).

Question 26

What are the other free radical scavengers (the second line of defense)?

Answer 26

Endogenous: Uric acid & CoQ10 Exogenous: Vitamin E & Vitamin C

Question 27

What is the third line of defense that mediates oxidative damage?

Answer 27

Repair de novo excision

Question 28

What is the fourth line of defense leading to diseases and aging?

Answer 28

Adaptation

Question 29

How do ROS/RNS/ROCl lead to oxidative stress?

Answer 29

They cause disturbance of redox balance

Question 30

How does oxidative stress lead to oxidative damage?

Answer 30

There is an oxidation of biological molecules

Question 31

What are the cellular and tissue locations of antioxidants?

Answer 31

Cellular: mitochondria, peroxisomes, and cytosol Tissue: liver, adrenals, and kidneys

Question 32

What metal is associated with cytosolic SOD?

Answer 32

Cooper and Zinc

Question 33

What metal is associated with mitochondrial SOD?

Answer 33

Manganese

Question 34

What metal is associated with GSH peroxidase?

Answer 34

Selenium

Question 35

Absorption of Vit C occurs where and by what means?

Answer 35

Distal small intestine; through a sodium dependent ascorbate transporter (SVCT1)

Question 36

How do other cells acquire Vit C?

Answer 36

They use either SVCT2 or GLUT 1 & GLUT 3 transporters.

Question 37

What is the primary scavenger/antioxidant that neutralizes radical oxygen and nitrogen species, peroxides, and superoxide?

Answer 37

Ascorbate

Question 38

Ascorbate is a free radical, why is it okay to have in the body?

Answer 38

It is free to move around the body, but it is VERY stable.

Question 39

What is required for the regeneration of the reduced form of Vit C?

Answer 39

Reducing agents: NADH, glutathione and an enzyme (NADH reductase, dehydroascorbate reductase, or thioredoxin reductase)

Question 40

Any antioxidant taken in too high of quantities can lead to pro-oxidant, what is an instance of this with Vit C?

Answer 40

High dose Vit C can lead to kidney stones and diarrhea as a result of oxalic acid.

Question 41

Where does Vit E come from?

Answer 41

It refers to a mixture of tocopherols and tocotrienols (vitamer). It is made from isoprenes and is an intermediate in biosynthesis of cholesterol.

Question 42

What specific part of Vit E is selectively extracted in the liver?

Answer 42

a-tocopherol

Question 43

How does Vit E function as an anti-oxidant?

Answer 43

It accumulates in membranes and lipoproteins for protection, and it donates electrons to free radical species to neutralize them (terminates membrane lipid oxidation through single electron transfers, forming a stable tocopherol species).

Question 44

How does a redox cycle regenerate reduced Vit E from reduced Vit C?

Answer 44

Vit E gets exposed to Vit C on the surface of membranes and a thiol cycle resets the radical scavengers to their reduced form.

Question 45

Maintaining RBC membranes depends upon the production of what two products?

Answer 45

NADPH and ATP from glycolysis.

Question 46

What is the purpose of NADPH in the removal of ROS?

Answer 46

NADPH reduces glutathione which ultimately removes the ROS

Question 47

What is an action of ROS?

Answer 47

It creates cross-linked hemoglobins, which shortens RBC life cycles.

Question 48

What enzymatic deficiency is the MOST COMMON genetic enzyme deficiency? And with which condition does it co-localize?

Answer 48

Glucose-6-phosphate dehydrogenase; it co-localizes with malaria

Question 49

What is the danger with having a G-6-P dehydrogenase deficiency?

Answer 49

It produces anemia and excessive destruction of RBCs

Question 50

What are some oxidant stressors that increase ROS in RBCs?

Answer 50

Infection, drugs (primaquine - anti-Malaria drug), and fava beans (vicine)

Question 51

What are the 3 isoforms of NOS?

Answer 51

eNOS - endothelial, nNO - nervous system, and iNOS - inducible by WBC

Question 52

How are NOS damaging of tissues?

Answer 52

Nitric oxide (NO) diffused through membranes (much like H2O2), HONO2 targets thiols and aromatic residues in proteins, and it reacts slowly with Vit C.