Oxidative Species and Disease

Question 1

Definition of epigenetics

Answer 1

-Study of how DNA may interact with intracellular compounds which may alter genes. Alterations may turn genes on or off. Epigenome alterations modify the structure of the DNA by tagging around mistime proteins, this disallows transcription of particular genes to occur

Question 2

Endogenous sources of oxidative stress

Answer 2

• Mitochondria, leakage at the electron transfer chain at complex I
• Lipoxygenase - family of non-haem iron containing enzymes that catalyse the dioxygenation of polyunsaturated lipids into autocrine signals
• Cytochrome p450 - a family of super enzymes mainly expressed in the liver, play a vital role in xenobiotic metabolism
• Peroxisomes - an enzyme found in some cells, contains the enzyme catalase which has a reducing ability. Involved in the breakdown of fatty acids for the phospholipid bi layer as well as generation of energy through catabolism. And to formate hydrogen peroxide by transfer of hydrogens to oxygen

Question 3

Types and names of antioxidants

Answer 3

-Enzymatic
Superoxide dismutase 
Glutathione Reductase 
Glutathione Peroxidase 
Catalase 

-Non enzymatic 
Vitamin A (Beta carotene)
Vitamin C (Ascorbic acid)
Vitamin E ( Alpha tocopherol)

Lactate and Pyruvate

Question 4

Beneficial roles of ROS

Answer 4

• Energy production
• activation of defence systems
• mediation of cellular signalling processes

Question 5

Oxidative stress occurrences and targets

Answer 5

• Lipids become peroxided
• Proteins are oxidised. This can lead to fragmentation of protein backbone, oxidation of amino acids will lead t formation of oxidation products but can cause side chain damage
• DNA/RNA is oxidised

-Free radicals usually attack double bond (unsaturated) lipids, particularly polyunsaturated lipids

Question 6

Types of side chain modification on amino acids

Answer 6

• Hydroxylation of amino acids, referred to as dimerisation
• Oxidation of sulphur containing amino acids, thinly radicals and methionine sulphoxides
• Peroxidation of aliphatic amino acids
• Carbonyl formation 1) Generation of peroxyl radical (ketones), 2) Decomposition of hydroperoxyl radical (aldehydes)

Question 7

Order of nucleic acid oxidation potential and methylation

Answer 7

(Least) -> adenine -> thymine -> cytosine -> guanine (Most)

Oxidative stress can evoke methylation of DNA, promoting more compact packing of DNA

Question 8

Damage of mitochondria effects that ensue (apoptotic pathway)

Answer 8

• ROS damage can lead to the release of cytochrome C from the phospholipid bilayer.
• Catalysed by cardiolipin hydroxyperoxidase, H202 is liberated to form water

1) Release of cytochrome c activates apoptosome named capase 9
2) smac/diablo binds to the inhibitor of apoptosis proteins (IAP) to free capases
3) Apoptosis inducing factor (AIF) degrades DNA

Question 9

Glutathione free radical scavenging mechanism

Answer 9

OH * + GSH –> H20 + GS*
GS* + GS* –> GSSG

GSSG is oxidised GSH and GSH:GSSG ratio is an indicator of the extent of cell oxidative stress

Question 10

Oxidative stress, NADPH and NOXs atherosclerosis

Answer 10

-Atherosclerosis can cause neurodegeneration through deposits of LDLs in the veins, also caused by NADPH oxidases produced by the endothelium of the arteries (NOXs are major source of ROS in the vasculature)

Question 11

changes in the brain in patients with Alzheimers

Answer 11

• Shrivelled cerebral cortex causing reduced adeptness in thinking planning and remembering
• Shrivelled hippocampus causing reduced adeptness in critical formation or new memories
• Vesicles filled with cerebrospinal fluid also grow larger
• Plaques and tangles of neutrons occur too

Question 12

Alzheimers effect on neutrons

Answer 12

1) Amyloid beta, fragment of larger protein called APP found in healthy nerve cells , sticker together in clumps in patients suffering Alzheimers having toxic effect
2) Tau, a protein that helps maintain structure and stability of microtubules in which nutrients and other constituents move around, breaks down and forms tangles. Without these microtubules necrosis occurs

• Higher levels of MDA, HNE and F2-isoprostanes in Alzheimers compared to age matched controls
• Enhances lipid per oxidation is detected in CSF and plasma
• Increases levels of 8-hydroxy-2-deoxyguanisone in AB plaques and neurofibrally tangles