Non-genotoxic Carcinogens

Question 1

What is the difference between and genotoxic and non-genotoxic carcinogen

Answer 1

Gentoxic: mutagenic = cancer
Non-genotoxic: non-mutagenic = cancer

Question 2

What kind of result would a non-genotoxic carcinogen show in an Ames test

Answer 2

Negative

Question 3

What is the most effective non-genotoxic carcinogen with implications for human health

Answer 3

Fibrate drugs

Question 4

Describe the Ames test

Answer 4

Use of bacteria that are unable to grow without the presence of a certain compound
E.g histidine auxotrophic mutants of salmonella = can’t synthesise histidine

Question 5

What would positive Ames test look like

Answer 5

Increased revertants near test chemical

Question 6

What can be added to the aims test to improve the accuracy

Answer 6

Rat liver microsomes (S9)

Question 7

Why does adding S9 improve Ames test accuracy

Answer 7

Compounds are often genotoxic after metabolism
S9 metabolises compounds to see if they are truly genotoxic

Question 8

What is atherosclerosis

Answer 8

Fatty plaques in blood vessels
Can cause vessel occlusion = heart attack

Question 9

What do Fibrate drugs treat

Answer 9

Atherosclerosis and high blood lipid levels
Rarely used

Question 10

How do lipids enter the blood after digestion

Answer 10

Lipids -> GI Tract -> Blood -> hepatic portal vein -> liver

Question 11

How does the lipid release lipids

Answer 11

Very low density lipoproteins (vLDL)

Question 12

How can cholesterol be transported

Answer 12

As cholesterol-esters

Question 13

What happens to vLDL as it moves around the body

Answer 13

vLDL -> LDL -> HDL
Becomes less dense due to losing lipids

Question 14

What is the role of adipose

Answer 14

Take up triglycerides for emergency storage in times of starvation
Will break down stores to fuel other tissues e.g muscles

Question 15

What does high HDL levels in the blood suggest

Answer 15

The body is capable of dealing with lipids and can remove lipids from circulation

Question 16

What is the typical molecular structure of fibrates

Answer 16

Carboxylic acids
Have ester bond that can produce carboxylic acids

Mimic fatty acid structure

Question 17

How do Fibrate drugs work

Answer 17

Act by decreasing serum triglycerides
Variable effects on LDL-cholesterol
Reduce production of cholesterol

Question 18

What is the effect of fibrates in mice

Answer 18

100% liver tumour incidence by year 1
Primary liver cancer is rare especially in rodents

Question 19

Describe hypertrophy as a result of fibrates in mice

Answer 19

Increase in cell size
Most likely an adaptive response and not adverse effect

Question 20

How is hepatocyte proliferation affected by fibrates in mice

Answer 20

Significant increase in proliferation

Question 21

How can hepatocyte proliferation be analysed

Answer 21

Inject mice 1 hour before euthanasia with BrdU (dT analogue)
Cells will incorporate BrdU
Those that are proliferating will have higher DNA conc = more BrdU incorpated

Question 22

How do fibrates effect peroxisomes proliferation

Answer 22

Significant increase

Question 23

What is the role of peroxisomes

Answer 23

Fatty acid metabolism

Question 24

Describe fatty acid metabolism (beta-oxidation)

Answer 24

Oxidise and remove 2 carbon units from fatty acid
Shorten the chain by 2 units each time

Question 25

What is the difference between fatty acid metabolism in the mitochondria and peroxisomes

Answer 25

Mitochondria produce Ac-CoA, 2xH2O and NADH Peroxisomes produce Ac-CoA, H20, H2O2 and NADH

Question 26

What is the mechanism that peroxisomes use to deal with the H2O2 produced

Answer 26

Low [Fe2+] and high levels of catalase (bind H2O2)

Question 27

Why is it dangerous to have high levels of H2O2 in cells

Answer 27

Fenton reaction produces hydroxyl radical from Fe2+ which reacts with everything instantly

Question 28

How is free Fe2+ kept low in cells

Answer 28

Bound to ferritin

Question 29

What CYP to fibrates induce

Answer 29

CYP4A

Question 30

What is the function of CYP4A

Answer 30

To oxidise fatty acids

Question 31

What is the proposed mechanism of action of fibrates

Answer 31

Induce CYP4A = monoxygenation of fatty acids to -COOH -> beta-oxidation can occur at both ends = double the rate of beta-oxidation = increase breakdown of fatty acids

Question 32

What nuclear receptor do fibrate drugs bind to

Answer 32

Peroxisome proliferator activated receptor -alpha PPARa

Question 33

What happens when a ligand binds to the PPARa

Answer 33

Receptor heterodimerises with another nuclear receptor and translocates to the nucleus Binds to response elements within the genes it regulates

Question 34

Where is PPARa mainly expressed

Answer 34

Liver and kidney

Question 35

What does PPARa regulate

Answer 35

Expression of genes associated with peroxisome proliferation B-oxidation of fatty acids Cholesterol reduction e.g HDL synthesis

Question 36

What happens is the PPARa is knocked out in mice

Answer 36

Removes all effects Suggest its responsible for directing biological responses in response to fibrates

Question 37

What evidence is there that Fibrate drugs will not cause liver cancer in humans

Answer 37

Only lipid lowering effect observed in humans No evidence of liver growth PPARa expression is only 5-10% of rodent liver

Question 38

What is the suggested mechanism of non-genotoxic carcinogens in rodents

Answer 38

The altered balance between proliferation and apoptosis