Week 2 Flashcards
What is a mutagen?
An agent that causes a genetic mutation.
What is a carcinogen?
An agent that increases the likelihood of developing cancer.
Are all carcinogens mutagens? Why?
- Most carcinogens are also mutagens, but some are not as their influence is not through genetic change.
How do physical agents cause cancer?
Damage DNA and can cause mutations following DNA replication.
How do infectious agents cause cancer?
Can cause and contribute to cell transformation and tumour progression.
Name some physical agents which cause cancer.
Radiation by natural light and sunbeds.
X-rays
Name some chemical agents that cause cancer.
Cigarette smoke, Nitrate and Nitrate preservatives, BBQ, Benzoyl Peroxide.
Name some infectious agents which can contribute to cancer formation.
HIV, Helicobacter pylori
Is all cancer genetic and inhertied?
All cancer is genetic but not all cancer is inherited.
What are genotoxic agents?
A chemical or another agent that damages cellular DNA, resulting in mutations or cancer.
Explain how BP (Benzoapyrene) can be carcinogenic and how it is thought to work.
BP-7-8-dihydrodiol-9,10-epoxide is the carcinogenic product of BP. This results in mutations in p53 and results in the loss of function muttions in tumour suppressor genes. BP causes G to T transversion mutations.
When are aromatic amines produced?
They are produced when muscle meat is cooked using high heat as amino acids and sugars are broken down by the high heat.
How are PAH’s produced?
PAH are present in smoke so are enriched when any smoked meat or food is cooked at high temperature.
WHat is genotoxicity testing?
This is the study of chemicals which can damage the genetic structure of living organisms (including humans) and thus cause problems such as mutations, cancer and birth defects.
What are the tiers of genotoxicity testing?
Tier 1 - In silico SAR/QSAR
Tier 2a - In vitro bacterial gene mutation assay
Tier 2b - In vitro mammalian assay using the Ames test
TIer 3 - in vivo mammalian assay using the micronucleus test
Tier 4 - supplementary tests
Explain how the tier 2a in vitro Ames test during genotoxic testing works and what it looks for.
A Salmonella auxotroph (which requires histidine) is used to screen for revertants which are histidine independent. The number of revertants relates to the strength of the mutagen.
What is the downside of using the Ames test during genotoxic testing to identify mutagens?
It can miss some mutagens such as bile acids.
Explain how the tier 2b in vivo micornucleus test during genotoxic testing works and what it looks for.
A variety of human and mammalian cell lines are utilised. A clastogen is a mutagenic agent giving rise to or including disruption or breakages of chromosomes, leading to sections of the chromosome being deleted, added or re-arranged.
What is a transversion mutation ?
o A transversion mutation is when purines have mutated to pyrimidines
WHat is a transition mutation?
A transition mutation a purine mutates to the other purine or a pyrimidine mutates to the other pyrimidine.
Why is regulatory testing carried out and what is used for this?
All new products are tested for DNA damaging ability using regulators such as FDA and EMA.
What happens if a medicine is found to be DNA damaging in regulatory testing?
Blocked in development or discarded by the company.
Outline issues with current in vitro testing approaches to identify cancer and changes in DNA.
- Sensitivity not specificity behind test design
o Leads to false positives - Precautionary, but leads to discarding some potentially safe products
- Heavy reliance on animals, used to de-risk misleading positive results in vitro.
- Most In vitro tests use non-human cell lines, producing confusing data.
- Simple cell models not always relevant to exposed human tissues.
- Simple single dosing experiments also not reflecting human exposure.
Name some scientific, environmental and ethical reasons why animal replacement science may be stopped.
- Scientific argument – humans are not big mice
- Economic argument – extremely high costs associated with animal testing
- Ethical concerns- broadly speaking, public opinion wants to reduce animal testing
How does in vitro testing identify any chemicals which may cause genetic damage.
In vitro, we can assess intrinsic cell factors. Any deviations from linear should be exacerbated in vivo due to excretion, detoxification etc.
Outline the linear dose methods to assess genetic damage that medicines / chemicals may cause.
- Regulatory agencies are conservative and label any substance producing a positive result in a test as a genotoxin.
- This is part of the ‘precautionary principle’ aimed at protection populations for DNA threats.
What is the purpose of standardising toxicology testing?
Standardising in vitro toxicology testing means that results are kept the same worldwide
What are the limitations of using the linear dose method to assess how genetically damaging some chemicals can be.
- But, may be overcautious and may lead to many new drugs not making the market.
- Tests often done at high doses, rather than at exposure doses.
Why must we be realistic in terms of dose when testing possibly harmful chemicals using the linear dose method.
Almost any compound can be found to be positive ina mutagenicity test if a high enough dose is used. This would be the case with salt and sucrose.
What types of cancer are likely to form due to over consumption of alcohol?
Larynx, Oesophagus, Oral cavity, Pharynx or Liver
What types of cancer are likely to be prevented due to diets that are high in fruit or vegetables?
bladder, cervix, pancreas, oesophagus, larynx, prostate, stomach, colorectal, lung and breasts
What type of cancer does a high fibre diet protect against?
Colorectal
How and why does obesity increase the risk of cancer?
Obesity influences the levels of a number of growth factors (IGF-1, insulin, leptin) which can promote the growth of cancerous cells.
Sex steroid hormones, some of which are synthesised in the adipose tissue, can be at increased levels and play a role in some cancers.
Elevated concentrations of a number of inflammatory biomarkers. Chronic inflammation is a conducive environment for cancer to develop and progress.
What are the WCRF recommendations for cancer prevention?
- Be as lean as possible within the normal range of body weight
- Be physically active as part of everyday life
- Limit consumption of energy-dense foods; avoid sugary drinks
- Eat mostly foods of plant origin
- Limit intake of red meat; avoid processed meat
- Limit alcoholic drinks
- Limit consumption of salt; avoid mouldy cereals (grains) or pulses (legumes)
- Aim to meet nutritional needs through diet alone (i.e. without dietary supplements)
Also: - Mothers to breastfeed; children to be breastfed
- Cancer survivors should follow same recommendations