Carcinogen

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A carcinogen is a substance which can cause cancer in a living organism[1]. Examples of carcinogens include tobacco smoke, ethanol and UV radiation. It is difficult to completely avoid carcinogens[2] as they also include air pollution, solar radiation and engine exhausts, all of which exist in everyday life[3].

Cancer is a change in the DNA of the cell, which leads to rapid uncontrolled cell division[4].

It is important to understand that exposure to one or even many carcinogens does not always result in cancer. How carcinogens act in the body and cause cancer is determined by other factors such as the individual's genetic makeup or their exposure to other carcinogens[5].

All carcinogens affect the body in different ways, and the body has defence mechanisms which help to prevent the carcinogen leading to cancer by disrupting and changing the organism's DNA.

Acetaldehyde is a product of alcohol metabolism and is formed when alcohol in the liver is broken down. This is catalysed by the enzyme alcohol dehydrogenase. In the body, the acetaldehyde is broken down by the enzyme acetaldehyde dehydrogenase and glutathione to non-toxic acetate. However, if the glutathione stores are low in the liver, acetaldehyde remains in the body in its toxic form for a longer period of time[6]. Acetaldehyde damages our cell's DNA and prevents cells from repairing the damage. It also causes liver cells to grow at a faster rate, meaning replication is faster and it is more likely that the cell will acquire 'cancer-inducing' mutations[7].

UV radiation is a carcinogen which causes cancer by penetrating either the epidermis or dermis of the skin, which causes DNA damage. If the body is unable to repair this damage, the cells divide uncontrollably due to normal cell death (apoptosis) being altered[8], which causes the formation of a malignant tumour[9].

Despite the carcinogens acting on the body in slightly different ways, the main outcome is DNA damage which the cell may be unable to repair. This results in cancer through uncontrolled cell division. Cancer cells also have a faulty version of the p53 gene. This is the gene which decides when the cell should undergo apoptosis. This means they are not repaired properly which could cause new mutations, metastasis and resistance to treatment[10]. Carcinogens can also cause affected cells to be less specialised and mask them from the immune system which means the body will not attempt to destroy them.

The body has a variety of defence mechanisms which it uses in order to prevent the carcinogen leading to cancer, such as:

These defence mechanisms can backfire, however. Biotransformation can actually make the carcinogen more carcinogenic, DNA damage may be too extensive for the cell's repair systems to eradicate and cytochrome p450 enzymes can activate and transform harmless molecules (procarcinogens) into carcinogens[13] by metabolism[14].

References:

  1. MedicineNet. Carcinogen. 2016 [cited 29/11/2017]; Available from: https://www.medicinenet.com/script/main/art.asp?articlekey=2625
  2. Fishwick C. How do I ... avoid carcinogens? 2015 [cited 29/11/2017]; Available from: https://www.theguardian.com/uk-news/2015/oct/30/cancer-carcinogens-avoid-i-die-exposure
  3. American Cancer Society. Known and Probable Human Carcinogens. 2016 [cited 29/11/2017]; Available from: https://www.cancer.org/cancer/cancer-causes/general-info/known-and-probable-human-carcinogens.html
  4. Cancer Research UK. What is cancer? 2017 [cited 29/11/2017]; Available from: http://www.cancerresearchuk.org/about-cancer/what-is-cancer
  5. National Cancer Institute. Environmental Carcinogens and Cancer Risk. 2015 [cited 29/11/2017]; Available from: https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/carcinogens
  6. Perry L. Biology of a Hangover: Acetaldehyde. 2004 [cited 29/11/2017]; Available from: https://health.howstuffworks.com/wellness/drugs-alcohol/hangover4.htm
  7. Cancer Research UK. How alcohol causes cancer. 2016 [cited 29/11/2017]; Available from: http://www.cancerresearchuk.org/about-cancer/causes-of-cancer/alcohol-and-cancer/how-alcohol-causes-cancer
  8. Helmenstine AM. How Carcinogens Work. 2017 [cited 29/11/2017]; Available from: https://www.thoughtco.com/carcinogen-definition-4146025
  9. Cancer Council NSW. How ultraviolet (UV) radiation causes skin cancer. 2015 [cited 29/11/2017]; Available from: https://www.cancercouncil.com.au/63295/cancer-prevention/sun-protection/sun-protection-sport-and-recreation/sun-protection-information-for-sporting-groups/how-ultraviolet-uv-radiation-causes-skin-cancer/
  10. Cancer Research UK. Cancer cells. 2014 [cited 29/11/2017]; Available from: http://www.cancerresearchuk.org/about-cancer/what-is-cancer/how-cancer-starts/cancer-cells
  11. Cancer Research UK. Cancer cells. 2014 [cited 29/11/2017]; Available from: http://www.cancerresearchuk.org/about-cancer/what-is-cancer/how-cancer-starts/cancer-cells
  12. Helmenstine AM. How Carcinogens Work. 2017 [cited 29/11/2017]; Available from: https://www.thoughtco.com/carcinogen-definition-4146025
  13. InterPro. Cytochrome P450. 2015 [cited 29/11/2017]; Available from: https://www.ebi.ac.uk/interpro/potm/2006_10/Page4.htm
  14. Helmenstine AM. How Carcinogens Work. 2017 [cited 29/11/2017]; Available from: https://www.thoughtco.com/carcinogen-definition-4146025
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