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Sunday May 25, 2014 MYT 12:00:00 AM
Monday May 26, 2014 MYT 5:32:33 PM
by tan shiow chin
Medical imaging and radiotherapy account for about 14% of human exposure to radiation. One percent is due to the nuclear industry, while the rest is from natural background radiation. – EPA
Worried about the potential risks of radiation exposure? A member of the vitamin E family found in palm oil might prove to be the solution to this problem.
WE are all radioactive.
According to the World Nuclear Association (WNA), an average adult weighing about 70kg undergoes 4,550 nuclear disintegrations per second due to the natural radioactive elements within our own body.
We are also being bombarded by invisible rays all the time, wherever we are.
Known as radiation, these rays can come in the form of sunlight, microwaves, radio waves, electromagnetic waves from mobile phones and laptops, X-rays and gamma rays, among others.
On average, human beings are exposed to about 2.4 millisieverts (mSv) of radiation a year from natural sources, i.e. the earth and outer space.
However, the amount of this inescapable background radiation varies greatly according to geographic location.
For example, the WNA reports that some 140,000 people living in the Indian states of Kerala and Madras are annually exposed to an average of 30 mSv of background radiation from gamma rays and radon – one of the largest populations exposed to such high amounts of radiation.
As a comparison, a regular chest X-ray gives 0.2 mSv of radiation.
But it is worth noting that there has been no evidence to date indicating that these people have a higher incidence of cancer or genetic mutation compared to those exposed to less background radiation.
Now, background radiation accounts for about 85% of human exposure to radiation, according to the WNA.
The next largest source of radiation comes from medical use, which accounts for about 14% of exposure. The remaining 1% comes from the nuclear industry.
To diagnose and heal
Radiation in medicine, specifically ionising radiation, has a crucial part to play in both the diagnosis and treatment of many medical conditions. (See Dangerous rays)
The current conservative view on radiation protection requires the assumption that any amount of extra radiation exposure, no matter how small, poses a potential risk to the recipient’s health.
However, for diagnostic and therapeutic purposes, the general rule-of-thumb is that the use of radiation in medical imaging and/or treatment in each case should be based on the more immediate benefits outweighing the future potential risk of developing radiation-induced cancer or injuries to normal tissues.
And for many patients, the invaluable information gained from CT scans and X-rays, or the effectiveness of radiotherapy in killing off cancer cells, especially in conditions like prostrate and bladder cancer, far outweighs the potential consequences of radiation.
But for those still leery of radiation overexposure, a professor of pharmaceutical sciences, surgery, and pathology at the University of Arkansas for Medical Sciences, United States, has dedicated his career to identifying the mechanisms of radiation injury and developing ways of preventing the adverse effects of radiotherapy in cancer patients.
Looking to vitamin E
Since 2005, Prof Dr Martin Hauer-Jensen has been looking specifically into the effects of gamma-tocotrienols in protecting against the effects of excessive radiation exposure.
Tocotrienols, along with tocopherols, form the two classes of vitamin E. They are differentiated by the type of chemical bonds they have in their side chain; tocotrienols have three double bonds, while tocopherols have single bonds.
Each class has four members each, namely, alpha, beta, gamma and delta.
Prof Hauer-Jensen shares via e-mail: “My interest in tocotrienols began in 2005 when I met Dr Sree Kumar of the Armed Forces Radiobiology Research Institute (AFRRI) in Bethesda, Maryland, at a meeting in Leicester, United Kingdom.
“Dr Kumar was already well aware of my strong focus on radiation effects on the cardiovascular system and endothelium, as well as of my interest in the statin drugs.
“When he suggested that we should collaborate to develop gamma-tocotrienol as a radiation countermeasure, I readily accepted his proposal.”
He explains that their focus on this specific member of the vitamin E family is due to gamma-tocotrienol’s tendency to concentrate in the endothelial cells, which form the lining of the circulatory and lymphatic systems, and ability to inhibit 3-hydroxy-3-methyl-glutaryl-Coenzyme A reductase (HMG-CoA reductase) – an action similar to the statin drugs that lower serum cholesterol – to a much greater extent than the other vitamin E analogs.
As the results of this research could also potentially be used as a non-toxic medical countermeasure for radiological or nuclear emergencies, it has been funded by a series of grants by the US Defense Threat Reduction Agency.
Of mice and men
Prof Hauer-Jensen, who is also a consultant on radiological emergencies for the World Health Organization, shares that the research into gamma-tocotrienols has currently reached a critical stage.
He will be collaborating with researchers at the Royal Marsden Hospital in London, to conduct a phase II clinical trial involving patients suffering from delayed radiation injury to the rectum as a result of radiotherapy.
The patients will be randomly assigned to treatment with a placebo or a combination of palm oil-derived tocotrienol-rich fraction capsules and pentoxifylline.
Palm oil contains some of the highest concentrations of tocotrienols in nature, while pentoxifylline, which is primarily used to improve blood flow in patients with peripheral circulatory problems, has also been shown to protect against radiation injury.
“The combination of vitamin E (alpha-tocopherol) and pentoxifylline has shown efficacy in clinical trials performed by others, and we hope to see superior efficacy of this combination with tocotrienols,” says Prof Hauer-Jensen.
On the other hand, he notes that countermeasures against radiation from nuclear accidents or attacks obviously cannot be tested in humans.
Therefore, he and his team have recently created a transgenic mouse model that overexpresses an inhibitory protein in the tetrahydrobiopterin (BH4) synthesis pathway.
“BH4 is an essential co-factor for nitric oxide synthase (NOS) and deficient levels of BH4 causes so-called uncoupling of NOS.
“In the uncoupled state, NOS, instead of producing nitric oxide, generates superoxide, a particularly damaging free radical.
“Gamma-tocotrienol has the ability to suppress an inhibitory protein in the BH4 synthesis pathway, and we assume that this property may be related to its efficacy as a radiation protector,” he explains.
He adds that this mouse model will be used to further explore the mechanisms by which gamma-tocotrienol protects cells against radiation.
Looking towards the future, Prof Hauer-Jensen hopes that the clinical trial at the Royal Marsden Hospital will produce positive results as a step towards obtaining regulatory approval of tocotrienols as an effective way to manage patients with delayed side effects after radiation therapy.
He also hopes to be able to explore the protective effects of gamma-tocotrienols against radiation in primate models, in order to support the use of these vitamin E compounds as a medical countermeasure in radiological and nuclear emergencies.
RADIATION can be divided into ionising and non-ionising radiation, with the more dangerous type being the former.
This high-frequency radiation gives out enough energy to break the bonds of electrons in atoms or molecules to create charged particles and free radicals.
There are three main kinds of ionising radiation: alpha particles, beta particles, and gamma rays.
·Alpha particles consist of two protons and two neutrons, and are positively charged.
·Beta particles are essentially electrons, which are negatively charged.
·Gamma rays are pure electromagnetic waves or photons.
Because they are charged, alpha and beta particles can interact directly with atoms and molecules, and disrupt them.
However, they are also easily blocked, as paper is sufficient to halt the progression of alpha particles, while beta particles can be stopped by aluminium.
Gamma rays have a more indirect effect on atoms and molecules as they are not charged, but they can penetrate through anything less thick than heavy concrete.
With high enough dosages, ionising radiation can break and mutate our DNA, and disrupt cellular function, usually resulting in cancer.
Tags / Keywords:
Health, Radiation, radiotherapy, nuclear accident, nuclear attack, tocotrienols, vitamin E, palm oil
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