Hi Julien,

they are rather different forms of radiation in fact. UV is non-ionizing, i.e. it has no capacity to break molecular bonds. Gamma radiation is one form of ionizing radiation (you may also know of x-rays, charged particles, and neutrons who are all also ionizing radiation).

The damage that the two can cause can be very different. If you are interested in biological material, then one can say that ionizing radiation is causing much more severe damage than UV.

UV does cause damage too, but this is easier to repair.

This may be too simplistic but I hope is a first step.

I am studying UV-induced DNA damage, and have found a lot of work has been done on ascertaining how deeply UV light can penetrate skin. UV is divided into three bands, UV A has the longest wavelength, and can penetrate to the basal layer of the epidermis, while UV B, potentially much more damaging, can only penetrate the outer layer of the skin. Luckily no UV C gets through the ozone layer. Gamma radiation, able to penetrate even through tissue, could cause significantly more damage than UV.

I concur with Massimo'c comments and would like to add a few things.

UV (mostly wavelengths less than about 320 nm -- the UVB -- is the damaging part of what is available in sunlight) and gamma rays both damage DNA, can cells and induce mutations and cancer.

As Massimo says, the lesions produced are different. For UVB, the main damages in DNA are cyclobutal pyrimidine dimers of 6-4 dipyrmimdines, both formed between adjacent pyrimidines on the same DNA strand. For the various types of ionizing radiations, the range of molecular damages is much greater, and include both single and double strand breaks plus what are called multiply damaged sites, which include multiple damaged bases or strand breaks involving both strands and located within a short length of DNA -- one turn or so of the double helix.

Another important difference is that UV does not penetrate the human body very well, so damages are limited to the skin and eyes. In contrast, gamma rays are very penetrating, which is why they are used in radiation oncology to destroy tumors deep within the body.

For more on UV, see the web site of the American or European Societies for Photobiology.

Should have been "...can kill cells ..."

Gamma ray induces DSB (double strand breaks) that are repaired by homologous recombination (HR) and Non-homologous endjoining (NHEJ) (Snoda et al. 2006 DNA repair; Weinstock et al. 2006 DNA repair)

UV induces T-T dimer that arrest progression of replication fork. Stalled replication fork can be released by HR and TLS (translesion DNA synthesis).

Thus, UV and gamma ray induce different type of DNA damages that might be repaired by distinct DNA repair pathway.

If you are looking for similarities in the DNA damage response between gamma and UV radiation, you will find them at the beginning of the signalling response cascade. Both these damages allow the histone variant 2AX to become phosphorylated (one of the first things that occurs after any DNA damage) and to form characteristic "repair foci". This is where the similarity stops. After this, a specific signalling cascade is then turned on (led by either ATM or ATR kinase - depending on the damage) to deal with different types of damages. As others have noted, the repair pathways that deal with damages from gamma radiation (double stranded DNA breaks) and UV radiation (mainly covalently linked adjacent pyrimidines - UVB, UVA also contributes some oxidative damage - 8-oxo-guanine) are distinct.

Possibility of phenomenon extrapolation depends on the nature of phenomenon. If you assume something related to iteration of radiation with a media, then it is quite different. However, there are some common effects of these emissions in local areas (at the boundary of media), such as the formation of some stable radicals. So, you question have no answer without indication what phenomena do you study.

Hi Julien Pompon,

The differences between two electromagnetic radiation include: the origin of production, gamma rays produce from the nucleus of energetic atoms whereas UV rays produce from atomic orbitals with lower energy levels, so gamma rays can cause ionization in media and penetrate deeper compared to UV irradiation with only atomic excitation. UV rays classified in 3 region according to wavelength from longest to shortest, A ,B and C. A sheet of a opac material for light is enough for protection of skin from UV rays, and also protective glasses for eyes. On the other hand, Lead and/or combination of Lead with concrete are suitable barriers for gamma rays.

There is also differences on biological damage for the two radiation, that I will explain if you needed.

kind regards

The essential difference between UV and Gamma radiations is in their energy content. UV radiation is weaker and, therefore, can only cause damage such as dimerization (T-T dimer, C-T dimer, etc.), deamination, hydration, etc. It cannot induce strand breaks. Therefore, it is also categorized as a non-ionizing radiation. Gamma radiation, on the other hand, is more energetic, can cause ionization in water molecules (Ionizing radiation) and induce such damage in DNA as strand breaks, etc. either by direct deposition of energy or indirectly, via ionization of water molecules in a cell.

I hope this will help you. Best wishes.

I have been doing an experience in radiobiology: evaluation of DNA damage in cells irradiated with high energy protons, that is ionizing radiation like gamma rays. In radiobiology there is a parameter very important to assess the radiation’s biological effects that is the relative biological effectiveness (RBE): the ratio of biological effectiveness of one type of ionizing radiation relative to another (reference radiation: X-rays usually), given the same amount of absorbed energy. The RBE is an empirical value that varies depending on the particles, energies involved, biological effects studied, cells/tissue types, experimental conditions, and so on . However it is a set of experimental measurements so extrapolating the data for UVR (NIR) from γ – rays results, without performing experiments, it isn’t very simply..in fact, as other researchers say, these radiations (γ and UV) have different energies, penetration capacity, LET…so each of them produces specific damages.

γ – rays mainly produce alkali-labile lesions, single-strand breaks (SSBs) and DSBs as well as oxidative damage that is generated directly by ionizing radiation either indirectly by ionization of water. Instead, UVR induced DNA lesions are cyclobutane-pyrimidine dimers (CPDs), 6-4 photoproducts (6-4PPs), and their Dewar valence isomers as well as DNA strand breaks. The latter type of damage could be primary but it surely is secondary to other types of damage.

Another difference is the repair system involved in DNA repair:

-Gamma rays - induced damage is repaired by BER, HR, NHJR ..

-CPDs and 6-4 PPs are both repaired through a process known as nucleotide excision repair (NER)

Your question isn’t very clear so you should account of all these variables when you’ll set your experiments but despite of the differences you can find something (endpoint) that lets you to compare these radiations. I could suggest you to focus on type of damage, e.g oxidative DNA damage that seems to be produced by both radiations, and then try to set the experimental conditions in order to minimize all the other variables (e.g immediately after irradiation) and find out a relation between the radiations…if it’s possible.

More information about UV: Molecular Mechanisms of Ultraviolet Radiation-Induced DNA Damage and Repair. Rajesh P. Rastogi, Richa, Ashok Kumar, Madhu B. Tyagi3 and Rajeshwar P. Sinha.Journal of Nucleic Acids Volume 2010, Article ID 592980, 32 pages

The gamma radiation is a ionizing radiation rather the UV radiation is a no-ionizing radiation.This mean that the gamma radiation can produce more important damage in living beings. The damage produced by UV radiation affects biological material in different aspects and depends of the type of UV radiation (UVA; UVB; UVC). Moreover, the UV radiation can produce permanent or reversible damage, according the intensity and exposition time of the radiation.

Hi all,

thank you very much for all your answers. There are many very interesting information in your responses.

As some of you pointed out, my question is not that clear. However, Barbara seemed to have grasped part of my problem with the relative biological effectiveness (RBE). I will try to specify my issue. I am actually studying the induction of apoptosis using gamma-ray. I use a certain dose (calculated in Gray) and would like to know what this dose in Gray corresponds to in terms of time and intensity of UV exposure. Ideally, I would like to extrapolate my findings using gamma-ray by stating that 10Gray causes as much damage (RBE in terms of apoptosis induction) as 4hours under a clear sky in Europe... or some other value. In other words, I need a relationship between apoptotic damage induced by UV and gamma-ray, in order to convert my dose of Gray into a UV dose.

I hope my request is clearer this time, and thank you again for your responses.

Cheers

Julien,

You are going to have difficulty determining the relative RBS for gamma rays and UV. As you indicate, the ionizing radiation community measures dose in Gray, which is the energy absorbed per unit mass (J/kg). The UV community, in contract, measures dose in terms of incident energy per unit area, the units being J/m^2.

In the case of UV, the damage is done by photons absorbed directly by DNA. Photons absorbed by other components of the target do not contribute to the critical damage.

For gamma rays, the actual damage to DNA is mostly NOT due to gamma rays absorbed by the DNA, but to electrons generated by absorption of the gammas by water or other components of the target, so "absorption per unit mass" is appropriate.

Julien,

I understand your point but you are, as you know, talking about two very different mechanisms of cell aggression. It is like to try to know how many bullets you need to make the same damage as 1 Kg of nitroglycerin. It depends on what damage you are talking about (killing people or opening a hole on a wall). You can work out an answer, but this equivalence will be very specific, depending on the parameter you want to have the equivalence (in your case, apoptosis induction). By this point of view, I do not believe in RBE (in the same sense we establish it for ionizing radiation) determination for this two (so) different types of mechanisms. However, I hope you can figure out an answer for your question!

Besides the answers received, another difference between gamma radiation and UV is that with UV radiation and biological damage, you can select the wavelength and determine what biological material best absorbs at that wavelength. For example, 2450 nm for DNA and 2800 nm for most proteins. Gamma radiation is more non-specific although in theory you can select the energy by using a radionuclide that has a single or predominate gamma ray spectrum. The energy of most gamma emitters is sufficient to break chemical bonds; whereas, UV typically is not of sufficient energy. The exception is UV-A (farthest from the visible spectrum). Back to the DNA damage, UV, as mentioned typically forms pyrimidine dimers where you have adjacent pyrimidines on one DNA strand. Gamma radiation will break both strands of DNA. The repair mechanisms are somewhat identical; however, the UV repair can use the complementary strand as the template but the gamma repair may not repair correctly as both strands are broken and have "sticky ends."

If you are interested in the effects of UV radiation you should use UV radiation. RBE depends on the biological sample, the energy, and the endpoint (apoptosis or DNA damages). If you find an appropriate RBE (same cell type, same conditions, same energy, same end-point - I do not believe it) then you will repeat experiments performed by others, what is not so interesting. I think you should design other experiments for your objectives.

Best regards,

Balázs

Hi all,

I think that I will need to establish a RBE relationship between UV and gamma-ray for my particular organs and organism.

Thank you very much to all of you

Julien.

In the case of chicken B rymphocyte DT40 cells, 6J/m2 of UV and 4Gy of gamma-ray killed comparable percent of the cells (only ~20% was alive).

The main difference from a physics point of view is that the energy of the photon is deposited mainly on the solvent (water) in the case of x-rays or gamma, but on the solute (biomolecule) in the case of UV radiation. Secondly, X-rays penetrate much deeper into biological material. The consequences are then: The damage by X-ray or gamma is usually much less specific for biological material per amount of energy deposited but it can affect well-hidden and well-protected, important, targets. For UV radiation it very much depends on the emission wavelength or the emission spectrum of the actual lightsource and on the absorption properties of your solute/your material.

UV radiation carries a lot of energy: A 300 nm photon carries roughly an energy of 400 kJ/mol, 200 nm approx 600 kJ/mol. That is enough to break most bonds or to ionize most biologically relevant molecules. However, the efficiency of bond-breaking or ionization is often low (this efficiency is the so called "quantum yield"). The physics following the absorption process can be very complicated (see deexitaion, fluorescence, phosphorescence).

You could, in principle, compare the energy deposition of the two experiments. However you need to dig into physical chemistry, calculate how much UV has been absorbed by your sample (irradiation power * time * (1-transmission)) and compare it to the dosimetry of your gamma source under the same conditions. But this is by no means simple or straightforward.

Thank you so much Thomas for your response.

I just want to have an idea of how UV and gamma ray can compare, and you gave a hint of the data I am looking for with the energy. Would you know the correspondance in energy between UVB and gamma ray?

All the best and thank you again for taking time to answer my question

The issue with ionizing radiation is, that you do not deposit all the energy of the photon in a sinhgle event. A gamma photon of a Cs137 source has an energy of 500keV, that is 50MJ/mol, Co60 has approx 1MeV. So the energy per photon is orders of magnitude higher than with UV. Per ionization event, you usually have a deposition of some 100 eV, the ejected electron has enough energy to further ionize surrounding molecules. What you get is something like a sphere with multiple ionization hits. This is called a "spur". With gamma or with fast electrons you can pictue a string of pearls, the spurs do not interact. With alpha particles the ionization power is so high, that the ionization events overlap and the radical density overlaps. This is why alpha irradiation is biologically so devastating. Therefore the Sv scale (biological effect) deviates from the Gy scale fir alpha, but not for beta or gamma.

In diluted aqueous solution you get 2.8 hydroxyl radical, 2.8 solvated electrons, and 0.6 hydrogen atom per 100 eV absorbed gamma energy, or approx 0.28 micromolar hydroxyl per Gy.

Sorry, I have to correct myself. 1eV is approx 100kJ/mol (Faraday Constant), so 500keV would be 50GJ/mol or 5e7 kJ/mol.

Dear Julien, I´m interested to read about your RBE comparison between UV and gamma rays. Hope you find a clear answer.

Regards

Why does everyone seem so biological in this thread, if we take a less biocentric view of the matter and consider the radiation stability of polymers then it is clear that gamma rays and UV should not be assumed to be similar.

Teflon is damaged with great ease by gamma rays, it turns into a viscous oil plus HF. While it should tolerate UV light very well.

Polystyrene without the anti UV protection chemicals is very easy to damage with UV light, however it is very resistant to gamma rays. Even with doses in the range of kGy 100 to 1 MGy it seems to be OK.

I am editing this answer to add a few more of my thoughts

Gamma rays in biological systems tend to create reactive species from the water present, these reactive species such as hydroxyl radicals then damage biomolecules such as DNA. The hydroxyl radical is a very general "molecule vandal" it will react almost at random with organic molecules. It is very able to abstract a hydrogen from most organic molecules.

On the other hand UV light can induce some specific reactions, I have read of [2+2] pericylic reactions occurring which link DNA bases together which are caused by UV light.

It is also interesting to note that UV light together with the right dyes can generate similar very reactive intermediates to those seen when water is irradiated. For example a UV laser pulse can form solvated electrons in a solution of 1,4-diaminobenzene (http://pubs.acs.org/doi/abs/10.1021/j100386a004?journalCode=jpchax). In a solution where oxygen is present these will then form oxidizing radicals similar to those seen in oxygenated water when an electron pulse is delivered to it. One option would be to saturate the solution of the diamine with nitrous oxide, this will convert solvated electrons into the hydroxyl radicals.

I know that in many biological systems that for beta / gamma that when oxygen is present that radiation is more able to damage cells than when oxygen is absent. I know for alpha that this effect is either much smaller or does not exist. This is a enduring problem in radiotherapy for cancer treatment. I would like to suggest that the biologists here consider the question of does oxygen make UV light more or less able to damage cells and biomolecules.

@Mark,

I think we have a clear question concerning RBE and therefore biological effects. And in radiobiology we have two kinds of molecules: water - 80% of the plasma volume - and biomolecules like proteins, DNA etc. So we care on the effects of these substances.

But I don´t contradict, that effects like you cited are also interesting.

This should depend on types of UV, endpoints and purpose you wish to compare.

In terms of cellular clonogenic survival, very roughly, the 10-fold higher J/m2 of UVB is necessary to induce the same effect of UVC. In my experiments, the clonogenic survival of human fibroblasts after irradiation with 2-6 Gy (J/kg) of X-rays was similar to 5-20 J/m2 of UVC. Similar comparisons can be made for other biological endpoints.

However, the damage induced by UV and ionizing radiation is not the same. Taken together, human health effects of UV and ionizing radiation are not the same: for example, exposure to UV, but not ionizing radiation, increases risks of melanoma in the skin and nuclear cataracts in the ocular lens.

I would like to add new information for Julien.

Gamma and UV radiations are IR and non-IR types, respectively, which essentially means that gamma is capable of breaking chemical bonds. Hence, it induces SSB/DSB type of damage in DNA strands, which is not known for UV radiation. However, under specific circumstances, we have shown that even UV radiation (germicidal UV - 254 nm - also known as UV-C) can induce SSBs in DNA - please see  our publication: Int. J. Radiat. Biol., Vol. 81, No. 12, December 2005, pp. 919–927). 

Good luck!

Regarding Rajesh Sharan's answer, I would like to point something out. There is no hard divide between UV and X-rays, the problem is that some X-rays such as Mg K lines have properties which are very similar to hard UV (short wavelength UV).

I recall that page four of the IRR99 (http://www.legislation.gov.uk/uksi/1999/3232/pdfs/uksi_19993232_en.pdf) in the UK (current radiation law) has the text that ionizing radiation is defined as

"“ionising radiation” means the transfer of energy in the form of particles or

electromagnetic waves of a wavelength of 100 nanometres or less or a frequency of 3 x 1015 hertz or more capable of producing ions directly or indirectly;"

This is a way of defining ionizing radiation without needing to mention UV, X-rays or gamma rays. Whoever wrote that should get a prize.

Thank you so much for these valuable answers