Magnetic fields, animal navigation and childhood leukaemia
A comment by Denis HenshawBSc PhD on the new study “Cellular autofluorescence is magnetic field sensitive” published in Proceedings of the National Academy of Sciences
22nd January 2921
Denis L Henshaw BSc PhD, Fellow Collegium Ramazzini Emeritus Professor of Human Radiation Effects, Atmospheric Chemistry Group, School of Chemistry University of Bristol,UK
Ikeya N, Woodward JR, 2021. Cellular autofluorescence is magnetic field sensitive. Proceedings of the National Academy of Sciences of the USA. Vol. 118 No. 3 e2018043118. https://doi.org/10.1073/pnas.2018043118
Magnetic fields, animal navigation and childhood leukaemia by Denis L Henshaw BSc PhD
It has long been known that all forms of life detect magnetic fields. Whether this ability is at all useful or indeed harmful has been the subject of much research. A new scientific paper published in the Proceedings of the National Academy of Sciences of the USA (PNAS) by Noboru Ikeya and Jonny Woodward at the University of Tokyo sheds new light on this topic.
The authors address two apparently disparate observations, that animals across a wide range of species detect small changes in the Earth’s magnetic field which many exploit for navigation, and the observation in epidemiological studies of a doubling of childhood leukaemia risk associated with electricity-supply magnetic fields at levels above 0.4 microtesla.
One key mechanism in understanding magnetic field sensing is the ability of such fields to alter the rate of chemical reactions and indeed to change the products of such reactions. Of particular interest, is the action of magnetic fields in a class of biological molecules known as cryptochromes.
Known as the Radical Pair Mechanism or RPM, this mechanism has been widely investigated in cryptochromes as the basis to the magnetic compass in birds and other species. While, the RPM has been explicitly demonstrated in chemical systems, this has not hitherto been the case in living cells. In a scientific first, Drs Ikeya and Woodward now demonstrate the action of the RPM in HeLa cells.
So how exactly does the RPM work?
The simplest example of a radical is the hydrogen atom, the lightest of all chemical elements consisting of a single proton as its nucleus around which orbits a single electron. In nature, hydrogen gas is composed of hydrogen molecules, each molecule consisting of two hydrogen atoms bound together each sharing two orbiting electrons. Each of these electrons is identical apart from one important property.
Rather like a spinning top, an electron spins and this can either be in a clockwise or an anticlockwise direction. So, the electron in a hydrogen atom likes to seek out a partner whose spin is in the opposite direction to itself, so that the net spin of the hydrogen molecule is zero. This principal applies to radicals in general which, like hydrogen, are characterised by a single electron seeking a partner of opposite spin
Cryptochromes are large protein molecules which can absorb light enabling an electron to transfer to another part of the molecule, thereby creating a pair of radicals. Ordinarily, these radicals will quickly come back together but under the influence of a magnetic field, the spin direction of one of the electrons can flip to the same direction as that of the other electron. Crucially, if a pair of radicals have the same spin direction they tend not to combine, instead they take part in chemical reactions with neighbouring molecules, producing different chemical products.
The cryptochromes at work in the animal compass appear to be located in the eyes where these changed chemical products comprise a signal sent to the brain that is the basis of magnetic field sensing. Cryptochromes, however, are found in all cells so that magnetic-field-induced changed chemical products occurring here could cause damage to DNA and hence the implications for health.
This suggests two ways in which the RPM may offer a mechanistic explanation for the magnetic field association with childhood leukaemia risk and by extension, other adverse health outcomes. As above, the RPM could result in damage to DNA in cells in general in the presence of magnetic fields. However, there is a more intriguing possibility. Cryptochromes are best known for their role in the control of the body’s circadian rhythms, the disruption of which can result in a number of adverse health outcomes including increased cancer risk.
One consequence of circadian disruption, in particular as a result of exposure to light-at-night, is the suppression of the nocturnal production in the pineal gland of the powerful anti-oxidant and natural anti-cancer agent melatonin. In shift workers, this is associated with increased risk of breast cancer and possibly other illnesses.
There is evidence that exposure to electricity-supply magnetic fields also disrupts nocturnal melatonin production, providing a further hypothesised mechanism by which magnetic field exposures acting on cryptochromes, increase the risk of childhood leukaemia.
In summary, the observations reported in PNAS by Drs Ikeya and Woodward take a vital step forward in demonstrating a mechanism deeply rooted in physics and chemistry to explain how magnetic fields are sensed and interact with biological systems.
Further reading
Ikeya N, Woodward JR, 2021. Cellular autofluorescence is magnetic field sensitive. Proceedings of the National Academy of Sciences of the USA. Vol. 118 No. 3 e2018043118. https://doi.org/10.1073/pnas.2018043118
Brocklehurst R, McLauchlan KA 1996. Free radical mechanism for the effects of environmental electromagnetic fields on biological systems. Int J Radiat Biol. 69:3-34.
Henshaw DL, Reiter RJ. 2005. Do magnetic fields cause increased risk of childhood leukaemia via melatonin disruption? Bioelectromagnetics Supplement 7:S86-S97
Juutilainen J, Herrala M, Luukkonen J, Naarala J. Hore PJ. 2018. Magnetocarcinogenesis: is there a mechanism for carcinogenic effects of weak magnetic fields? Proc. R. Soc. B 285: 20180590. http://dx.doi.org/10.1098/rspb.2018.0590
IARC Monographs of the Evaluation of Carcinogenic Risks to Humans, volume 98, 2010: Painting, Frefighting and Shiftwork. Published by the International Agency for Research on Cancer, 150 cours Albert Thomas, 69372 Lyon Cedex 08, France. International Agency for Research on Cancer. ISBN 978 92 832 1298 0.
The paper by Ikeya N, Woodward is also reviewed by David Bressan in Forbes magazine Jan 8, 2021: Scientists Observe Cells Responding To Magnetic Fields For First Time.
Denis L. Henshaw BSc PhD
Denis L Henshaw BSc PhD is Emeritus Professor of Human Radiation Effects at the University of Bristol and Scientific Director at Children with Cancer UK . As an MRC Programme Grant Holder, using newly developed techniques, Denis researched low-level alpha-radioactivity in the human body, principally in the lung and the skeleton, but more especially the accumulation of polonium-210 in Children’s teeth and transplacental transfer of alpha-radionuclides to the fetus. The same techniques were also used widely in the environment for analysing naturally occurring radon gas and radioactivity in contamination zones such as the area around Chernobyl.
In 1990, he published a link between domestic radon exposure and childhood leukaemia which, in high radon areas, could be an important contributive cause. He later studied the mechanisms by which exposure to electric and magnetic fields from powerlines and the electricity supply in general may lead to increased risk of childhood leukaemia and other illnesses.
Denis has published over 260 scientific papers and served on a number of Government Committees. He was for ten years an Associate Editor of the International Journal of Radiation Biology.
