Magnetocarcinogenesis: is there a mechanism for carcinogenic effects of weak magnetic fields?

Abstract

Extremely low-frequency (ELF) magnetic fields have been classified as possibly carcinogenic, mainly based on rather consistent epidemiological findings suggesting a link between childhood leukaemia and 50-60 Hz magnetic fields from power lines. However, causality is not the only possible explanation for the epidemiological associations, as animal and in vitro experiments have provided only limited support for carcinogenic effects of ELF magnetic fields. Importantly, there is no generally accepted biophysical mechanism that could explain such effects. In this review, we discuss the possibility that carcinogenic effects are based on the radical pair mechanism (RPM), which seems to be involved in magnetoreception in birds and certain other animals, allowing navigation in the geomagnetic field. We review the current understanding of the RPM in magnetoreception, and discuss cryptochromes as the putative magnetosensitive molecules and their possible links to cancer-relevant biological processes. We then propose a hypothesis for explaining the link between ELF fields and childhood leukaemia, discuss the strengths and weaknesses of the current evidence, and make proposals for further research.

Keywords: ELF magnetic fields; cancer; cryptochrome; genomic instability; radical pair mechanism.

Figure 1.

A simple radical pair reaction scheme. Reactant molecules, AB, are converted into products, C, via a short lived radical pair, [A^•+ B^•−], formed by the transfer of an electron from A to B (black arrow). The electron spins, one in each radical, can have either a singlet (red) or a triplet (blue) configuration. Singlet and triplet states differ in the relative orientation of the two spins: anti-parallel (singlet) or parallel (triplet). The red and blue arrows represent spin-selective chemical reactions: reversion of the singlet to AB by back electron transfer and forward reaction of the triplet to form C. The curved arrows represent the oscillatory, quantum mechanical interconversion of the singlet and triplet states, driven by internal magnetic interactions within the radicals. Whether a given radical pair reacts to form AB or C depends on the probability that it is singlet or triplet at the moment of reaction. If application of a magnetic field increases the triplet probability, the result will be an increased yield of the product C. Note that the radical pair need not be formed by electron transfer and that other reaction schemes are possible. (Online version in colour.)

Figure 2.

Hypothesis. The primary interaction mechanism is magnetic field (MF) effects on radical reactions in cryptochromes. Because the circadian clock is closely coupled with the regulation of responses to DNA damage and ROS, the primary interaction could lead to dysregulation of these systems, impaired DNA damage responses, genomic instability and finally to cancer. (Online version in colour.)