Radical triads, not pairs, may explain effects of hypomagnetic fields on neurogenesis

Abstract

Adult hippocampal neurogenesis and hippocampus-dependent cognition in mice have been found to be adversely affected by hypomagnetic field exposure. The effect concurred with a reduction of reactive oxygen species in the absence of the geomagnetic field. A recent theoretical study suggests a mechanistic interpretation of this phenomenon in the framework of the Radical Pair Mechanism. According to this model, a flavin-superoxide radical pair, born in the singlet spin configuration, undergoes magnetic field-dependent spin dynamics such that the pair’s recombination is enhanced as the applied magnetic field is reduced. This model has two ostensible weaknesses: a) the assumption of a singlet initial state is irreconcilable with known reaction pathways generating such radical pairs, and b) the model neglects the swift spin relaxation of free superoxide, which abolishes any magnetic sensitivity in geomagnetic/hypomagnetic fields. We here suggest that a model based on a radical triad and the assumption of a secondary radical scavenging reaction can, in principle, explain the phenomenon without unnatural assumptions, thus providing a coherent explanation of hypomagnetic field effects in biology.

Radical pairs and superoxide amplification can explain magnetic field effects on planarian regeneration

“…Kattnig et al have proposed that fast spin relaxation of the O -2 can be dealt with by involving a third scavenger radical [66][67][68]. Babcock et al [69] have also suggested that radical scavenging could resolve the challenge posed by electron-electron dipolar interactions.…”

“…Given a suitable choice of scavenger radical, we have shown that such a radical triad model can explain the observed effects (See the supporting information). Because of the fast spin relaxation of superoxide, no magnetic effect is expected for the substitution of 16 O with 17 O [68] in this scenario.…”

“…Radical triad calculations were carried out in a similar fashion to RPM (see Ref. [68] for details). We assumed instantaneous relaxation of superoxide, and no relaxation was assumed for the other two radicals.…”

“…Ramsay and Kattnig [68] have suggested that in the case of bound flavin, the correct approach would be to take an anisotropic HF coupling tensor. Then, the yields should be averaged over the orientation of the magnetic field with respect to the radicals.…”

Hypomagnetic field effects as a potential avenue for testing the radical pair mechanism in biology

“…It should also be noted that an extended version of the radical pair mechanism, the radical triad mechanism [49][50][51], has been proposed as an explanation for weak magnetic field effects. Radical triads may provide more sensitivity and circumvent issues such as weakening effects from dipolar interactions and fast spin relaxation of superoxide.…”