Magnetic resonance spectroscopy of the brain under mild hypothermia indicates changes in neuroprotection-related metabolites

Brain hypothermia has demonstrated pronounced neuroprotective effect in patients with cardiac arrest, ischemia and acute liver failure. However, its underlying neuroprotective mechanisms remain to be elucidated in order to improve therapeutic outcomes. Single voxel proton magnetic resonance spectroscopy (1H-MRS) was performed using a 7 Tesla MRI scanner on normal Sprague-Dawley rats (N = 8) in the same voxel under normothermia (36.5 °C) and 30 min mild hypothermia (33.5 °C). Levels of various brain proton metabolites were compared. The level of lactate (Lac) and myo-inositol (mI) increased in the cortex during hypothermia. In the thalamus, taurine (Tau), a cryogen in brain, increased and choline (Cho) decreased. These metabolic alterations indicated the onset of a number of neuroprotective processes that include attenuation of energy metabolism, excitotoxic pathways, brain osmolytes and thermoregulation, thus protecting neuronal cells from damage. These experimental findings demonstrated that 1H-MRS can be applied to investigate the changes of specific metabolites and corresponding neuroprotection mechanisms in vivo noninvasively, and ultimately improve our basic understanding of hypothermia and ability to optimize its therapeutic efficacy.