Temperature Dependence of Paramagnetic Species in the Human Brain Tissue: An X-Band EPR Study

Paramagnetic ions are distributed throughout the human brain. The increased accumulation of these metals, such as iron and copper, can induce cellular death and the development of neurological diseases. Electron Paramagnetic Resonance (EPR) is a spectroscopic technique capable of detecting these ions in a given biological sample.

Samples from 17 human brain structures of 8 ex vivo subjects were extracted, lyophilized, and triturated for EPR measurements at variable temperatures ranging from 193 to 293 K. Simulations were performed using the EasySpin toolbox to calculate qualitative parameters and the EPR absorption of high-spin iron (Fe(III)), copper ion (Cu(II)), and ferritin (Ft) signals in all obtained EPR spectra.

The simulated parameters showed a considerable percentage variation relative to the input values, which resulted in spectral visual changes of each paramagnetic ion signal. The simulated EPR brain spectra demonstrated temperature dependence, with an increase in the amplitude of Fe(III), Cu(II), and Ft signals as the temperature decreased.

The magnetic behavior of these paramagnetic species exhibited linearity with the inverse of temperature for the Cu(II) EPR absorption across all brain structures, while Fe(III) and Ft signals showed a nonlinear pattern in the EPR absorption, with heterogeneity among all brain regions and subjects.