Distribution and chemical state analysis of iron in the Parkinsonian substantia nigra using synchrotron radiation micro beams

Abstract

Metallic elements and their organic compounds have dynamic regulatory functions in cells. Iron concentrations have been observed in the neuromelanin granules in the substantia nigra of brain tissues of patients with Parkinson’s disease. Iron has been linked to cell death because of its potential to promote free radicals, leading to oxidative stress. In the present study, we have used synchrotron radiation X-ray fluorescence spectroscopy (SXRF) and Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy, to investigate distributions and chemical states of iron. The samples were brain tissues from monkeys which had been injected with MPTP (1-metyl-4-phenyl-1,2,3,6-tetrahydropyridine). SXRF analyses were performed for elemental mapping, using 7.16 keV energy beam. The chemical state analyses were performed between 7.16 and 7.12 keV energies. The lower limit was chosen to be slightly above the Fe 2+ absorption edge, in order to suppress the excitation of Fe 3+. FeO (Fe 2+) and Fe 2O 3 (Fe 3+) powders were used for XANES analyses as reference samples. The data were measured in fluorescence mode for the biological specimens and in transmission mode for the reference samples. The results for the Fe 2+/Fe 3+ ratios from the neuromelanin granules showed significant variations, which were correlated with the level of iron concentration. Cells containing high level of iron had high level of Fe 2+. With Fe 2+ having been suggested to potentially promote more free radicals than Fe 3+, the high concentrations of iron may be the critical factor leading to cell death due to the presence of more free radicals.