Individual dopaminergic neurons show raised iron levels in Parkinson disease

Evidence suggests that abnormal iron metabolism is associated with Parkinson disease (PD), with raised iron levels found in pathologically affected areas in PD. It is unknown if this elevated iron is actually associated with neurons or reactive glia, and we therefore addressed this issue by determining if raised iron was present in single dopaminergic neurons. We used unfixed frozen sections from postmortem tissue of PD patients and elderly normal individuals to avoid metal contamination and translocation. Levels of iron and other elements were measured using sensitive and specific wavelength dispersive electron probe x-ray microanalysis coupled with cathodoluminescence spectroscopy in individual substantia nigra dopaminergic neurons. We identified raised intraneuronal iron in single defined substantia nigra neurons in PD (mean neuronal iron 2,838 vs 1,611, p < 0.0001) but not in other movement disorders such as Huntington disease. These findings were unrelated to the density of remaining neurons. Primary changes in neuronal iron could lead to neurodegeneration in Parkinson disease.