Friedreich's ataxia (FRDA) causes selective atrophy of the large neurons of the dentate nucleus (DN). High iron (Fe) concentration and failure to clear the metal from the affected brain tissue are potential risk factors in the progression of the lesion. The DN also contains relatively high amounts of copper (Cu) and zinc (Zn), but the importance of these metals in FRDA has not been established. This report describes nondestructive quantitative X-ray fluorescence (XRF) and "mapping" of Fe, Cu, and Zn in polyethylene glycol–dimethylsulfoxide (PEG/DMSO)-embedded DN of 10 FRDA patients and 13 controls. Fe fluorescence arose predominantly from the hilar white matter, whereas Cu and Zn were present at peak levels in DN gray matter. Despite collapse of the DN in FRDA, the location of the peak Fe signal did not change. In contrast, the Cu and Zn regions broadened and overlapped extensively with the Fe-rich region. Maximal metal concentrations did not differ from normal (in micrograms per milliliter of solid PEG/DMSO as means ± S.D.): Fe normal, 364 ± 117, FRDA, 344 ± 159; Cu normal, 33 ± 13, FRDA, 33 ± 18; and Zn normal, 32 ± 16, FRDA, 33 ± 19. Tissues were recovered from PEG/DMSO and transferred into paraffin for matching with immunohistochemistry of neuron-specific enolase (NSE), glutamic acid decarboxylase (GAD), and ferritin. NSE and GAD reaction products confirmed neuronal atrophy and grumose degeneration that coincided with abnormally diffuse Cu and Zn zones. Ferritin immunohistochemistry matched Fe XRF maps, revealing the most abundant reaction product in oligodendroglia of the DN hilus. In FRDA, these cells were smaller and more numerous than normal. In the atrophic DN gray matter of FRDA, anti-ferritin labeled mostly hypertrophic microglia. Immunohistochemistry and immunofluorescence of the Cu-responsive proteins Cu,Zn-superoxide dismutase and Cu++-transporting ATPase α-peptide did not detect specific responses to Cu redistribution in FRDA. In contrast, metallothionein (MT)-positive processes were more abundant than normal and contributed to the gliosis of the DN. The isoforms of MT, MT-1/2, and brain-specific MT-3 displayed only limited co-localization with glial fibrillary acidic protein. The results suggest that MT can provide effective protection against endogenous Cu and Zn toxicity in FRDA, similar to the neuroprotective sequestration of Fe in holoferritin.

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Friedreich's ataxia (FRDA) causes progressive atrophy of the large neurons of the dentate nucleus (DN). Possible contributing factors to FRDA pathogenesis are the high iron (Fe) concentration in the DN and failure to clear the metal from the damaged tissue. Fe, copper (Cu), and zinc (Zn) content in the DN was imaged and quantified by X‐ray fluorescence of PEG‐embedded tissue from 10 FRDA patients and 13 controls. In normal DN, Fe occurred predominantly in central white matter and hilus whereas Cu and Zn were present at peak levels in the gray matter. The location of maximum Fe signal did not change in FRDA DN, but the Cu region broadened overlapping extensively with the Fe‐rich region. Maximal metal concentrations did not change. The most abundant immunochemical reaction (ICR) for ferritin was in oligodendroglia of the central white matter of the DN. Ferritin‐ reactive oligodendroglia in the DN hilus of FRDA were much smaller than normal and more numerous. ICR for Cu, Zn‐superoxide dismutase (SOD) and Cu++‐transporting ATPase α‐peptide (ATP7A, Menkes disease protein) was present in microglia and vessel walls, respectively, but FRDA did not cause a distinct change in ICR from the normal state. The shift of Cu into the Fe‐rich white matter may cause greater oxidative injury. Supported by: NIH‐NS069454‐02; Friedreichˈs Ataxia Research Alliance; National Ataxia Foundation; and Neurochemical Research, Inc