Chronic or intermittent extravasations of blood into the subarachnoid space, and dissemination of heme by circulating cerebrospinal fluid, are the only established causes of superficial siderosis of the central nervous system (CNS). We studied the autopsy tissues of nine patients by iron histochemistry, immunocytochemistry, single- and double-label immunofluorescence, electron microscopy of ferritin, and high-definition X-ray fluorescence. In one case, frozen brain tissue was available for quantitative assay of total iron and ferritin. Siderotic tissues showed extensive deposits of iron and ferritin, and infiltration of the cerebellar cortex was especially severe. In addition to perivascular collections of hemosiderin-laden macrophages, affected tissues displayed iron-positive anuclear foamy structures in the neuropil that resembled axonal spheroids. They were especially abundant in eighth cranial nerves and spinal cord. Double-label immunofluorescence of the foamy structures showed co-localization of neurofilament protein and ferritin but comparable merged images of myelin-basic protein and ferritin, and ultrastructural visualization of ferritin, did not allow the conclusion that axonopathy was simply due to dilatation and rupture of fibers. Heme-oxygenase-1 (HO-1) immunoreactivity persisted in macrophages of siderotic cerebellar folia. Siderosis caused a large increase in total CNS iron but high-definition X-ray fluorescence of embedded tissue blocks excluded the accumulation of other metals. Holoferritin levels greatly exceeded the degree of iron accumulation. The susceptibility of the cerebellar cortex is likely due to Bergmann glia that serve as conduits for heme; and the abundance of microglia. Both cell types biosynthesize HO-1 and ferritin in response to heme. The eighth cranial nerves are susceptible because they consist of CNS axons, myelin, and neuroglial tissue along their subarachnoid course. The persistence of HO-1 protein implies continuous exposure of CNS to free heme or an excessively sensitive transcriptional response of the HO-1 gene. The conversion of heme iron to hemosiderin probably involves both translational and transcriptional activation of ferritin biosynthesis.

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.

Summary Determination of the microdistribution of trace elements in bone at low concentrations has previously been performed with proton induced X-ray emission (PIXE), high-energy synchrotron source X-ray fluorescence (XRF) and laser ablation - inductively coupled plasma mass spectrometry (LA-ICP-MS). Several commercial benchtop XRF systems with micrometer-scale resolution are currently available. While providing convenient, non-destructive mapping capability, they appear to lack the sensitivity required for detection of trace elements in biological tissues such as bone. We investigated the application of a prototype benchtop XRF system for the measurement of strontium and lead at physiological levels in bone. Detection of several elements of interest, including Sr and Pb was achieved with an experimental set up based on focused monochromatic microbeam X-ray fluorescence (Mµ-XRF) instrumentation with a low power source (45 W molybdenum tube) coupled to doubly curved crystal (DCC) optics. A cross-section of bone about 5 mm × 8 mm size was mapped with 80-µm resolution showing heterogeneous distribution of Sr and Pb. The data showed that Mµ-XRF coupled to DCC is powerful method for measurement of the spatial distribution of trace elements in bone.

Doubly curved crystal (DCC) X-ray optics provide an enabling technology for new portable, remote, and in situ applications of monochromatic X-rays for composition and structure analysis of amorphous, polycrystalline, and crystalline solids. Femtogram sensitivity for surface contamination, parts-per-billion (ppb) impurity levels for solids, and composition, structure and uniformity of thin films with compact, low power (20–50 W) source optic combinations are possible.

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