Cell specific quantitative iron mapping on brain slices by immuno-µPIXE in healthy elderly and Parkinson’s disease

Iron is essential for neurons and glial cells, playing key roles in neurotransmitter synthesis, energy production and myelination. In contrast, high concentrations of free iron can be detrimental and contribute to neurodegeneration, through promotion of oxidative stress. Particularly in Parkinson's disease (PD) changes in iron concentrations in the substantia nigra (SN) was suggested to play a key role in degeneration of dopaminergic neurons in nigrosome 1. However, the cellular iron pathways and the mechanisms of the pathogenic role of iron in PD are not well understood, mainly due to the lack of quantitative analytical techniques for iron quantification with subcellular resolution. Here, we quantified cellular iron concentrations and subcellular iron distributions in dopaminergic neurons and different types of glial cells in the SN both in brains of PD patients and in non-neurodegenerative control brains (Co). To this end, we combined spatially resolved quantitative element mapping using micro particle induced X-ray emission (mu PIXE) with nickel-enhanced immunocytochemical detection of cell type-specific antigens allowing to allocate element-related signals to specific cell types. Distinct patterns of iron accumulation were observed across different cell populations. In the control (Co) SNc, oligodendroglial and astroglial cells hold the highest cellular iron concentration whereas in PD, the iron concentration was increased in most cell types in the substantia nigra except for astroglial cells and ferritin-positive oligodendroglial cells. While iron levels in astroglial cells remain unchanged, ferritin in oligodendroglial cells seems to be depleted by almost half in PD. The highest cellular iron levels in neurons were located in the cytoplasm, which might increase the source of non-chelated Fe3+, implicating a critical increase in the labile iron pool. Indeed, neuromelanin is characterised by a significantly higher loading of iron including most probable the occupancy of low-affinity iron binding sites. Quantitative trace element analysis is essential to characterise iron in oxidative processes in PD. The quantification of iron provides deeper insights into changes of cellular iron levels in PD and may contribute to the research in iron-chelating disease-modifying drugs

Cell specific quantitative iron mapping on brain slices by immuno-μPIXE in healthy elderly and Parkinson’s disease

Iron is essential for neurons and glial cells, playing key roles in neurotransmitter synthesis, energy production and myelination. In contrast, high concentrations of free iron can be detrimental and contribute to neurodegeneration, through promotion of oxidative stress. Particularly in Parkinson’s disease (PD) changes in iron concentrations in the substantia nigra (SN) was suggested to play a key role in degeneration of dopaminergic neurons in nigrosome 1. However, the cellular iron pathways and the mechanisms of the pathogenic role of iron in PD are not well understood, mainly due to the lack of quantitative analytical techniques for iron quantification with subcellular resolution. Here, we quantified cellular iron concentrations and subcellular iron distribution in dopaminergic neurons and different types of glial cells in the SN both in brains of PD patients and in non-neurodegenerative control brains (Co). To this end, we combined spatially resolved quantitative element mapping using micro particle induced X-ray emission (μPIXE) with nickel-enhanced immunocytochemical detection of cell type-specific antigens allowing to allocate element-related signals to specific cell types. Distinct patterns of iron accumulation were observed across different cell populations. In the control (Co) SNc, oligodendroglial and astroglial cells hold the highest cellular iron concentration whereas in PD, the iron concentration was increased in most cell types in the substantia nigra except for astroglial cells and ferritin-positive oligodendroglial cells. While iron levels in astroglial cells remain unchanged, ferritin in oligodendroglial cells seems to be depleted by almost half in PD. The highest cellular iron levels in neurons were located in the cytoplasm, which might increase the source of non-chelated Fe3+, implicating a critical increase in the labile iron pool. Indeed, neuromelanin is characterised by a significantly higher loading of iron including most probable the occupancy of low-affinity iron binding sites. Quantitative trace element analysis is essential to characterise iron in oxidative processes in PD. The quantification of iron provides deeper insights into changes of cellular iron levels in PD and may contribute to the research in iron-chelating disease-modifying drugs

Imaging subcortical white matter by high resolution 7 T MRI in vivo: Towards potential u-fiber density mapping in humans

Subcortical white matter (SWM) is a thin layer of white matter (WM) residing just below the cortex. Its structure, metabolism and function differ substantially from deep WM. Importantly, SWM incorporates short association fibers, the intra-hemispheric connections between adjacent gyri, referred to as U-fibers. Despite their importance for cortico-cortical connectivity little is known about the distribution of U-fibers in humans mainly due to the lack of appropriate imaging methods. SWM mapping by structural magnetic resonance imaging (MRI), came into reach only very recently by the availability of ultra high resolution MRI vivo required to image this ultra-thin, geometrically complex structure. No study has explored this potential so far and the underlying biophysical MR contrast mechanisms in SWM are still unclear. Herein, we investigate multiple MR contrasts in human SWM with high-resolution in-vivo 7T MRI. We demonstrate that the transverse relaxation rate (R2), effective transverse relaxation rate (R2)* and magnetic susceptibility are increased in SWM exhibiting strong contrast to both adjacent grey matter (GM) and deep WM. Combination of increased R2* and increased susceptibility points toward an elevated levels of paramagnetic iron as a driving contrast mechanism. This hypothesis was tested in a post-mortem human brain sample with 7T MRI, classical histology and quantitative iron and myelin mapping. Quantitative iron maps were obtained at scales ranging from 1 to 100μm by proton induced X-ray emission (PIXE) and Laser Ablation Inductively Coupled Plasma Mass Spectroscopic Imaging (LA ICP MSI). Elevated iron level in oligodendrocytes and iron-rich fibers in SWM was confirmed as the dominant contrast mechanism. In addition, we showed that SWM contrast in MRI vanished after de-ironing the brain tissue sample in deferroxamine solution. We therefore conclude that the SWM appearance in MR images is solely driven by elevated iron concentration. Furthermore, using a novel SWM segmentation method we demonstrated that SWM contrast is not uniform across the brain. U-fiber-rich frontal, temporal and parietal association areas showed higher SWM contrast, while primary motor, sensory and auditory areas with high intracortical myelination showed lower SWM contrast. This suggests that iron accumulation in SWM is area-dependent and might reflect U-fiber density and distinct myelination patterns of overlying cortical areas. These new findings are of paramount importance and may pave the way for future in-vivo segmentation strategies for this crucial white matter structure and for potential non-invasive U-fiber density mapping in humans

Classification of buried soils, cultural, and colluvial deposits in the Viking town Hedeby

Objective classification of settlement deposits is a prerequisite for understanding human-environment interactions at habitation sites. This paper presents a novel approach combining a relatively fine-scale sampling strategy, a multimethod geoarchaeological investigation of cores and multivariate statistics to aid in the classification and interpretation of complex and intricately stratified archaeological deposits. Heterogeneous settlement deposits, buried soils, colluvial, fluvial, and fluvioglacial sediments from cores retrieved in the Viking settlement Hedeby were investigated using six cost-effectively measurable geoecological parameters: loss on ignition at 550°C, magnetic susceptibility, contents of stones, artifacts, bones, and charcoal with wood. Principal component analysis allowed identifying variables that would sufficiently describe data and cluster analysis enabled the classification of the materials. As a result, 13 classes were distinguished with a detailed and reliable differentiation of materials of natural and cultural genesis. Based on spatial distribution patterns of the classes, hypotheses regarding land use in the adjacent areas were made: Waste disposal in the valley of Hedeby-brook and metallurgic activities north of it. This approach is valuable for coring-based research at settlements, in particular at tightly managed heritage sites, and for surveys to identify potential excavation sites, whereas the set of variables must be adjusted according to local conditions