Elemental micro-imaging and quantification of human substantia nigra using synchrotron radiation based x-ray fluorescence--in relation to Parkinson's disease

Elemental quantification and analysis of structural abnormalities in neurons from Parkinson's-diseased brains by X-ray fluorescence microscopy and diffraction

In this work we use scanning X-ray microscopy to study the structure and elemental composition of neuromelanin-positive neurons in substantia nigra tissue of Parkinson patients (PD) and controls. A total of 53 neurons were analyzed with X-ray fluorescence (XRF) and diffraction using sub-µm-focused synchrotron radiation. A statistical evaluation identified copper as the most group-discriminating element and indicated that interindividual and intraindividual variations are of great relevance in tissue measurements of diseased patients and prevent from automated group clustering. XRF analyses of two Lewy bodies (LBs) highlight a heterogeneity in elemental distributions in these LBs, whereas an innovative X-ray diffraction-based method approach was used to reveal β-sheet-rich crystalline structures in LBs. Overall, sub-µm-focus X-ray microscopy highlighted the elemental heterogeneity in PD pathology.

Imaging of neuronal tissues by x-ray diffraction and x-ray fluorescence microscopy: evaluation of contrast and biomarkers for neurodegenerative diseases

We have used scanning X-ray diffraction (XRD) and X-ray fluorescence (XRF) with micro-focused synchrotron radiation to study histological sections from human substantia nigra (SN). Both XRF and XRD mappings visualize tissue properties, which are inaccessible by conventional microscopy and histology. We propose to use these advanced tools to characterize neuronal tissue in neurodegeneration, in particular in Parkinson's disease (PD). To this end, we take advantage of the recent experimental progress in x-ray focusing, detection, and use automated data analysis scripts to enable quantitative analysis of large field of views. XRD signals are recorded and analyzed both in the regime of small-angle (SAXS) and wide-angle x-ray scattering (WAXS). The SAXS signal was analyzed in view of the local myelin structure, while WAXS was used to identify crystalline deposits. PD tissue scans exhibited increased amounts of crystallized cholesterol. The XRF analysis showed increased amounts of iron and decreased amounts of copper in the PD tissue compared to the control.

Combined micro-XRF and TXRF methodology for quantitative elemental imaging of tissue samples

Local differences in structural properties of biological specimens pose a major limitation to quantitative X-ray fluorescence imaging. This is because both the various tissue compartments of different density and variation in the sample thickness upon frequently used freeze-drying come up with the different values of the sample mass per unit area to be taken into account. Even though several solutions to tackle this problem based on the home-made standards for quantification in terms of thickness- and density-independent elemental mass fractions have been proposed, this issue is not addressed enough due to the samples' heterogeneity. In our recent study, we propose a calculation scheme based on combined external-standard micro X-ray fluorescence (micro-XRF) imaging and internal-standard total reflection X-ray fluorescence (TXRF) analysis to determine the corrected elemental mass fraction distributions in commonly analysed rat tissues: kidney, liver and spleen. The results of TXRF analysis of digested large tissue sections together with the mean values of elemental masses per unit area obtained with micro-XRF were employed to determine the average masses per unit area of the samples. The correction for variation of the tissue thickness and density was done through with the use of Compton intensities. Importantly, by its versatility, our novel approach can be used to produce elemental contrast in a variety of biological specimens where local variations in either the sample density or thickness are no longer the issue.

Bioanalytics in Quantitive (Bio)imaging/Mapping of Metallic Elements in Biological Samples

The aim of this article is to describe selected analytical techniques and their applications in the quantitative mapping/(bio)imaging of metals in biological samples. This work presents the advantages and disadvantages as well as the appropriate methods of scope for research. Distribution of metals in biological samples is currently one of the most important issues in physiology, toxicology, pharmacology, and other disciplines where functional information about the distribution of metals is essential. This issue is a subject of research in (bio)imaging/mapping studies, which use a variety of analytical techniques for the identification and determination of metallic elements. Increased interest in analytical techniques enabling the (bio)imaging of metals in a variety of biological material has been observed more recently. Measuring the distribution of trace metals in tissues after a drug dose or ingestion of poison-containing metals allows for the studying of pathomechanisms and the pathophysiology of various diseases and disorders related to the management of metals in human and animal systems.

The neurotoxicity of iron, copper and manganese in Parkinson's and Wilson's diseases

Impaired cellular homeostasis of metals, particularly of Cu, Fe and Mn may trigger neurodegeneration through various mechanisms, notably induction of oxidative stress, promotion of α-synuclein aggregation and fibril formation, activation of microglial cells leading to inflammation and impaired production of metalloproteins. In this article we review available studies concerning Fe, Cu and Mn in Parkinson's disease and Wilson's disease. In Parkinson's disease local dysregulation of iron metabolism in the substantia nigra (SN) seems to be related to neurodegeneration with an increase in SN iron concentration, accompanied by decreased SN Cu and ceruloplasmin concentrations and increased free Cu concentrations and decreased ferroxidase activity in the cerebrospinal fluid. Available data in Wilson's disease suggest that substantial increases in CNS Cu concentrations persist for a long time during chelating treatment and that local accumulation of Fe in certain brain nuclei may occur during the course of the disease. Consequences for chelating treatment strategies are discussed.

Laminar-specific distribution of zinc: evidence for presence of layer IV in forelimb motor cortex in the rat

The rat is the most widely studied pre-clinical model system of various neurological and neurodegenerative disorders affecting hand function. Although brain injury to the forelimb region of the motor cortex in rats mostly induces behavioral abnormalities in motor control of hand movements, behavioral deficits in the sensory-motor domain are also observed. This questions the prevailing view that cortical layer IV, a recipient of sensory information from the thalamus, is absent in rat motor cortex. Because zinc-containing neurons are generally not found in pathways that run from the thalamus, an absence of zinc (Zn) in a cortical layer would be suggestive of sensory input from the thalamus. To test this hypothesis, we used synchrotron micro X-ray fluorescence imaging to measure Zn distribution across cortical layers. Zn maps revealed a heterogeneous layered Zn distribution in primary and secondary motor cortices of the forelimb region in the adult rat. Two wider bands with elevated Zn content were separated by a narrow band having reduced Zn content, and this was evident in two rat strains. The Zn distribution pattern was comparable to that in sensorimotor cortex, which is known to contain a well demarcated layer IV. Juxtaposition of Zn maps and the images of brain stained for Nissl bodies revealed a "Zn valley" in primary motor cortex, apparently starting at the ventral border of pyramidal layer III and ending at the close vicinity of layer V. This finding indicates the presence of a conspicuous cortical layer between layers III and V, i.e. layer IV, the presence of which previously has been disputed. The results have implications for the use of rat models to investigate human brain function and neuropathology, such as after stroke. The presence of layer IV in the forelimb region of the motor cortex suggests that therapeutic interventions used in rat models of motor cortex injury should target functional abnormalities in both motor and sensory domains. The finding is also critical for future investigation of the biochemical mechanisms through which therapeutic interventions can enhance neural plasticity, particularly through Zn dependent pathways.