Synchrotron-radiation X-ray absorption spectroscopy (XAS) is a direct method for speciation analysis with atomic resolution, providing information about the local chemical environment of the probed ...element. This article gives an overview of the basic principles of XAS and its application to element speciation in biomedical research. The basic principle and experimental modalities of XAS are introduced, followed by a discussion of both its limitations, such as beam damage or detection limits, and practical advices to improve experiments. An updated review of biomedical studies involving XAS published over the last 5 years is then provided, paying special attention to metal-based drug biotransformation, metal and nanoparticle toxicology, and element speciation in cancer, neurological, and general pathophysiology. Finally, trends and future developments such as hyphenated methods, in situ correlative imaging and speciation, in vivo X-ray Absorption Near Edge Spectroscopy (XANES), full-field XANES, and X-ray Free Electron Laser (XFEL) XAS are presented.
•Principle of direct element speciation with synchrotron X-ray absorption spectroscopy (XAS).•Experimental modalities for bulk- and micro-XAS speciation and their limitations.•Review (2012–2017) of XAS in pharmacology, metals and nanoparticles toxicology, physiopathology.•Future directions and developments of XAS speciation for biomedical research.
Environmental exposure to neurotoxic metals and metalloids such as arsenic, cadmium, lead, mercury, or manganese is a global health concern affecting millions of people worldwide. Depending on the ...period of exposure over a lifetime, environmental metals can alter neurodevelopment, neurobehavior, and cognition and cause neurodegeneration. There is increasing evidence linking environmental exposure to metal contaminants to the etiology of neurological diseases in early life (e.g., autism spectrum disorder) or late life (e.g., Alzheimer’s disease). The known main molecular mechanisms of metal-induced toxicity in cells are the generation of reactive oxygen species, the interaction with sulfhydryl chemical groups in proteins (e.g., cysteine), and the competition of toxic metals with binding sites of essential metals (e.g., Fe, Cu, Zn). In neurons, these molecular interactions can alter the functions of neurotransmitter receptors, the cytoskeleton and scaffolding synaptic proteins, thereby disrupting synaptic structure and function. Loss of synaptic connectivity may precede more drastic alterations such as neurodegeneration. In this article, we will review the molecular mechanisms of metal-induced synaptic neurotoxicity.
The direct detection of biologically relevant metals in single cells and of their speciation is a challenging task that requires sophisticated analytical developments. The aim of this article is to ...present the recent achievements in the field of cellular chemical element imaging, and direct speciation analysis, using proton and synchrotron radiation X-ray micro- and nano-analysis. The recent improvements in focusing optics for MeV-accelerated particles and keV X-rays allow application to chemical element analysis in subcellular compartments. The imaging and quantification of trace elements in single cells can be obtained using particle-induced X-ray emission (PIXE). The combination of PIXE with backscattering spectrometry and scanning transmission ion microscopy provides a high accuracy in elemental quantification of cellular organelles. On the other hand, synchrotron radiation X-ray fluorescence provides chemical element imaging with less than 100 nm spatial resolution. Moreover, synchrotron radiation offers the unique capability of spatially resolved chemical speciation using micro-X-ray absorption spectroscopy. The potential of these methods in biomedical investigations will be illustrated with examples of application in the fields of cellular toxicology, and pharmacology, bio-metals and metal-based nano-particles.
Environmental exposure to metallic neurotoxicants is a matter of growing concern, since it may have very significant consequences for human health, from impairing neurodevelopment in children to the ...neurodegeneration processes involved in aging ...
Abstract Synchrotron-based x-ray fluorescence microscopy, immunofluorescence, and Western blotting were used to investigate changes in copper (Cu) and Cu-associated pathways in the vulnerable ...substantia nigra (SN) and locus coeruleus (LC) and in nondegenerating brain regions in cases of Parkinson's disease (PD) and appropriate healthy and disease controls. In PD and incidental Lewy body disease, levels of Cu and Cu transporter protein 1, were significantly reduced in surviving neurons in the SN and LC. Specific activity of the cuproprotein superoxide dismutase 1 was unchanged in the SN in PD but was enhanced in the parkinsonian anterior cingulate cortex, a region with α-synuclein pathology, normal Cu, and limited cell loss. These data suggest that regions affected by α-synuclein pathology may display enhanced vulnerability and cell loss if Cu-dependent protective mechanisms are compromised. Additional investigation of copper pathology in PD may identify novel targets for the development of protective therapies for this disorder.
Exposure to high levels of manganese (Mn) in children has recently been associated with adverse neurodevelopmental effects. Current infant formula regulations for Mn content were set between 1981 ...(United States), 2006 (European Union, France), and 2007 (Codex Alimentarius) prior to the publication of much of the growing body of research on the developmental neurotoxicity of Mn. In this study, we sought to measure the concentrations of Mn in some infant formulas and young child nutritional beverages available on the United States (US) and French markets using ion beam analysis by particle induced X-ray emission (PIXE) spectrometry and then compare the analytical results to concentrations reported in the literature for breast milk and applicable infant formula regulations and guidelines. We were particularly interested in measuring Mn concentrations in product types for which there is very little data from previous surveys, especially soy-based, rice-based, goat-milk based, chocolate-flavored, and nutritional beverages for young children that are not regulated as infant or follow-on formulas (e.g. "toddler formulas" and "toddler powders"). We purchased 44 infant formulas and young child nutritional beverage products in the US and France with varying protein sources (cow-milk, goat-milk, soy, rice) labelled for birth to 3 years. We selected these samples using maximum variation sampling to explore market extremes to facilitate comparisons to regulatory limits. Since this sampling method is non-probabilistic, other inferences cannot be made beyond this set of samples to the overall markets. We used ion beam analysis to measure the concentrations of Mn in each product. The range of measured Mn concentrations in the products is 160-2,800 μg/L, substantially higher than the 3-6 μg/L mean Mn concentration reported in human breast milk. All products satisfied national and Codex Alimentarius Commission (CAC) international standards for minimum Mn content in infant formulas; however, 7/25 of the products purchased in the US exceeded the CAC Guidance Upper Level of 100 μg Mn/kcal for infant formula.
Zinc and copper are involved in neuronal differentiation and synaptic plasticity but the molecular mechanisms behind these processes are still elusive due in part to the difficulty of imaging trace ...metals together with proteins at the synaptic level. We correlate stimulated-emission-depletion microscopy of proteins and synchrotron X-ray fluorescence imaging of trace metals, both performed with 40 nm spatial resolution, on primary rat hippocampal neurons. We reveal the co-localization at the nanoscale of zinc and tubulin in dendrites with a molecular ratio of about one zinc atom per tubulin-αβ dimer. We observe the co-segregation of copper and F-actin within the nano-architecture of dendritic protrusions. In addition, zinc chelation causes a decrease in the expression of cytoskeleton proteins in dendrites and spines. Overall, these results indicate new functions for zinc and copper in the modulation of the cytoskeleton morphology in dendrites, a mechanism associated to neuronal plasticity and memory formation.
Altered homeostasis of metal ions is suspected to play a critical role in neurodegeneration. However, the lack of analytical technique with sufficient spatial resolution prevents the investigation of ...metals distribution in neurons. An original experimental setup was developed to perform chemical element imaging with a 90 nm spatial resolution using synchrotron-based X-ray fluorescence. This unique spatial resolution, combined to a high brightness, enables chemical element imaging in subcellular compartments. We investigated the distribution of iron in dopamine producing neurons because iron-dopamine compounds are suspected to be formed but have yet never been observed in cells. The study shows that iron accumulates into dopamine neurovesicles. In addition, the inhibition of dopamine synthesis results in a decreased vesicular storage of iron. These results indicate a new physiological role for dopamine in iron buffering within normal dopamine producing cells. This system could be at fault in Parkinson's disease which is characterized by an increased level of iron in the substantia nigra pars compacta and an impaired storage of dopamine due to the disruption of vesicular trafficking. The re-distribution of highly reactive dopamine-iron complexes outside neurovesicles would result in an enhanced death of dopaminergic neurons.
•Natural uranium is cytotoxic towards dopaminergic cells but only at high concentrations (> 125 μM) which are not relevant for the vast majority of human exposures.•Uranium is located in defined ...cytoplasmic regions suggesting its accumulation within organelles yet to be determined.•Among the dopamine-related genes investigated, monoamine oxidase B gene expression is decreased even at 10 μM uranium exposure, far from cytotoxicity threshold.
Natural uranium is an ubiquitous element present in the environment and human exposure to low levels of uranium is unavoidable. Although the main target of acute uranium toxicity is the kidney, some concerns have been recently raised about neurological effects of chronic exposure to low levels of uranium. Only very few studies have addressed the molecular mechanisms of uranium neurotoxicity, indicating that the cholinergic and dopaminergic systems could be altered. The main objective of this study was to investigate the mechanisms of natural uranium toxicity, after 7-day continuous exposure, on terminally differentiated human SH-SY5Y cells exhibiting a dopaminergic phenotype. Cell viability was first assessed showing that uranium cytotoxicity only occurred at high exposure concentrations (> 125 μM), far from the expected values for uranium in the blood even after occupational exposure. SH-SY5Y differentiated cells were then continuously exposed to 1, 10, 125 or 250 μM of natural uranium for 7 days and uranium quantitative subcellular distribution was investigated by means of micro-PIXE (Particle Induced X-ray Emission). The subcellular element imaging revealed that uranium was located in defined perinuclear regions of the cytoplasm, suggesting its accumulation in organelles. Uranium was not detected in the nucleus of the differentiated cells. Quantitative analysis evidenced a very low intracellular uranium content at non-cytotoxic levels of exposure (1 and 10 μM). At higher levels of exposure (125 and 250 μM), when cytotoxic effects begin, a larger and disproportional intracellular accumulation of uranium was observed. Finally the expression of dopamine-related genes was quantified using real time qRT-PCR. The expression of monoamine oxidase B (MAO-B) gene was statistically significantly decreased after exposure to uranium while other dopamine-related genes were not modified. The down regulation of MAO-B was confirmed at the protein level. This original result suggests that the inhibition of dopamine catabolism, but also of other MAO-B substrates, could constitute selective effects of uranium neurotoxicity.
Drip irrigation –surface (DI) and subsurface (SDI)– is one of the best irrigation systems to increase both irrigation and water use efficiency. The objective of this research is to assess and compare ...the response of fodder corn to SDI treatments at two depths with DI in Mendoza. A full factorial experimental design was used on random plots and measurements were replicated through time. Tests were run in two consecutive cycles. Germination percentage (GP), yield, water use efficiency (WUE) and water productivity (WP) were assessed. High yields ranging from 70,214 to 105,771 kg ha-1 of green matter and from 10,020 to 22,476 kg ha-1 of dry matter (DM) were obtained in both cycles, respectively.
DM production from the first sowing was significantly higher in both cycles under SDI treatment than under DI. No significant differences in WP or WUE were found. GP and soil moisture (SM) did not show differences between treatments, but significant differences were found in SM (p=<0.0001) between the first soil layer and the other two layers.
Highlights
Germination percentage was not affected by the depth of the drip irrigation lines.
No significant differences were found in green matter yields between treatments in both crop cycles.
High crop water use was achieved. WUE values were 12 percent (and up to 41 percent) higher.
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