Characterization of selenium in ambient aerosols and primary emission sources

Atmospheric selenium (Se) in aerosols was investigated using X-ray absorption near-edge structure (XANES) spectroscopy and X-ray fluorescence (XRF) microscopy. These techniques were used to determine the oxidation state and elemental associations of Se in common primary emission sources and ambient aerosols collected from the greater Atlanta area. In the majority of ambient aerosol and primary emission source samples, the spectroscopic patterns as well as the absence of elemental correlations suggest Se is in an elemental, organic, or oxide form. XRF microscopy revealed numerous Se-rich particles, or hotspots, accounting on average for ∼16% of the total Se in ambient aerosols. Hotspots contained primarily Se(0)/Se(-II). However, larger, bulk spectroscopic characterizations revealed Se(IV) as the dominant oxidation state in ambient aerosol, followed by Se(0)/Se(-II) and Se(VI). Se(IV) was the only observed oxidation state in gasoline, diesel, and coal fly ash, while biomass burning contained a combination of Se(0)/Se(-II) and Se(IV). Although the majority of Se in aerosols was in the most toxic form, the Se concentration is well below the California Environmental Protection Agency chronic exposure limit (∼20000 ng/m(3)).

Quantitation and localization of intracellular redox active metals by X-ray fluorescence microscopy in cortical neurons derived from APP and APLP2 knockout tissue

The amyloid precursor protein (APP) gene family includes APP and the amyloid precursor-like proteins, APLP1 and APLP2. These proteins contain metal binding sites for copper, zinc and iron and are known to have physiological roles in modulating the metal homeostasis in brain cells. Here we report the application of X-ray fluorescence microscopy (XFM) to investigate the subcellular distribution patterns of the metal ions Cu, Zn, Fe, and Ca in individual neurons derived from APP and APLP2 knockout mice brains to further define their role in metal homeostasis. These studies add to the growing body of data that the APP family of proteins are metalloproteins that have shared as well as distinct effects on metals. As we continue to delineate the cellular effects of the APP family of proteins it is important to consider how metals are involved in their actions.

Maca reduces blood pressure and depression, in a pilot study in postmenopausal women

OBJECTIVE

Lepidium meyenii (Maca) has been used for centuries for its fertility-enhancing and aphrodisiac properties. In an Australian study, Maca improved anxiety and depressive scores. The effects of Maca on hormones, lipids, glucose, serum cytokines, blood pressure, menopausal symptoms and general well-being in Chinese postmenopausal women were evaluated.

METHODS

A randomized, double-blind, placebo-controlled, cross-over study was conducted in 29 postmenopausal Hong Kong Chinese women. They received 3.3 g/day of Maca or placebo for 6 weeks each, in either order, over 12 weeks. At baseline, week 6 and week 12, estradiol, follicle stimulating hormone (FSH), sex hormone binding globulin (SHBG), thyroid stimulating hormone (TSH), full lipid profiles, glucose and serum cytokines were measured. The Greene Climacteric, SF-36 Version 2, Women's Health Questionnaire and Utian Quality of Life Scales were used to assess the severity of menopausal symptoms and health-related quality of life.

RESULTS

There were no differences in estradiol, FSH, TSH, SHBG, glucose, lipid profiles and serum cytokines amongst those who received Maca as compared to the placebo group; however, significant decreases in diastolic blood pressure and depression were apparent after Maca treatment.

CONCLUSIONS

Maca did not exert hormonal or immune biological action in the small cohort of patients studied; however, it appeared to reduce symptoms of depression and improve diastolic blood pressure in Chinese postmenopausal women. Although results are comparable to previous similar published studies in postmenopausal women, there might be a cultural difference among the Chinese postmenopausal women in terms of symptom reporting.

The Bionanoprobe: hard X-ray fluorescence nanoprobe with cryogenic capabilities

Hard X-ray fluorescence microscopy is one of the most sensitive techniques for performing trace elemental analysis of biological samples such as whole cells and tissues. Conventional sample preparation methods usually involve dehydration, which removes cellular water and may consequently cause structural collapse, or invasive processes such as embedding. Radiation-induced artifacts may also become an issue, particularly as the spatial resolution increases beyond the sub-micrometer scale. To allow imaging under hydrated conditions, close to the `natural state', as well as to reduce structural radiation damage, the Bionanoprobe (BNP) has been developed, a hard X-ray fluorescence nanoprobe with cryogenic sample environment and cryo transfer capabilities, dedicated to studying trace elements in frozen-hydrated biological systems. The BNP is installed at an undulator beamline at sector 21 of the Advanced Photon Source. It provides a spatial resolution of 30 nm for two-dimensional fluorescence imaging. In this first demonstration the instrument design and motion control principles are described, the instrument performance is quantified, and the first results obtained with the BNP on frozen-hydrated whole cells are reported.

Epidermal growth factor receptor targeted nuclear delivery and high-resolution whole cell X-ray imaging of Fe3O4@TiO2 nanoparticles in cancer cells

Sequestration within the cytoplasm often limits the efficacy of therapeutic nanoparticles that have specific subcellular targets. To allow for both cellular and subcellular nanoparticle delivery, we have created epidermal growth factor receptor (EGFR)-targeted Fe3O4@TiO2 nanoparticles that use the native intracellular trafficking of EGFR to improve internalization and nuclear translocation in EGFR-expressing HeLa cells. While bound to EGFR, these nanoparticles do not interfere with the interaction between EGFR and karyopherin-β, a protein that is critical for the translocation of ligand-bound EGFR to the nucleus. Thus, a portion of the EGFR-targeted nanoparticles taken up by the cells also reaches cell nuclei. We were able to track nanoparticle accumulation in cells by flow cytometry and nanoparticle subcellular distribution by confocal fluorescent microscopy indirectly, using fluorescently labeled nanoparticles. More importantly, we imaged and quantified intracellular nanoparticles directly, by their elemental signatures, using X-ray fluorescence microscopy at the Bionanoprobe, the first instrument of its kind in the world. The Bionanoprobe can focus hard X-rays down to a 30 nm spot size to map the positions of chemical elements tomographically within whole frozen-hydrated cells. Finally, we show that photoactivation of targeted nanoparticles in cell nuclei, dependent on successful EGFR nuclear accumulation, induces significantly more double-stranded DNA breaks than photoactivation of nanoparticles that remain exclusively in the cytoplasm.

Methylmercury targets photoreceptor outer segments

Human populations experience widespread low level exposure to organometallic methylmercury compounds through consumption of fish and other seafood. At higher levels, methylmercury compounds specifically target nervous systems, and among the many effects of their exposure are visual disturbances, including blindness, which previously were thought to be due to methylmercury-induced damage to the visual cortex. Here, we employ high-resolution X-ray fluorescence imaging using beam sizes of 500 × 500 and 250 × 250 nm(2) to investigate the localization of mercury at unprecedented resolution in sections of zebrafish larvae ( Danio rerio ), a model developing vertebrate. We demonstrate that methylmercury specifically targets the outer segments of photoreceptor cells in both the retina and pineal gland. Methylmercury distribution in both tissues was correlated with that of sulfur, which, together with methylmercury's affinity for thiolate donors, suggests involvement of protein cysteine residues in methylmercury binding. In contrast, in the lens, the mercury distribution was different from that of sulfur, with methylmercury specifically accumulating in the secondary fiber cells immediately underlying the lens epithelial cells rather than in the lens epithelial cells themselves. Since methylmercury targets two main eye tissues (lens and photoreceptors) that are directly involved in visual perception, it now seems likely that the visual disruption associated with methylmercury exposure in higher animals including humans may arise from direct damage to photoreceptors, in addition to injury of the visual cortex.

Iron accumulates in Huntington's disease neurons: protection by deferoxamine

Huntington’s disease (HD) is a progressive neurodegenerative disorder caused by a polyglutamine-encoding CAG expansion in the huntingtin gene. Iron accumulates in the brains of HD patients and mouse disease models. However, the cellular and subcellular sites of iron accumulation, as well as significance to disease progression are not well understood. We used independent approaches to investigate the location of brain iron accumulation. In R6/2 HD mouse brain, synchotron x-ray fluorescence analysis revealed iron accumulation as discrete puncta in the perinuclear cytoplasm of striatal neurons. Further, perfusion Turnbull’s staining for ferrous iron (II) combined with transmission electron microscope ultra-structural analysis revealed increased staining in membrane bound peri-nuclear vesicles in R6/2 HD striatal neurons. Analysis of iron homeostatic proteins in R6/2 HD mice revealed decreased levels of the iron response proteins (IRPs 1 and 2) and accordingly decreased expression of iron uptake transferrin receptor (TfR) and increased levels of neuronal iron export protein ferroportin (FPN). Finally, we show that intra-ventricular delivery of the iron chelator deferoxamine results in an improvement of the motor phenotype in R6/2 HD mice. Our data supports accumulation of redox-active ferrous iron in the endocytic / lysosomal compartment in mouse HD neurons. Expression changes of IRPs, TfR and FPN are consistent with a compensatory response to an increased intra-neuronal labile iron pool leading to increased susceptibility to iron-associated oxidative stress. These findings, together with protection by deferoxamine, support a potentiating role of neuronal iron accumulation in HD.

Aging results in copper accumulations in glial fibrillary acidic protein-positive cells in the subventricular zone

Analysis of rodent brains with X-ray fluorescence (XRF) microscopy combined with immunohistochemistry allowed us to demonstrate that local Cu concentrations are thousands of times higher in the glia of the subventricular zone (SVZ) than in other cells. Using XRF microscopy with subcellular resolution and intracellular X-ray absorption spectroscopy we determined the copper (I) oxidation state and the sulfur ligand environment. Cu K-edge X-ray absorption near edge spectroscopy is consistent with Cu being bound as a multimetallic Cu-S cluster similar to one present in Cu-metallothionein. Analysis of age-related changes show that Cu content in astrocytes of the SVZ increases fourfold from 3 weeks to 9 months, while Cu concentration in other brain areas remain essentially constant. This increase in Cu correlates with a decrease in adult neurogenesis assessed using the Ki67 marker (both, however, can be age-related effects). We demonstrate that the Cu distribution and age-related concentration changes in the brain are highly cell specific.

X-ray fluorescence imaging of single human cancer cells reveals that the N-heterocyclic ligands of iodinated analogues of ruthenium anticancer drugs remain coordinated after cellular uptake

Analogues of KP1019 containing iodinated indazole ligands were prepared to investigate the biological fate of the Ru-N-heterocycle bond in this class of anticancer agents. The new complexes, 5-iodoindazolium trans-tetrachloridobis(5-iodoindazole)ruthen(III)ate (1) and 5-iodoindazolium trans-tetrachlorido(dimethyl sulfoxide)(5-iodoindazole)ruthen(III)ate (3), were characterized by elemental analysis, mass spectrometry and UV-vis spectrophotometry. Tetramethylammonium salts of these complexes (2 and 4) were synthesized and characterized in a similar manner. Half-maximum inhibitory concentrations of 2 and 4 with regard to A549 cells at 24 h were determined on the basis of the dose-response curves derived from real-time cell adhesion impedance measurements and were shown to be in the same range as those determined for KP1019 and NAMI-A using the same method. X-ray fluorescence imaging of single cultured A549 cells treated with 2 or 4 showed that, in both cases, the distribution of ruthenium and iodine was identical, indicating that the Ru-N bonds in the anionic complexes remained intact after incubation in culture medium and subsequent cellular uptake and processing.

Mapping the subcellular localization of Fe3O4@TiO2 nanoparticles by X-ray Fluorescence Microscopy

The targeted delivery of Fe₃O₄@TiO2 nanoparticles to cancer cells is an important step in their development as nanomedicines. We have synthesized nanoparticles that can bind the Epidermal Growth Factor Receptor, a cell surface protein that is overexpressed in many epithelial type cancers. In order to study the subcellular distribution of these nanoparticles, we have utilized the sub-micron resolution of X-ray Fluorescence Microscopy to map the locationof Fe₃O4@TiO₂ NPs and other trace metal elements within HeLa cervical cancer cells. Here we demonstrate how the higher resolution of the newly installed Bionanoprobe at the Advanced Photon Source at Argonne National Laboratory can greatly improve our ability to distinguish intracellular nanoparticles and their spatial relationship with subcellular compartments.

Subcellular redistribution and mitotic inheritance of transition metals in proliferating mouse fibroblast cells

Synchrotron X-ray fluorescence microscopy of non-synchronized NIH 3T3 fibroblasts revealed an intriguing redistribution dynamics that defines the inheritance of trace metals during mitosis. At metaphase, the highest density areas of Zn and Cu are localized in two distinct regions adjacent to the metaphase plate. As the sister chromatids are pulled towards the spindle poles during anaphase, Zn and Cu gradually move to the center and partition into the daughter cells to yield a pair of twin pools during cytokinesis. Colocalization analyses demonstrated high spatial correlations between Zn, Cu, and S throughout all mitotic stages, while Fe showed consistently different topographies characterized by high-density spots distributed across the entire cell. Whereas the total amount of Cu remained similar compared to interphase cells, mitotic Zn levels increased almost 3-fold, suggesting a prominent physiological role that lies beyond the requirement of Zn as a cofactor in metalloproteins or messenger in signaling pathways.

Coupling transmission electron microscopy with synchrotron radiation X-ray fluorescence microscopy to image vascular copper

Recently, using synchrotron radiation X-ray fluorescence microscopy (SRXRF), the copper accumulation in rat aortic elastin and copper topography in human THP-1 cell monolayer have been described. However, it is necessary to locate more accurately cellular copper in the vascular cells and tissues. In the current study, SRXRF coupling with transmission electron microscopy (TEM) was used to image copper in sections of human THP-1 cells and mouse aorta. The results showed that sections of 1 µm thickness are required for SRXRF producing a correlative image with TEM between copper topography and cellular ultrastructure. As compared with SRXRF alone, coupling TEM with SRXRF can clearly identify the location of copper in the nucleus and nucleolus in non-dividing THP-1 cell sections, and can differentiate the copper location at elastic laminae from collagen in mouse aortic sections. Thus, these results revealed new information about the copper topography in vascular cells and tissues and highlighted the potential of TEM-SRXRF to investigate the role of copper in macrophage and aortic homeostasis.

Does cytotoxicity of metallointercalators correlate with cellular uptake or DNA affinity?

The cytotoxicity of the metallointercalators, [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1R,2R-diaminocyclohexane)](2+) ([56MERR]) and [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1S,2S-diaminocyclohexane)](2+) ([56MESS]), towards A549 human lung cancer cells was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The IC(50) value obtained following exposure of A549 cells to [56MESS] for 4 h was approximately three times smaller than that obtained when [56MERR] was administered under the same conditions, indicating that the former complex displayed greater cytotoxicity. Both IC(50) values were greater than that obtained after exposure of A549 cells to cisplatin, demonstrating that the latter compound was the most cytotoxic of the three examined. Microprobe synchrotron radiation X-ray fluorescence (SR-XRF) analyses of metallointercalator-treated A549 cells showed that platinum became localised in DNA-rich regions of the nucleus. In contrast, when the same cells were treated with cisplatin the metal became distributed throughout the cell. Determination of the maximum concentration of platinum present inside the cells using graphite furnace atomic absorption spectrophotometry (GFAAS) of platinum-treated cells suggested that there was greater uptake of [56MERR] compared to [56MESS] by the A549 cells, and that platinum uptake did not account for the greater toxicity of [56MESS], as assessed by the MTT assay. Electrospray ionization mass spectrometric (ESI-MS) and circular dichroism (CD) spectroscopic studies of solutions containing either [56MERR] or [56MESS], and a duplex hexadecamer molecule, showed the two metallointercalators displayed very similar affinity towards the nucleic acid. Overall these results indicate that the difference in cytotoxicity of the two platinum metallointercalators is probably the result of variations in their interactions with other cellular components.

Iron solubility related to particle sulfur content in source emission and ambient fine particles

The chemical factors influencing iron solubility (soluble iron/total iron) were investigated in source emission (e.g., biomass burning, coal fly ash, mineral dust, and mobile exhaust) and ambient (Atlanta, GA) fine particles (PM2.5). Chemical properties (speciation and mixing state) of iron-containing particles were characterized using X-ray absorption near edge structure (XANES) spectroscopy and micro-X-ray fluorescence measurements. Bulk iron solubility (soluble iron/total iron) of the samples was quantified by leaching experiments. Major differences were observed in iron solubility in source emission samples, ranging from low solubility (<1%, mineral dust and coal fly ash) up to 75% (mobile exhaust and biomass burning emissions). Differences in iron solubility did not correspond to silicon content or Fe(II) content. However, source emission and ambient samples with high iron solubility corresponded to the sulfur content observed in single particles. A similar correspondence between bulk iron solubility and bulk sulfate content in a series of Atlanta PM2.5 fine particle samples (N = 358) further supported this trend. In addition, results of linear combination fitting experiments show the presence of iron sulfates in several high iron solubility source emission and ambient PM2.5 samples. These results suggest that the sulfate content (related to the presence of iron sulfates and/or acid-processing mechanisms by H(2)SO(4)) of iron-containing particles is an important proxy for iron solubility.

β-Cell subcellular localization of glucose-stimulated Mn uptake by X-ray fluorescence microscopy: implications for pancreatic MRI

Manganese (Mn) is a calcium (Ca) analog that has long been used as a magnetic resonance imaging (MRI) contrast agent for investigating cardiac tissue functionality, for brain mapping and for neuronal tract tracing studies. Recently, we have extended its use to investigate pancreatic β-cells and showed that, in the presence of MnCl(2), glucose-activated pancreatic islets yield significant signal enhancement in T(1)-weigheted MR images. In this study, we exploited for the first time the unique capabilities of X-ray fluorescence microscopy (XFM) to both visualize and quantify the metal in pancreatic β-cells at cellular and subcellular levels. MIN-6 insulinoma cells grown in standard tissue culture conditions had only a trace amount of Mn, 1.14 ± 0.03 × 10(-11)µg/µm(2), homogenously distributed across the cell. Exposure to 2 mM glucose and 50 µM MnCl(2) for 20 min resulted in nonglucose-dependent Mn uptake and the overall cell concentration increased to 8.99 ± 2.69 × 10(-11) µg/µm(2). When cells were activated by incubation in 16 mM glucose in the presence of 50 µM MnCl(2), a significant increase in cytoplasmic Mn was measured, reaching 2.57 ± 1.34 × 10(-10) µg/µm(2). A further rise in intracellular concentration was measured following KCl-induced depolarization, with concentrations totaling 1.25 ± 0.33 × 10(-9) and 4.02 ± 0.71 × 10(-10) µg/µm(2) in the cytoplasm and nuclei, respectively. In both activated conditions Mn was prevalent in the cytoplasm and localized primarily in a perinuclear region, possibly corresponding to the Golgi apparatus and involving the secretory pathway. These data are consistent with our previous MRI findings, confirming that Mn can be used as a functional imaging reporter of pancreatic β-cell activation and also provide a basis for understanding how subcellular localization of Mn will impact MRI contrast.

Submicron hard X-ray fluorescence imaging of synthetic elements

Synchrotron-based X-ray fluorescence microscopy (XFM) using hard X-rays focused into sub-micron spots is a powerful technique for elemental quantification and mapping, as well as microspectroscopic measurements such as μ-XANES (X-ray absorption near edge structure). We have used XFM to image and simultaneously quantify the transuranic element plutonium at the L(3) or L(2)-edge as well as Th and lighter biologically essential elements in individual rat pheochromocytoma (PC12) cells after exposure to the long-lived plutonium isotope (242)Pu. Elemental maps demonstrate that plutonium localizes principally in the cytoplasm of the cells and avoids the cell nucleus, which is marked by the highest concentrations of phosphorus and zinc, under the conditions of our experiments. The minimum detection limit under typical acquisition conditions with an incident X-ray energy of 18 keV for an average 202 μm(2) cell is 1.4 fg Pu or 2.9×10(-20) moles Pu μm(-2), which is similar to the detection limit of K-edge XFM of transition metals at 10 keV. Copper electron microscopy grids were used to avoid interference from gold X-ray emissions, but traces of strontium present in naturally occurring calcium can still interfere with plutonium detection using its L(α) X-ray emission.

The role of CAX1 and CAX3 in elemental distribution and abundance in Arabidopsis seed

The ability to alter nutrient partitioning within plants cells is poorly understood. In Arabidopsis (Arabidopsis thaliana), a family of endomembrane cation exchangers (CAXs) transports Ca(2+) and other cations. However, experiments have not focused on how the distribution and partitioning of calcium (Ca) and other elements within seeds are altered by perturbed CAX activity. Here, we investigate Ca distribution and abundance in Arabidopsis seed from cax1 and cax3 loss-of-function lines and lines expressing deregulated CAX1 using synchrotron x-ray fluorescence microscopy. We conducted 7- to 10-μm resolution in vivo x-ray microtomography on dry mature seed and 0.2-μm resolution x-ray microscopy on embryos from lines overexpressing deregulated CAX1 (35S-sCAX1) and cax1cax3 double mutants only. Tomograms showed an increased concentration of Ca in both the seed coat and the embryo in cax1, cax3, and cax1cax3 lines compared with the wild type. High-resolution elemental images of the mutants showed that perturbed CAX activity altered Ca partitioning within cells, reducing Ca partitioning into organelles and/or increasing Ca in the cytosol and abolishing tissue-level Ca gradients. In comparison with traditional volume-averaged metal analysis, which confirmed subtle changes in seed elemental composition, the collection of spatially resolved data at varying resolutions provides insight into the impact of altered CAX activity on seed metal distribution and indicates a cell type-specific function of CAX1 and CAX3 in partitioning Ca into organelles. This work highlights a powerful technology for inferring transport function and quantifying nutrient changes.

The role of CAX1 and CAX3 in elemental distribution and abundance in Arabidopsis seed

The ability to alter nutrient partitioning within plants cells is poorly understood. In Arabidopsis (Arabidopsis thaliana), a family of endomembrane cation exchangers (CAXs) transports Ca(2+) and other cations. However, experiments have not focused on how the distribution and partitioning of calcium (Ca) and other elements within seeds are altered by perturbed CAX activity. Here, we investigate Ca distribution and abundance in Arabidopsis seed from cax1 and cax3 loss-of-function lines and lines expressing deregulated CAX1 using synchrotron x-ray fluorescence microscopy. We conducted 7- to 10-μm resolution in vivo x-ray microtomography on dry mature seed and 0.2-μm resolution x-ray microscopy on embryos from lines overexpressing deregulated CAX1 (35S-sCAX1) and cax1cax3 double mutants only. Tomograms showed an increased concentration of Ca in both the seed coat and the embryo in cax1, cax3, and cax1cax3 lines compared with the wild type. High-resolution elemental images of the mutants showed that perturbed CAX activity altered Ca partitioning within cells, reducing Ca partitioning into organelles and/or increasing Ca in the cytosol and abolishing tissue-level Ca gradients. In comparison with traditional volume-averaged metal analysis, which confirmed subtle changes in seed elemental composition, the collection of spatially resolved data at varying resolutions provides insight into the impact of altered CAX activity on seed metal distribution and indicates a cell type-specific function of CAX1 and CAX3 in partitioning Ca into organelles. This work highlights a powerful technology for inferring transport function and quantifying nutrient changes.