Yuxi Gao

Potential neurological lesion after nasal instillation of TiO2 nanoparticles in the anatase and rutile crystal phases

Nanoscale titanium dioxide (TiO(2)) is massively produced and widely used in living environment, which hence make the potential risk to human health. Central nervous system (CNS) is the potential susceptible target of inhaled nanoparticles, but the studies on this aspect are limited so far. We report the accumulation and toxicity results in vivo of two crystalline phases of TiO(2) nanoparticles (80nm, rutile and 155nm, anatase; purity >99%). The female mice were intranasally instilled with 500microg of TiO(2) nanoparticles suspension every other day for 30 days. Synchrotron radiation X-ray fluorescence analysis (SRXRF) and inductively coupled plasma mass spectrometry (ICP-MS) were used to determine the contents of titanium in murine brain. Then, the pathological examination of brain tissue, oxidative stress-mediated responses, and levels of neurochemicals in the brain of exposed mice were also analyzed. The obvious morphological changes of hippocampal neurons and increased GFAP-positive astrocytes in the CA4 region were observed, which were in good agreements with higher Ti contents in the hippocampus region. Oxidative stress occurred obviously in whole brain of exposed mice such as lipid peroxidation, protein oxidation and increased activities of catalase, as well as the excessive release of glutamic acid and nitric oxide. These findings indicate anatase TiO(2) nanoparticles exhibited higher concern on some tested biological effects. To summarize, results provided the preliminary evidence that nasal instilled TiO(2) nanoparticles could be translocated into the central nervous system and cause potential lesion of brain, and the hippocampus would be the main target within brain.

Elimination efficiency of different reagents for the memory effect of mercury using ICP-MS

The present study was carried out to solve the problems of long washout time and non-linear calibration curves encountered in mercury analysis using inductively coupled plasma mass spectrometry. Comparisons of the washing efficiency for different reagents to eliminate the mercury memory effect were made. Of all the selected washing reagents, mercapto reagents such as 2-mercaptoethanol and L-cysteine could efficiently clean the instrument. Taking the toxicity and odor of mercaptoalkanol into account, L-cysteine was preferred as the most suitable washing reagent and was added into the standard and sample solutions. A good linear calibration curve was obtained with the correlation coefficient of 0.9999. The detetion limit for addition of L-cysteine was 0.024 μg l−1. Addition of 0.18% L-cysteine into the sample solution also facilitates the washout of mercury even using deionized water. The recoveries of mercury in certified reference materials, i.e. human hair and dogfish muscle, were 97.2% and 98.3%, respectively, when using 0.18% L-cysteine in the sample solutions.

Mapping technique for biodistribution of elements in a model organism, Caenorhabditis elegans, after exposure to copper nanoparticles with microbeam synchrotron radiation X-ray fluorescence

To investigate the toxicological effects of nanomaterials, experimental studies on the absorption and accumulation in organisms are of broad interest. In the present study, Caenorhabditis elegans (C. elegans) was used as a “model” organism to investigate the bioaccumulation and toxicological effects of engineered copper nanoparticles with a scanning technique of microbeam synchrotron radiation X-ray fluorescence (μ-SRXRF). The adult hermaphrodite is anatomically simple with 959 somatic cells and 1 mm in length. The mapping results of the whole organism indicate that the exposure to copper nanoparticles can result in an obvious elevation of Cu and K levels, and a change of bio-distribution of Cu in nematodes. Accumulation of Cu occurs in the head and at a location 1/3 of the way up the body from the tail compared to the un-exposed control. In contrast, a higher amount of Cu was detected in other portion of worm body, especially in its excretory cells and intestine when exposed to Cu2+. The results compared well with total Cu levels in nematodes, which were 4.10 ± 0.54, 12.32 ± 0.49 and 5.22 ± 0.63 μg g−1 dry weight for the PBS, Cu2+ and Cu nanoparticle groups, respectively, measured by ICP-MS. The nondestructive and multi-elemental μ-SRXRF provides an important tool for mapping the elemental distribution in the whole body of a single tiny nematode at lower levels.

Organic selenium supplementation increases mercury excretion and decreases oxidative damage in long-term mercury-exposed residents from Wanshan, China.

Due to a long history of extensive mercury mining and smelting activities, local residents in Wanshan, China, are suffering from elevated mercury exposure. The objective of the present study was to study the effects of oral supplementation with selenium-enriched yeast in these long-term mercury-exposed populations. One hundred and three volunteers from Wanshan area were recruited and 53 of them were supplemented with 100 μg of organic selenium daily as selenium-enriched yeast while 50 of them were supplemented with the nonselenium-enriched yeast for 3 months. The effects of selenium supplementation on urinary mercury, selenium, and oxidative stress-related biomarkers including malondialdehyde and 8-hydroxy-2-deoxyguanosine were assessed. This 3-month selenium supplementation trial indicated that organic selenium supplementation could increase mercury excretion and decrease urinary malondialdehyde and 8-hydroxy-2-deoxyguanosine levels in local residents.

Detection of metalloproteins in human liver cytosol by synchrotron radiation X-ray fluorescence after sodium dodecyl sulphate polyacrylamide gel electrophoresis

An improved method of analysis of metals in protein bands with synchrotron radiation X-ray fluorescence (SRXRF) after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) separation is introduced and applied to human liver cytosol. Through a step of drying the gel before SRXRF determination, the continuous background resulting mainly from the Compton-scattering of X-rays by the gel matrix was substantially reduced, and the detection of biological trace elements, such as Cu, Fe, and Zn in protein bands was thereby made possible. With the new procedure, six Zn-containing proteins with molecular weights (MWs) of 17.5, 20.5, 27, 35, 55, and 63 kDa, respectively were found in human liver cytosol, among which the 63 kDa Zn-containing band was shown to be the dominant form of zinc. In addition, at least four Fe containing proteins with MWs of 20, 23, 43, and 83.5 kDa, respectively, were present in the samples. The metal contents in some metalloproteins, such as the 63 kDa Zn-containing protein, the 23 and 83.5 kDa Fe-containing proteins, and a 22 kDa Cu-containing protein were more closely related to the metal level in the sample. It is demonstrated that the procedure could be widely used to further investigate metal-binding proteins in biological samples

Selenium inhibits the phytotoxicity of mercury in garlic (Allium sativum)

To investigate the influence of selenium on mercury phytotoxicity, the levels of selenium and mercury were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) in garlic tissues upon exposure to different dosages of inorganic mercury (Hg(2+)) and selenite (SeO3(2-)) or selenate (SeO4(2-)). The distributions of selenium and mercury were examined with micro-synchrotron radiation X-ray fluorescence (μ-SRXRF), and the mercury speciation was investigated with micro-X-ray absorption near edge structure (μ-XANES). The results show that Se at higher exposure levels (>1mg/L of SeO3(2-) or SeO4(2-)) would significantly inhibit the absorption and transportation of Hg when Hg(2+) levels are higher than 1mg/L in culture media. SeO3(2-) and SeO4(2-) were found to be equally effective in reducing Hg accumulation in garlic. The inhibition of Hg uptake by Se correlates well with the influence of Se on Hg phytotoxicity as indicated by the growth inhibition factor. Elemental imaging using μ-SRXRF also shows that Se could inhibit the accumulation and translocation of Hg in garlic. μ-XANES analysis shows that Hg is mainly present in the forms of Hg-S bonding as Hg(GSH)2 and Hg(Met)2. Se exposure elicited decrease of Hg-S bonding in the form of Hg(GSH)2, together with Se-mediated alteration of Hg absorption, transportation and accumulation, may account for attenuated Hg phytotoxicity by Se in garlic.

Advanced nuclear analytical techniques for metalloproteomics

Metalloproteomics is an emerging scientific field. It is focused to investigate the distributions and compositions of all metalloproteins in a proteome, their structural and functional characterization and their structural metal-binding moieties. Various nuclear analytical techniques, such as neutron activation analysis, X-ray fluorescence, isotope tracer, Mossbauer spectrometry, X-ray absorption spectrometry and neutron scattering and diffraction, are powerful tools to study a number of the basic issues in metalloproteomics. In this paper, the applications of the advanced nuclear techniques in this field are selectively outlined, along with their advantages and limitations.

Simultaneous speciation of selenium and mercury in human urine samples from long-term mercury-exposed populations with supplementation of selenium-enriched yeast by HPLC-ICP-MS

The present study was carried out to establish a method for simultaneous speciation analysis of selenium and mercury. Batch-wise elution using two different mobile phases that are suitable for selenium and mercury speciation leads to successful determination of both selenium and mercury standards in 30 minutes with good efficiency and resolution. The detection limits are in the range of 0.05–0.3 μg L−1 for selenium species, except TMSe, which has a poorer detection limit (1.48 μg L−1), and 2.5 μg L−1 for inorganic mercury (Hg2+) and 2.0 μg L−1 for organic mercury (CH3Hg+). The method was applied to analysis of urine samples from people who were long-term mercury exposed and supplemented with selenium-enriched yeast for 90 days. Selenocystine (SeCys) was found to be a major selenium form, while inorganic mercury is the major mercury form. The recoveries of spiked species were between 93 and 117% in all cases. The increased mercury concentrations in urine after 90-day selenium supplementation suggest that selenium is beneficial to the excretion of mercury from urine. The proposed technique may help to increase our understanding of the in vivo interaction between selenium and mercury in human body.

Detection of metalloproteins in human liver cytosol by synchrotron radiation X-ray fluorescence combined with gel filtration chromatography and isoelectric focusing separation

Synchrotron radiation X-ray fluorescence (SRXRF) spectroscopy is an advanced method of quantitative multielemental analysis with space resolution of several microm and sensitivities in the microg g(-1) range. It can be used for keeping track of trace elements after an electrophoretic separation of biological samples. In this paper, proteins in human liver cytosol were separated with gel filtration chromatography and thin layer isoelectric focusing (IEF). The contents of metal ions in protein bands were determined by SRXRF. The results showed that in the molecular weight (MW) range of 10 approximately 25 kDa, there were at least 2 Zn-containing bands with isoelectric point (pI) of 5 approximately 6 and 6.2 approximately 7, respectively and about 11 Fe-containing proteins with pI of 4.4, 4.6, 4.8, 5.0, 5.2, 5.3, 5.5, 5.6, 6.6, 6.8, and 7.2, respectively, present in human liver cytosol. The Zn-containing band with pI of 5-6 is the dominant species of zinc in this MW range. In addition, the Cu-containing bands with pI of 5.0 and below 4.8 were also detected. It is demonstrated that the procedure could be widely used in further investigations of the chemical species of trace elements in biological samples.

Mercury modulates selenium activity via altering its accumulation and speciation in garlic (Allium sativum)

Combined pollution of selenium (Se) and mercury (Hg) has been known in Wanshan district (Guizhou Province, China). A better understanding of how Se and Hg interact in plants and the phytotoxicity thereof will provide clues about how to avoid or mitigate adverse effects of Se/Hg on local agriculture. In this study, the biological activity of Se has been investigated in garlic with or without Hg exposure. Se alone can promote garlic growth at low levels (<0.1 mg L(-1)), whereas it inhibits garlic growth at high levels (>1 mg L(-1)). The promotive effect of Se in garlic can be enhanced by low Hg exposure (<0.1 mg L(-1)). When both Se and Hg are at high levels, there is a general antagonistic effect between these two elements in terms of phytotoxicity. Inductively coupled plasma mass spectrometry (ICP-MS) data suggest that Se is mainly concentrated in garlic roots, compared to the leaves and the bulbs. Se uptake by garlic in low Se medium (<0.1 mg L(-1)) can be significantly enhanced as Hg exposure levels increase (P < 0.05), while it can be inhibited by Hg when Se exposure levels exceed 1 mg L(-1). The synchrotron radiation X-ray fluorescence (SRXRF) mapping further shows that Se is mainly concentrated in the stele of the roots, bulbs and the veins of the leaves, and Se accumulation in garlic can be reduced by Hg. The X-ray absorption near edge structure (XANES) study indicates that Se is mainly formed in C-Se-C form in garlic. Hg can decrease the content of inorganic Se mainly in SeO3(2-) form in garlic while increasing the content of organic Se mainly in C-Se-C form (MeSeCys and its derivatives). Hg-mediated changes in Se species along with reduced Se accumulation in garlic may account for the protective effect of Hg against Se phytotoxicity.