1,720,967 research outputs found
Selenium biochemistry and its role for human health
Get PDFDespite its very low level in humans, selenium plays an important and unique role among the (semi)metal trace essential elements because it is the only one for which incorporation into proteins is genetically encoded, as the constitutive part of the 21st amino acid, selenocysteine. Twenty-five selenoproteins have been identified so far in the human proteome. The biological functions of some of them are still unknown, whereas for others there is evidence for a role in antioxidant defence, redox state regulation and a wide variety of specific metabolic pathways. In relation to these functions, the selenoproteins emerged in recent years as possible biomarkers of several diseases such as diabetes and several forms of cancer. Comprehension of the selenium biochemical pathways under normal physiological conditions is therefore an important requisite to elucidate its preventing/therapeutic effect for human diseases. This review summarizes the most recent findings on the biochemistry of active selenium species in humans, and addresses the latest evidence on the link between selenium intake, selenoproteins functionality and beneficial health effects. Primary emphasis is given to the interpretation of biochemical mechanisms rather than epidemiological/observational data. In this context, the review includes the following sections: (1) brief introduction; (2) general nutritional aspects of selenium; (3) global view of selenium metabolic routes; (4) detailed characterization of all human selenoproteins; (5) detailed discussion of the relation between selenoproteins and a variety of human diseases
Fast speciation analysis of selenoproteins in a micro-drop of human serum by microbore affinity-HPLC hyphenated to ICP-sector field-MS
No full textFor the rst time a new ecient analytical approach based on microbore AF-HPLC hyphenated
to ICP-sector eld MS is proposed for the simultaneous speciation analysis of the selenoproteins
glutathione peroxidase, selenoprotein P and seleno-albumin in human serum without prior sam-
ple preparation or mathematical correction of the spectral interferences. Microbore AF-HPLC
allows the reduction of sample volume to a single micro-drop (5 L) and the decrease of chro-
matographic run time to 7 min. A high-eciency sample introduction system is also proposed
to achieve an enhancement in sensitivity of more than one order of magnitude
Elemental speciation analysis, from environmental to biochemical challenge
No full textInformation regarding the distribution of
metallic/metalloid chemical species in biological compartments is required
for understanding their biochemical impact on living organisms. To obtain
such information implies the use of a dedicated measurement approach, namely
speciation analysis. The current trend in (elemental) speciation analysis regards bioinorganic
applications. New analytical methodologies are therefore necessary for
identification, detection and characterization of metal(loids) complexed or
incorporated into biomolecules. The established element-speciation
approaches developed for the determination of low molecular mass metal(loid)
species (e.g. organometallic compounds) in environmental, food,
toxicological and health sciences are presently being adapted for the
determination of high molecular mass metal-species, generally related to
biological processes. This is one of the newest approaches in terms of
element speciation and is called metallomics; this concept refers to the totality of
metal species in a cell and covers the inorganic element content and the
ensemble of its complexes with biomolecules, particularly proteins,
participating in the organisms' response to beneficial or harmful
conditions. Compared to conventional elemental speciation analysis, the
approach applied to bioinorganic analysis is challenging, particularly given
the difficulties in identification/characterization of the organic (e.g.
protein) content of such species. In addition, quantification is not
feasible with the conventional approaches, which led to the exploitation of
the unique feature of (post-column) online isotope dilution-mass
spectrometry for species quantification in metallomics
Towards method validation for selenium speciation analysis in human serum
No full textSe is one of the most investigated trace essential elements in the last years, mostly due to its cancer prevention properties. Nevertheless, the accurate determination of its biologically active species present in human serum, such as selenoproteins (SeProt), is currently a challenging task. This is because of the lack of appropriate quantification standards, certified reference materials (CRMs) and/or reference measurement methods. Additionally, most of the methods developed so far for the determination of SeProt in human serum were applied to the analysis of control (volunteers) serums, which are not available to other laboratories, therefore making the method inter-comparison virtually impossible. We present here for the first time indicative levels of SeProt in a commercially available human serum, namely the BCR-637 CRM (with certified level of total Se). The selenium levels associated with glutathione peroxidase (GPx), selenoprotein P (SelP) and selenoalbumin (SeAlb) in this serum were calculated by means of the results obtained by using 13 different analytical methods on the basis of (double column) affinity HPLC coupled to ICP-MS. The indicative levels of SeProt in the BCR-637 serum can be used as preliminary reference values for validation of methods dealing with the determination of SeProt in human serum
Speciation analysis of selenoproteins in human serum by microbore affinity-HPLC hyphenated with ICP-SFMS using a high efficiency sample introduction system
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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