1,721,083 research outputs found
Reduction of senescence‐associated beta‐galactosidase activity by vitamin E in human fibroblasts depends on subjects’ age and cell passage number
No full textCell senescence is due to the permanent cell cycle arrest that occurs as a result of the inherent limited replicative capacity toward the Hayflick limit (replicative senescence), or in response to various stressors (stress‐induced premature senescence, SIPS). With the acquisition of the senescence‐associated secretory phenotype (SASP), cells release several molecules (cytokines, proteases, lipids), and express the senescence‐associated beta‐galactosidase (SA‐β‐Gal). Here we tested whether vitamin E affects SA‐β‐Gal in an in vitro model of cell ageing. Skin fibroblasts from human subjects of different age (1, 13, 29, 59, and 88 years old) were cultured until they reached replicative senescence. At different passages (Passages 2, 9, 13, and 16), these cells were treated with vitamin E for 24 hr. Vitamin E reduced SA‐β‐Gal in all cells at passage 16, but at earlier passage numbers it reduced SA‐β‐Gal only in cells isolated from the oldest subjects. Therefore, short time treatment with vitamin E decreases SA‐β‐Gal in cells both from young and old subjects when reaching replicative senescence; but in cells isolated from older subjects, a decrease in SA‐β‐Gal by vitamin E occurs also at earlier passage numbers. The possible role of downregulation of CD36 by vitamin E, a scavenger receptor essential for initiation of senescence and SASP, is discussed
Tocopherol-binding proteins: their function and physiological significance.
No full textThe present review is a continuation of earlier essays on the uptake mechanisms and the biological function of vitamin E. There are eight naturally occurring homologues of vitamin E, which differ in their structure and in biological activity in vivo and in vitro. Various studies have suggested that after normal gastrointestinal absorption of dietary vitamin E specific mechanisms favor the preferential accumulation of one of its homologues, alpha-tocopherol, in the human body. This process is thought to be mediated in part by the alpha-tocopherol transfer protein (alpha-TTP) in the liver cytoplasm. The mechanism and pathway by which alpha-TTP specifically incorporates alpha-tocopherol into plasma lipoproteins is not yet fully understood. Because alpha-tocopherol is widely distributed in tissues in various concentrations but alpha-TTP resides only in liver, its role as intracellular carrier of alpha-tocopherol seems unlikely. However, recent data indicate that a system of alpha-tocopherol-binding proteins is involved in these processes that favor the localization of alpha-tocopherol at the sites where it is required. The current status of the evidence for the regulation of alpha-tocopherol levels and their impact on cellular signaling is discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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