1,720,999 research outputs found
Natural and naturally-derived compounds as new chemopreventive agents
Full text linkChemoprevention is an approach based on the use of natural or synthetic compounds to inhibit, suppress or reverse the development and progression of cancer. In order to overcome the cancer disease, the identification of chemopreventive compounds is of particular interest. Among them, antimutagens prevent the mutagen-induced DNA-injury or promote the repair and/or the reversion of damage. In addition to antimutagenicity, some agents also act as chemosensitizers, by increasing the effectiveness of cancer chemotherapy and radiotherapy, when used in combination with chemotherapeutical agents. This approach is very interesting to prevent the development of multidrug resistance (MDR), which makes cancer cells not-sensitive to a broad range of drugs. In this context, present study was aimed at evaluating the potential chemopreventive properties of some natural and naturally-derived compounds, particularly the sesquiterpenes β-caryophyllene (CRY) and β-caryophyllene oxide (CRYO), and the aldehyde α-hexylcinnamal (HCA). The antimutagenic activity was evaluated by the reverse bacterial mutation assay (Ames test), on different strains of Salmonella typhimurium and Escherichia coli, both in absence and presence of the S9-metabolic activation system. As mutagens, 2- nitrofluorene (2NF), sodium azide (SA), methyl methanesulfonate (MMS), 2-aminoanthracene (2AA), benzo[a]pyrene (BaP), 4-nitroquinoline N-oxide (4NQO), 1-nitropyrene (1NP), 1,8-dinitropyrene (1,8-DNP) and a sample of condensed smoke (CSC) from standard 3R4F cigarette were used. In addition to antimutagenicity studies, the potential chemosensitizing properties of CRY, CRYO and HCA and their ability to interfere with ABC-transporter function were evaluated, in Caco-2, CEM/ADR5000 and CCRF/CEM human cancer cells. For each compound, low concentrations (IC10 and IC20) were assayed in order to verify their potential additive, synergistic or antagonistic effects with the anticancer doxorubicin. The nature and the extent of the interaction were evaluated by the combination index (CI) and the isobologram analysis, respectively; conversely, the potential enhancement of drug effectiveness was quantified by cytotoxicity enhancement ratio (RR). The interaction between test compounds and ABC-transporters was studied by the rhodamine 123 assay. HCA exhibited an antimutagenic activity against different nitro-compounds and in various experimental protocols, suggesting the involvement of both desmutagenic and bioantimutagenic mechanisms. The sesquiterpenes CRY and CRYO resulted able to inhibit the mutagenicity of CSC, although with different potency and specificity: CRYO was the most potent compound, acting at concentrations about ten-times lower than CRY. The antimutagenicity was highlighted in different strains and in all experimental protocols, suggesting the overlapping of various protective mechanisms; the inhibition of CSC-induced oxidative stress seems to be likely and deserves further investigations. In human cancer cells, the substances produced cytotoxic effects at high concentrations both in resistant and in sensitive cell lines: HCA was the most effective substance, especially in the sensitive CCRF-CEM cells. All the compounds synergistically acted with doxorubicin, although HCA was the most potent: IC20 HCA increased the doxorubicin cytotoxicity of about six, seven and fourthy-seven folds, in Caco-2, CEM/ADR5000, and CCRF-CEM, respectively. In addition, a remarkable inhibition of ABCtrasporter was produced by HCA in the cancer cells tested: the effect was higher than that of the standard inhibitior verapamil. Also CRY and CRYO inhibited the ABC transporters but with lower potency than verapamil. The antimutagenic and chemosensitizing properties of β-caryophyllene, β-caryophyllene oxide and the α-hexylcinnamaldehyde deserves attention and represent a starting point to better evaluate their potential applications in the field of chemoprevention
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
The effect of chronic nandrolone decanoate treatment on emotional behavior and neurochemical changes in rats
No full textVariations 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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