1,720,957 research outputs found
Modulation of ion channels by natural products - identification of hERG channel inhibitors and GABAA receptor ligands from plant extracts
Full text linkIon channels are expressed in virtually all cell types in the human body and are involved in various physiological processes. Hence, it is not surprising that ion channels play an important role in modern drug discovery. Lead compounds are nowadays routinely tested against a panel of ion channels to evaluate selectivity and potential off-target activities.
The human ether-à-go-go-related gene (hERG) channel, a voltage-gated potassium channel, is the currently most critical antitarget with respect to cardiac safety. Inhibition of the hERG channel can prolong the QT interval on the electrocardiogram (ECG) and, as a consequence, lead to life-threatening arrhythmia. Considering the daily intake of plant-derived foods and herbal products, surprisingly few natural products have been tested for hERG blocking properties. In the course of an interdisciplinary hERG project, a selection of widely used herbal drugs and dietary plants was screened by means of a two-microelectrode voltage-clamp assay with Xenopus oocytes. Moderate hERG block was observed for the traditional Chinese herbal drug Coptidis rhizoma and black pepper fruits, and successfully tracked by HPLC-based activity profiling to dihydroberberine and piperine, respectively. The hERG blocking activity of cinnamon, guarana, and nutmeg, in contrast, was attributed to tannins. Our screening data suggest that major European medicinal plants and frequently consumed food plants are associated with a low risk for hERG inhibition. However, the case of Coptidis rhizoma pointed towards a need for a more thorough assessment of herbal drugs of the traditional Chinese medicine (TCM). Subsequent screening of a plant-derived alkaloid library led to the identification of several potent hERG blockers. Further investigations are certainly warranted to assess the cardiac safety profile of these alkaloids.
Dehydroevodiamine (DHE), a major bioactive constituent of the traditional Chinese herbal drug Evodiae fructus, has been previously shown to inhibit several cardiac ion currents in vitro. For further evaluation of its in vivo pharmacological and toxicological properties, gram amounts of DHE were needed. Since DHE is not commercially available, we developed an efficient method for its gram-scale isolation from a crude Evodia extract. Our approach is based on a combination of cation-exchange chromatography and preparative RP-HPLC. Moreover, the DHE content in commercially available Evodia products was assessed by HPLC-PDA analysis. A daily intake of up to mg amounts of DHE was calculated from recommended doses of these products. We also devised a procedure for the production of DHE-depleted Evodia products, should DHE indeed turn out to be toxicologically relevant.
The gamma-aminobutyric acid type A (GABAA) receptor, a ligand-gated chloride channel, mediates fast inhibitory neurotransmission in the central nervous system (CNS), and is thus a clinically important drug target. In the search for positive α1β2γ2S GABAA receptor modulators of plant origin, we investigated an extract of Curcuma kwangsiensis rhizomes. HPLC-based activity profiling was used in combination with a two-microelectrode voltage-clamp assay on Xenopus oocytes to identify the active constituents. Targeted isolation afforded a series of 11 structurally related labdane diterpenoids, including four new natural products. Structure elucidation was achieved by comprehensive analysis of HR-ESI-TOF-MS and NMR data. The absolute configuration of the compounds was assigned by electronic circular dichroism (ECD). The highest GABAA receptor modulating activity was observed for zerumin A.
From a more general perspective, this study demonstrates that HPLC-based activity profiling is an effective strategy to characterize bioactive compounds in crude natural extracts
Editorial: Ethnopharmacology in Central and Eastern Europe in the Context of Global Research Developments
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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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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