1,721,061 research outputs found
Simultaneous HS-SPME GC-MS determination of short chain fatty acids, trimethylamine and trimethylamine N-oxide for gut microbiota metabolic profile
No full textTrimethylamine (TMA), trimethylamine-N-oxide (TMAO) and short chain fatty acids (SCFAs), as acetic, propionic, butyric and valeric acids are among the most important products of the gut microbiota (GM) metabolism. The present study is aimed at the determination of TMA, TMAO and SCFAs by a double step headspace-solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) analysis, allowing the simultaneous quantitation of both the acidic and basic metabolites in faecal samples. TMAO amount was evaluated after its reduction to TMA by using Fe(II)-EDTA complex as a reagent. Under the fully validated experimental conditions, adequate sensitivity (LOQ 0.011–0.23 μmol g−1), good accuracy (79 – 110%) and precision (CV% < 11%) were achieved for all the target analytes. The presented method is successfully applied to the quantitation of the considered gut metabolites in faecal samples from Italian healthy volunteers
Study on the photostability of guaiazulene by high-performance liquid chromatography/mass spectrometry and gas chromatography/mass spectrometry
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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
Analysis of fecal bile acids and metabolites by high resolution mass spectrometry in farm animals and correlation with microbiota
Full text linkThere is a growing interest in the named "acidic sterolbiome" and in the genetic potential of the gut microbiome (GM) to modify bile acid (BA) structure. Indeed, the qualitative composition of BAs in feces correlates with the bowel microorganisms and their collective genetic material. GM is responsible for the production of BA metabolites, such as secondary and oxo-BAs. The specific BA profiles, as microbiome-host co-metabolic products, could be useful to investigate the GM-host interaction in animals under physiological conditions, as well as in specific diseases. In this context, we developed and validated an ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry method for the simultaneous analysis of up to 21 oxo-BAs and their 9 metabolic precursors. Chromatographic separation was achieved in 7 min with adequate analytical performance in terms of selectivity, sensitivity (LOQ from 0.05 to 0.1 mu g/mL), accuracy (bias% < 5%), precision (CV% < 5%) and matrix effect (ME% < 10%). A fast solvent extraction protocol has been fine-tuned, achieving recoveries > 90%. In parallel, the gut microbiota assessment in farming animals was evaluated by 16S rRNA next-generation sequencing, and the correlation with the BA composition was performed by multivariate analysis, allowing to reconstruct species-specific associations between the BA profile and specific GM components
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
Analytical approaches in Alzheimer’s disease Drug Discovery
No full textThe research efforts in drug discovery field are based on the knowledge of the molecular aspects of the disease and on the development of new techniques necessary to investigate the biological
systems at molecular level. The selection of new leads is therefore a challenging task and involve
various essential steps, the first being the identification/validation of new targets, then the
selection of molecules able to bind to the target(s), and finally the study of the effects of hitting
the target at molecular, cellular and whole animal level. In the case of Alzheimer’s disease (AD), the
most common form of dementia in adults, acetylcholinesterase (AChE) has been the first target for
the development of new drugs since the discovery of the cholinergic deficit in the central nervous
system. However, basic research showed that cognitive impairment could be due not only to a
cholinergic deficit but also to a cascade of biochemical events leading to the accumulation in the
brain of proteins such as ß-amyloid (Ab) and hyper-phosphorylated tau protein. Important targets
are amyloid fibrillogenesis, beta-secretase (BACE1), one of the enzymes which cleave APP (amyloid
precursor protein) and GSK3b, a tau protein phosphorylating kinase. On the other hand, other
non cholinergic role of AChE in the AD has been discovered: some evidences suggest that AChE
peripheral binding site may play a key role in the development of senile plaques, accelerating
Ab deposition. Once the disease targets have been selected, the determination of the activity of
the new compounds must be carried out quickly and in a way that allows the verification of the
design hypothesis. Drug activity is in fact mediated by different types of interactions with specific
biological targets and the esteem of these interactions may elucidate the mechanism of action.
To this aim, in a first instance, high throughput screening methods (HTS) of a large number of
compounds for the selection of few lead compounds are required. Secondly, specific methods,
which elucidate the selected compound mechanism of action, must be employed, before the
ultimate and most advanced tools, transgenic animal models of the disease, can be used to study
the effects of single compounds on the disease phenotype.
Here we report the development of purposely designed integrated methodologies to define the
multifunctional activity profile for new AD drug discovery. With regard to the assessment of the
activity of chemical libraries, the affinity chromatography on HPLC immobilized-enzyme column (or
immobilized enzyme reactors, IMER) is one of most promising methodologies for HTS applications.
Human recombinant AChE and BACE1 monolithic micro-IMERs (immobilized enzyme reactor)
have been developed for on-line automated HT HPLC inhibition studies (IC50 and mechanism of
inhibition); secondly, fluorometric, circular dichroism, mass spectrometry, AFM methods were
optimised for monitoring the inhibition of AChE-induced Ab fibril formation and the inhibition
of spontaneous Ab aggregation, elucidating at which intermediate level of the Ab aggregation
cascade the inhibitors halt the process (monomer, soluble oligomers, protofibrils, fibrils). Finally,
mass spectrometry combined with UHPLC was applied to investigate the mechanism of action of
GSK3b inhibitors. By the application of these integrated approaches, new leads as the prototype
of new classes of multifunctional compounds for AD treatment were discovered
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