1,720,973 research outputs found
Detoxication of microcystins mediated by human GSTs: comparison among variants with different hydrophilicity
No full textIt has been hypothesized that kinetics can be a key determinant of (MC) congener-specific toxicity. The in vitro inhibition potency of PP1/PP2A by single MC is comparable: therefore, the toxicokinetic of MC seems to be the critical point to explain congener-dependent toxicity. Those variants, such as MC-LW and MC-YR, having hydrophobic amino acids (e.g. tyrosine, tryptophan) may be more cell permeable than MC-LR. Glutathione conjugation, occurring either spontaneously or catalyzed by GST, is the accepted main step in MC detoxification. Recently, we characterized the in vitro human conjugation of MC-LR and MC-RR showing some differences in the presence of GSH depletion. This study was carried out to understand possible dependence of detoxication reaction on lipophilicity. Using single human hepatic recombinant isoforms (GSTA1, A2, A4, M1, T1 T2, P1, and O1) and human liver cytosol (HLC, pool of 200 donors) the kinetic parameters Vmax, Km and Cli were calculated. The efficiencies of recombinant GSTs used are quite similar (0.022-0.066 pmolGSMCLW/( μgprot*min*μM and 0.048-0.09 pmolGSMC-YR/(μgprot*min*μM); the highest Cli were shown by GSTP1 and A1 for MC-LW and P1=O1>A1 for MC-YR. Since GSTA1 is the most abundant hepatic GST, it is expected to give the highest contribution to MCLW and MCYR detoxification. Using the HLC a typical saturation curve was evidenced for MC-LW whilst the reaction was still linear for MCYR. Beside the differences in the kinetic behavior, comparing in the Cli of MC-LR, MC-LW, MC-YR and MC-RR, the variants which is most efficiently detoxified is MC-RR, which is the least acutely toxic. Acknowledgements: This study was partially supported by : the European Food Safety Authority (EFSA) under the grant agreement no.GA/EFSA/SCER/2015/01
Phosmet: Cinetica di biotrasformazione mediata dalle isoforme del Citocromo P450 e interazione con il Chlorpyrifos
No full textI composti organofosforotionati (OPT) sono pesticidi ampiamente utilizzati e l’esposizione avviene sia a livello occupazionale sia per la popolazione generale, per la presenza di residui su derrate alimentari e presenza nell’ambiente. Gli OP hanno effetto neurotossici mediati dalla inibizione dell’acetilcolinesterasi per la desulfurazione del composto parentale al metabolita tossico oxon da parte del citocromo P450 (CYP), metabolita che viene poi detossificato da parte di esterasi come la paraoxonasi. L’interesse per questa classe di pesticidi è alta perché spesso l’esposizione è stata associata all’insorgenza di malattie neurodegenerative (es. Parkinson) o a problemi di del neurosviluppo per esposizione peri- e post-natale. In letteratura sono riportati vari studi sulla biotrasformazione di alcuni di OPT: i vari CYP possono formare il metabolita tossico oxon ma anche prodotti dealchilati, che sono privi di tossicità. La diversa struttura chimica degli OPT, lineari o aromatici, possono influenzare l’efficienza catalitica delle due reazioni (desulfurazione/ dealchilazione) e la disponibilità delle informazioni cinetiche è risultata fondamentale per poter costruire modelli PB-PK e fare estrapolazioni in vitro-in vivo. Nel presente lavoro è stato utilizzato il Phosmet, insetticida utilizzato non solo in agricoltura ma anche come antiparassitario per gli animali, un OPT per il quale al momento non sono disponibili informazioni tossicocinetiche. Mediante un approccio integrato con l’uso di singoli CYP ricombinanti, microsomi umani epatici (HLM) ed intestinali (HIM) si sono determinati i parametri cinetici (Vmax, Km e CLi) dei CYP coinvolti nella formazione del metabolita tossico phosmet-oxon utilizzando un metodo HPLC con gradiente MeOH:H2O. I dati sperimentali mostrano che le isoforme più efficienti nel bioattivare il phosmet sono quelle della famiglia 2C secondo il seguente ordine decrescente: 2C18>2C19>2C9≈1A1>1A2>2D6>3A4>2A6, differenziandosi così da molti altri OPT con struttura diversa, per i quali gli enzimi più attivi soprattutto alle basse concentrazioni erano il CYP1A2 e il 2B6. Ciò indica che pur appartenendo alla stessa famiglia, gli OPT hanno un comportamento cinetico non sempre comparabile. Utilizzando gli HLM, è stata ottenuta una classica curva di saturazione senza evidenze di un contributo relativo diverso di alcuni CYP alle varie concentrazioni, mentre gli HIM mostrano una curva di tipo allosterico, probabilmente dovuta alla predominanza nell’intestino del CYP3A4, non nuovo a questo tipo di comportamento cinetico cooperativo. Poiché esiste la possibilità che diversi OPT siano usati contemporaneamente, è stata anche valutata la possibile interazione metabolica tra phosmet e chlorpyrifos, considerando che la reazione di desulfurazione provoca l’inattività dell’isoforma coinvolta per inibizione suicida dovuta allo zolfo liberato, attraverso la misura della Ki (costante di inibizione).
Lo studio è stato parzialmente finanziato dalla Convenzione Istituto Superiore di Sanità-Ministero della Salute. Fasc 4S0
An integrated in vitro approach to study Microcystyn detoxification by Glutathione-S-Transferases: from toxicokinetic parameters to the possible identification of differently susceptible population groups
No full textDaily we are exposed to xenobiotics via the environment, water and food which can be toxic, in relation to the exposure dose. These substances are generally lipophilic, therefore organisms, as a defence, promote their excretion, through biotransformation or conjugation catalysed by specific enzymes as Glutathione-S-Transferases (GSTs) characterized by different polymorphic isoforms. Our work has been focused on the application of an integrated approach to study the in vitro detoxification (that is conjugation with glutathione mediated by GSTs) of two variants of Microcystins (MC), a group of natural hepatotoxic compounds with more than 100 congeners. MC are characterized by very similar structure but the difference in some amino-acidic groups leads to different in vivo toxicity. The in vitro inhibition potency of protein phosphatase by single MC congener, the first step of their mechanism of toxicity is comparable: therefore the toxicokinetic of MC seems to be the critical point to explain congener-dependent toxicity. Human hepatic recombinant isoforms (GST A1, A2, A4, M1, T1 T2, P1, and O1) were used followed by human hepatic cytosol, where all the isoforms are present. The different affinity of the single recombinant isoforms was evidenced and the kinetic parameters Vmax, Km and Cli, were derived. Differences in GSTs contribution at low and high MC and/or GSH concentrations have been evidenced. Considering that some GSTs, as T1 and M1 are highly polymorphic (these enzymes are lacking in the 50% of Caucasian population) the toxicokinetic information can suggest different susceptibility of population groups to MC toxic effects
lectin binding properties of bovine resting cartilage.
No full textThe aim of this study was to evaluate the differential localisation of glycoconjugates of bovine hyaline cartilage matrix by lectin histochemistry, to compare the results of lectin histochemistry with those that can be obtained in the same tissue with PAS and alcian blue. Frozen and paraffin sections were stained with HE, PAS and alcian blue (pH 1.8). Alcian blue staining was carried out also after 1 and 24 hour digestion with bovine testicular hyaluronidase. Peroxidase conjugated WGA, PNA and RS lectins were tested on all sections before and after 1 hour digestion with bovine testicular hyaluronidase. The results show that all the lectins used in this study react with sugars linked to proteoglycans of territorial matrix, the reaction being increased in territorial, and induced in interterritorial matrix by 1 hour hyaluronidase digestion. Alcian blue at pH 1.8 and PAS were complementary, the former staining territorial, and the latter interterritorial matrix. After 1 hour hyaluronidase digestion, alcian blue stained also the interterritorial matrix. These results suggest that lectins react with low molecular weight proteoglycans and that short hyaluronidase digestion causes depolymerization of high molecular weight proteoglycans without loss of their glucidic components, allowing: a) penetration of alcian blue molecules into the macromolecular proteoglycan network; b) an increase of sugar residuals available for lectin histochemistry. Lectin histochemistry can be useful for differential localisation of glycoconjugates in bovine cartilage, especially if associated with short hyaluronidase digestion and conventional histochemical techniques
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
Scuola per genitori
No full textmigliorare le relazioni tra genitori e figli attraverso un percorso di formazione realizzato con modalità di ricerca-azione che ha coinvolto genitori e figli adolescenti di un IPSI
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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