A Guide to Human Zinc Absorption: General Overview and Recent Advances of In Vitro Intestinal Models

Zinc absorption in the small intestine is one of the main mechanisms regulating the systemic homeostasis of this essential trace element. This review summarizes the key aspects of human zinc homeostasis and distribution. In particular, current knowledge on human intestinal zinc absorption and the influence of diet-derived factors on bioaccessibility and bioavailability as well as intrinsic luminal and basolateral factors with an impact on zinc uptake are discussed. Their investigation is increasingly performed using in vitro cellular intestinal models, which are continually being refined and keep gaining importance for studying zinc uptake and transport via the human intestinal epithelium. The vast majority of these models is based on the human intestinal cell line Caco-2 in combination with other relevant components of the intestinal epithelium, such as mucin-secreting goblet cells and in vitro digestion models, and applying improved compositions of apical and basolateral media to mimic the in vivo situation as closely as possible. Particular emphasis is placed on summarizing previous applications as well as key results of these models, comparing their results to data obtained in humans, and discussing their advantages and limitations.DFG, 316442145, FOR 2558: Interaktionen von essenziellen Spurenelementen in gesunden und erkrankten älteren Menschen (TraceAge)DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Newsrooms as Sites of Community and Identity:Exploring the Importance of Material Place for Journalistic Work

Recent research has examined the sociomaterial contexts that shape journalistic practice within and beyond the newsroom, considering relationships between humans, and between humans and (non)physical artifacts like desks, computers, or software. While much of that research has focused on the use and role of technology, recent research also suggests an affective dimension of materiality like the sense of stability provided by physical news spaces. The newsroom as a material and lived place and place of power relations can greatly shape journalists’ work practices and identity. However, the relevance of the newsroom as a physical place for journalistic practice has so far been taken for granted. This study investigates the role of the newsroom as a physical, material place for journalistic practice and how it contributes to journalists’ sense of belonging and identity. Drawing on interviews with 18 Austrian journalists, we find that newsrooms as sociomaterial places facilitate proximity and serendipity which is perceived as relevant for creative and effective work, as well as a visible manifestation of in-group belonging. As such this study contributes to a better understanding of the meaning and relevance of newsrooms as material places for journalistic work.</p

Free Zinc as a Predictive Marker for COVID-19 Mortality Risk

Free zinc is considered to be the exchangeable and biological active form of zinc in serum, and is discussed to be a suitable biomarker for alterations in body zinc homeostasis and related diseases. Given that coronavirus disease 2019 (COVID-19) is characterized by a marked decrease in total serum zinc, and clinical data indicate that zinc status impacts the susceptibility and severity of the infection, we hypothesized that free zinc in serum might be altered in response to SARS-CoV-2 infection and may reflect disease severity. To test this hypothesis, free zinc concentrations in serum samples of survivors and nonsurvivors of COVID-19 were analyzed by fluorometric microassay. Similar to the reported total serum zinc deficit measured by total reflection X-ray fluorescence, free serum zinc in COVID-19 patients was considerably lower than that in control subjects, and surviving patients displayed significantly higher levels of free zinc than those of nonsurvivors (mean ± SD; 0.4 ± 0.2 nM vs. 0.2 ± 0.1 nM; p = 0.0004). In contrast to recovering total zinc concentrations (r = 0.706, p < 0.001) or the declining copper–zinc ratio (r = −0.646; p < 0.001), free zinc concentrations remained unaltered with time in COVID-19 nonsurvivors. Free serum zinc concentrations were particularly low in male as compared to female patients (mean ± SD; 0.4 ± 0.2 nM vs. 0.2 ± 0.1 nM; p = 0.0003). This is of particular interest, as the male sex is described as a risk factor for severe COVID-19. Overall, results indicate that depressed free serum zinc levels are associated with increased risk of death in COVID-19, suggesting that free zinc may serve as a novel prognostic marker for the severity and course of COVID-19.DFG, 316442145, FOR 2558: Interaktionen von essenziellen Spurenelementen in gesunden und erkrankten älteren Menschen(TraceAge)DFG, 424957847, TRR 296: Lokale Kontrolle der Schilddrüsenhormonwirkung (LocoTact

Time- and Zinc-Related Changes in Biomechanical Properties of Human Colorectal Cancer Cells Examined by Atomic Force Microscopy

Monitoring biomechanics of cells or tissue biopsies employing atomic force microscopy (AFM) offers great potential to identify diagnostic biomarkers for diseases, such as colorectal cancer (CRC). Data on the mechanical properties of CRC cells, however, are still scarce. There is strong evidence that the individual zinc status is related to CRC risk. Thus, this study investigates the impact of differing zinc supply on the mechanical response of the in vitro CRC cell lines HT-29 and HT-29-MTX during their early proliferation (24&ndash;96 h) by measuring elastic modulus, relaxation behavior, and adhesion factors using AFM. The differing zinc supply severely altered the proliferation of these cells and markedly affected their mechanical properties. Accordingly, zinc deficiency led to softer cells, quantitatively described by 20&ndash;30% lower Young&rsquo;s modulus, which was also reflected by relevant changes in adhesion and rupture event distribution compared to those measured for the respective zinc-adequate cultured cells. These results demonstrate that the nutritional zinc supply severely affects the nanomechanical response of CRC cell lines and highlights the relevance of monitoring the zinc content of cancerous cells or biopsies when studying their biomechanics with AFM in the future

Untersuchungen zur Zinkresorption mit in vitro-Intestinalmodellen

The essential trace element zinc is mainly resorbed in the small intestine, where the luminal available cation is absorbed by enterocytes of the intestinal epithelium and transported into the blood circulation. In the past four decades substantial progress in the overall understanding of zinc homeostasis was made by elucidating that the intestinal zinc resorption regulates the systemic homeostasis of the metal. This was further complemented by the discovery of the intestinal zinc transporters as well as the zinc binding protein metallothionein and their regulatory role for zinc resorption. Despite these accomplishments, molecular parameters that control intestinal zinc resorption are still scarce and dietary factors affecting its luminal availability for the intestinal epithelium have to be further scrutinized. For this, in vitro intestinal models provide a standardized and versatile microenvironment to analyze zinc uptake into enterocytes and its subsequent transport into the blood. Hence, this thesis aimed to investigate intestinal zinc resorption with innovative in vitro intestinal cell models. For this, a three-dimensional in vitro model to analyze zinc transport via the intestinal epithelium had to be developed, which is closer to the in vivo situation than the already existing ones. Herein, luminal and basolateral factors as well as cellular composition should be optimized investigating their impact on zinc resorption. Moreover, the scope of this thesis was to establish intestinal model systems to investigate cellular zinc uptake with chemical- and protein-based fluorescent zinc sensors in addition to conventional analytical approaches (such as inductively-coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS)). For investigation of zinc transport in an experimental setting closer to the physiological environment in vivo, a three-dimensional co-culture of Caco-2 cells and the mucin-producing goblet cell line HT-29-MTX was established. This Caco-2/HT-29-MTX model improves various disadvantages of conventional Caco-2 monocultures, including the lack of a mucus layer covering the cell monolayer as well as optimized luminal and basolateral buffer composition. More precisely, the luminal and basolateral medium composition was adapted with regard to its future application for zinc resorption studies, excluding apical addition of proteins (such as fetal calf serum (FCS)) which would severely impact zinc availability and does not represent the luminal situation in vivo, and including albumin in the basolateral compartment to resemble the blood serum in vivo. In fact, zinc transport studies in both improved Caco-2 monocultures and co-cultures demonstrated that basolateral albumin is certainly important for investigating the in vitro zinc resorption and acts as a basolateral zinc acceptor increasing cellular zinc release into the basolateral compartment. Interestingly, the optimized in vitro model Caco-2/HT-29-MTX showed enhanced net absorption of apically applied physiological zinc concentrations (25-100 µM) compared to conventional Caco-2 monocultures. Lastly, the amounts of actually transported zinc with this in vitro model are quite similar to the estimated amounts transported in vivo. Furthermore, the present work suggests that the mucus layer plays a beneficial role in intestinal zinc absorption, making it an integral part of intestinal zinc resorption. More specific, mucins bind zinc with physiologically relevant affinity and provide several binding sites for the metal. Consequently these glycoproteins buffer the available zinc concentration for intestinal cells, as demonstrated in short-term zinc uptake experiments. The presence of mucins increased zinc absorption and yielded higher transport of the cation to the basolateral side of three-dimensional models, suggesting that this physical barrier even facilitates zinc resorption and act as a zinc delivery system to the underlying epithelium. In addition, the intestinal cell line Caco-2 was stably transfected with the zinc Förster resonance energy transfer (FRET)-biosensor eCalwy and characterized regarding enterocyte-specific properties and its maintenance of intracellular zinc homeostasis compared to Caco-2 wildtype cells; generating a well characterized intestinal model system for future investigations of zinc uptake in enterocytes. In fact, applying the low molecular weight sensor Zinpyr-1 and Caco-2-eCalwy cells to analyze free zinc in intestinal cells, even small changes in cellular zinc can be determined which is of particular interest for short-term zinc uptake. Moreover, these sensors provide the promising option to investigate spatial distribution of zinc upon its uptake into enterocytes and to illuminate the zinc transfer in enterocytes throughout the intestinal resorption process. To this end, involvement of two different cellular free zinc pools in the maintenance of enterocytes’ zinc homeostasis during zinc resorption could be illuminated. In conclusion, findings of this thesis indicate that mucins assist apical zinc uptake and what is more, basolateral albumin increases enterocytes’ zinc release to the blood side. This contributes profoundly to our knowledge of the in vitro and in vivo zinc uptake and transport processes on the apical mucosal membrane as well as on the serosal side of enterocytes. Consequently, combining these luminal and basolateral factors in the three-dimensional in vitro model Caco-2/HT-29-MTX, this in vitro model represents a suitable platform to investigate intestinal zinc transport as well as further elucidate molecular mechanisms that regulate intestinal zinc resorption. By applying Caco-2-eCalwy clones and the low molecular weight sensor Zinpyr-1 in Caco-2 the cellular distribution of the essential metal upon its absorption and its transfer during its resorption can be additionally examined.Das essentielle Spurenelement Zink wird hauptsächlich im Dünndarm resorbiert. Hier wird luminal verfügbares ionisches Zink von Enterozyten des intestinalen Epithels aufgenommen und an das Blut abgegeben. Die Forschung der letzten vier Jahrzehnte hat maßgeblich zum Verständnis der Zink-Homöostase beigetragen; bedeutende Fortschritte waren dabei vor allem die Aufklärung der regulatorischen Rolle der intestinalen Zinkresorption in der Aufrechterhaltung der Homöostase des Mikronährstoffes und die Zink-abhängige Expression der intestinalen Zinktransporter und des Zink-bindenden Proteins Metallothionein. Dennoch gibt es weiterhin Forschungsbedarf bezüglich der molekularen Parameter der Regulation der intestinalen Zinkresorption sowie nahrungsbedingten Faktoren, die die Verfügbarkeit des Kations im intestinalen Lumen beeinflussen. In vitro Intestinalmodelle stellen hierfür eine standardisierte und vielseitig einsetzbare Mikro-Umgebungen dar, in denen sowohl die Aufnahme des Metalls in die Enterozyten als auch dessen Transport über das intestinale Epithel in die Blutzirkulation detaillierter analysiert werden können. Das Ziel dieser Arbeit war daher, die intestinale Zinkresorption mit geeigneten in vitro Intestinalmodellen zu untersuchen. Hierfür sollte zum einen ein drei-dimensionales in vitro Modell für die Analyse des intestinalen Zinktransportes entwickelt werden, dass die in vivo Situation im Darm so nah wie möglich abbildet. Dabei sollten luminale und basolaterale Faktoren sowie die zelluläre Zusammensetzung optimiert und deren Einfluss auf die Zinkresorption näher aufgeklärt werden. Des Weiteren sollten intestinale Modellsysteme etabliert werden, mit denen die zelluläre Zinkaufnahme, zusätzlich zu der Anwendung von konventionellen analytischen Methoden, wie zum Beispiel der Massenspektrometrie mit induktiv gekoppeltem Plasma (ICP-MS) und Atomabsorptionsspektrometrie (AAS), mit chemischen und Protein-basierten Zink-Fluoreszenzsonden analysiert werden können. Zur Untersuchung des Zinktransportes wurde eine Ko-kultur aus Caco-2 Zellen und der Muzin-produzierenden Becherzelllinie HT-29-MTX etabliert. Das Caco-2/HT-29-MTX Modell entspricht der physiologischen Situation in vivo besser als konventionelle Caco-2 Monokulturen, da es eine Mukusschicht beinhaltet und die apikale und basolaterale Pufferzusammensetzung an eine ideale Umgebung für Zinkresorptionsstudien angepasst ist. Hierbei wird zum einen auf den apikalen Zusatz von Proteinen (wie fötales Kälberserum (FKS)) verzichtet, da diese das zellulär verfügbare Zink stark beeinflussen würden und nicht der in vivo Situation im Lumen entsprechen, zum anderen muss der basolateralen Seite des Modells Albumin zugesetzt werden, um die Umgebung im Blutserum in vivo darzustellen. Demgemäß zeigten Zinktransportstudien mit Caco-2 Mono- und Ko-kulturen, dass Serumalbumin einen wichtigen Faktor für die in vitro Zinkresorption darstellt, indem es als basolateraler Zinkakzeptor fungiert und die zelluläre Zinkabgabe in das basolaterale Kompartiment erhöht. Zinktransportstudien mit dem optimierten in vitro Intestinalmodell dieser Arbeit ergaben dabei nicht nur eine erhöhte fraktionelle Resorption nach apikaler Zugabe von physiologischer Zinkkonzentration, sondern zeigten zusätzlich, dass die absolut transportierten Zinkmengen vergleichbar mit den geschätzten Werten in der Humanresorption in vivo sind. Zudem legt diese Arbeit dar, dass der intestinale Mukusschicht eine förderliche und unter Umständen regulatorische Rolle in der Zinkresorption hat. Die Ergebnisse dieser Arbeit belegen, dass Muzine eine Vielzahl an möglichen Zinkbindungsstellen mit einer physiologisch relevanten Affinität für das Kation enthalten und dadurch die verfügbare Zinkkonzentration für die darunterliegenden Intestinalzellen puffern. In drei-dimensionalen Zellkulturstudien nahm die Zinkaufnahme in Anwesenheit von Muzinen in das intestinale Epithel zu und führte zu einem erhöhten Zinktransport zur basolateralen Seite. Diese Ergebnisse deuten darauf hin, dass die Mukusschicht die intestinale Zinkresorption erleichtert und somit als eine Art Zink-Transportsystem für das darunterliegende intestinale Epithel darstellt. Des Weiteren wurde in dieser Arbeit die intestinale Zelllinie Caco-2 mit der Förster Resonanzenergietransfer (FRET)-basierten Zinksonde eCalwy stabil transfiziert und hinsichtlich Enterozyten-spezifischer Eigenschaften und der Aufrechterhaltung der Zinkhomöostase mit dem Caco-2 Wildtyp verglichen. So wurde ein gut charakterisiertes Modellsystem geschaffen, dass für zukünftige Studien der Zinkaufnahme in Enterozyten angewendet werden kann. Die Anwendung der niedermolekularen Sonden Zinpyr-1 in Caco-2 und des Caco-2-eCalwy Modells in dieser Arbeit verdeutlicht, dass diese eine geeignete Methode darstellen, um bereits kleine Änderungen des zellulären Zinkgehaltes nach Zinkaufnahme nachzuverfolgen. Das ist besonders relevant bei der Analyse von Kurzzeit-Zinkaufnahmen. Diese Sonden liefern weiterhin die ideale Möglichkeit, auch die intrazelluläre Verteilung des freien Zinks in Enterozyten nach dessen Aufnahme aufzuklären und den Zinktransfer durch den Enterozyten während des Resorptionsprozesses zu untersuchen. Auf diese Weise konnte gezeigt werden, dass zwei verschiedene zelluläre Zinkpools in der Aufrechterhaltung der Zinkhomöostase in Enterozyten während der Zinkaufnahme beteiligt sind. Zusammenfassend zeigen die Ergebnisse dieser Arbeit, dass die intestinale Mukusschicht und basolaterales Serumalbumin wichtige Faktoren für die Zinkresorption darstellen, was zur Aufklärung der Prozesse an der apikalen und basolateralen Membran der Enterozyten während der intestinalen Zinkresorption beiträgt. Das Caco-2/HT-29-MTX Model kombiniert diese luminalen und basolateralen Faktoren und stellt somit ein geeignetes in vitro Intestinalmodell zur Verfügung, mit dem der intestinale Zinktransport sowie molekulare Regulationsmechanismen der Zinkresorption weiter aufgeklärt werden können. Durch die Anwendung von Caco-2-eCalwy Klonen und Zinpyr-1 in Caco-2 Zellen können zudem bereits kleine Änderungen des intrazellulären Zinkgehaltes nach dessen Aufnahme in Enterozyten erfasst werden und die zelluläre Verteilung des Metalls während des Resorptionsprozesses aufgeklärt werden

Working on the margins: Comparative perspectives on the roles and motivations of peripheral actors in journalism

As a consequence of digitization and other environmental trends, journalism is changing its forms and arguably also its functions – both in fundamental ways. While ‘legacy’ news media continue to be easily distinguishable by set characteristics, new content providers operating in an increasingly dense, chaotic, interactive and participatory information environment still remain somewhat understudied. However, at a time when non-traditional formats account for an ever-growing portion of journalistic or para-journalistic work, there is an urgent need to better understand these new peripheral actors and the ways they may be transforming the journalistic field. While journalism scholarship has begun to examine peripheral actors’ motivations and conceptualizations of their roles, our understanding is still fairly limited. This relates particularly to comparative studies of peripheral actors, of which there have been very few, despite peripheral journalism being a global phenomenon. This study aims to address this gap by presenting evidence from 18 in-depth interviews with journalists in Australia, Germany and the United Kingdom. In particular, it examines how novel journalistic actors working for a range of organisations discursively contrast their work from that of others. The findings indicate that journalists’ motivations to engage in journalism in spite of the rise of precarious labour were profoundly altruistic: indeed, journalists pledged allegiance to an ideology of journalism still rooted in a pre-crisis era – one which sees journalism as serving a public good by providing an interpretative, sense-making role