1,952 research outputs found
Perceptions, Actors, Innovations
With Agenda 2030, the UN adopted wide-ranging Sustainable Development Goals (SDGs) that integrate development and environmental agendas. This book has a unique focus on the political tensions between environmental and socio-economic objectives and advocates for a cooperative shift towards environmentally sound sustainability
The Fallacy of Systemic Racism in the American Criminal Justice System
Critics of the criminal justice system have repeatedly charged it with systemic racism. It is a tenet of the âwarâ on the âWar on Drugs,â it is a justification used by the so-called âprogressive prosecutorsâ to reject the âBroken Windowsâ theory of law enforcement, and it is an article of faith of the âDefund the Police!â movement. Even President Joe Biden and his chief lieutenants leveled the same allegation early in this administration. Although the President has eschewed the belief that Americans are a racist people, others have not, proclaiming that virtually anyone who is white is a racist.
Yet, few people have defined what they mean by that term. This Article examines what it could mean and tests the truth of the systemic racism claim under each possible definition. None stands up to scrutiny. One argument is that the American citizens who run our many institutions are motivated by racial animus. But the evidence is that racial animus is no longer tolerated in society, and what is more, the criminal justice system strives to identify it when it does occur and to remedy it. Another argument says that the overtly racist beliefs and practices of the past have created lingering racist effects, but this argument cherry-picks historical facts (when it does not ignore them altogether) and fails to grapple with the countryâs historic and ongoing efforts to eliminate racial discrimination. It also assumes a causal relationship between past discrimination and present disparities that is unsupported and often contradicted by the evidence. Yet another argument relies psychological research to claim that white Americans are animated by a subconscious racial animus. That research, however, has been debunked. Still another argument says that the criminal justice system is systemically racist because it has disparate effects across racial groups, but this argument looks only at the offendersâ side of the criminal justice system and fails to consider the effect of the criminal justice system on victims.
Proponents of the systemic racism theory often proffer âsolutionsâ to it. This Article examines those too and finds that many would, in fact, harm the very people they aim to help. In the context of the âWar on Drugs,â where so much of the rhetoric is focused, the authors examine these arguments and solutions. The bottom line is this: the claim of systemic racism in the criminal justice system is unjustified
Distributed Ledger Technology (DLT) Applications in Payment, Clearing, and Settlement Systems:A Study of Blockchain-Based Payment Barriers and Potential Solutions, and DLT Application in Central Bank Payment System Functions
Payment, clearing, and settlement systems are essential components of the financial markets and exert considerable influence on the overall economy. While there have been considerable technological advancements in payment systems, the conventional systems still depend on centralized architecture, with inherent limitations and risks. The emergence of Distributed ledger technology (DLT) is being regarded as a potential solution to transform payment and settlement processes and address certain challenges posed by the centralized architecture of traditional payment systems (Bank for International Settlements, 2017). While proof-of-concept projects have demonstrated the technical feasibility of DLT, significant barriers still hinder its adoption and implementation. The overarching objective of this thesis is to contribute to the developing area of DLT application in payment, clearing and settlement systems, which is still in its initial stages of applications development and lacks a substantial body of scholarly literature and empirical research. This is achieved by identifying the socio-technical barriers to adoption and diffusion of blockchain-based payment systems and the solutions proposed to address them. Furthermore, the thesis examines and classifies various applications of DLT in central bank payment system functions, offering valuable insights into the motivations, DLT platforms used, and consensus algorithms for applicable use cases. To achieve these objectives, the methodology employed involved a systematic literature review (SLR) of academic literature on blockchain-based payment systems. Furthermore, we utilized a thematic analysis approach to examine data collected from various sources regarding the use of DLT applications in central bank payment system functions, such as central bank white papers, industry reports, and policy documents. The study's findings on blockchain-based payment systems barriers and proposed solutions; challenge the prevailing emphasis on technological and regulatory barriers in the literature and industry discourse regarding the adoption and implementation of blockchain-based payment systems. It highlights the importance of considering the broader socio-technical context and identifying barriers across all five dimensions of the social technical framework, including technological, infrastructural, user practices/market, regulatory, and cultural dimensions. Furthermore, the research identified seven DLT applications in central bank payment system functions. These are grouped into three overarching themes: central banks' operational responsibilities in payment and settlement systems, issuance of central bank digital money, and regulatory oversight/supervisory functions, along with other ancillary functions. Each of these applications has unique motivations or value proposition, which is the underlying reason for utilizing in that particular use case
The KINGS mouse as a model of beta cell endoplasmic reticulum (ER) stress and sex differences in diabetes.
Background: The KINGS mouse is a novel model of beta cell endoplasmic reticulum (ER) stress which shows stark sex differences in diabetes, with males developing overt and progressive hyperglycaemia whilst females are protected. Beta cell ER stress has been implicated in many types of diabetes and underpins numerous factors known to drive beta cell failure. Sex differences also exist in diabetes in humans with premenopausal women having a lower diabetes incidence compared to men. Further characterisation of the KINGS mice may provide valuable insight into these phenomena. Aims: The objectives of this thesis were to 1) further characterise beta cell ER stress and associated cellular response in the KINGS mice, 2) investigate the influence of sex hormones and beta cell ER stress manipulation on glycaemic control in the KINGS mice and 3) investigate whether diabetes development can be prevented in the male KINGS mice. Methods: Western blotting and immunofluorescent staining were used to investigate the expression of ER stress and unfolded protein response (UPR) markers in KINGS islets, as well as beta cell turnover and mass. To determine the influence of oestradiol on the KINGS phenotype, endogenous oestradiol was removed from female mice via ovariectomy, and exogenous oestradiol was delivered to male KINGS mice through implantation of oestradiol- containing capsules. A western diet was used to exacerbate beta cell ER stress in female KINGS mice, whilst liraglutide administration, TUDCA administration and removal of endogenous testosterone (via orchidectomy) was used in an attempt to reduce ER stress and prevent diabetes in the male KINGS mice. For all in vivo studies, glycaemic control was assessed through blood glucose concentration monitoring, glucose tolerance testing and insulin tolerance testing. Results: Male KINGS mice developed diabetes by 5-6 weeks of age whereas female KINGS mice were protected, in line with previous studies. Protein markers of ER stress and the UPR were observed in KINGS islets from 4 weeks of age and a sex difference was observed in expression profiles with males largely showing an increased expression of markers. Despite this, we did not observe a loss of beta cell mass in either male or female KINGS mice. However, subtle changes in beta cell proliferation and apoptosis in the male KINGS mice are suggestive of mild changes to beta cell turnover which may contribute to diabetes development. A western diet exacerbated beta cell ER stress in female KINGS mice, however this only led to a mild impairment in glycaemic control which was not as severe as that seen in male KINGS mice. This may suggest that even under conditions of further ER stress, female mice are still able to respond adaptively. Removal of endogenous oestradiol also exacerbated beta cell ER stress, however again this was only associated with a subtle impairment in glycaemic control. On the contrary, exogenous oestradiol delivery in the male KINGS mice prevented the development of overt diabetes. Treatment with liraglutide was used in an attempt to alleviate ER stress in the male KINGS mice. Although liraglutide prevented the development of diabetes and reduced blood glucose concentrations once diabetes was established, this protection only lasted during the treatment window and cessation of treatment was associated with increases in blood glucose concentrations. In addition, liraglutide had no effect on beta cell ER stress levels. Treatment with TUDCA, a chemical chaperone previously found to reduce beta cell ER stress, had no impact on blood glucose concentrations in the KINGS mice. However, removal of endogenous testosterone through orchidectomy prevented the development of overt diabetes. Conclusion: In this study we have confirmed that the KINGS mutation drives beta cell ER stress and that sex differences exist in beta cell response to this. Interestingly, an adaptive response to beta cell ER stress was still maintained in female KINGS mice when ER stress was exacerbated through a western diet. We also found that whilst oestradiol likely contributes in-part to sex differences in diabetes, it cannot be the sole mediator and other factors must be involved. Indeed, we found that endogenous testosterone removal prevented the development of diabetes in male mice. Liraglutide treatment also prevented diabetes development in male mice, however this was likely to be mediated through mechanisms unrelated to beta cell ER stress. Further study is required to investigate how testosterone removal and liraglutide protect male mice.</div
Advances and Applications of DSmT for Information Fusion. Collected Works, Volume 5
This ïŹfth volume on Advances and Applications of DSmT for Information Fusion collects theoretical and applied contributions of researchers working in different ïŹelds of applications and in mathematics, and is available in open-access. The collected contributions of this volume have either been published or presented after disseminating the fourth volume in 2015 in international conferences, seminars, workshops and journals, or they are new. The contributions of each part of this volume are chronologically ordered.
First Part of this book presents some theoretical advances on DSmT, dealing mainly with modiïŹed Proportional ConïŹict Redistribution Rules (PCR) of combination with degree of intersection, coarsening techniques, interval calculus for PCR thanks to set inversion via interval analysis (SIVIA), rough set classiïŹers, canonical decomposition of dichotomous belief functions, fast PCR fusion, fast inter-criteria analysis with PCR, and improved PCR5 and PCR6 rules preserving the (quasi-)neutrality of (quasi-)vacuous belief assignment in the fusion of sources of evidence with their Matlab codes.
Because more applications of DSmT have emerged in the past years since the apparition of the fourth book of DSmT in 2015, the second part of this volume is about selected applications of DSmT mainly in building change detection, object recognition, quality of data association in tracking, perception in robotics, risk assessment for torrent protection and multi-criteria decision-making, multi-modal image fusion, coarsening techniques, recommender system, levee characterization and assessment, human heading perception, trust assessment, robotics, biometrics, failure detection, GPS systems, inter-criteria analysis, group decision, human activity recognition, storm prediction, data association for autonomous vehicles, identiïŹcation of maritime vessels, fusion of support vector machines (SVM), Silx-Furtif RUST code library for information fusion including PCR rules, and network for ship classiïŹcation.
Finally, the third part presents interesting contributions related to belief functions in general published or presented along the years since 2015. These contributions are related with decision-making under uncertainty, belief approximations, probability transformations, new distances between belief functions, non-classical multi-criteria decision-making problems with belief functions, generalization of Bayes theorem, image processing, data association, entropy and cross-entropy measures, fuzzy evidence numbers, negator of belief mass, human activity recognition, information fusion for breast cancer therapy, imbalanced data classiïŹcation, and hybrid techniques mixing deep learning with belief functions as well
Development of Novel Therapeutic Strategies to Target Therapy Resistance and Cancer Stem Cells
This thesis focuses on the core issues of multidrug resistance (MDR) in cancer, a process that hinders the success of chemotherapeutic treatments. MDR involves various mechanisms, including the upregulation of ABC transporter pumps, like MRP1, and increased cancer stemness, which contributes to malignancy and recurrence.
The thesis comprises seven chapters: a literature review (Chapter 1), methodology (Chapter 2), results (Chapters 3-5), and discussions on findings and future studies (Chapters 6) and final discussion and overall summary (Chapter 7).
Chapter 3 delves into the novel roles of MRP1 in cellular iron metabolism and proliferation, its interaction with c-Myc, and the effects on cellular proliferation. Silencing and inhibition studies reveal MRP1's role in regulating iron regulatory proteins through c-Myc.
Chapter 4 investigates the role of ABC transporters in cancer stemness, revealing their connection with stemness states in different tumor types.
Chapter 5 explores strategies for targeting drug-resistant cancer cells, demonstrating how doxycycline reduces the stemness marker SOX2 across multiple tumor types through a unique pathway.
Chapter 6 examines the alteration of metabolism and stemness in drug-resistant cancer cells and strategies for targeting the cysteine metabolism pathway. The findings provide insights into cancer stemness regulation and potential therapeutic strategies, improving the efficacy of chemotherapeutics.
The work reported in this thesis reveals an underlying and unique mechanism in regulation of SOX2-mediated cancer stemness. Moreover, the use of DXC to remove stemness was demonstrated to be a promising therapeutic strategy in combination with other common chemotherapeutics agents. These findings presented in this thesis enables us to understand cancer stemness better and improve the efficacy of current chemotherapeutics, which ultimately improve overall quality of life
Evaluation Methodologies in Software Protection Research
Man-at-the-end (MATE) attackers have full control over the system on which
the attacked software runs, and try to break the confidentiality or integrity
of assets embedded in the software. Both companies and malware authors want to
prevent such attacks. This has driven an arms race between attackers and
defenders, resulting in a plethora of different protection and analysis
methods. However, it remains difficult to measure the strength of protections
because MATE attackers can reach their goals in many different ways and a
universally accepted evaluation methodology does not exist. This survey
systematically reviews the evaluation methodologies of papers on obfuscation, a
major class of protections against MATE attacks. For 572 papers, we collected
113 aspects of their evaluation methodologies, ranging from sample set types
and sizes, over sample treatment, to performed measurements. We provide
detailed insights into how the academic state of the art evaluates both the
protections and analyses thereon. In summary, there is a clear need for better
evaluation methodologies. We identify nine challenges for software protection
evaluations, which represent threats to the validity, reproducibility, and
interpretation of research results in the context of MATE attacks
Recommended from our members
The impact of employees' working relations in creating and retaining trust: the case of the Bahrain Olympic Committee
Introduction: This thesis investigates the impact of employeesâ working relations in creating, maintaining and retaining trust in the Bahrain Olympic Committee (BOC).
Aim: The main aim of this thesis is to determine how the three groups of Organisational Trust variables, namely Social System Elements (SSE), Factors of Trustworthiness (FoT) and Third-Party Gossip (TPG), affect employeesâ Organisational Trust (OTR) in the BOC and promote Organisational Citizenship Behaviour (OCB). To answer this main aim, a conceptual framework was created that focused on exploring the following research aims: (1) the interrelationship between SSE and FoT, (2) the effect of SSE on OTR, (3) the impact of TPG on OTR and (4) the effect of OTR on overall OCB.
Methodology: The study uses a mixed-method case study research style that included in-depth semi-structured interviews with 17 managers, an online questionnaire survey with 320 employees of the BOC and an analysis of the BOCâs Annual Reports from 2015 to 2018.
Results: The qualitative and quantitative findings indicate, firstly, that there is a significant interrelationship between SSE and FoT, establishing that SSEâs perception of organisational justice (OJ), including that FoTs benevolence and integrity as the most important factors in yielding employeesâ trust in the BOC. Secondly, it has been established that SSEs have significant direct and indirect effects on OTR. Thirdly, negative and positive TPG concurrently occurred in the BOC and the prevalence of negative TPG poses more impact on OTR. Finally, this studyâs findings demonstrated OTRâs effect in generating OCB, including that Civic Virtue was rated as the most preferred of the five OCB themes; this indicates the managersâ and the employeesâ strong emotional attachment and support of the activities taking place at the BOC.
Contributions: Overall, this thesis substantially contributes to OTR literature, particularly in the context of the Middle East. It also proposes several insightful recommendations for future research and practical implications for practitioners in the field of Organisational Trust
Rational development of stabilized cyclic disulfide redox probes and bioreductive prodrugs to target dithiol oxidoreductases
Countless biological processes allow cells to develop, survive, and proliferate. Among these, tightly balanced regulatory enzymatic pathways that can respond rapidly to external impacts maintain dynamic physiological homeostasis. More specifically, redox homeostasis broadly affects cellular metabolism and proliferation, with major contributions by thiol/disulfide oxidoreductase systems, in particular, the Thioredoxin Reductase Thioredoxin (TrxR/Trx) and the Glutathione Reductase-Glutathione-Glutaredoxin (GR/GSH/Grx) systems.
These cascades drive vital cellular functions in many ways through signaling, regulating other proteins' activity by redox switches, and by stoichiometric reductant transfers in metabolism and antioxidant systems. Increasing evidence argues that there is a persistent alteration of the redox environment in certain pathological states, such as cancer, that heavily involve the Trx system: upregulation and/or overactivity of the Trx system may support or drive cancer progression, making both TrxR and Trx promising targets for anti-cancer drug development.
Understanding the biochemical mechanisms and connections between certain redox cascades requires research tools that interact with them. The state-of-the-art genetic tools are mostly ratiometric reporters that measure reduced:oxidized ratios of selected redox pairs or the general thiol pool. However, the precise cellular roles of the central oxidoreductase systems, including TrxR and Trx, remain inaccessible due to the lack of probes to selectively measure turnover by either of these proteins. However, such probes would allow measuring their effective reductive activity apart from expression levels in native systems, including in cells, animals, or patient samples. They are also of high interest to identify chemical inhibitors for TrxR/Trx in cells and to validate their potential use as anti-cancer agents (to date, there is no selective cellular Trx inhibitor, and most known TrxR inhibitors were not comprehensively evaluated considering selectivity and potential off-targets). However, small molecule redox imaging tools are underdeveloped: their protein specificity, spectral properties, and applicability remain poorly precedented.
This work aimed to address this opportunity gap and develop novel, small molecule diagnostic and therapeutic tools to selectively target the Trx system based on a modular trigger cargo design: artificial cyclic disulfide substrates (trigger) for oxidoreductases are tethered to molecular agents (cargo) such that the cargoâs activity is masked and is re-established only through reduction by a target protein.
The rational design of these novel reduction sensors to target the cell's strongest disulfide-reducing enzymes was driven by the following principles: (i) cyclic disulfide triggers with stabilized ring systems were used to gain low reduction potentials that should resist reduction except by the strongest cellular reductases, such as Trx; and (ii) the cyclic topology also offers the potential for kinetic reversibility that should select for dithiol-type redox proteins over the cellular monothiol background. Creating imaging agents based on such two-component designs to selectively measure redox protein activity in native cells required to combine the correct trigger reducibility, probe activation kinetics, and imaging modalities and to consider the overall molecular architecture.
The major prior art in this field has applied cyclic 5-membered disulfides (1,2 dithiolanes) as substrates for TrxR in a similar way to create such tools. However, this motif was described elsewhere as thermodynamically instable and was due to widely used for dynamic covalent cascade reactions. By comparing a novel 1,2 dithiolane-based probe to the state-of-the-art probes, including commercial TrxR sensors, by screening a conclusive assay panel of cellular TrxR modulations, I clarified that 1,2 dithiolanes are not selective substrates for TrxR in biological settings (Nat Commun 2022).
Instead, aiming for more stable ring systems and thus more robust redox probes, during this work, I developed bicyclic 6 membered disulfides (piperidine fused 1,2 dithianes) with remarkably low reduction potentials. I showed that molecular probes using them as reduction sensors can be mostly processed by thioredoxins while being stable against reduction by GSH. The thermodynamically stabilized decalin like topology of the cis-annelated 1,2 dithianes requires particularly strong reductants to be cleaved. They also select for dithiol type redox proteins, like Trx, based on kinetic reversibility and offer fast cyclization due to the preorganization by annelation (JACS 2021).
This work further expanded the systemâs modularity with structural cores based on piperazine-fused 1,2 dithianes with the two amines allowing independent derivatization. Diagnostic tools using them as reduction sensors proved equally robust but with highly improved activation kinetics and were thus cellularly activated. Cellular studies evolved that they are substrates for both Trxs and their protein cousins Grxs, so measuring the cellular dithiol protein pool rather than solely Trx activity (preprint 2023).
Finally, a trigger based on a slightly adapted reduction sensor, a desymmetrized 1,2 thiaselenane, was designed for selective reduction by TrxRâs selenol/thiol active site, then combined with a precipitating large Stokesâ shift fluorophore and a solubilizing group, to evolve the first selective probe RX1 to measure cellular TrxR activity, which even allowed high throughput inhibitor screening (Chem 2022).
The central principle of this work was further advanced to therapeutic prodrugs based on the duocarmycin cargo (CBI) with tunable potency (JACS Au 2022) that can be used to create off-to-on therapeutic prodrugs. Such CBI prodrugs employing stabilized 1,2 dichalcogenide triggers proved to be cytotoxins that depend on Trx system activity in cells. They could further be exploited for cell-line dependent reductase activity profiling by screening their redox activation indices, the reduction-dependent part of total prodrug activation, in 177 cell lines. Beyond that, these prodrugs were well-tolerated in animals and showed anti-cancer efficacy in vivo in two distinct mouse tumor models (preprint 2022).
Taken together, I introduced unique monothiol-resistant reducible motifs to target the cellular Trx system with chemocompatible units for each for TrxR and Trx/Grx, where the cyclic nature of the dichalcogenides avoids activation by GSH. By using them with distinct molecular cargos, I developed novel selective fluorescent reporter probes; and introduced a new class of bioreductive therapeutic constructs based on a common modular design. These were either applied to selectively measure cellular reductase activity or to deliver cytotoxic anti cancer agents in vivo. Ongoing work aims to differentiate between the two major redox effector proteins Trx and Grx, requiring additional layers of selectivity that may be addressed by tuned molecular recognition. The flexible use of various molecular cargos allows harnessing the same cellular redox machinery by either probes or prodrugs. This allows predictive conclusions from diagnostics to be directly translated into therapy and offers great potential for future adaptation to other enzyme classes and therapeutic venues.Die zellulĂ€re Redox-Homöostase hĂ€ngt von Thiol/Disulfid-Oxidoreduktasen ab, die den Stoffwechsel, die Proliferation und die antioxidative Antwort von Zellen beeinflussen. Die wichtigsten Netzwerke sind die Thioredoxin Reduktase-Thioredoxin (TrxR/Trx) und Glutathion Reduktase-Glutathion-Glutaredoxin (GR/GSH/Grx) Systeme, die ĂŒber Redox-Schalter in Substratproteinen lebenswichtige zellulĂ€re Funktionen steuern und so an der Redox-Regulation und -SignalĂŒbertragung beteiligt sind. Persistente VerĂ€nderungen des Redoxmilieus in pathologischen ZustĂ€nden, wie z. B. bei Krebs, sind in hohem MaĂe mit dem Trx-System verbunden. Eine Hochregulierung und/oder ĂberaktivitĂ€t des Trx-Systems, die bei vielen Krebsarten auftreten, unterstĂŒtzt zudem das Fortschreiten des Krebswachstums, was TrxR/Trx zu vielversprechenden Zielproteinen fĂŒr die Entwicklung neuer Krebsmedikamente macht.
Um die biochemischen Prozesse dahinter zu erforschen, sind spezielle Techniken zur Visualisierung und Messung enzymatischer AktivitĂ€t nötig. Die hierzu geeigneten, meist genetischen Sensoren messen ratiometrisch das VerhĂ€ltnis reduzierter/oxidierter Spezies in zellulĂ€rem Umfeld oder spezifisch ausgewĂ€hlte Redoxpaare. Die weitere Erforschung der exakten Funktion von TrxR/Trx und deren Substrate ist jedoch durch mangelnde Nachweismethoden limitiert. Diese sind auĂerdem zur Validierung chemischer Hemmstoffe fĂŒr TrxR/Trx in Zellen und deren potenziellen Verwendung als Krebsmittel von groĂem Interesse. Bislang gibt es keinen selektiven zellulĂ€ren Trx-Inhibitor und potenzielle Off-Target-Effekte der bekannten TrxR-Inhibitoren wurden nicht abschlieĂend bewertet.
Ziel dieser Arbeit ist die Entwicklung niedermolekularer, diagnostischer und therapeutischer Werkzeuge, die selektiv auf das Trx-System abzielen und auf einem modularen Trigger-Cargo Design basieren. Hierzu werden zyklische Disulfid-Substrate (Trigger) fĂŒr Oxidoreduktasen so mit molekularen Wirkstoffen (Cargo) verknĂŒpft, dass dabei die WirkstoffaktivitĂ€t maskiert, und erst nach Reduktion durch ein Zielprotein wiederhergestellt wird. Diese neuartigen, synthetischen Reduktionssensoren basieren auf den folgenden Grundprinzipien: (i) Zyklische Disulfide sind thermodynamisch stabilisiert und können nur durch die stĂ€rksten Reduktasen gespalten werden; und (ii) die zyklische Topologie ermöglicht die kinetische ReversibilitĂ€t der zwei Thiol-Disulfid-Austauschreaktionen, die eine erste Reaktion mit Monothiolen, wie z. B. GSH, sofort umkehrt und so eine vollstĂ€ndige Reduktion verhindert.
Die meisten frĂŒheren Arbeiten auf diesem Gebiet verwendeten ein zyklisches, fĂŒnfgliedriges Disulfid (1,2 Dithiolan) als Substrat fĂŒr TrxR. Das gleiche Strukturmotiv wurde jedoch an anderer Stelle als thermodynamisch instabil beschrieben und aufgrund dieser Eigenschaft explizit fĂŒr dynamische Kaskadenreaktionen verwendet. Deshalb vergleicht diese Arbeit zu Beginn einen neuen 1,2 Dithiolan basierten fluorogenen Indikator mit bestehenden, z. T. kommerziellen, Redox Sonden fĂŒr TrxR in einer Reihe von Zellkultur-Experimenten unter Modulation der zellulĂ€ren TrxR AktivitĂ€t und stellt so einen Widerspruch in der Literatur klar: 1,2 Dithiolane eignen sich nicht als selektive Substrate fĂŒr TrxR, da sie labil sowohl gegen die Reduktion durch andere Redoxproteine, als auch gegen den Monothiol Hintergrund in Zellen sind (Nat. Commun. 2022).
Als alternatives Strukturmotiv wird in dieser Arbeit ein bizyklisches sechsgliedriges Disulfid (anneliertes 1,2 Dithian) etabliert. Durch sein niedriges Reduktionspotenzial, also seine hohe Resistenz gegen Reduktion, werden molekulare Sonden basierend auf diesem 1,2 Dithian als Reduktionssensor fast ausschlieĂlich von Trx aktiviert, nicht aber von TrxR oder GSH (JACS 2021). Dieses Kernmotiv bestimmt dabei die Reduzierbarkeit, und damit die EnzymspezifitĂ€t, durch seine zyklische Natur und die Annelierung, auch unter Verwendung unterschiedlicher Farb-/Wirkstoffe. Auf dieser Grundlage konnte die molekulare Struktur durch einen weiteren Modifikationspunkt fĂŒr die flexible Verwendung weiterer funktioneller Einheiten ergĂ€nzt werden. Obwohl zellulĂ€re Studien ergaben, dass diese neuartigen 1,2 Dithian Einheiten in Zellen sowohl Trx als auch das strukturell verwandte Grx adressieren, sind die daraus resultierenden diagnostischen MolekĂŒle wertvoll, um den katalytischen Umsatz zellulĂ€rer Dithiol-Reduktasen, der sogenannten Trx Superfamilie, selektiv anzuzeigen (Preprint 2023).
BegĂŒnstigt durch das modulare MolekĂŒldesign stellt diese Arbeit zudem das erste Reportersystem RX1 zum selektiven Nachweis der TrxR-AktivitĂ€t in Zellen vor. Es basiert auf der Verwendung eines zyklischen, unsymmetrischen Selenenylsulfid-Sensors (1,2 Thiaselenan), der selektiv von dem einzigartigen Selenolat der TrxR angegriffen wird, und dadurch letztlich nur von TrxR reduziert werden kann. RX1 eignete sich zudem fĂŒr eine Hochdurchsatz-Validierung bestehender TrxR Inhibitoren und unterstreicht dadurch den kommerziellen Nutzen derartiger Diagnostika (Chem 2022).
Das zentrale Trigger-Cargo Konzept dieser Arbeit wurde fĂŒr therapeutische Zwecke weiterentwickelt und nutzt dabei den einzigartigen Wirkmechanismus der Duocarmycin-Naturstoffklasse (CBI) (JACS Au 2022) zur Entwicklung reduktiv aktivierbarer Therapeutika. CBI Prodrugs basierend auf stabilisierten Redox-Schaltern (1,2 Dithiane fĂŒr Trx; 1,2 Thiaselenan fĂŒr TrxR) reagierten signifikant auf TrxR-Modulation in Zellen. Sie wurden darĂŒber hinaus durch das Referenzieren ihrer AktivitĂ€t gegenĂŒber nicht-reduzierbaren KontrollmolekĂŒle fĂŒr die Erstellung zelllinienabhĂ€ngiger Profile der ReduktaseaktivitĂ€t in 177 Zelllinien genutzt. SchlieĂlich waren diese neuen Krebsmittel im Tiermodell gut vertrĂ€glich und zeigten in zwei verschiedenen Mausmodellen eine krebshemmende Wirkung (Preprint 2022b).
Zusammenfassend prĂ€sentiert diese Dissertation monothiol-resistente reduzierbare Trigger-Einheiten fĂŒr das zellulĂ€re Trx-System zur Entwicklung neuartiger, selektiver Reporter-Sonden, sowie eine neue Klasse reduktiv aktivierbarer Krebsmittel auf Basis eines adaptierbaren Trigger-Cargo Designs. Diese fanden entweder zur selektiven Messung zellulĂ€rer ProteinaktivitĂ€t oder zum Einsatz als Antikrebsmittel Verwendung. Es wurden chemokompatible Motive sowohl fĂŒr TrxR als auch fĂŒr Trx/Grx identifiziert, wobei deren zyklische Natur eine Aktivierung durch GSH verhindert. Eine weitere Differenzierung zwischen den beiden Redox-Proteinen Trx und Grx und anderen Proteinen der Trx-Superfamilie erfordert eine zusĂ€tzliche Ebene der Selektierung, z. B. durch molekulare Erkennung, und ist Gegenstand laufender Arbeiten.
Die flexible Verwendung verschiedener molekularer Wirkstoffe ermöglicht dabei die âPipeline-Entwicklungâ von Diagnostika und Therapeutika, die von der zellulĂ€ren Redox-Maschinerie analog umgesetzt werden, und dadurch Schlussfolgerungen aus der Diagnostik direkt auf eine Therapie ĂŒbertragbar machen. Dies birgt groĂes Potenzial fĂŒr kĂŒnftige Entwicklungen bei einer potenziellen Ăbertragung des modularen Konzepts auf andere Enzymklassen und therapeutische Einsatzgebiete
Discrete Element Modelling of Damage and Fracture of Brittle Materials
Concretes are widely used in civil engineering, such as bridges, roads, and water dams. However, damage occurs as the service age of the infrastructure increases. Investigations into the damage process can elucidate the fracture mechanisms and help to reduce the damage. Despite the fact that much research has been conducted on this topic, concrete fracture mechanisms remain unclear. Directly collecting microscale and/or meso-scale information (e.g., crack population, size, strength, and stress distribution) through laboratory experiments is challenging, However, this information is necessary for understanding the fracture process. Numerical simulation serves as a promising alternative as it can dynamically trace microcracking events and evaluate the spatial and temporal variations of stress in materials. Among the many numerical models, the discrete element method (DEM) is exceptionally successful in studying rocks and rock-like materials. Nevertheless, further improvements to DEM models are required to more accurately characterise materials' mechanical and fracture behaviours.
To address the aforementioned problems, the present study developed superior discrete element models, including both homogeneous and heterogeneous models. The models were validated against finite element solutions and experiments, revealing that they can capture numerous behaviours of rock-like materials. The models were then used to study the mechanical and fracture behaviours of concretes under different loading conditions. The results indicate that the inhomogeneity of concrete strongly affects its fracture behaviours. Crack growth and stress distribution dynamically influence each other. Moreover, the crack population decreased exponentially with the crack length in the pre-peak stage. Crack proliferation usually initiated from the interior and grew outwards until the concrete disintegrated. The final disintegration of concrete usually resulted from the growth of several long-length cracks. The change in concrete strength was a consequence of the trade-off between strengthening aggregates and weakening ITZs. Furthermore, the introduction of vibration-assisted cutting mitigated crack growth in concretes and reduced spiking forces in the chipping process
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