Measurement of K +- pi +- gamma gamma decays

The goal of this thesis was an experimental test of an effective theory of strong interactions at low energy, called Chiral Perturbation Theory (ChPT). Weak decays of kaon mesons provide such a test. In particular, K± → π±γγ decays are interesting because there is no tree-level O(p2) contribution in ChPT, and the leading contributions start at O(p4). At this order, these decays include one undetermined coupling constant, ĉ. Both the branching ratio and the spectrum shape of K± → π±γγ decays are sensitive to this parameter. O(p6) contributions to K± → π±γγ ChPT predict a 30-40% increase in the branching ratio. From the measurement of the branching ratio and spectrum shape of K± → π±γγ decays, it is possible to determine a model dependent value of ĉ and also to examine whether the O(p6) corrections are necessary and enough to explain the rate.About 40% of the data collected in the year 2003 by the NA48/2 experiment have been analyzed and 908 K± → π±γγ candidates with about 8% background contamination have been selected in the region with z = mγγ2/mK2 ≥ 0.2. Using 5,750,121 selected K± → π±π0 decays as normalization channel, a model independent differential branching ratio of K± → π±γγ has been measured to be:BR(K± → π±γγ, z ≥ 0.2) = (1.018 ± 0.038stat ± 0.039syst ± 0.004ext) ∙10-6. From the fit to the O(p6) ChPT prediction of the measured branching ratio and the shape of the z-spectrum, a value of ĉ = 1.54 ± 0.15stat ± 0.18syst has been extracted. Using the measured ĉ value and the O(p6) ChPT prediction, the branching ratio for z =mγγ2/mK2 <0.2 was computed and added to the measured result. The value obtained for the total branching ratio is:BR(K± → π±γγ) = (1.055 ± 0.038stat ± 0.039syst ± 0.004ext + 0.003ĉ -0.002ĉ) ∙10-6, where the last error reflects the uncertainty on ĉ.The branching ratio result presented here agrees with previous experimental results, improving the precision of the measurement by at least a factor of five. The precision on the ĉ measurement has been improved by approximately a factor of three. A slight disagreement with the O(p6) ChPT branching ratio prediction as a function of ĉ has been observed. This mightrnbe due to the possible existence of non-negligible terms not yet included in the theory. Within the scope of this thesis, η-η' mixing effects in O(p4) ChPT have also been measured.

Measurement of the elastic electron-proton cross section and separation of the electric and magnetic form factor in the Q 2 range from 0.004 to 1 (GeV/c) 2

The electromagnetic form factors of the proton are fundamental quantities sensitive to the distribution of charge and magnetization inside the proton. Precise knowledge of the form factors, in particular of the charge and magnetization radii provide strong tests for theory in the non-perturbative regime of QCD. However, the existing data at Q^2 below 1 (GeV/c)^2 are not precise enough for a hard test of theoretical predictions.rnrnFor a more precise determination of the form factors, within this work more than 1400 cross sections of the reaction H(e,e′)p were measured at the Mainz Microtron MAMI using the 3-spectrometer-facility of the A1-collaboration. The data were taken in three periods in the years 2006 and 2007 using beam energies of 180, 315, 450, 585, 720 and 855 MeV. They cover the Q^2 region from 0.004 to 1 (GeV/c)^2 with counting rate uncertainties below 0.2% for most of the data points. The relative luminosity of the measurements was determined using one of the spectrometers as a luminosity monitor. The overlapping acceptances of the measurements maximize the internal redundancy of the data and allow, together with several additions to the standard experimental setup, for tight control of systematic uncertainties.rnTo account for the radiative processes, an event generator was developed and implemented in the simulation package of the analysis software which works without peaking approximation by explicitly calculating the Bethe-Heitler and Born Feynman diagrams for each event.rnTo separate the form factors and to determine the radii, the data were analyzed by fitting a wide selection of form factor models directly to the measured cross sections. These fits also determined the absolute normalization of the different data subsets. The validity of this method was tested with extensive simulations. The results were compared to an extraction via the standard Rosenbluth technique.rnrnThe dip structure in G_E that was seen in the analysis of the previous world data shows up in a modified form. When compared to the standard-dipole form factor as a smooth curve, the extracted G_E exhibits a strong change of the slope around 0.1 (GeV/c)^2, and in the magnetic form factor a dip around 0.2 (GeV/c)^2 is found. This may be taken as indications for a pion cloud. For higher Q^2, the fits yield larger values for G_M than previous measurements, in agreement with form factor ratios from recent precise polarized measurements in the Q2 region up to 0.6 (GeV/c)^2.rnrnThe charge and magnetic rms radii are determined as rn⟨r_e⟩=0.879 ± 0.005(stat.) ± 0.004(syst.) ± 0.002(model) ± 0.004(group) fm,rn⟨r_m⟩=0.777 ± 0.013(stat.) ± 0.009(syst.) ± 0.005(model) ± 0.002(group) fm.rnThis charge radius is significantly larger than theoretical predictions and than the radius of the standard dipole. However, it is in agreement with earlier results measured at the Mainz linear accelerator and with determinations from Hydrogen Lamb shift measurements. The extracted magnetic radius is smaller than previous determinations and than the standard-dipole value.

Advanced Techniques for Face Recognition under Challenging Environments

Automatically recognizing faces captured under uncontrolled environments has always been a challenging topic in the past decades. In this work, we investigate cohort score normalization that has been widely used in biometric verification as means to improve the robustness of face recognition under challenging environments. In particular, we introduce cohort score normalization into undersampled face recognition problem. Further, we develop an effective cohort normalization method specifically for the unconstrained face pair matching problem. Extensive experiments conducted on several well known face databases demonstrate the effectiveness of cohort normalization on these challenging scenarios. In addition, to give a proper understanding of cohort behavior, we study the impact of the number and quality of cohort samples on the normalization performance. The experimental results show that bigger cohort set size gives more stable and often better results to a point before the performance saturates. And cohort samples with different quality indeed produce different cohort normalization performance. Recognizing faces gone after alterations is another challenging problem for current face recognition algorithms. Face image alterations can be roughly classified into two categories: unintentional (e.g., geometrics transformations introduced by the acquisition devide) and intentional alterations (e.g., plastic surgery). We study the impact of these alterations on face recognition accuracy. Our results show that state-of-the-art algorithms are able to overcome limited digital alterations but are sensitive to more relevant modifications. Further, we develop two useful descriptors for detecting those alterations which can significantly affect the recognition performance. In the end, we propose to use the Structural Similarity (SSIM) quality map to detect and model variations due to plastic surgeries. Extensive experiments conducted on a plastic surgery face database demonstrate the potential of SSIM map for matching face images after surgeries.

Extending Implicit Computational Complexity and Abstract Machines to Languages with Control

The Curry-Howard isomorphism is the idea that proofs in natural deduction can be put in correspondence with lambda terms in such a way that this correspondence is preserved by normalization. The concept can be extended from Intuitionistic Logic to other systems, such as Linear Logic. One of the nice conseguences of this isomorphism is that we can reason about functional programs with formal tools which are typical of proof systems: such analysis can also include quantitative qualities of programs, such as the number of steps it takes to terminate. Another is the possiblity to describe the execution of these programs in terms of abstract machines. In 1990 Griffin proved that the correspondence can be extended to Classical Logic and control operators. That is, Classical Logic adds the possiblity to manipulate continuations. In this thesis we see how the things we described above work in this larger context.

Genus Bifidobacterium: taxonomy studies and gene expression analysis on folate pathway

Folates (vitamin B9) are essential water soluble vitamins, whose deficiency in humans may contribute to the onset of several diseases, such as anaemia, cancer, cardiovascular diseases, neurological problems as well as defects in embryonic development. Human and other mammals are unable to synthesize ex novo folate obtaining it from exogenous sources, via intestinal absorption. Recently the gut microbiota has been identified as an important source of folates and the selection and use of folate producing microorganisms represents an innovative strategy to increase human folate levels. The aim of this thesis was to gain a fundamental understanding of folate metabolism in Bifidobacterium adolescentis. The work was subdivided in three main phases, also aimed to solve different problems encountered working with Bifidobacterium strains. First, a new identification method (based on PCR-RFLP of hsp60 gene) was specifically developed to identify Bifidobacterium strains. Secondly, Bifidobacterium adolescentis biodiversity was explored in order to recognize representing strains of this species to be screened for their folate production ability. Results showed that this species is characterized by a wide variability and support the idea that a possible new taxonomic re-organization would be required. Finally B. adolescentis folate metabolism was studied using a double approach. A quantitative analysis of folate content was complemented by the examination of expression levels of genes involved in folate related pathways. For the normalization process, required to increase the robustness of the qRT-PCR analysis, an appropriate set of reference genes was tested using two different algorithms. Results demonstrate that B.adolescentis strains may represent an endogenous source of natural folate and they could be used to fortify fermented dairy products. This bio-fortification strategy presents many advantages for the consumer, providing native folate forms more bio-available, and not implicated in the discussed controversy concerning the safety of high intake of synthetic folic acid.

Genexpressionsanalyse der fötalen Wachstumsfuge des Rindes

Erkrankungen des Skelettapparats wie beispielsweise die Osteoporose oder Arthrose gehören neben den Herz-Kreislauferkrankungen und Tumoren zu den Häufigsten Erkrankungen des Menschen. Ein besseres Verständnis der Bildung und des Erhalts von Knochen- oder Knorpelgewebe ist deshalb von besonderer Bedeutung. Viele bisherige Ansätze zur Identifizierung hierfür relevanter Gene, deren Produkte und Interaktionen beruhen auf der Untersuchung pathologischer Situationen. Daher ist die Funktion vieler Gene nur im Zusammenhang mit Krankheiten beschrieben. Untersuchungen, die die Genaktivität bei der Normalentwicklung von knochen- und knorpelbildenden Geweben zum Ziel haben, sind dagegen weit weniger oft durchgeführt worden. rnEines der entwicklungsphysiologisch interessantesten Gewebe ist die Epiphysenfuge der Röhrenknochen. In dieser sogenannten Wachstumsfuge ist insbesondere beim fötalen Gewebe eine sehr hohe Aktivität derjenigen Gene zu erwarten, die an der Knochen- und Knorpelbildung beteiligt sind. In der vorliegenden Arbeit wurde daher aus der Epiphysenfuge von Kälberknochen RNA isoliert und eine cDNA-Bibliothek konstruiert. Von dieser wurden ca. 4000 Klone im Rahmen eines klassischen EST-Projekts sequenziert. Durch die Analyse konnte ein ungefähr 900 Gene umfassendes Expressionsprofil erstellt werden und viele Transkripte für Komponenten der regulatorischen und strukturbildenden Bestandteile der Knochen- und Knorpelentwicklung identifiziert werden. Neben den typischen Genen für Komponenten der Knochenentwicklung sind auch deutlich Bestandteile für embryonale Entwicklungsprozesse vertreten. Zu ersten gehören in erster Linie die Kollagene, allen voran Kollagen II alpha 1, das mit Abstand höchst exprimierte Gen in der fötalen Wachstumsfuge. Nach den ribosomalen Proteinen stellen die Kollagene mit ca. 10 % aller auswertbaren Sequenzen die zweitgrößte Gengruppe im erstellten Expressionsprofil dar. Proteoglykane und andere niedrig exprimierte regulatorische Elemente, wie Transkriptionsfaktoren, konnten im EST-Projekt aufgrund der geringen Abdeckung nur in sehr geringer Kopienzahl gefunden werden. Allerdings förderte die EST-Analyse mehrere interessante, bisher nicht bekannte Transkripte zutage, die detaillierter untersucht wurden. Dazu gehören Transkripte die, die dem LOC618319 zugeordnet werden konnten. Neben den bisher beschriebenen drei Exonbereichen konnte ein weiteres Exon im 3‘-UTR identifiziert werden. Im abgeleiteten Protein, das mindestens 121 AS lang ist, wurden ein Signalpeptid und eine Transmembrandomäne nachgewiesen. In Verbindung mit einer möglichen Glykosylierung ist das Genprodukt in die Gruppe der Proteoglykane einzuordnen. Leicht abweichend von den typischen Strukturen knochen- und knorpelspezifischer Proteoglykane ist eine mögliche Funktion dieses Genprodukts bei der Interaktion mit Integrinen und der Zell-Zellinteraktion, aber auch bei der Signaltransduktion denkbar. rnDie EST-Sequenzierungen von ca. 4000 cDNA-Klonen können aber in der Regel nur einen Bruchteil der möglichen Transkripte des untersuchten Gewebes abdecken. Mit den neuen Sequenziertechnologien des „Next Generation Sequencing“ bestehen völlig neue Möglichkeiten, komplette Transkriptome mit sehr hoher Abdeckung zu sequenzieren und zu analysieren. Zur Unterstützung der EST-Daten und zur deutlichen Verbreiterung der Datenbasis wurde das Transkriptom der bovinen fötalen Wachstumsfuge sowohl mit Hilfe der Roche-454/FLX- als auch der Illumina-Solexa-Technologie sequenziert. Bei der Auswertung der ca. 40000 454- und 75 Millionen Illumina-Sequenzen wurden Verfahren zur allgemeinen Handhabung, der Qualitätskontrolle, dem „Clustern“, der Annotation und quantitativen Auswertung von großen Mengen an Sequenzdaten etabliert. Beim Vergleich der Hochdurchsatz Blast-Analysen im klassischen „Read-Count“-Ansatz mit dem erstellten EST-Expressionsprofil konnten gute Überstimmungen gezeigt werden. Abweichungen zwischen den einzelnen Methoden konnten nicht in allen Fällen methodisch erklärt werden. In einigen Fällen sind Korrelationen zwischen Transkriptlänge und „Read“-Verteilung zu erkennen. Obwohl schon simple Methoden wie die Normierung auf RPKM („reads per kilo base transkript per million mappable reads“) eine Verbesserung der Interpretation ermöglichen, konnten messtechnisch durch die Art der Sequenzierung bedingte systematische Fehler nicht immer ausgeräumt werden. Besonders wichtig ist daher die geeignete Normalisierung der Daten beim Vergleich verschieden generierter Datensätze. rnDie hier diskutierten Ergebnisse aus den verschiedenen Analysen zeigen die neuen Sequenziertechnologien als gute Ergänzung und potentiellen Ersatz für etablierte Methoden zur Genexpressionsanalyse.rn

The dynamics of early-type galaxies as a tool to understand their hot coronae and their IMF

Dynamical models of galaxies are a powerful tool to study and understand several astrophysical problems related to galaxy formation and evolution. This thesis is focussed on a particular type of dynamical models, that are widely used in literature, and are based on the solution of the Jeans equations. By means of a numerical Jeans solver code, developed on purpose and able to build state-of-the-art advanced axisymmetric galaxy models, two of the main currently investigated issues in the field of research of early-type galaxies (ETGs) are addressed. The first topic concerns the hot and X-ray emitting gaseous coronae that surround ETGs. The main goal is to explain why flat and rotating galaxies generally exhibit haloes with lower gas temperatures and luminosities with respect to rounder and velocity dispersion supported systems. The second astrophysical problem addressed concerns instead the stellar initial mass function (IMF) of ETGs. Nowadays, this is a very controversial issue due to a growing number of works on ETGs, based on different and independent techniques, that show evidences of a systematic variation of the IMF normalization as a function of galaxy velocity dispersion or mass. These studies are changing the previous opinion that the IMF of ETGs was the same as that of spiral galaxies, and hence universal throughout the whole large family of galaxies.

Normare la vita. Biocontrollo e nuove tecnologie

Questa ricerca, suddivisa in due parti, si concentra sulle problematiche connesse alla normazione della vita e dei corpi delle donne al tempo delle biotecnologie. La Parte I è una genealogia filosofico-politica che ripercorre le tappe analitico-concettuali del dibattito intorno a biopolitica e tecnoscienza, a partire dai contributi teorici di poststrutturalismo e femminismo neomaterialista, e risponde alle domande: Cosa sono diventati i corpi nell’attuale società bio-info-modificata? Qual'è il ruolo delle scienze nelle metamorfosi che interessano soggettività e rapporti di potere? La Parte II è una cartografia dei modi in cui le biotecnologie, riguardanti i corpi delle donne, si sono sviluppate e diffuse. Essa indaga in modo transdisciplinare come in Italia, e più in generale in Europa, sono state normate le tecniche di interruzione volontaria di gravidanza e fecondazione in vitro. Ampio spazio è dedicato ai modi in cui gli attori della bioetica, istituzionale e non, i medici, laici e cattolici, e le case farmaceutiche hanno affrontato questi temi e quello della contraccezione ormonale maschile. Medicina riproduttiva e rigenerativa sono tematizzate sempre in relazione al quadro normativo, per mostrare in che modo esso influenzi l’accesso ai diritti alla salute e all’autodeterminazione delle donne. Il quadro normativo è analizzato, a sua volta, alla luce dei fatti storici più rilevanti e delle culture più diffuse. L’obiettivo della ricerca è duplice: da un lato essa ha il fine di mostrare il modo in cui i corpi delle donne, e la relativa potenza generatrice, siano diventati uno snodo fondamentale nell’articolazione del biocontrollo e nell'apertura dei nuovi mercati legati a medicina riproduttiva e rigenerativa; dall’altro si propone di argomentare come un biodiritto flessibile, a contenuto storico variabile, condiviso e partecipato, sia un’ipotesi praticabile e virtuosa, utile all'eliminazione del gender gap ancora esistente in materia di diritti riproduttivi e sessuali.

Algorithmen zur labelfreien quantitativen Proteomanalyse auf Basis datenunabhängig-akquirierter LC-MS-Daten

Moderne ESI-LC-MS/MS-Techniken erlauben in Verbindung mit Bottom-up-Ansätzen eine qualitative und quantitative Charakterisierung mehrerer tausend Proteine in einem einzigen Experiment. Für die labelfreie Proteinquantifizierung eignen sich besonders datenunabhängige Akquisitionsmethoden wie MSE und die IMS-Varianten HDMSE und UDMSE. Durch ihre hohe Komplexität stellen die so erfassten Daten besondere Anforderungen an die Analysesoftware. Eine quantitative Analyse der MSE/HDMSE/UDMSE-Daten blieb bislang wenigen kommerziellen Lösungen vorbehalten. rn| In der vorliegenden Arbeit wurden eine Strategie und eine Reihe neuer Methoden zur messungsübergreifenden, quantitativen Analyse labelfreier MSE/HDMSE/UDMSE-Daten entwickelt und als Software ISOQuant implementiert. Für die ersten Schritte der Datenanalyse (Featuredetektion, Peptid- und Proteinidentifikation) wird die kommerzielle Software PLGS verwendet. Anschließend werden die unabhängigen PLGS-Ergebnisse aller Messungen eines Experiments in einer relationalen Datenbank zusammengeführt und mit Hilfe der dedizierten Algorithmen (Retentionszeitalignment, Feature-Clustering, multidimensionale Normalisierung der Intensitäten, mehrstufige Datenfilterung, Proteininferenz, Umverteilung der Intensitäten geteilter Peptide, Proteinquantifizierung) überarbeitet. Durch diese Nachbearbeitung wird die Reproduzierbarkeit der qualitativen und quantitativen Ergebnisse signifikant gesteigert.rn| Um die Performance der quantitativen Datenanalyse zu evaluieren und mit anderen Lösungen zu vergleichen, wurde ein Satz von exakt definierten Hybridproteom-Proben entwickelt. Die Proben wurden mit den Methoden MSE und UDMSE erfasst, mit Progenesis QIP, synapter und ISOQuant analysiert und verglichen. Im Gegensatz zu synapter und Progenesis QIP konnte ISOQuant sowohl eine hohe Reproduzierbarkeit der Proteinidentifikation als auch eine hohe Präzision und Richtigkeit der Proteinquantifizierung erreichen.rn| Schlussfolgernd ermöglichen die vorgestellten Algorithmen und der Analyseworkflow zuverlässige und reproduzierbare quantitative Datenanalysen. Mit der Software ISOQuant wurde ein einfaches und effizientes Werkzeug für routinemäßige Hochdurchsatzanalysen labelfreier MSE/HDMSE/UDMSE-Daten entwickelt. Mit den Hybridproteom-Proben und den Bewertungsmetriken wurde ein umfassendes System zur Evaluierung quantitativer Akquisitions- und Datenanalysesysteme vorgestellt.

Limiting theorems in statistical mechanics. The mean-field case.

The Curie-Weiss model is defined by ah Hamiltonian according to spins interact. For some particular values of the parameters, the sum of the spins normalized with square-root normalization converges or not toward Gaussian distribution. In the thesis we investigate some correlations between the behaviour of the sum and the central limit for interacting random variables.

Hierarchical clustering of flow cytometry data for the study of conventional central chondrosarcoma

We have investigated the use of hierarchical clustering of flow cytometry data to classify samples of conventional central chondrosarcoma, a malignant cartilage forming tumor of uncertain cellular origin, according to similarities with surface marker profiles of several known cell types. Human primary chondrosarcoma cells, articular chondrocytes, mesenchymal stem cells, fibroblasts, and a panel of tumor cell lines from chondrocytic or epithelial origin were clustered based on the expression profile of eleven surface markers. For clustering, eight hierarchical clustering algorithms, three distance metrics, as well as several approaches for data preprocessing, including multivariate outlier detection, logarithmic transformation, and z-score normalization, were systematically evaluated. By selecting clustering approaches shown to give reproducible results for cluster recovery of known cell types, primary conventional central chondrosacoma cells could be grouped in two main clusters with distinctive marker expression signatures: one group clustering together with mesenchymal stem cells (CD49b-high/CD10-low/CD221-high) and a second group clustering close to fibroblasts (CD49b-low/CD10-high/CD221-low). Hierarchical clustering also revealed substantial differences between primary conventional central chondrosarcoma cells and established chondrosarcoma cell lines, with the latter not only segregating apart from primary tumor cells and normal tissue cells, but clustering together with cell lines from epithelial lineage. Our study provides a foundation for the use of hierarchical clustering applied to flow cytometry data as a powerful tool to classify samples according to marker expression patterns, which could lead to uncover new cancer subtypes.

Expression of human cathepsin L or human cathepsin V in mouse thymus mediates positive selection of T helper cells in cathepsin L knock-out mice

A genetic deficiency of the cysteine protease cathepsin L (Ctsl) in mice results in impaired positive selection of conventional CD4+ T helper cells as a result of an incomplete processing of the MHC class II associated invariant chain or incomplete proteolytic generation of positively selecting peptide ligands. The human genome encodes, in contrast to the mouse genome, for two cathepsin L proteases, namely cathepsin L (CTSL) and cathepsin V (CTSV; alternatively cathepsin L2). In the human thymic cortex, CTSV is the predominately expressed protease as compared to CTSL or other cysteine cathepsins. In order to analyze the functions of CTSL and CTSV in the positive selection of CD4+ T cells we employed Ctsl knock-out mice crossed either with transgenic mice expressing CTSL under the control of its genuine human promoter or with transgenic mice expressing CTSV under the control of the keratin 14 (K14) promoter, which drives expression to the cortical epithelium. Both human proteases are expressed in the thymus of the transgenic mice, and independent expression of both CTSL and CTSV rescues the reduced frequency of CD4+ T cells in Ctsl-deficient mice. Moreover, the expression of the human cathepsins does not change the number of CD4+CD25+Foxp3+ regulatory T cells, but the normalization of the frequency of conventional CD4+ T cell in the transgenic mice results in a rebalancing of conventional T cells and regulatory T cells. We conclude that the functional differences of CTSL and CTSV in vivo are not mainly determined by their inherent biochemical properties, but rather by their tissue specific expression pattern.

Statin therapy and the expression of genes that regulate calcium homeostasis and membrane repair in skeletal muscle

In skeletal muscle of patients with clinically diagnosed statin-associated myopathy, discrete signs of structural damage predominantly localize to the T-tubular region and are suggestive of a calcium leak. The impact of statins on skeletal muscle of non-myopathic patients is not known. We analyzed the expression of selected genes implicated in the molecular regulation of calcium and membrane repair, in lipid homeostasis, myocyte remodeling and mitochondrial function. Microscopic and gene expression analyses were performed using validated TaqMan custom arrays on skeletal muscle biopsies of 72 age-matched subjects who were receiving statin therapy (n = 38), who had discontinued therapy due to statin-associated myopathy (n = 14), and who had never undergone statin treatment (n = 20). In skeletal muscle, obtained from statin-treated, non-myopathic patients, statins caused extensive changes in the expression of genes of the calcium regulatory and the membrane repair machinery, whereas the expression of genes responsible for mitochondrial function or myocyte remodeling was unaffected. Discontinuation of treatment due to myopathic symptoms led to a normalization of gene expression levels, the genes encoding the ryanodine receptor 3, calpain 3, and dystrophin being the most notable exceptions. Hence, even in clinically asymptomatic (non-myopathic) patients, statin therapy leads to an upregulation in the expression of genes that are concerned with skeletal muscle regulation and membrane repair.

Evaluation of a bolus/infusion protocol for 11C-ABP688, a PET tracer for mGluR5

(11)C-ABP-688 is a selective tracer for the mGluR5 receptor. Its kinetics is fast and thus favourable for an equilibrium approach to determine receptor-related parameters. The purpose of this study was to test the hypothesis that the pattern of the (11)C-ABP688 uptake using a bolus-plus-infusion (B/I) protocol at early time points corresponds to the perfusion and at a later time point to the total distribution volume. METHODS: A bolus and a B/I study (1 h each) was performed in five healthy male volunteers. With the B/I protocol, early and late scans were normalized to gray matter, cerebellum and white matter. The same normalization was done on the maps of the total distribution volume (Vt) and K(1) which were calculated in the study with bolus only injection and the Logan method (Vt) and a two-tissue compartment model (K(1)). RESULTS: There was an excellent correlation close to the identity line between the pattern of the late uptake in the B/I study and Vt of the bolus-only study for all three normalizations. The pattern of the early uptake in the B/I study correlated well with the K(1) maps, but only when normalized to gray matter and cerebellum, not to white matter. CONCLUSION: It is demonstrated that with a B/I protocol the (11)C-ABP688 distribution in late scans reflects the pattern of the total distribution volume and is therefore a measure for the density pattern of mGluR5. The early scans following injection are related to blood flow, although not in a fully quantitative manner. The advantage of the B/I protocol is that no arterial blood sampling is required, which is advantageous in clinical studies.

Abolishing myofibroblast arrhythmogeneicity by pharmacological ablation of α-smooth muscle actin containing stress fibers

Rationale: Myofibroblasts typically appear in the myocardium after insults to the heart like mechanical overload and infarction. Apart from contributing to fibrotic remodeling, myofibroblasts induce arrhythmogenic slow conduction and ectopic activity in cardiomyocytes after establishment of heterocellular electrotonic coupling in vitro. So far, it is not known whether α-smooth muscle actin (α-SMA) containing stress fibers, the cytoskeletal components that set myofibroblasts apart from resident fibroblasts, are essential for myofibroblasts to develop arrhythmogenic interactions with cardiomyocytes. Objective: We investigated whether pharmacological ablation of α-SMA containing stress fibers by actin-targeting drugs affects arrhythmogenic myofibroblast–cardiomyocyte cross-talk. Methods and Results: Experiments were performed with patterned growth cell cultures of neonatal rat ventricular cardiomyocytes coated with cardiac myofibroblasts. The preparations exhibited slow conduction and ectopic activity under control conditions. Exposure to actin-targeting drugs (Cytochalasin D, Latrunculin B, Jasplakinolide) for 24 hours led to disruption of α-SMA containing stress fibers. In parallel, conduction velocities increased dose-dependently to values indistinguishable from cardiomyocyte-only preparations and ectopic activity measured continuously over 24 hours was completely suppressed. Mechanistically, antiarrhythmic effects were due to myofibroblast hyperpolarization (Cytochalasin D, Latrunculin B) and disruption of heterocellular gap junctional coupling (Jasplakinolide), which caused normalization of membrane polarization of adjacent cardiomyocytes. Conclusions: The results suggest that α-SMA containing stress fibers importantly contribute to myofibroblast arrhythmogeneicity. After ablation of this cytoskeletal component, cells lose their arrhythmic effects on cardiomyocytes, even if heterocellular electrotonic coupling is sustained. The findings identify α-SMA containing stress fibers as a potential future target of antiarrhythmic therapy in hearts undergoing structural remodeling.