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Cell culture models are helpful tools to study inflammatory diseases, like rheumatoid arthritis (RA), osteoarthritis (OA), arteriosclerosis or asthma, which are linked to increased matrix metalloproteinase (MMP) activity. Such cell culture models often focus on the secretion of cytokines and growth factors or the direct effects of disease on tissue destruction. Even though the crucial role of MMPs in inflammatory diseases is known, the results of MMP studies are contradictious and the use of MMPs as biomarkers is inconsistent. MMPs play an important role in disease pathology, as they are involved in elastin degradation in the walls of alveoli in chronic obstructive pulmonary disease (COPD), tumor angiogenesis and metastasis and in cartilage and bone degradation in arthropathies. In RA and OA MMPs are secreted by osteocytes, synoviocytes, and by infiltrating immune cells in response to the increased concentration of inflammatory mediators, like growth factors and cytokines. MMPs are zinc and calcium-dependent proteinases and play an important role in physiological and pathological extracellular matrix (ECM) turn over. Their substrate specificity gives them the ability to degrade all major ECM components, like aggrecan, elastin, gelatin, fibronectin and all types of collagen even the triple helix of collagen monomers. The ECM consists of two large three-dimensional cross-linked macromolecule classes: one are fibrous proteins, like collagen and elastin fibers that are responsible for ECM’s structure, tensile strength, resiliency, reversible extensibility, and deformability and the second class is comprised of proteoglycans composed of glycosaminoglycan (GAG) chains covalently attached to protein cores that are multifunctionally involved in signaling pathways and cell interactions. ECM is present within all tissues and organs and changes in ECM structure contribute to pathogenesis, e.g. wounded and fibrotic tissue, COPD or tumours.
This thesis primarily focuses on the development of a diagnostic peptide system, that enables to gain information on MMP activity from ECM by deploying the isobaric mass encoding strategy. The core element of the developed system is an isotopically labelled peptide sequence (mass tag), that is released in response to elevated levels of MMPs and allows multiplexed detection in tandem mass spectrometry (LC-MS/MS). The mass reporters possess a modular structure with different functionalities. C-terminal either a transglutaminase (TG) recognition sequence or a high molecular weight polyethylene glycol (PEG) moiety was attached to immobilize the mass reporters covalently or physically at the injection site. The following matrix metalloproteinase substrate sequence (MSS) is incorporated in two different versions with different sensitivity to MMPs. The MSS were applied in pairs for relative quantification consisting of the cleavable version synthesized with natural L-amino acids and the non-cleavable D-amino acid variant. The mass tag was synthesized with isotopically labelled amino acids and is separated from the MSS by a UV light-sensitive molecule. N-terminal the mass tag is followed by a tobacco etch virus protease (TEV) sensitive sequence, that is responsible to separate the mass tag from the affinity tag, which was either the Strep-tag II sequence or biotin and were added for purification purposes.
Chapter 1 presents a step-by-step protocol on how to design a mass tag family allowing for multiplexed analysis by LC-MS/MS. The multiplexing is achieved by developing an isobar mass tag family with four family members, which are chromatographically indistinguishable, but due to the mass encoding principles they fragment in distinct y-type ions with a mass difference of 1 or 2 Da each in MS2. Furthermore, it is explained how to covalently attach the mass reporter peptides onto ECM by the activated calcium-catalyzed blood coagulation transglutaminase factor XIII (FXIIIa). The lysine of mass reporter’s TG sequence (D-domain of insulin-like growth factor-I (IGF-I)) and a glutamine in fibronectin are covalently crosslinked by FXIIIa and build an isopeptide bond. Elevated levels of MMP release the mass reporters from ECM by recognizing the inter-positioned MSS.
The designed mass reporters were able to monitor enzyme activity in an in vitro setting with cell-derived ECM, which was shown in Chapter 2. The modular structured mass reporters were investigated in a proof of concept study. First, the different modules were characterized in terms of their MMP responsiveness and their sensitivity to TEV protease and UV light. Then the FXIIIa-mediated coupling reaction was detailed and the successful coupling on ECM was visualized by an immunosorbent assay or confocal laser scanning microscopy. Finally, the immobilized mass reporters on ECM were incubated with MMP-9 to investigate their multiplexing ability of MMP activity. The cleaved mass reporter fragments were purified in three steps and mass tags were analyzed as mix of all four in LC-MS/MS.
Chapter 3 describes the change from an immobilizing system as seen in chapter 1 and 2 to a soluble enzyme activity monitoring system that was applied in an osteoarthritic mouse model. Instead of the immobilizing TG sequence the C-terminal MMS was extended with two amino acids where one holds an azide moiety to perform a strain-promoted azide-alkyne cycloaddition to a high molecular weight dibenzocyclooctyne-polyethylene glycol (DBCO-PEG), which was chosen to retain the mass reporters at the injection site. Furthermore, the N-terminal affinity tag was extended with a 2.5 kDa PEG chain to increase the half-life of the mass reporter peptides after MMP release. The systems biocompatibility was proved but its enzyme monitoring ability in an in vivo setting could not be analyzed as samples degraded during shipping resulting from the Chinese customs blocking transport to Germany.
In summary the diagnostic peptide system was developed in two variants. The immobilized version one from chapter 1 and 2 was designed to be covalently attached to ECM by the transglutaminase-mediated cross-linking reaction. In an in vitro setting the functionality of the mass reporter system for the detection of MMP activity was successfully verified. The second variant comprises of a soluble mass reporter system that was tested in an OA mouse model and showed biocompatibility. With these two designed systems this thesis provides a flexible platform based on multiplexed analysis with mass-encoded peptides to characterize cell culture models regarding their MMP activity, to deploy cell-derived ECM as endogenous depot scaffold and to develop a mass tag family that enables simultaneous detection of at least four mass tags.
Die biochemische Diagnostik von Phäochromozytomen und Paragangliomen (PPGL) basiert auf einem gesteigerten Katecholaminmetabolismus in dessen Folge es zu erhöhten Plasmametanephrinkonzentrationen (Normetanephrin NMN und/oder Metanephrin MN) kommt. Die variable endokrine Aktivität der Tumoren sowie Hormonzentrationen im Nanomol-pro-Liter-Bereich stellen hohe Anforderungen an analytische Messmethoden. Nicht oder spät diagnostizierte PPGL können lebensbedrohliche katecholaminerge Krisen verursachen. Demzufolge sind präzise Nachweisverfahren und validierte Messmethoden für die biochemische Diagnostik unerlässlich. Inwiefern die Messverfahren enzymgekoppelter Immunoassay (EIA) und Flüssigkeitschromatographie mit Tandem-Massenspektrometrie (LC-MS/MS) zur Analyse von Plasmametanephrinen in gleichem Maße geeignet sind, ist aufgrund der kontroversen Studienlage unklar.
Hierfür wurde eine Substudie im Rahmen der prospektiven monoaminproduzierenden Tumor (PMT)-Studie an fünf europäischen Zentren durchgeführt. Es wurden 341 Patienten (174 Männer, 167 Frauen), darunter 54 Patienten mit PPGL eingeschlossen. Die Blutproben wurden unter Standardbedingungen entnommen und mit beiden Messmethoden in spezialisierten Zentren analysiert. Für den EIA zeigte sich ein negativer Bias von
60% für NMN und 39% für MN. Dieser führte unter Verwendung oberer Grenzwerte nach Herstellerangaben zu einer Sensitivität von 74,1% und einer Spezifität von 98,9%. Für LC-MS/MS wurde eine signifikant höhere Sensitivität von 98,1% und eine Spezifität von 99,7% gezeigt. Die Berechnung der area under the curve (AUC) im Zuge der receiver-operating-characteristic (ROC)-Kurven-Analyse indizierte jedoch eine vergleichbar hohe diagnostische Testleistung für EIA (0,993) und LC-MS/MS (0,985). Durch eine Bias-korrigierte Grenzwertoptimierung stieg die Sensitivität des EIAs auf 96,2% bei einer Spezifität von 95,1% und führte dadurch zu einer vergleichbaren diagnostischen Testqualität wie
LC-MS/MS.
Fazit: Bei diesem kommerziell erhältlichen EIA resultiert die Verwendung oberer Grenzwerte nach Herstellerangaben in einer insuffizienten Sensitivität. Dies birgt das Risiko, Patienten mit PPGL nicht zu diagnostizieren. Eine Rekalibrierung des EIAs sowie eine Validierung der Referenzintervalle sind erforderlich.
Das Nebennierenrindenkarzinom (ACC) ist eine sehr seltene maligne Erkrankung, die mit einer infausten Prognose vergesellschaftet ist. In Zeiten apparativ geprägter Medizin treten suspekte Befunde der Nebenniere gehäufter auf als je zuvor. Diese Nebennierenraumforderungen, die zumeist bei Bildgebungen auffallen, die aus anderen Gründen indiziert waren, werden Nebenniereninzidentalome genannt und sind meist benigne Befunde. Dennoch wird es angesichts dieser steigenden Zahl an Inzidentalomen immer wichtiger, die Entität der gefundenen Raumforderung schnell zu sichern, um die entsprechende Therapie einleiten zu können. Somit sollen das Zeitfenster bis zur Krebstherapie verkleinert und gleichsam unnötige chirurgische Eingriffe bei Patient*innen mit benignen Nebennierentumoren vermieden werden. Um die diagnostischen Schritte weiter zu verbessern, wurde in der vorliegenden Arbeit eine bioinformatische Regressionsanalyse an Steroidhormonkonzentrationen von ACC-Patient*innen und Kontrollen durchgeführt und der diagnostische Wert der berechneten Steroidsignaturen untersucht. Dabei zeigte sich im geschlechtsspezifischen Modell jeweils eine 6-Steroid-Signatur mit bester Trennschärfe zwischen benignen und malignen NN-Befunden. So konnte mit der 6-Steroid-Signatur in der männlichen Patientengruppe mit einer Sensitivität von 80% und Spezifität von 97%, in der weiblichen Patientinnengruppe mit einer Sensitivität von 78% und Spezifität von 97% die Diagnose richtig zugewiesen werden. Im Rahmen der targeted Metabolomics Untersuchung konnten Tumor-assoziierte Stoffwechselalterationen aufgezeigt werden. Eine Plasma-Metabolit-Signatur zur Differenzierung von ACCs und Nebennierenadenomen, welche die gängige Diagnostik bei der Abklärung von unklaren Nebennierentumoren erleichtern könnte, erscheint jedoch angesichts der großen Anzahl an zu bestimmenden Metaboliten - auch unter ökonomischen Gesichtspunkten - zu diesem Zeitpunkt noch nicht mit der Routine-Patient*innenversorgung vereinbar.
In this thesis eight robust and reliable LC-MS/MS methods were developed and validated to analyze atorvastatin, clopidogrel, furosemide, itraconazole, loratadine, naproxen, nisoldipine and sunitinib in human plasma. The active metabolites 2-hydroxyatorvastatin, 4-hydroxyatorvastatin, hydroxyitraconazole, descarboethoxy-loratadine, 4-hydroxynisoldipine and N-desethylsunitinib were also included in the corresponding methods. Due to the different physical, chemical and pharmacokinetic properties of the analytes a wide spectrum regarding sample preparation techniques, chromatography and mass spectrometric detection was covered. Protein precipitation methods were developed for furosemide, itraconazole, naproxen, nisoldipine and sunitinib. Liquid-liquid extraction methods were developed for atorvastatin, clopidogrel and loratadine. Criteria to choose protein precipitation or liquid-liquid extraction were the final plasma concentrations of the drugs, which are mainly dependant on the dose, bioavailability and t1/2 and of course cost-effectiveness. Altogether, the methods have a concentration range from 0.001 ng/mL (LLOQ of clopidogrel) to 50000 ng/mL (highest calibration point for naproxen), covering 5 x 107 orders of magnitude. The runtime of the methods ranged from 2 to 4 minutes, facilitating a high sample throughput. All developed methods were validated according to recent guidelines as they were used to analyze sampes from clinical trials. Excellent linearity, intra-day and inter-day precision and accuracy were observed in the validated calibration ranges. Hemolyzed, lipemic and different batches of human plasma as well as sample dilution did not affect the determiantion of the analytes. Clopidogrel, loratadine, nisoldipine and sunitinib and if available their metabolites were subjected to a matrix effect test, resulting in no influence of different batches of human plasma on the analytical methods. Noteworthy is clopidogrel that shows a slight effect on one of the two used mass spectrometers. However, that effect was reproducible and did therefore not affect clopidogrel determination. No evidence of instability during chromatography, extraction and sample storage processes for all analytes except 4-hydroxyatorvastatin was found, for which a significant decrease was observed after three months. During incurred sample reanalysis of study samples 95 % of the samples were within ±15 % with respect to the first analysis. Moreover, the atorvastatin, loratadine and clopidogrel method were compared on two generations of triple quadrupole mass spectrometers, the API 3000™ and the API 5000™. The new ion source and the changes in the ion path of the API 5000™ provided higher sensitivity, the extend depending on the substance. However, the API 3000™ had very good precision in the performed system comparison. The validated methods showed excellent performance and quality data during routine sample analysis of eight clinical trials. Moreover, they are suitable for high sample throughput due to their short run times.