Purpose: Measurement of endogenous uracil (U) is increasingly being used as a dose-individualization method in the treatment of cancer patients with fluoropyrimidines. However, instability at room... Show morePurpose: Measurement of endogenous uracil (U) is increasingly being used as a dose-individualization method in the treatment of cancer patients with fluoropyrimidines. However, instability at room temperature (RT) and improper sample handling may cause falsely increased U levels. Therefore we aimed to study the stability of U and dihydrouracil (DHU) to ensure proper handling conditions.Methods: Stability of U and DHU in whole blood, serum, and plasma at RT (up to 24 h) and long-term stability (>= 7 days) at - 20 degrees C were studied in samples from 6 healthy individuals. U and DHU levels of patients were compared using standard serum tubes (SSTs) and rapid serum tubes (RSTs). The performance of our validated UPLC-MS/MS assay was assessed over a period of 7 months.Results: U and DHU levels significantly increased at RT in whole blood and serum after blood sampling with increases of 12.7 and 47.6% after 2 h, respectively. A significant difference (p = 0.0036) in U and DHU levels in serum was found between SSTs and RSTs. U and DHU were stable at - 20 degrees C at least 2 months in serum and 3 weeks in plasma. Assay performance assessment fulfilled the acceptance criteria for system suitability, calibration standards, and quality controls.Conclusion: A maximum of 1 h at RT between sampling and processing is recommended to ensure reliable U and DHU results. Assay performance tests showed that our UPLC-MS/MS method was robust and reliable. Additionally, we provided a guideline for proper sample handling, processing and reliable quantification of U and DHU. Show less
This work describes several studies into the electroreduction of carbon dioxide (CO2RR), both regarding mechanistical aspects and catalyst stability considerations. Mechanistic insights into carbon... Show moreThis work describes several studies into the electroreduction of carbon dioxide (CO2RR), both regarding mechanistical aspects and catalyst stability considerations. Mechanistic insights into carbon-carbon bond formation on a silver catalyst are described in Ch 2, were we find an acetaldehyde-like surface adsorbate to be a key intermediate. Gold stability in alkaline environment under strongly reducing conditions and the effect of near-surface CO on said stability is reported on in Ch 3, showing catalyst degradation under reductive conditions which is furthermore exacerbated by CO adsorption. Chapter 4 details the voltammetric behavior of variously oriented copper surfaces when prepared via a non-standard methodology, showing good agreement with prior literature. The last chapter (Ch 5) contains investigations into the stability of copper under reductive conditions in near-neutral buffered electrolyte and in alkaline electrolyte, where it was observed that copper is morphologically stable under strongly alkaline conditions and neutral conditions in the presence of CO2 and buffer ions, so long as strictly reducing potentials are applied. Show less
Hoogendoorn, K.H.; Crommelin, D.J.A.; Jiskoot, W. 2021
The formulation of cell-based medicinal products (CBMPs) poses major challenges because of their complexity, heterogeneity, interaction with their environment (e.g., the formulation buffer,... Show moreThe formulation of cell-based medicinal products (CBMPs) poses major challenges because of their complexity, heterogeneity, interaction with their environment (e.g., the formulation buffer, interfaces), and susceptibility to degradation. These challenges can be quality, safety, and efficacy related. In this commentary we discuss the current status in formulation strategies of off-the-shelf and non-off-the-shelf (patient-specific) CBMPs and highlight advantages and disadvantages of each strategy. Analytical tools for the characterization and stability assessment of CBMP formulations are addressed as well. Finally, we discuss unmet needs and make some recommendations regarding the formulation of CBMPs. (C) 2020 American Pharmacists Association?. Published by Elsevier Inc. All rights reserved. Show less
The focus of this thesis is (oxy)lipid analysis. An introductory overview is given of lipids, lipidomics, and lipid mediators in inflammation; and in subsequent chapters the focus is on... Show moreThe focus of this thesis is (oxy)lipid analysis. An introductory overview is given of lipids, lipidomics, and lipid mediators in inflammation; and in subsequent chapters the focus is on development of lipidomic methods for the analysis of oxidized lipids. This touches on different extraction methods of the (target) analytes, sample handling/preparation and storage, separation techniques, and finally the MS detection/resolution/ specificity etc. These methods are then utilized, mainly on human plasma and synovial fluid (SF) samples. Special focus is on the targeted analysis of hydroxylated fatty acids (hFAs), specialized pro-resolving mediators (SPMs) and their intermediates, and other oxylipids present in inflammation and its resolution in rheumatic diseases. For example, the bioactivity of oxylipids and LMs is highly stereospecific, and some difficulties have arisen in the chromatographic separation and resolution of these stereoisomers using classical reversed phase liquid chromatography tandem MS (RPLC-MS/MS), perhaps sometimes resulting in wrong conclusions being drawn, one isomer being confused with another. The work in this thesis was therefore focused on further development and application of analysis platforms for oxidized lipids; their identification, separation and levels in different matrices. All of which, work that can be further used in inflammatory or rheumatoid research. Show less
Natural deep eutectic solvents (NADES) ionic liquids (ILs) and deep eutectic solvents (DES) were proposed by our group to extend the range of ILs and DES, particularly to develop cheap, nontoxic,... Show moreNatural deep eutectic solvents (NADES) ionic liquids (ILs) and deep eutectic solvents (DES) were proposed by our group to extend the range of ILs and DES, particularly to develop cheap, nontoxic, and low viscosity green solvents, and to apply them in health-related fields. They are liquid supramolecules composed of common metabolites in certain molar ratios, including some water in some cases, which are characterized by extensive intermolecular interactions e.g. hydrogen bonds and ionic bonds. NADES present many advantages including low cost, simple preparation, low or negligible toxicity profile and sustainability in view of environment and economics benefits. Their preparation methods, physicochemical properties, supramolecules structures are reported in this thesis. For application, compare to conventional solvents, they show higher solubilization and extraction ability, especially for non-water soluble compounds. They are stable liquids even below zero oC, and their physicochemical properties can be adjusted by changing the water content. In the presence of NADES, anthocyanins and phenolic compounds such as carthamin show higher stability. In addition, we hypothesize that NADES might be involved in the biosynthesis, storage, and transport of various non-water soluble metabolites in cells. In-vitro evidences for their possible functions are also explored in this thesis. Show less
In this study temperature-dependent instability of the cTnI subunit of the three-protein complex NIST SRM2921 was demonstrated using a mass spectrometric tryptic peptide mapping approach. The... Show moreIn this study temperature-dependent instability of the cTnI subunit of the three-protein complex NIST SRM2921 was demonstrated using a mass spectrometric tryptic peptide mapping approach. The results were compared to the cTnI subunit obtained as a protein standard from Calbiochem with identical amino acid sequence. Both the three-protein complex from NIST as well as the cTnI subunit were incubated at elevated temperatures and then evaluated with respect to the primary sequence. The corresponding peptide maps were analyzed using LC–MS/MS. From a Mascot database search in combination with “semiTrypsin” tolerance it was found that two peptide backbone cleavages had occurred in subunit cTnI in NIST SRM2921 material upon incubation at 37°C, namely between amino acids at 148/149 and 194/195. The Calbiochem standard did not show increased levels of “unexpected” peptides in tryptic peptide maps. One of the two peptide backbone cleavages could also be monitored using a “single-step” MALDI-MS approach, i.e. without the need for peptide separation. The amount of degradation appeared rather constant in replicate temperature-instability experiments. However, for accurate quantification internal labelled standards are needed. Show less
The present work discusses several problems related to the stability of ground states with broken supersymmetry in supergravity, and to the existence and stability of cosmic strings in various... Show moreThe present work discusses several problems related to the stability of ground states with broken supersymmetry in supergravity, and to the existence and stability of cosmic strings in various supersymmetric models. In particular we study the necessary conditions to truncate consistently a sector of an N=1 supergravity theory while preserving supersymmetry, and on those models where these conditions are met we discuss how the breaking of supersymmetry in the light sector affects the stability of the truncated fields. In this thesis we also present a new type of supersymmetric cosmic string solutions in N = 2 supergravity. The corresponding model admits a family of cosmic string solutions with the same energy but different core radius. We study the stability of these strings against perturbations in a cosmological context, where the zero mode connecting different solutions within a family could be excited, leading to the spread of the magnetic flux and the disappearence of the string. Show less
Boks, M.A.; Kager-Groenland, J.R.; Haasjes, M.S.P.; Zwaginga, J.J.; Ham, S.M. van; Brinke, A. ten 2012
This thesis deals with Markov operators and semigroups. A Markov operator is a positive linear operator on the space of finite measures on some state space that preserves mass. A Markov semigroup... Show moreThis thesis deals with Markov operators and semigroups. A Markov operator is a positive linear operator on the space of finite measures on some state space that preserves mass. A Markov semigroup is a family of Markov operators parametrised by the positive real numbers, satisfying the semigroup property. These appear naturally in various places: deterministic dynamical systems, iterated function systems, structured population models and more generally Markov chains and Markov processes. We will study general Markov operators and semigroups in a functional analytic framework. Because the usual topology on the space of measures, given by the total variation norm, is often too strong for applications, we consider weaker topologies on the space of measures. and study continuity properties of Markov semigroups and their restriction to invariant subspaces. In the latter part of the thesis we provide ergodic decompositions, yielding, among other things, a characterisation of ergodic measures and an 'explicit' integral decomposition of invariant measures into ergodic measures. Under extra equicontinuity assumptions the ergodic decompositions have some nice properties, allowing us to find various characterisations for the existence, uniqueness, mean ergodicity and stability of invariant measures, and giving us extra information on the set of ergodic measures. Show less
This thesis introduces a novel T cell vaccination method that uses a tattoo machine to inject DNA in the skin of the vaccinee. In comparison to other experimental vaccination methods DNA tattooing... Show moreThis thesis introduces a novel T cell vaccination method that uses a tattoo machine to inject DNA in the skin of the vaccinee. In comparison to other experimental vaccination methods DNA tattooing is very strong: besides small laboratory animals also large animals mount strong T cell responses upon tattoo DNA vaccination. Show less
