David Clases is Postdoctoral Researcher who was awarded a Fellowship by the German Research Foundation to undertake basic and applied research on the role of trace metals and associated transport proteins in the aging brain. He obtained his PhD at the University of Muenster (Germany) and is a member of the Atomic Medicine Initiative.
Can supervise: YES
Elemental Speciation and Imaging
Analytical Chemistry 3
Du, Z, Gupta, A, Clarke, C, Cappadona, M, Clases, D, Liu, D, Yang, Z, Karan, S, Price, W & Xu, X 2020, 'Porous Upconversion Nanostructures as Bimodal Biomedical Imaging Contrast Agents', JOURNAL OF PHYSICAL CHEMISTRY C, vol. 124, no. 22, pp. 12168-12174.View/Download from: Publisher's site
Clases, D, de Vega, RG, Funke, S, Lockwood, TE, Westerhausen, MT, Taudte, RV, Adlard, PA & Doble, PA 2020, 'Matching sensitivity to abundance: high resolution immuno-mass spectrometry imaging of lanthanide labels and endogenous elements in the murine brain', JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, vol. 35, no. 4, pp. 728-735.View/Download from: Publisher's site
Rao, SS, Lago, L, Gonzalez de Vega, R, Bray, L, Hare, DJ, Clases, D, Doble, PA & Adlard, PA 2020, 'Characterising the spatial and temporal brain metal profile in a mouse model of tauopathy', METALLOMICS, vol. 12, no. 2, pp. 301-313.View/Download from: Publisher's site
Clases, D, Fingerhut, S, Jeibmann, A, Sperling, M, Doble, P & Karst, U 2019, 'LA-ICP-MS/MS improves limits of detection in elemental bioimaging of gadolinium deposition originating from MRI contrast agents in skin and brain tissues.', Journal of trace elements in medicine and biology : organ of the Society for Minerals and Trace Elements (GMS), vol. 51, pp. 212-218.View/Download from: Publisher's site
A novel analytical method to detect the retention of gadolinium from contrast agents for magnetic resonance imaging (MRI) in tissue samples of patients is presented. It is based on laser ablation - inductively coupled plasma - triple quadrupole - mass spectrometry (LA-ICP-MS/MS). Both Gd and P were monitored with a mass shift of +16, corresponding to mono-oxygenated species, as well as Zn, Ca, and Fe on-mass. This method resulted in a significantly reduced background and improved limits of detection not only for phosphorus, but also for gadolinium. These improvements were essential to perform elemental bioimaging with improved resolution of 5 μm x 5 μm, allowing the detection of small Gd deposits in fibrotic skin and brain tumour tissue with diameters of approximately 50 μm. Detailed analyses of these regions revealed that most Gd was accompanied with P and Ca, indicating co-precipitation.
Clases, D, Gonzalez De Vega, R, Adlard, PA & Doble, PA 2019, 'On-line reverse isotope dilution analysis for spatial quantification of elemental labels used in immunohistochemical assisted imaging mass spectrometry: Via LA-ICP-MS', Journal of Analytical Atomic Spectrometry, vol. 34, no. 2, pp. 407-412.View/Download from: Publisher's site
© 2019 The Royal Society of Chemistry. We present a novel on-line isotope dilution analysis (IDA) approach for the quantification of isotopically enriched metal labels used in immunohistochemical assisted imaging mass spectrometry. This technique advances recently reported on-line IDA for laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) by performing on-line reverse IDA of isotopically enriched elements commonly used as labels for antibodies. This approach allows relative quantification of biomolecules and is superior to other methods that have long acquisition times such as three-dimensional LA-ICP-MS, or when higher sample throughput is required. As a proof of concept, anti-tyrosine hydroxylase was labelled with Yb isotopes and incubated on two parallel cryocut sections of a mouse brain. IDA dependent parameters were determined by ablation of matrix-matched standards. Quantification by IDA was compared against external calibration and was a more robust method, unaffected by sensitivity changes originating from plasma drifts or spontaneous plasma fluctuations.
Clases, D, Gonzalez de Vega, R, Bishop, D & Doble, P 2019, 'SEC-ICP-MS and on-line isotope dilution analysis for characterisation and quantification of immunochemical assays.', Analytical and bioanalytical chemistry, vol. 411, no. 16, pp. 3553-3560.View/Download from: Publisher's site
This study presents a novel size exclusion chromatography-inductively coupled plasma-mass spectrometry (SEC-ICP-MS) method for the characterisation and quantification of immunoassays with lanthanide-labelled antibodies. SEC-ICP-MS in combination with a double isotope dilution approach enabled facile validation of the antibodies' integrity, the determination of the batch to batch labelling efficiency, monitoring of each labelling step, and quantification of the immunocomplexes after incubation with the target protein. The addition of oxygen into the dynamic reaction cell improved the detection of sulphur as a marker for the antibodies and target protein via mass-shifting (LOD = 3.7 ng/mL), whilst maintaining sufficient sensitivity for the analysis of the lanthanides. Ultra-high performance liquid chromatography (UHPLC) SEC ensured a rapid chromatographic method with separation times under 7 min of the labelled and unlabelled antibodies, the immunocomplexes, and the unconjugated polymer used to lanthanide-label the antibodies. SEC calibration estimated the molecular weights of all peaks and provided valuable insights in immunochemical reactions and the stoichiometry of the reactants and products. A novel on-line isotope dilution analysis (IDA) enabled absolute quantification of sulphur and lanthanide signals and the protein of interest. The chromatographic separation of immunocomplexes and labelled antibodies allowed the simultaneous determination of the antibody/metal stoichiometry and target protein concentration from a single mass flow chromatogram. An immunoglobulin protein was quantified after incubation with an 153Eu-labelled primary polyclonal antibody. The procedure was validated with direct labelling of the target protein with 156Gd for parallel, simultaneous quantification. The concentration determined via direct labelling of the protein deviated 1.9% from the immunochemical approach employing 153Eu-labelled polyclonal antibodies. Graphical abstract.
Eijkelkamp, BA, Morey, JR, Neville, SL, Tan, A, Pederick, VG, Cole, N, Singh, PP, Ong, C-LY, Gonzalez de Vega, R, Clases, D, Cunningham, BA, Hughes, CE, Comerford, I, Brazel, EB, Whittall, JJ, Plumptre, CD, McColl, SR, Paton, JC, McEwan, AG, Doble, PA & McDevitt, CA 2019, 'Dietary zinc and the control of Streptococcus pneumoniae infection.', PLoS pathogens, vol. 15, no. 8.View/Download from: Publisher's site
Human zinc deficiency increases susceptibility to bacterial infection. Although zinc supplementation therapies can reduce the impact of disease, the molecular basis for protection remains unclear. Streptococcus pneumoniae is a major cause of bacterial pneumonia, which is prevalent in regions of zinc deficiency. We report that dietary zinc levels dictate the outcome of S. pneumoniae infection in a murine model. Dietary zinc restriction impacts murine tissue zinc levels with distribution post-infection altered, and S. pneumoniae virulence and infection enhanced. Although the activation and infiltration of murine phagocytic cells was not affected by zinc restriction, their efficacy of bacterial control was compromised. S. pneumoniae was shown to be highly sensitive to zinc intoxication, with this process impaired in zinc restricted mice and isolated phagocytic cells. Collectively, these data show how dietary zinc deficiency increases sensitivity to S. pneumoniae infection while revealing a role for zinc as a component of host antimicrobial defences.
González de Vega, R, Clases, D, Fernández-Sánchez, ML, Eiró, N, González, LO, Vizoso, FJ, Doble, PA & Sanz-Medel, A 2019, 'MMP-11 as a biomarker for metastatic breast cancer by immunohistochemical-assisted imaging mass spectrometry.', Analytical and bioanalytical chemistry, vol. 411, no. 3, pp. 639-646.View/Download from: Publisher's site
MMP-11 is a member of the matrix metalloproteinase family (MMPs) which are overexpressed in cancer cells, stromal cells and the adjacent microenvironment. The MMP protein family encompasses zinc-dependent endopeptidases that degrade the extracellular matrix (ECM), facilitating the breakdown of the basal membrane and matrix connective tissues. This function is believed to be important in cancer development and metastasis. This paper investigated a gold nanoparticle-based immunohistochemical assay to visualise the distribution of MMP-11 in human breast cancer tissues from eight patients with and without metastases by employing laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The expression of MMP-11 was increased and more heterogeneous in metastatic specimens compared to non-metastatic tumour samples. These findings demonstrate that imaging breast tumours by LA-ICP-MS may be a useful tool to aid the prognosis and treatment of breast cancer. As an example, samples of two patients are presented who were diagnosed with matching characteristics and grades of breast cancer. Although both patients had a similar prognosis and treatment, only one developed metastases.
Westerhausen, MT, Lockwood, TE, Gonzalez de Vega, R, Röhnelt, A, Bishop, DP, Cole, N, Doble, PA & Clases, D 2019, 'Low background mould-prepared gelatine standards for reproducible quantification in elemental bio-imaging.', The Analyst, vol. 144, no. 23, pp. 6881-6888.View/Download from: Publisher's site
Standard preparation for elemental bio-imaging by laser ablation-inductively coupled plasma-mass spectrometry is confounded by the chemical and physical differences between standard and sample matrices. These differences lead to variable ablation, aerosol generation and transportation characteristics and must be considered when designing matrix-matched standards for reliable calibration and quantification. The ability to precisely mimic sample matrices is hampered due to the complexity and heterogeneity of biological tissue and small variabilities in standard matrices and sample composition often negatively impact accuracy, precision and robustness. Furthermore, cumbersome preparation protocols may limit reproducibility and traceability. This work presents novel facile methods for the preparation of gelatine standards using both commercial and laboratory-made moulds. Surface roughness, thickness and robustness of the mould-prepared standards were compared against cryo-sectioned gelatine and homogenised brain tissue standards. The mould-prepared standards had excellent thickness accuracy and signal precision which allowed robust quantification, were easier to prepare and therefore easier to reproduce. We also compared gelatine standards prepared from a variety of animal sources and discuss their suitability to calibrate low level elemental concentrations. Finally, we present a simple method to remove background metals in gelatine using various chelating resins to increase the dynamic calibration range and to improve limits of analysis.
Axer, A, Hermann, S, Kehr, G, Clases, D, Karst, U, Fischer-Riepe, L, Roth, J, Fobker, M, Schäfers, M, Gilmour, R & Faust, A 2018, 'Harnessing the Maltodextrin Transport Mechanism for Targeted Bacterial Imaging: Structural Requirements for Improved in vivo Stability in Tracer Design.', ChemMedChem, vol. 13, no. 3, pp. 241-250.View/Download from: Publisher's site
Diagnosis and localization of bacterial infections remains a significant clinical challenge. Harnessing bacteria-specific metabolic pathways, such as the maltodextrin transport mechanism, may allow specific localization and imaging of small or hidden colonies. This requires that the intrabacterial tracer accumulation provided by the transporter is matched by high serum stability of the tracer molecule. Herein, radiolabeled maltodextrins of varying chain lengths and with free nonreducing/reducing ends are reported and their behavior against starch-degrading enzymes in the blood, which compromise their serum stability, is evaluated. Successful single-photon emission computed tomography (SPECT) imaging is shown in a footpad infection model in vivo by using the newly developed model tracer, [99m Tc]MB1143, and the signal is compared with that of 18 F-fluorodeoxyglucose positron emission tomography ([18 F]FDG-PET) as a nonbacterial specific marker for inflammation. Although the [99m Tc]MB1143 imaging signal is highly specific, it is low, most probably due to insufficient serum stability of the tracer. A series of stability tests with different 18 F-labeled maltodextrins finally yielded clear structural guidelines regarding substitution patterns and chain lengths of maltodextrin-based tracers for nuclear imaging of bacterial infections.
Clases, D, Sperling, M & Karst, U 2018, 'Analysis of metal-based contrast agents in medicine and the environment', TrAC - Trends in Analytical Chemistry, vol. 104, pp. 135-147.View/Download from: Publisher's site
© 2017 Elsevier B.V. Technetium (Tc) and Gadolinium (Gd) are the two most widely used metals in diagnostic medicine for scintigraphies and magnet resonance imaging (MRI), respectively. They play a crucial role for the generation or enhancement of contrast and are indispensable in countless diagnostic applications. However, the use of such contrast agents has caused severe health issues and environmental anomalies. This review aims to point out current issues and developments regarding the role and the analysis of these trace metals in medicine and the environment. Basic principles, issues and state of art of analytical methodologies are summarized. Current and future trends and the suggested implementation of novel methodologies and instrumentation are presented.
Bishop, DP, Hare, DJ, Clases, D & Doble, PA 2018, 'Applications of liquid chromatography-inductively coupled plasma-mass spectrometry in the biosciences: A tutorial review and recent developments', TrAC - Trends in Analytical Chemistry, vol. 104.View/Download from: Publisher's site
© 2017. The biological function of minor and trace elements is ordinarily determined by their association with specific proteins, peptides and other biomolecules. Therefore, measuring the total elemental content of a biological sample provides limited information, particularly when a specific effect is due to an individual metal-protein complex. Speciation of metalloproteins, heteroatom-containing molecules or other compounds tagged with an exogenous metal can be used to overcome this limitation. A range of chromatographic separation techniques with on-line elemental detection using inductively coupled plasma-mass spectrometry (ICP-MS) have been applied to the biosciences, and each technique has intrinsic features that must be considered when designing speciation experiments. This tutorial review provides an overview of speciation in the biosciences, highlighting the unique abilities and limitations encountered. A selection of recent technical advances and new applications, the challenges of sample preparation and implementation of new technical developments are discussed, as well as the future directions of technology that is rapidly gaining a foothold in the contemporary biochemistry laboratory.
Clases, D, Birka, M, Sperling, M, Faust, A & Karst, U 2017, 'Isobaric dilution analysis as a calibration tool for long lived radionuclides in ICP-MS.', Journal of Trace Elements in Medicine and Biology, vol. 40, pp. 97-103.View/Download from: Publisher's site
A novel quantification method named isobaric dilution analysis (IBDA) is introduced for internal calibration using inductively coupled plasma mass spectrometry (ICP-MS). Unlike isotope dilution analysis (IDA), where a sample to be analysed for a target analyte element is spiked with an isotopically enriched solution of the same element, IBDA uses the fact that conventional mass analysers cannot distinguish between two isobaric isotopes of different elements. Therefore, in IBDA, the sample with the element of interest is spiked with a solution of a different element, which shares at least one isobaric isotope and shows similar chemical properties resulting in a similar response. This method offers a less expensive alternative to conventional IDA especially for long-lived radionuclides of elements for which a spiking element that fulfils the above mentioned requirements can be provided. In addition, IBDA offers the advantage of making certain metastable, sometimes monoisotopic elements accessible to internal calibration using a strategy analogous to IDA. One of the elements accessible by the new calibration strategy is technetium (Tc), which suffers from a lack of standards due to safety requirements associated with its radioactivity. In this work, the principle of IBDA is first demonstrated for a certified gadolinium standard, which was diluted with a dysprosium spike exhibiting an isobaric isotope with m/z 160. The results obtained by IBDA were compared with those obtained by a conventional IDA. The concept of IBDA was subsequently used for the determination of 99Tc in a contrast agent. Since no certified Tc standards are available, the response of 99Tc was interpolated allowing accurate determinations with an uncertainty of 1%.