BIOMAP · Simultaneous Elemental and Molecular Imaging of Biological Targets – A New Paradigm for the Study of Disease and its Treatment

Simultaneous Elemental and Molecular Imaging of Biological Targets – A New Paradigm for the Study of Disease and its Treatment

Marie Curie Incoming Fellowship: BIOMAP (272957): Simultaneous Elemental and Molecular Imaging of Biological Targets – A New Paradigm for the Study of Disease and its Treatment. Wang Meng, Barry L Sharp and Helen J Reid, Centre for Analytical Science, Department of Chemistry, Loughborough University, Loughborough, LE11 3TU, UK. 1 Introduction Imaging of biological targets such as tissue sections, cell assemblies or individual cells is a rapidly developing science that plays a key role in the diagnosis, treatment and understanding of the aetiology of disease processes. At the atomic and molecular level, mass spectrometry is a key technique for mapping individual molecular or elemental signatures. Whilst molecular imaging is well established, elemental imaging may be regarded as an emerging discipline. The principal aims of this project were to investigate the feasibility of simultaneous molecular and elemental imaging on a single instrumental platform and to develop new techniques of engineering cells to contain elemental labels to enhance their detection. A new and exciting application of single cell imaging is the tracking of cells used in cell-based therapies, such as immune suppression following transplant surgery, as in the FP7 project the ONE Study in which our laboratory is a participant. 2 Results i) Imaging Technology Elemental and molecular signals were obtained from a common instrumental platform based on the equipment employed for laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS); previously this technology has been used solely for elemental imaging. However, the current generation of laser equipment was not capable of yielding simultaneous molecular and elemental imaging. A new laser system is being developed, in collaboration with commercial partners and informed by the findings of BIOMAP, which will address these shortcomings. The target molecule for this study was the peptide glutathione which contains a sulphur atom that is readily detected by elemental mass spectrometry (see Figure 1). Coupling the laser to the biological target is a key component of imaging technology and during this project our laboratory developed a new high speed laser interface, primarily to meet the demands of the ONE Study. Components of this system were used in BIOMAP, but the full system awaits delivery of the new laser instrumentation. This new technology provides single cell signals of 10 ms duration which is 3-10 times faster than current systems allied with a 6 fold improvement in absolute sensitivity (see Figure 2). ii) Detection of Engineered Cells Two novel and successful approaches to labelling of individual cells have been investigated in BIOMAP. The first involves the development of a lanthanide nano-particle based on encapsulation in an apoferritin complex (see Figure 3). These nano-complexes can host several hundred lanthanide atoms providing a significant amplification of the element signal from the host cell. Alternatively, such particles can be used as a tag to enable the detection/quantification of ferritin by coupling to a specific ferritin antibody immobilised onto a suitable substrate. Thus a competitive binding assay was demonstrated in which ferritin antibodies were immobilised in wells and the element signals recorded by elemental mass spectrometry. The second project employed gold nano-particles as the cellular elemental tag and whilst these have been used previously, the key issue here was to establish a calibration method for the amount of gold contained in individual cells. Thus ink-jet printing technology was used to print gold standard dots onto glass slides that were then probed alongside the target cells by LA-ICP-MS (see Figure 4). 3 Beneficiaries and Societal Impact The principal target group are scientists involved in bio-medical research and we illustrate this here with specific examples from our own work, thus: the study of age-related diseases such as macular degeneration where elements such as Zn are known to be a key factor in the disease pathways; in the use of metallo-drugs such as the Pt-based drugs used in cancer chemotherapy; the detection of implanted therapeutic cells as in the ONE Study. The primary societal impacts of this project will derive from applying its findings to improving the health of the EU citizens, as exemplified in the examples given above. A further benefit has derived from establishing a scientific collaboration with the Key Laboratory of Nuclear Radiation and Nuclear Energy Technology / Key Laboratory for Biomedical Effects of Nano-materials and Nano-safety, Beijing and the interaction of our young researchers with BIOMAP and Dr Wang the Marie Curie Fellow. List of Figures Figure 1 – TIC and Full Mass Scan spectrum of glutathione desorbed from DHB MALDI matrix. The molecular ion signal MH+ at m/z 308.25 was detected by an ion trap mass spectrometer, although the signal-to-noise ratio was relatively low. Figure 2 – 238U+ signal profile from the laser ablation of NIST 613 glass reference material obtained using a new high-speed laser interface. Figure 3 – Schematic of the synthesis of apoferritin-templated lanthanide phosphate nanoparticles (Ln: Lanthanide). Figure 4 – Image of droplet residues of 2 µg g-1Au standards on a glass slide under a light microscope. The scale bar is 100 µm.

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