Matrix assisted laser desorption ionisation ion mobility separation mass spectrometry imaging of ex-vivo human skin
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ORIGINAL RESEARCH
Matrix assisted laser desorption ionisation ion mobility separation mass spectrometry imaging of ex-vivo human skin Philippa J. Hart & Simona Francese & M. Nicola Woodroofe & Malcolm R. Clench
Received: 20 November 2012 / Revised: 23 January 2013 / Accepted: 6 February 2013 / Published online: 27 February 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract Matrix assisted laser desorption ionisation ion mobility separation mass spectrometry imaging (MALDI-IMSMSI) has been employed to image the distribution of proteins in ex-vivo human skin. Using a “bottom-up” proteomics approach employing “on-tissue” digestion the distribution of abundant skin proteins; collagen, keratin, decorin and serum albumin could be mapped. Images have been recorded at 150 and 30 μm spatial resolution. Multivariate statistical analysis of the data has been employed to associate specific proteins with layers of the skin. The improved specificity given by the use of ion mobility separation in mass spectrometric imaging has been demonstrated by separation of peptide ions from phospholipids. Keywords MALDI . Skin . MALDI-imaging . Peptides
Introduction The use of a MALDI-ion mobility-TOF-MS imaging instrument for improved specificity in image generation was first reported in 2007 [1]. Using this instrument the authors imaged the distribution of lipids within coronal brain sections after ion mobility separation. We have also been investigating the use of matrix assisted laser desorption ionisation ion-mobility separation mass spectrometry imaging (MALDI-IMS-MSI). In our work we have utilised Waters Synapt HDMS™ and Waters Synapt G2 HDMS™ instruments which both incorporate a Triwave™ device. This type of instrument has been described in detail by Giles et al. [2]. Briefly the instruments are QTOF hybrid P. J. Hart : S. Francese : M. N. Woodroofe : M. R. Clench (*) Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S11WB, UK e-mail: [email protected]
type instruments which contain in place of the conventional RF only quadrupole collision cell a Triwave™ cell. This of consists of three distinct parts the “Trap” which acts as an ion guide, but also gates the ions into the travelling wave ion mobility cell (T-WAVE IMS) in “bunches” for ion mobility separation. Once the ions have been separated within the TWAVE IMS cell they enter the “Transfer” region, which is another ion guide and is used to transfer the ions into the TOF analyser. We have used these instruments to study the distribution of the anti-cancer drug Vinblastine in whole body tissue sections [3] and have investigated “bottom-up” proteomics strategies that utilise ion-mobility separation to improve peptide identification for the study of fresh frozen pancreatic tumours and in the study of protein induction in vascular targeted therapies [4, 5]. This approach was also applied to formalin fixed paraffin embedded (FFPE) tissue in studies of the induction of GRP78 and tumour classification in tissue microarrays [6, 7]. Digestion of pep
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