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Abstract No.: ThP-140
Session: Instrumentation and Methodologies for Imaging MS
Presentation date: Thu, Aug 31, 2006
Presentation time: 14:30 – 16:00

Use of Principal Components Analysis to Aid Profiling of Lipids in Colorectal Liver Metastasis by Imaging MALDI-MS

Malcolm Ronald Clench1, Sally Jane Atkinson1, Vikki Amanda Carolan1, Ali Majeed2, Nigel Bird2, David Mangnall2, Michael M. Burrell3

1 Sheffield Hallam University, Sheffield, United Kingdom
2 Royal Hallamshire Hospital, Sheffield, United Kingdom
3 University of Sheffield, Sheffield, United Kingdom

Correspondence address: Malcolm Ronald Clench, Sheffield Hallam University, Biomedical Research Centre, Howard Street, Sheffield, S1 1WB United Kingdom.

Keywords: Biomarkers; MALDI; Phospholipids; Principal Component Analysis.

Novel aspect: Combination of imaging MALDI and PCA to examine phopholipids in tumours.

 

Introduction
Metastatic disease of the liver is a frequent event for patients with colorectal cancer and remains a major cause of cancer-related death. Growth and invasion of the liver by cancer metastasis requires signalling between tumour cells and the tissue in which it is growing in order that the tumour grows without causing the inflammatory responses that would inhibit such invasion. Lipids have important cellular functions as second messengers in events such as growth, proliferation and cell death and are involved in important signal transduction processes including cancer development. We have combined imaging MALDI-MS with principal component analysis in order to study lipid variations at the tumour:liver margin to help to understand these processes.

Methods
Samples were obtained in the operating theatre following fully informed patient consent and local ethical approval. 30 µm sections were taken and coated with α-CHCA (25mg/ml 100% ethanol 0.1%TFA) using an airspray technique. Data were acquired on an Applied Biosystem "Q-Star Pulsar-i" hybrid QTof instrument. Full scan mass spectra were recorded in both positive and negative ion mode using a 200 µm raster pattern. Spectra were recorded for 2.5 sec at a laser energy of 3.4 µJ (30% laser power) and a repetition rate of 1kHz. Following data acquisition signal intensities were normalised to the matrix ion at m/z 190 and data were submitted for PCA analysis using "Markerview".

Preliminary results
A range of phospholipids were readily identifiable in the liver tissue by MALDI the spectra obtained are comparable with DESI data reported previously by Cooks et al. In positive ion mode of interest were peaks at m/z 703.5, 732.5, 734.5, 758.5, 760.5, 772.5, 782.5, 786.5, 788.5, 808.5, 810.5, which could be tentatively identified as [M+H]+ ions for sphingomyelin (SM) 16:0, phosphatidylcholine (PC) 32:1, PC 32:0, phospahtidylcholine ether (PCO) 36:2, PC 36:3, PC 36:1, PC 38:3, and PC 38:4 respectively. Images of the distribution of these ions were produced following normalisation to the matrix peak at m/z 190 in each pixel. These images showed a remarkable agreement with those obtained by conventional histology (H&E) staining with tumour, margin and healthy tissue being readily identifiable. PCA analysis also clearly grouped data into separate regions of the tissue in the scores plot, by using Pareto scaling target ions for imaging could be identified in the loadings plot.