Exploring extra dimensions to capture saliva metabolite fingerprints from metabolically healthy and unhealthy obese pati
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RESEARCH PAPER
Exploring extra dimensions to capture saliva metabolite fingerprints from metabolically healthy and unhealthy obese patients by comprehensive two-dimensional gas chromatography featuring Tandem Ionization mass spectrometry Marta Cialiè Rosso 1 & Federico Stilo 1 & Simone Squara 1 & Erica Liberto 1 & Stefania Mai 2 & Chiara Mele 2,3 & Paolo Marzullo 2,3 & Gianluca Aimaretti 3 & Stephen E. Reichenbach 4,5 & Massimo Collino 1 & Carlo Bicchi 1 & Chiara Cordero 1 Received: 3 August 2020 / Revised: 1 October 2020 / Accepted: 13 October 2020 # The Author(s) 2020
Abstract This study examines the information potential of comprehensive two-dimensional gas chromatography combined with time-offlight mass spectrometry (GC×GC-TOF MS) and variable ionization energy (i.e., Tandem Ionization™) to study changes in saliva metabolic signatures from a small group of obese individuals. The study presents a proof of concept for an effective exploitation of the complementary nature of tandem ionization data. Samples are taken from two sub-populations of severely obese (BMI > 40 kg/m2) patients, named metabolically healthy obese (MHO) and metabolically unhealthy obese (MUO). Untargeted fingerprinting, based on pattern recognition by template matching, is applied on single data streams and on fused data, obtained by combining raw signals from the two ionization energies (12 and 70 eV). Results indicate that at lower energy (i.e., 12 eV), the total signal intensity is one order of magnitude lower compared to the reference signal at 70 eV, but the ranges of variations for 2D peak responses is larger, extending the dynamic range. Fused data combine benefits from 70 eV and 12 eV resulting in more comprehensive coverage by sample fingerprints. Multivariate statistics, principal component analysis (PCA), and partial least squares discriminant analysis (PLS-DA) show quite good patient clustering, with total explained variance by the first two principal components (PCs) that increases from 54% at 70 eV to 59% at 12 eV and up to 71% for fused data. With PLSDA, discriminant components are highlighted and putatively identified by comparing retention data and 70 eV spectral signatures. Within the most informative analytes, lactose is present in higher relative amount in saliva from MHO patients, whereas Nacetyl-D-glucosamine, urea, glucuronic acid γ-lactone, 2-deoxyribose, N-acetylneuraminic acid methyl ester, and 5aminovaleric acid are more abundant in MUO patients. Visual feature fingerprinting is combined with pattern recognition algorithms to highlight metabolite variations between composite per-class images obtained by combining raw data from individuals belonging to different classes, i.e., MUO vs. MHO. Keywords Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry . Variable ionization energy . Untargeted fingerprinting by template matching . Saliva metabolome . Fused data from multiplexed ionization Marta Cialiè Rosso and Federico Stilo contributed equally to this work. Electronic supplementary mater
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