Tackling the Peak Overlap Issue in NMR Metabolomic Studies: 1D Projected Correlation Traces from Statistical Correlation Analysis on 2D 1H NMR J-Resolved Nontilted Spectra"

CHARRIS-MOLINA, ANDRÉS; RIQUELME, GABRIEL; BURDISSO, PAULA; HOIJEMBERG, PABLO ARIEL

Ciudad Autónoma de Buenos Aires

Taller; IV Taller de Resonancia Magnética; 2018

Fundación Instituto Leloir

The identification of metabolites in complex biological matrices is a challenging task in 1D 1H NMR based metabolomic studies. Statistical TOtal Correlation SpectroscopY (STOCSY) has emerged for aiding with compound ID by revealing the peaks that present high correlation to a driver peak of interest, which would all likely belong to the same molecule (Anal. Chem. 2005, 77, 1282). However, in these 1D 1H NMR studies the signals from molecules are normally present as a mixture of overlapping resonances, limiting the performance of STOCSY. In the past, 2D 1H homonuclear J-resolved spectra (JRES) were projected (in its usual tilted and symmetrized processed form) and STOCSY was applied on these 1D projections (pJRES-STOCSY) as an alternative to avoid the overlap issue, but this approach suffers in cases where the signals are very close (Anal Chem. 2017, 89, 11405) and does not promptly provide a full peak list for database (DB) searches. With these limitations in mind, we propose a new methodology called COrrelation COmparison Analysis for Peak Overlap Detection (COCOA-POD), based on the application of STOCSY on a set of 2D nontilted JRES spectra (ntJRES-STOCSY), detecting peaks that would overlap in 1D spectra of the same sample set. A projection of it serves to create a peak list for DB queries from a STOCSY-like 1D trace, but due to the spread of peaks in JRES spectra it performs better than the direct 1D STOCSY analysis.For example, COCOA-POD was able to distinguish in a set of blood serum spectra an interesting case of peak overlap occurring at f2 = 1.189 ppm, where a peak from the ethanol triplet overlaps with a peak from the 3-hydroxybutyric acid (3-HBA) doublet. Fig. 1 shows COCOA-POD applied to the driver peak at f2 = 1.189 ppm and f1 = +0.005 ppm (purple crosses). The 1D STOCSY on the projections from ntJRES spectra (Fig. 1C) reveals the profile of the ethanol spectrum, indicating that its correlation surpasses that of the 3-HBA peak at f2 = 1.189 ppm. In contrast, Fig. 1D presents an evident high correlation to the other doublet peak for 3-HBA, together with the two doublets of doublets and the low intensity peaks around 4.1 ppm (the singlets for acetone and acetoacetate also appear, due to biological correlation).