Background Carboxyl-containing metabolites (CCMs) widely exist in the living system and are the essential components of life. Global characteristics of CCMs in biological samples represent a challenge due to enormous polarity difference, structural diversity, high structural similarity, and poor ionisation efficiency in mass spectrometry.
Methods An innovative mass spectrometry probe, 5-(diisopropylamino)amyline (DIAA), was developed for mapping the profile of CCMs using derivatization-liquid chromatography-mass spectrometry.
Results With this innovative methodology, the sensitivity was enhanced up to 25,000-fold. Moreover, the hydrophobicity of polar CCMs, amino acids, TCA cycle intermediates and short-chain fatty acids, and the hydrophilicity of low-polar CCMs, long-chain fatty acids and bile acids, were significantly increased, resulting in a remarkable separation efficiency for which 68 different CCMs can be simultaneously determined. The polarity-reversal was revealed to be induced by the different impacts of aliphatic chains and nitrogen atom in DIAAA, the latter existing as a cation in the acidic mobile phase. Furthermore, a novel isotope labelled probe, DIAA-d 14, was also synthesised and utilised to develop an isotope labelling method based on DIAA/DIAA-d 14 pair for quickly and accurately hunting for the potential biomarkers in colorectal cancer (CRC), which is the second leading cause of death in the world. Finally, 52 CCMs were detected in the sera of CRC patients and 28 CCMs related with amino acids metabolism, TCA cycle, fatty acid metabolism, and gut flora metabolism were found to have a significant difference with that in healthy controls. The decrease of five SCFAs, including propionic acid (PA), butyric acid (BA), isobutyric acid (IBA), isovaleric acid (IVA) and valeric acid (VA) in the sera (figure 1). It was further confirmed in line with that of ApcMin/+ mice, a well-established animal model of intestinal cancer.
Conclusions These results clearly indicated a close relationship of the change of serum SCFAs with CRC for the first time. This innovative mass spectrometry probe via polarity-reversal derivatization was confirmed to be a valuable tool for metabolomics study with high sensitivity and separation efficiency in various biological samples.
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