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Metabolomic Coverage of Chemical-Group-Submetabolome Analysis: Group Classification and 4-Channel Chemical Isotope Labeling LC-MS.

Shuang Zhao,Hao Li,W. Han,W. Chan,Liang Li

Published 2019 in Analytical Chemistry

ABSTRACT

Chemical isotope labeling (CIL) liquid chromatography mass spectrometry (LC-MS) is a powerful technique for in-depth metabolome analysis with high quantification accuracy. Unlike conventional LC-MS, it analyzes chemical-group-based submetabolomes and uses the combined results to represent the whole metabolome. Due to analysis time and cost constraint, not all submetabolomes can be profiled and thus knowledge of chemical group classification is important in guiding submetabolome selection. Herein we report a study of determining the distribution of functional groups of compounds in a database and then examine how well we can experimentally analyze the major chemical groups in two representative samples (i.e., human plasma and yeast). We developed a computer algorithm to classify chemical structures according to their functional groups. After removing lipids which are targeted molecules in lipidomic analysis, inorganic species and other molecules that are unique to drug, food, plant and environmental origins, five groups (i.e., amine, phenol, hydroxyl, carboxyl and carbonyl) are found to be the dominant classes. In the databases of MCID (2,683 filtered metabolites), HMDB (5,506), KEGG (11,598), YMDB (1,107) and ECMDB (1,462), 94.7%, 85.7%, 86.4%, 85.7% and 95.8% of the filtered metabolites belong to one or more of the five groups, respectively. These groups can be analyzed in 4-channel CIL LC-MS where hydroxyls (H), amines and phenols (A), carboxyls (C) and carbonyls or ketones/aldehydes (K) are separately profiled as individual channels using dansyl and DmPA labeling reagents. A total of 7,431 peak pairs were detected with 6,109 unique-mass pairs from plasma, while 5,629 pairs with 4,955 unique-mass pairs were detected in yeast. Compared to group distributions of database compounds, hydroxyl-containing metabolites were severely under-detected, which might indicate that the current method is less than optimal for analyzing this group of metabolites. As a result, the overall experimental coverage is likely significantly lower than the database-derived coverage. In short, this study has shown that high metabolome coverage is theoretically attainable by analyzing only the H, A, C and K-submetabolomes and the group classification information should be helpful in guiding future analytical method development and choices of submetabolomes to be analyzed.

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