Untargeted Analysis of Mass Spectrometry Data for Elucidation of Metabolites and Function of Enzymes

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Abstract
A Matlab-based computer program termed Discovery of General Endo- and Xenobiotics (DoGEX) was developed, which uses wavelets and morphological analysis to process liquid chromatography−mass spectrometry (LC−MS) data. The output of the program is a list of integration areas as a function of retention time and molecular mass. A feature of the computer program is spectral filtering to facilitate the detection of chromatographic peaks with a particular isotopic ratio. The program DoGEX was used to automatically select oxidation products formed from felodipine (i.e., two chlorine atoms) and bromocriptine (one bromine atom) with cytochrome P450 3A4. The recognized isotope ratio can be changed to permit a natural or artificial mixture of isotopes to be monitored for selections. This computer program can be used to analyze LC−MS data for untargeted metabolic profiling experiments, e.g., to assign endogenous functions to newly characterized cytochrome P450 enzymes. In a representative example, an incubation of testosterone, NADPH, and a 1:1 16O2/18O2 mixture yielded products with M and M + 2 ions resembling bromine doublets. Another use of the program is the subtraction of one set of tR, m/z data from another, e.g., in comparisons of changes in patterns during enzyme reactions.