Simultaneous determination of indole metabolites of tryptophan in rat feces by chemical labeling assisted liquid chromatography-tandem mass spectrometry

Abstract

As the connecting part of diet and host physiology, intestinal microbes can convert the ingested diet into a huge number of physiologically active small molecules. Indole metabolites of tryptophan are precursors or signal molecules for many biologically active substances, which are involved in serotonin and microbial catabolism pathways. To understand the influence of tryptophan metabolism in the intestinal environment on the neurological and immune systems at the molecular level, it is important to establish a high-coverage analytical method to comprehensively analyze the metabolites involved in tryptophan metabolism. However, due to a small molecular weight and poor response during mass spectrometry analysis, as well as weak retention on the reversed-phase chromatography, determination of indole metabolites of tryptophan is challenging. Here, we proposed a method for the simultaneous determination of 20 indole metabolites of tryptophan in a single run on reversed-phase chromatography by chemical labeling coupled to liquid chromatography-tandem mass spectrometry analysis. 4-(Dimethylamino)benzaldehyde (DMAB) was used for the labeling of indole metabolites of tryptophan, which could significantly improve the detection sensitivities and retention of these metabolites on reversed-phase chromatography. With the developed method, we realized the sensitive detection and comprehensive analysis of 15 endogenous indole metabolites of tryptophan in rat feces samples with functional dyspepsia intervention by acupuncture. The developed method offers a useful tool for studying tryptophan metabolism-related diseases.