Targeted metabolomics analysis of aromatic amino acids and their gut microbiota-host cometabolites in rat serum and urine by liquid chromatography coupled with tandem mass spectrometry

Gut microbiota-host cometabolites are closely related to various diseases. Monitoring dynamic changes of cometabolites can provide a more comprehensive understanding of pathophysiology. Here, a novel liquid chromatography-tandem mass spectrometry method was performed for the analysis of aromatic amino acids and their gut microbiota-host cometabolites in rat serum and urine. In the developed method, seven key gut microbiota-host cometabolites were chromatographically separated on a Kinetex Phenyl-Hexyl column by gradient elution, and the run time was 6 min. Serum and urine were extracted by protein precipitation. This method was linear between 10.20 and 1000.00 ng/mL for phenylalanine and p-cresyl sulfate; 25.60-2500.00 ng/mL for tryptophan; 51.20-5000.00 ng/mL for tyrosine, indole, and indoxyl sulfate; and 75.50-7500.00 ng/mL for p-cresol. The linearity, accuracy, precision, and recovery of seven analytes were all satisfactory. The method was sufficiently sensitive and robust. It was successfully applied to characterize the alterations of gut microbiota-host cometabolites in inflammatory disorders. All of these results suggest that the developed method is able to simultaneously monitor aromatic amino acids and their gut microbiota-host cometabolites. This method will be expected to be a valuable tool for clinical researches and comprehensive studies of the pathophysiological roles.