Rapid simultaneous determination of gut microbial phenylalanine, tyrosine, and tryptophan metabolites in rat serum, urine, and faeces using LC-MS/MS and its application to a type 2 diabetes mellitus study.

Gut microbial phenylalanine, tyrosine, and tryptophan metabolites are closely linked to various diseases. Monitoring the alterations of the related metabolites is vital to facilitate the understanding of pathophysiology of diseases. Herein, a rapid and sensitive assay based on LC-tandem mass spectrometry has been developed to analyze 20 gut microbial metabolites derived from phenylalanine, tyrosine, and tryptophan in rat serum, urine, and faeces. These microbial-derived metabolites were separated on a phenyl-hexyl column and simultaneously determined in a single run of 8 min. The detection limit for analytes ranged between 1.08 and 32.4 ng/mL. All calibration curves exhibited good linear relationships (R  ≥ 0.9982). Intra- and inter-assay precision values were below 15% and accuracies ranged from 85% to 115% for all analytes. The selectivity, matrix effect, and recovery of this method were all satisfactory. The validated method was successfully applied to characterize the alterations of these metabolites in type 2 diabetes mellitus rat. In general, the developed assay is suitable for high-throughput monitoring of gut microbial phenylalanine, tyrosine, and tryptophan metabolites and provides a useful approach for exploring the mechanisms of microbial-derived metabolites in diseases.