Simultaneous determination of serum tryptophan metabolites in an older Chinese population

Abstract Tryptophan (TRP) and its metabolites exhibit significant biological effects and are strongly associated with age‐related disease and mortality. However, reports on quantitatively analyzing these metabolites in older individuals are not available. We used ultra‐high‐performance liquid chromatography–tandem mass spectrometry to optimize and validate a method for isotope dilution analysis of TRP metabolites in older individuals. The targeted analytes are TRP, serotonin or 5‐hydroxytryptamine, kynurenine, kynurenic acid, xanthurenic acid, indole‐3‐acetic acid, indole‐3‐propionic acid, and tryptamine. The serum sample was purified using solid‐phase extraction and was separated on a Waters HSS T3 column (100 mm × 2.1 mm, 1.8 μm). The analytes were detected in the multiple reaction monitoring mode under positive ionization. TRP was confirmed and measured after being diluted 100 times. This method exhibited satisfactory linearity ( r > 0.99). The intrabatch and interbatch accuracies (85.7–114%) and precisions (<15%) were acceptable. The standard‐normalized matrix effects ranged from 51.6 to 145%. This method was successfully applied to a cohort of 1021 older Chinese individuals, and this study may enable further understanding of the metabolic phenotypes associated with TRP in other populations.