Profiling of tryptophan-related plasma indoles in patients with carcinoid tumors by automated, on-line, solid-phase extraction and HPLC with fluorescence detection

Background: Profiling of the plasma indoles tryptophan, 5-hydroxytryptophan (5-HTP), serotonin, and 5-hydroxyindoleacetic acid (5-HIAA) is useful in t he diagnosis and follow-up of patients with carcinoid tumors. We describe a n automated method for the profiling of these indoles in protein-containing matrices as well as the plasma indole concentrations in healthy controls a nd patients with carcinoid tumors. Methods: Plasma, cerebrospinal fluid, and tissue homogenates were prepurifi ed by automated on-line solid-phase extraction (SPE) in Hysphere Resin SH S PE cartridges containing strong hydrophobic polystyrene resin. Analytes wer e eluted from the SPE cartridge by column switching. Subsequent separation and detection were performed by reversed-phase HPLC combined with fluoromet ric detection in a total cycle time of 20 min. We obtained samples from 14 healthy controls and 17 patients with metastasized midgut carcinoid tumors for plasma indole analysis. In the patient group, urinary excretion of 5-HI AA and serotonin was compared with concentrations of plasma indoles. Results: Within- and between-series CVs for indoles in platelet-rich plasma were 0.6-6.2% and 3.7-12%, respectively. Results for platelet-rich plasma serotonin compared favorably with those obtained by single-component analys is. Plasma 5-HIAA, but not 5-HTP was detectable in 8 of 17 patients with ca rcinoid tumors. In the patient group, platelet-rich plasma total tryptophan correlated negatively with platelet-rich plasma serotonin (P = 0.021; r = -0.56), urinary 5-HIAA (P = 0.003; r = -0.68), and urinary serotonin (P <0. 0001; r = -0.80). Conclusions: The present chromatographic approach reduces analytical variat ion and time needed for analysis and gives more detailed information about metabolic deviations in indole metabolism than do manual, single-component analyses. (C) 2001 American Association for Clinical Chemistry.