{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T20:00:18Z","timestamp":1790712018526,"version":"4.1.0"},"reference-count":39,"publisher":"Oxford University Press (OUP)","issue":"11","license":[{"start":{"date-parts":[[2019,11,1]],"date-time":"2019-11-01T00:00:00Z","timestamp":1572566400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/academic.oup.com\/journals\/pages\/open_access\/funder_policies\/chorus\/standard_publication_model"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2019,11,1]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:sec>\n                  <jats:title>BACKGROUND<\/jats:title>\n                  <jats:p>Currently, several indole markers are measured separately to support diagnosis and follow-up of patients with neuroendocrine tumors (NETs). We have developed a sensitive mass spectrometry method that simultaneously quantifies all relevant tryptophan-related indoles (tryptophan, 5-hydroxytryptophan, serotonin, 5-hydroxyindoleacetic acid) in platelet-rich plasma. Direct-matrix derivatization was used to make the chemical properties of the indoles uniform and to improve the analytical sensitivity and specificity of the assay.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>METHODS<\/jats:title>\n                  <jats:p>In situ derivatization was performed directly in platelet-rich plasma with propionic anhydride at an ambient temperature. The derivatized indoles were extracted by online solid-phase extraction and eluted to the analytical column for separation followed by mass spectrometric detection. The method was validated according to international guidelines. Platelet-rich plasma samples from 68 healthy individuals and 40 NET patients were analyzed for tryptophan, 5-hydroxytryptophan, serotonin, and 5-hydroxyindoleacetic acid.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>RESULTS<\/jats:title>\n                  <jats:p>The method reproducibly quantified relevant indoles in 8.5 min, including online sample cleanup. Intra- and interassay imprecision, evaluated at 3 different concentrations, ranged from 2.0% to 12% and 1.9% to 13%, respectively. The limit of quantification was sufficient to measure endogenous concentrations of all 4 indoles. Healthy individuals and NET patients had different concentrations of 5-hydroxytryptophan, serotonin, and 5-hydroxyindoleacetic acid, but tryptophan concentrations were the same.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>CONCLUSIONS<\/jats:title>\n                  <jats:p>Direct-matrix derivatization in combination with LC-MS\/MS is a powerful tool for the simultaneous quantification of all tryptophan-related indoles in platelet-rich plasma. Simultaneous profiling of relevant indoles improves the biochemical characterization and follow-up of NETs.<\/jats:p>\n               <\/jats:sec>","DOI":"10.1373\/clinchem.2019.305359","type":"journal-article","created":{"date-parts":[[2019,9,24]],"date-time":"2019-09-24T21:25:52Z","timestamp":1569360352000},"page":"1388-1396","source":"Crossref","is-referenced-by-count":24,"title":["Quantitative Profiling of Platelet-Rich Plasma Indole Markers by Direct-Matrix Derivatization Combined with LC-MS\/MS in Patients with Neuroendocrine Tumors"],"prefix":"10.1093","volume":"65","author":[{"given":"Martijn","family":"van Faassen","sequence":"first","affiliation":[{"name":"Department of Laboratory Medicine, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Grytsje","family":"Bouma","sequence":"additional","affiliation":[{"name":"Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lotte D","family":"de Hosson","sequence":"additional","affiliation":[{"name":"Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marloes A M","family":"Peters","sequence":"additional","affiliation":[{"name":"Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gursah","family":"Kats-Ugurlu","sequence":"additional","affiliation":[{"name":"Department of Pathology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elisabeth G E","family":"de Vries","sequence":"additional","affiliation":[{"name":"Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Annemiek M E","family":"Walenkamp","sequence":"additional","affiliation":[{"name":"Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ido P","family":"Kema","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"286","published-online":{"date-parts":[[2019,11,1]]},"reference":[{"key":"2020100805242489400_B1","doi-asserted-by":"crossref","first-page":"265","DOI":"10.1159\/000368363","article-title":"Neuroendocrine tumor biomarkers: 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