Plasma tryptophan, kynurenine and 3-hydroxykynurenine measurement using automated on-line solid-phase extraction HPLC–tandem mass spectrometry

Quantitative profiling of tryptophan metabolites in serum, urine, and cell culture supernatants by liquid chromatography–tandem mass spectrometry

“…LC-MS/MS was also employed to measure both intracellular and extracellular levels of Trp, KYN, HK, and HAA [23]. In 2009, de Jong et al [24] developed an LC-MS/MS method that enabled the simultaneous extraction, concentration, separation, and mass selective detection of Trp, KYN, and HK in plasma. The most comprehensive method to date was introduced by Midttun et al [25], who employed LC-MS/ MS to quantify plasma levels of Trp, KYN, HK, KA, AA, XA, and HAA.…”

Status of cellular immunity lacks prognostic significance in vulvar squamous carcinoma

“…Furthermore, the intracellular enzyme indoleamine 2,3-dioxygenase (IDO) is currently considered an important immune escape mechanisms in cancer. IDO catalyses the first and rate-limiting steps in the breakdown of the essential amino acid tryptophan along the kynurenine pathway where several downstream metabolites are formed [21]. IDO expression can occur in several cell types (e.g.…”

Indoleamine 2,3-dioxygenase activity and clinical outcome following induction chemotherapy and concurrent chemoradiation in stage III non-small cell lung cancer.

“…Other studies have used plasma Kyn/Trp ratios as an indirect measure for IDO activity ( Table 3) and these correlate well with immunohistochemical data. 43 However, plasma Kyn/Trp ratios are not a direct measure of IDO activity. In particular, other Trp catabolizing enzymes, including tryptophan 2,3-dioxygenase and the IDO splice variant known as IDO2 contribute to Kyn production as well.…”

“…Moreover, our study did not mandate uniform timing for blood draws. Since plasma Trp levels may vary by as much as 20% in the same subject depending on the distance of the last meal and the diurnal cycle, 44 we acknowledge this as a potential confounder. Nonetheless, plasma Kyn has only minor diurnal variation, 43 and the changes that we observed in Kyn/Trp ratios appeared predominantly attributable to Kyn (Fig.…”