A modified HPLC method improves the simultaneous determination of plasma kynurenine and tryptophan concentrations in patients following maintenance hemodialysis

The ratio between plasma kynurenine (Kyn) and tryptophan (Trp) serves as a marker of indoleamine 2,3-dioxygenase, a critical immunomodulatory molecule. Simultaneous detection of the two markers may be performed using high-pressure liquid chromatography (HPLC). However, for uremic patients, the conventional detection method may be affected by a range of accumulated toxins. The current study aimed to establish a method for the simultaneous measurement of Kyn and Trp in patients following maintenance hemodialysis via HPLC-ultraviolet detection. The procedure involved the use of a SinoChrom ODS-BP C18 column (4.6×150 mm; inner diameter, 4.5 μm) and a mobile phase of 15 mmol/l sodium acetate acetic acid solution (containing 5% acetonitrile, pH 4.8). The modified method was verified using plasma samples from 10 healthy controls and 91 maintenance hemodialysis patients. The results demonstrated that the modified method was successful in simultaneously detecting the concentrations of Trp and Kyn in the healthy controls and maintenance hemodialysis patients. The method is simple, fast, accurate and suitable for clinical and research purposes in maintenance hemodialysis patients.