Determination of tryptophan and its major metabolites in fluid from the anterior chamber of the eye in diabetic patients with cataract by liquid chromotography mass spectrometry (LC-MS/MS)

Abstract

Tryptophan (TRP) is to an essential amino acid and its catabolites are significant to human health. By using ultra-high-performance liquid chromatography coupled to electrospray ionization triple quadrupole mass spectrometry (UHPLC-ESI-MS/MS), levels of three major components of kynurenic pathway namely tryptophan (TRP), kynurenic acid (KYNA) and kynurenine (KYN) in fluid from the anterior chamber of the eye were determined. The analysis was carried out on a Synergi 4 μ Fusion-RP column using gradient elution mode. For quantitative determination, L-tryptophan-amino-15N, 99 ATOM % 15N was used as an internal standard. The method was linear in the concentration range 4–2000 ng mL−1 for TRP, KYNA and KYN. The mean recoveries measured at four concentration levels for TRP, KYN and KYNA included the following ranges 94.3–96.1; 91.0–95.0; and 96.0–97.6%, respectively. The intra-day precision parameters were smaller than 4.4, 6.4 and 5% respectively. The developed method was applied to study the level of TRP, KYNA and KYN in eye fluid for the retrospective case series which included 28 patients suffering from cataracts and diabetes (n = 8). The experimental data was subjected to statistical analysis. The Mann-Whitney U-test revealed clear differences in the level of TRP catabolites and the ratios of TRP/KYN representing the activities of specific enzyme of kynurenine pathway in examined groups of patients. A level of probability p < 0.05 was used throughout a paper to denote statistically significant differences between the groups.