A sensitive UPLC-MS/MS method for the simultaneous determination of the metabolites in the tryptophan pathway in rat plasma

Tryptophan (TRP) metabolism plays a crucial role in pathology and physiology. An imbalance in TRP metabolism has been implicated in the pathology of renal failure. To explore the changes in the TRP profile that occurred in renal failure, we induced experimental models of renal ischemia-reperfusion injury (RIRI) and chronic renal failure (CRF) in rats. A simple, rapid and sensitive method coupling ultra-high-performance liquid chromatography to triple quadrupole mass spectrometry (UPLC-MS/MS) was developed for the simultaneous determination of TRP and its seven major metabolites in plasma. The method was validated base on linearity, accuracy, precision, stability, recovery and the matrix effect. In the RIRI group, the levels of kynurenine (KYN), 5-hydroxyindoleacetic acid (5-HIAA), tryptamine (Trpm) and kynurenic acid (KA) were increased, and the level of TRP was decreased significantly compared with those of sham group. Moreover, the levels of most of the metabolites measured using the proposed method changed significantly with CRF progression. In the CRF group, the levels of KYN, 5-HIAA, Trpm, KA, 3-hydroxyanthranilic acid (3-HAA) and 3-hydroxykynurenine (3-HK) were dramatically elevated, and the level of TRP was markedly reduced compared with those of the CON group. Plasma precursor metabolite/product metabolite ratios were calculated to characterize enzyme activity. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) of the metabolites were performed for both groups. A Spearman correlation coefficient analysis between the metabolite concentrations and renal injury indicators was performed. We identified KYN, TRP, and 5-HIAA as potential metabolite biomarkers for AKI, and 5-HIAA, TRP, 3-HAA, KA, KYN and 3-HK as potential metabolite biomarkers for CRF (VIP>1 and p < 0.05). These results showed significant changes in the tryptophan metabolism profile under the two types of renal failure. In summary, the results of our study depict the changes in the TRP pathway, reveal the role of the TRP pathway in AKI and CRF, and provide insight into finding potential peripheral biomarkers of renal failure and elucidating the mechanism of diseases related to TRP metabolism disorders.