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The role of tryptophan 2,3-dioxygenase in the hormonal control of tryptophan metabolism in isolated rat liver cells. Effects of glucocorticoids and experimental diabetes.

ABSTRACT: The metabolism of L-tryptophan by isolated liver cells prepared from control, adrenalectomized, glucocorticoid-treated, acute-diabetic, chronic-diabetic and insulin-treated chronic-diabetic rats was studied. Liver cells from adrenalectomized rats metabolized tryptophan at rates comparable with the minimum diurnal rates of controls, but different from rates determined for cells from control rats 4h later. Administration of dexamethasone phosphate increased the activity of tryptophan 2,3-dioxygenase (EC 1.13.11.11) 7-8-fold, and the flux through the kynurenine pathway 3-4-fold, in cells from both control and adrenalectomized rats. Increases in flux through kynureninase (EC 3.7.1.3) and to acetyl-CoA can be explained in terms of increased substrate supply from tryptophan 2,3-dioxygenase. The metabolism of tryptophan was increased 3-fold in liver cells isolated from acutely (3 days) diabetic rats, with a 7-8-fold increase in the maximal activity of tryptophan 2,3-dioxygenase. The oxidation of tryptophan to CO2 and metabolites of the glutarate pathway increased 4-5-fold, consistent with an increase in picolinate carboxylase (EC 4.1.1.45) activity. Liver cells isolated from chronic (10 days) diabetic rats metabolized tryptophan at rates comparable with those of cells from acutely diabetic rats, but with a 50% decrease in the activity of tryptophan 2,3-dioxygenase. The proportion of flux from tryptophan 2,3-dioxygenase to acetyl-CoA, however, was increased by 50%; this was indicative of further increases in the activity of picolinate carboxylase. Administration of insulin partially reversed the effects of chronic diabetes on the activity of tryptophan 2,3-dioxygenase and flux through the kynurenine pathway, but had no effect on the increased activity of picolinate carboxylase. The role of tryptophan 2,3-dioxygenase in regulating the blood tryptophan concentration is discussed with reference to its sensitivity to the above conditions.

SUBMITTER: Salter M

PROVIDER: S-EPMC1145083 | biostudies-other | 1985 Jul

REPOSITORIES: biostudies-other

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Project description:ObjectivesExtrahepatic tryptophan (Trp)-kynurenine (Kyn) metabolism via indoleamine 2,3-dioxygenase 1 (IDO1) induction was found to be associated with intrinsic immune regulation. However, the Trp-Kyn metabolism-associated immune regulation in dermatomyositis (DM) remains unknown. Therefore, we aimed to investigate the clinical relevance of the Trp-Kyn metabolism via IDO1 induction in DM.MethodsLiquid chromatography-mass spectrometry (HPLC-MS) was used to examine the serum Kyn and Trp concentrations in DM. In addition, we used X-tile software to determine the optimal cutoff value of the Kyn/Trp ratio, a surrogate marker for Trp-Kyn metabolism. Spearman analysis was performed to evaluate the association of Trp-Kyn metabolism with muscle enzymes and inflammatory markers.ResultsDM patients had significantly higher serum Kyn/Trp ratio (× 10-3) when compared with the healthy controls. The serum Kyn/Trp ratio was positively correlated with the levels of muscle enzymes and inflammatory markers. In addition, the serum Kyn/Trp ratio significantly decreased (36.89 (26.00-54.00) vs. 25.00 (18.00-37.00), P = 0.0006) after treatment. DM patients with high serum Kyn/Trp ratio had a significantly higher percentage of muscle weakness symptoms (62.5% vs. 20.0%, P = 0.019) and higher levels of LDH (316.0 (236.0-467.0) vs. 198.0 (144.0-256.0), P = 0.004) and AST (56.5 (35.0-92.2) vs. 23.0 (20.0-36.0), P = 0.002)) than those with low serum Kyn/Trp ratio. Multiple Cox regression analyses identified ln(Kyn/Trp) (HR 4.874, 95% CI 1.105-21.499, P = 0.036) as an independent prognostic predictor of mortality in DM.ConclusionsDM patients with enhanced Trp-Kyn metabolism at disease onset are characterized by more severe disease status and poor prognosis. Intrinsic immune regulation function via enhanced Trp-Kyn metabolism by IDO1 induction may be a potential therapeutic target in DM. Key Points • HPLC-MS identified increased serum Kyn/Trp ratio in DM patients, which positively correlated with levels of muscle enzymes and inflammatory markers and was downregulated upon treatment. • Cox regression analyses identified ln(Kyn/Trp) as an independent prognostic predictor of mortality in DM. • Monitoring intrinsic immune regulation function should be considered a potential therapeutic target in DM patients.

Project description:Kynurenine (Kyn), a metabolite of tryptophan (Trp), is a key regulator of mammal immune responses such as cancer immune tolerance. Indoleamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO) are main enzymes regulating the first and rate-limiting step of the Kyn pathway. To identify new small molecule inhibitors of TDO, we selected A172 glioblastoma cell line constitutively expressed TDO. Characterization of this cell line using kinase inhibitor library resulted in identification of MEK/ERK pathway-dependent TDO expression. After knowing the properties for TDO expression, we further proceeded to screen chemical library for TDO inhibitors. We previously determined that S-benzylisothiourea derivatives are enzymatic inhibitors of indoleamine 2,3-dioxygenase 1 (IDO1) and suggested that the isothiourea moiety could be an important pharmacophore for binding to heme. Based on this premise, we screened an in-house library composed of various isothiourea derivatives and identified a bisisothiourea derivative, PVZB3001, as an inhibitor of TDO. Interestingly, PVZB3001 also inhibited the enzymatic activity of IDO1 in both cell-based and cell-free assays but did not inhibit other heme enzymes. Molecular docking studies suggested the importance of isothiourea moieties at the ortho position of the phenyl ring for the inhibition of catalytic activity. PVZB3001 showed competitive inhibition against TDO, and this was supported by the docking simulation. PVZB3001 recovered natural killer (NK) cell viability and functions by inhibiting Kyn accumulation in conditioned medium of both IDO1- and TDO-expressing cells. Furthermore, oral administration of IDO1-overexpressing tumor-bearing mice with PVZB3001 significantly inhibited tumor growth. Thus, we identified a novel selective dual inhibitor of IDO1 and TDO using the Kyn production assay with a glioblastoma cell line. This inhibitor could be a useful pharmacological tool for modulating the Kyn pathway in a variety of experimental systems.

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The role of tryptophan 2,3-dioxygenase in the hormonal control of tryptophan metabolism in isolated rat liver cells. Effects of glucocorticoids and experimental diabetes.

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