Kidney and liver kynurenine pathway enzymes in chronic renal failure.
ABSTRACT It has been suggested that kynurenine pathway may be an important pathological factor during the chronic renal failure (CRF) development. Therefore in the present study, in rats with end-stage of chronic renal failure, we measured the plasma and tissues (kidney and liver) concentrations of tryptophan, kynurenine, 3-hydroxykynurenine. We also evaluated the activity of tryptophan 2,3-dioxygenase in the liver (TDO), indoleamine 2,3-dioxygenase in kidney (IDO) and kynurenine 3-hydroxylase (HK) in the liver and in the kidney. The plasma and tissues tryptophan concentrations were decreased, whereas the concentrations of its metabolites increased when compared to control group. The increase in the TDO and 3-HK activity was observed, while IDO activity remains unchanged. In conclusion, the increase in the activity of TDO and HK along with disturbances of renal excreting function may be responsible for the elevation in the kynurenine and 3-hydroxykynurenine concentrations in experimental chronic renal failure.
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ABSTRACT: A major challenge in systems biology is integration of molecular findings for individual enzyme activities into a cohesive high-level understanding of cellular metabolism and physiology/pathophysiology. However, meaningful prediction for how a perturbed enzyme activity will globally impact metabolism in a cell, tissue or intact organisms is precluded by multiple unknowns, including in vivo enzymatic rates, subcellular distribution and pathway interactions. To address this challenge, metabolomics offers the potential to simultaneously survey changes in thousands of structurally diverse metabolites within complex biological matrices. The present study assessed the capability of untargeted plasma metabolite profiling to discover systemic changes arising from inactivation of xanthine oxidoreductase (XOR), an enzyme that catalyzes the final steps in purine degradation. Using LC-MS coupled with a multivariate statistical data analysis platform, we confidently surveyed >3,700 plasma metabolites (50-1,000 Da) for differential expression in XOR wildtype vs. mice with inactivated XOR, arising from gene deletion or pharmacological inhibition. Results confirmed the predicted derangements in purine metabolism, but also revealed unanticipated perturbations in metabolism of pyrimidines, nicotinamides, tryptophan, phospholipids, Krebs and urea cycles, and revealed kidney dysfunction biomarkers. Histochemical studies confirmed and characterized kidney failure in xor-nullizygous mice. These findings provide new insight into XOR functions and demonstrate the power of untargeted metabolite profiling for systemic discovery of direct and indirect consequences of gene mutations and drug treatments.PLoS ONE 01/2012; 7(6):e37149. · 3.73 Impact Factor
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ABSTRACT: The first step in the kynurenine pathway of tryptophan catabolism is the cleavage of the 2,3-double bond of the indole ring of tryptophan. In mammals, this reaction is performed independently by indoleamine 2,3-dioxygenase-1 (IDO1), tryptophan 2,3-dioxygenase (TDO) and the recently discovered indoleamine 2,3-dioxygenase-2 (IDO2). Here we describe characteristics of a purified recombinant mouse IDO2 enzyme, including its pH stability, thermal stability and structural features. An improved assay system for future studies of recombinant/isolated IDO2 has been developed using cytochrome b (5) as an electron donor. This, the first description of the interaction between IDO2 and cytochrome b (5), provides further evidence of the presence of a physiological electron carrier necessary for activity of enzymes in the "IDO family". Using this assay, the kinetic activity and substrate range of IDO2 were shown to be different to those of IDO1. 1-Methyl-D-tryptophan, a current lead IDO inhibitor used in clinical trials, was a poor inhibitor of both IDO1 and IDO2 activity. This suggests that its immunosuppressive effect may be independent of pharmacological inhibition of IDO enzymes, in the mouse at least. The different biochemical characteristics of the mouse IDO proteins suggest that they have evolved to have distinct biological roles.Amino Acids 02/2010; 39(2):565-78. · 3.91 Impact Factor
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ABSTRACT: Indoleamine 2,3-dioxygenase (IDO) is the first enzyme in the kynurenine pathway. The kynurenines formed in this pathway chemically modify proteins and cause apoptosis in cells. Evidence suggests that kynurenines and their protein modifications are involved in cataract formation, but this has yet to be directly demonstrated. We generated transgenic (Tg) mouse lines that overexpress human IDO in the lens. Homozygous Tg (homTg) lenses had higher IDO immunoreactivity, approximately 4.5 times greater IDO mRNA, and approximately 8 times higher IDO activity compared to lenses from hemizygous Tg (hemTg) animals. The kynurenine content was threefold higher in homTg than in hemTg but was not detected in wild-type (Wt) lenses. Kynurenine modifications were approximately 2.6 times greater in homTg than in hemTg or Wt. HomTg lenses had vacuoles in the epithelium and cortical fiber cells. Kynurenine modifications coincided with apoptosis in the secondary fiber cells of homTg lenses. Caspase-3 and caspase-9 activities were markedly higher in homTg than in hemTg and Wt. The glutathione content was approximately 36% lower in homTg compared to hemTg and Wt lenses. HomTg animals also developed bilateral cataracts within 3 months of birth. Together these data demonstrate that IDO-mediated production of kynurenines results in defects in fiber cell differentiation and their apoptosis and suggest that IDO activity is kept low in the lens to prevent deleterious effects by kynurenines.Laboratory Investigation 04/2009; 89(5):498-512. · 3.96 Impact Factor