Kynurenine metabolism in central nervous system in experimental chronic renal failure

Tryptophan metablolism via kynureninc pathway leads to the formation of several neuroactive substances including kynurenine, anthranilic acid and quinolinic acid, which are involved in numerous neurodegenerative diseases. Also chronic renal insufficiency is associated with neurological disturbances but it is still not clear which substances are responsible for those disorders. Thus, the aim of our study was to evaluate the concentration of tryptophan, kynurenine and anthranilic acid in plasma as well as in different brain regions in uremic rats. We have shown that tryptophan concentrations in plasma and in brain were decreased, whereas kynurenine and anthranilic acid levels were elevated, both in plasma and in central nervous system. Only in cerebellum and hippocampus were no difference in concentration of antranilic acid between control and uremic rats. Accumulation of tryptophan metabolites in nervous tissue may be involved in pathogenesis of several neurological disorders in uremia.

Kidney and Liver Kynurenine Pathway Enzymes in Chronic Renal Failure

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.

Increased levels of 3-hydroxykynurenine in different brain regions of rats with chronic renal insufficiency

Tryptophan (TRP) metabolism via the kynurenine pathway leads to formations of neuroactive substances like kynurenine (KYN) and 3-hydroxykynurenine (3-HK), which may be involved in the pathogenesis of several human brain diseases. 3-Hydroxykynurenine especially is known to have strong neurotoxic properties. The generation of reactive oxygen species (ROS) leads to neuronal cell death with apoptotic features. Because the chronic renal insufficiency (CRI) results in disturbances in the functioning of the central nervous system (CNS), it is conceivable that the metabolism of some kynurenines may be altered and could play an important role in uremic encephalopathy. The levels of TRP, KYN and 3-HK were measured in the plasma and in different brain regions of uremic rats. The total plasma concentration of TRP as well as in all the studied brain samples was significantly diminished during uremia. Surprisingly, the level of KYN and 3-HK were elevated both in the plasma and different brain regions of CRI animals. KYN concentrations were approximately two times higher in the cerebellum, midbrain and cortex compared to the control group. The changes of 3-HK levels were more pronounced in the striatum and medulla than in other structures. This data suggests that CRI results in deep disturbances on the kynurenine pathway in CNS, which could be responsible for neurological abnormalities seen in uremia.

Behavioral changes in the course of chronic renal insufficiency in rats

In addition to the changes in various biochemical parameters chronic renal insufficiency (CRI) leads to progressive behavioral disturbances both in humans and rats. To further characterize these changes, the present study aimed to investigate locomotor, exploratory and emotional activity of rats with experimental CRI. Our experiments with the open field test have shown a marked decrease in locomotor, exploratory and emotional activity of the animals suffering from CRI. These changes were parallel with an increased water intake, reduced food intake and body weight. Thus, behavioral disturbances accompanying CRI in rats are similar to those occurring in human patients. The experimental model of CRI described by us seems to be a good tool for pharmacological studies.