Summary
In the last twenty years we are made remarkable progress in the handling of the chronic renal failure both predialytic and dialytic, however the mortality rate significantly remains high with respect to the general population and quality of life remains unsatisfactory for the beginning of neuropsychyatric alterations of several nature. In particular under the neurological point of view alterations have been described about peripheral nervous system (uremic neuropathy) and central nervous system (uremic encephalopathy). In uremic encephalopathy the first demonstrations consist in personality alterations, irritabilities, anxious syndrome, difficulty in the attention, loss of the memory, sleep disorders with drowsiness in the day and night insomnia, up to the development of Depressive Syndrome, especially in patient undergoing substitutive treatments. The DOPPS study (Dialysis Outcomes and Practice Patterns Study) has recently highlighted as the depression of for itself represents an independent factor predicitive of mortality and hospitalization in dialyzed patients. On the basis of this observation we have decided to investigate the physiopathologic mechanisms which take to the development of these conditions in the chronic renal failure.
In the last few years the depression has been considered as a neurodegenerative disorder, characterized by atrophy and cellular death of glia and neurons in the cortex and the hippocampus.
This theory is based on the observation that in this patients, beyond to well known reduction in norepinephrine and serotonin contents, neurotrophins levels are decreased, especially of Brain Derived Neurotrophic Factor (BDNF); this molecule plays an important role in the cellular trophism, as it promotes mechanisms of differentiation, cellular survival, synaptic plasticity and neurogenesis. To confirm the crucial role of these mediators, it has been shown that the therapy with antidepressants determines an increase in the neurotrophin levels associated with a morpho- anatomical and sintomatologic recovery.
In patients affected by chronic renal failure, it do not exist any data in literature regarding modifications of such factors. Therefore, we have decided to draw a project fitted to investigate the role of neurotrophins in this special condition.
Materials and methods
The experimental phase has been performed on 30 female Wistar rats, which have been randomised in three different groups: control rats (C), nephrectomised rats (Nx) and nephrectomised rats treated with Fluoxetin (Nx-F). The nephrectomised rats have been submitted to the surgical procedure of subtotal nephrectomy with right kidney extirpation and then resection of the upper and lower poles of the left kidney. All the animals have been sacrificed at the twelfth week.
Nx-F group animals have received the drug to the dose of 15 mg/kg for the last two week, during which the body weights have been registered and urines have been collected. Upon the sacrifice,
samples of serum, liquor, prefrontal cortex, hippocampus and kidney have been also taken. Kidneys have been included in paraffin for the histological analysis with PAS. Samples of cortex and hippocampus have been omogenated to evaluate BDNF levels. BDNF has been also dosed in the samples of liquor, serum, plasma and urines. For the evaluation of BDNF has been used an immunoenzimatic assay (ELISA) using suitable kits (BDNF Emax Immunoassay-Promega, USA) and following the protocols elaborated by the builder.
Results
The levels of BDNF in the Nx liquor (73.4 ± 24.3 pg BDNF/ml) resulted significantly reduced with respect to the C group (128.7 ± 35.3 pg BDNF/ml), while they partially conserved in the Nx-F group (Nx-F: 95.6 ± 23.1 pg BDNF/ml) in a significant way with respect to the Nx group, but not the controls. In the prefrontal cortex, BDNF levels were significantly reduced in the Nx group with respect to the C group (Nx: 28,7 ± 7,3 pg BDNF/mg prot vs c: 66.2±10.2 pg BDNF/mg prot;
p<0.05) and showed a partial recovery in the Nx-F group (48.3 ± 8.2 pg BDNF/mg prot). In the hippocampus, BDNF levels showed differences between the three groups, with an increase in the Nx group (Nx: 238 ± 54.3 pg BDNF/mg prot; C: 90.1 ± 29.4 pg BDNF/mg prot; Nx-F: 112.5 ± 55.1 pg BDNF/mg prot). The tissutal expression of total ERK 1/2 reflects the tissutal trend of BDNF, both in the cortex and in the hippocampus; similar results were obtained with the active form. As regards the peripheral levels of BDNF in rats of the Nx group, we found a significant reduction in urines (29.2 ± 12.5 pg/mg creat vs 90.3 ± 99.3 pg/mg creat. in the controls) and analogously in plasma (228.7 ± 90.7 pg/ml vs 429.7 ± 137.4 pg/ml in the controls), while in the Nx-F group was evidenced a partial recovery (54.6 ± 25.8 pg/mg creat and 364.6 ± 112.4 pg/ml, respectively ).
Conclusions
Our study demonstrated a total reduction of BDNF plasma levels in IRC together with a reduction of its urinary excretion. This result seems to confirm that this neurotrophin has filtered to glomerular level. This phenomenon can happen if we have a reduced BDNF secretion in the circulatory torrent: if this was not, we should be detected its plasmatic increase, how it happens for creatinine. However these results partially reflect the highlighted situation in the central nervous system: while at liquor and cortex level a decrease of BDNF is registered, in the hippocampus it is present exactly at the opposite. In the Nx rats BDNF levels are significantly higher. This result was confirmed by tissutal expression of total and activated ERK 1/2, indicators of an activation of the signal translation pathway activated by BDNF. This last observation could be explained by the fact that while the cortex is damaged, in the hippocampus it is present an attempt of repair of the damage caused by chronic renal failure. Finally, Fluoxetin administration to the dosages commonly
used for the treatment of depressive syndromes, shows a partial effectiveness in restoring the BDNF levels, inducing to assume the existence of specific mechanisms of damage in chronic renal failure.
