Guanine and adenine nucleotidase activities in rat cerebrospinal fluid

Cerebrospinal fluid purinomics as a biomarker approach to predict outcome after severe traumatic brain injury

Severe traumatic brain injury (TBI) is associated with high rates of mortality and long-term disability linked to neurochemical abnormalities. Although purine-derivatives play important roles in TBI pathogenesis in preclinical models, little is known about potential changes in purine levels and their implications in human TBI. We assessed cerebrospinal fluid (CSF) levels of purines in severe TBI patients as potential biomarkers that predict mortality and long-term dysfunction. This was a cross-sectional study performed in 17 severe TBI patients (Glasgow Coma Scale < 8) and 51 controls. Two to four hours after admission to ICU, patients were submitted to ventricular drainage and CSF collection for quantification of adenine and guanine purine-derivatives by HPLC. TBI patients survival was followed up to 3 days from admission. A neurofunctional assessment was performed through the modified Rankin Scale (mRS) two years after ICU admission. Purine levels were compared between control and TBI patients, and between surviving and non-surviving patients. Relative to controls, TBI patients presented increased CSF levels of GDP, guanosine, adenosine, inosine, hypoxanthine, and xanthine. Further, GTP, GDP, IMP, and xanthine levels were different between surviving and non-surviving patients. Among the purines, guanosine was associated with improved mRS (p=0.042; r= -0.506). Remarkably, GTP displayed predictive value (AUC=0.841, p=0.024) for discriminating survival vs. non-survival patients up to three days from admission. These results support TBI-specific purine signatures, suggesting GTP as a promising biomarker of mortality, and guanosine as an indicator of long-term functional disability.

High fat diet-induced obesity causes a reduction in brain tyrosine hydroxylase levels and non-motor features in rats through metabolic dysfunction, neuroinflammation and oxidative stress

Obesity is a health problem that has been associated with neuroinflammation, decreased cognitive functions and development of neurodegenerative diseases. Parkinson's disease (PD) is a chronic neurodegenerative condition characterized by motor and non-motor abnormalities, increased brain inflammation, α-synuclein protein aggregation and dopaminergic neuron loss that is associated with decreased levels of tyrosine hydroxylase (TH) in the brain. Diet-induced obesity is a global epidemic and its role as a risk factor for PD is not clear. Herein, we showed that 25 weeks on a high-fat diet (HFD) promotes significant alterations in the nigrostriatal axis of Wistar rats. Obesity induced by HFD exposure caused a reduction in TH levels and increased TH phosphorylation at serine 40 in the ventral tegmental area. These effects were associated with insulin resistance, increased tumor necrosis factor-α levels, oxidative stress, astrogliosis and microglia activation. No difference was detected in the levels of α-synuclein. Obesity also induced impairment of locomotor activity, total mobility and anxiety-related behaviors that were identified in the open-field and light/dark tasks. There were no changes in motor coordination or memory. Together, these data suggest that the reduction of TH levels in the nigrostriatal axis occurs through an α-synuclein-independent pathway and can be attributed to brain inflammation, oxidative/nitrosative stress and metabolic disorders induced by obesity.

Sustained elevation of cerebrospinal fluid glucose and lactate after a single seizure does not parallel with mitochondria energy production

Generalized seizures trigger excessive neuronal firing that imposes large demands on the brain glucose/lactate availability and utilization, which synchronization requires an integral mitochondrial oxidative capability. We investigated whether a single convulsive crisis affects brain glucose/lactate availability and mitochondrial energy production. Adult male Wistar rats received a single injection of pentylentetrazol (PTZ, 60 mg/kg, i.p.) or saline. The cerebrospinal fluid (CSF) levels of glucose and lactate, mitochondrial respirometry, [¹⁴C]-2-deoxy-D-glucose uptake, glycogen content and cell viability in hippocampus were measured. CSF levels of glucose and lactate (mean ± SD) in control animals were 68.08 ± 11.62 mg/dL and 1.17 ± 0.32 mmol/L, respectively. Tonic-clonic seizures increased glucose levels at 10 min (96.25 ± 13.19) peaking at 60 min (113.03 ± 16.34) returning to control levels at 24 h (50.12 ± 12.81), while lactate increased at 10 min (3.23 ± 1.57) but returned to control levels at 360 min after seizures (1.58 ± 0.21). The hippocampal [¹⁴C]-2-deoxy-D-glucose uptake, glycogen content, and cell viability decreased up to 60 min after the seizures onset. Also, an uncoupling between mitochondrial oxygen consumption and ATP synthesis via FoF1-ATP synthase was observed at 10 min, 60 min and 24 h after seizures. In summary, after a convulsive seizure glucose and lactate levels immediately rise within the brain, however, considering the acute impact of this metabolic crisis, mitochondria are not able to increase energy production thereby affecting cell viability.

Changes in Purines Concentration in the Cerebrospinal Fluid of Pregnant Women Experiencing Pain During Active Labor

Labor pain has been reported as a severe pain and can be considered as a model of acute visceral pain. It is well known that extracellular purines have an important role in pain signaling in the central nervous system. This study analyzes the relationship between extracellular purines and pain perception during active labor. A prospective observational study was performed. Cerebrospinal fluid (CSF) levels of the purines and their metabolites were compared between women at term pregnancy with labor pain (n = 49) and without labor pain (Caesarian section; n = 47). Control groups (healthy men and women without chronic or acute pain-n = 40 and 32, respectively) were also investigated. The CSF levels of adenosine were significantly lower in the labor pain group (P = 0.026) and negatively correlated with pain intensity measured by a visual analogue scale (r = -0.48, P = 0.0005). Interestingly, CSF levels of uric acid were significantly higher in healthy men as compared to women. Additionally, pregnant women showed increased CSF levels of ADP, GDP, adenosine and guanosine and reduced CSF levels of AMP, GTP, and uric acid as compared to non-pregnant women (P < 0.05). These findings suggest that purines, in special the nucleoside adenosine, are associated with pregnancy and labor pain.

Some aspects of purinergic signaling in the ventricular system of porcine brain

BACKGROUND

Numerous signaling pathways function in the brain ventricular system, including the most important - GABAergic, glutaminergic and dopaminergic signaling. Purinergic signalization system - comprising nucleotide receptors, nucleotidases, ATP and adenosine and their degradation products - are also present in the brain. However, the precise role of nucleotide signalling pathway in the ventricular system has been not elucidated so far. The aim of our research was the identification of all three elements of purinergic signaling pathway in the porcine brain ventricular system.

RESULTS

Besides nucleotide receptors on the ependymocytes surface, we studied purines and pyrimidines in the CSF, including mechanisms of nucleotide signaling in the swine model (Sus scrofa domestica). The results indicate presence of G proteins coupled P2Y receptors on ependymocytes and also P2X receptors engaged in fast signal transmission. Additionally we found in CSF nucleotides and adenosine in the concentration sufficient to P receptors activation. These extracellular nucleotides are metabolised by adenylate kinase and nucleotidases from at least two families: NTPDases and NPPases. A low activity of these nucleotide metabolising enzymes maintains nucleotides concentration in ventricular system in micromolar range. ATP is degraded into adenosine and inosine.

CONCLUSIONS

Our results confirm the thesis about cross-talking between brain and ventricular system functioning in physiological as well as pathological conditions. The close interaction of brain and ventricular system may elicit changes in qualitative and quantitative composition of purines and pyrimidines in CSF. These changes can be dependent on the physiological state of brain, including pathological processes in CNS.

Effects of chronic administration of tryptophan with or without concomitant fluoxetine in depression-related and anxiety-like behaviors on adult rat

Depression and anxiety play an important role in decreasing quality of life worldwide. Since tryptophan is a serotonin precursor and low levels of serotonin seems to be related to depression, the effect of oral tryptophan has been investigated for possible potentiation of the action of antidepressant drugs. We investigated the effects of chronically administered tryptophan (50mg/kg/day, p.o.) with or without concomitant fluoxetine (10mg/kg/day, s.c.) on adult rats regarding depression-related and anxiety-like behaviors. Tryptophan levels in cerebrospinal fluid (CSF) were measured 4h after a single administration of daily dosages of chronic treatments. We found that tryptophan increased depressive-related behavior, but did not alter anxiety-like behavior. However, fluoxetine decreased depression-related behavior and was anxiogenic. Tryptophan with concomitant fluoxetine did not alter anxiety-like behavior. Moreover, our data suggests that the antidepressant effect of fluoxetine was not enhanced by concomitant administration of tryptophan, which could be associated with increased levels of tryptophan in CSF. Further investigations are needed to elucidate the related mechanisms.

Nucleoside triphosphate diphosphohydrolases role in the pathophysiology of cognitive impairment induced by seizure in early age

Studies have shown that seizures in young animals lead to later cognitive deficits. There is evidence that long-term potentiation (LTP) and long-term depression (LTD) might contribute to the neural basis for learning and memory mechanism and might be modulated by ATP and/or its dephosphorylated product adenosine produced by a cascade of cell-surface transmembrane enzymes, such as E-NTPDases (ecto-nucleoside triphosphate diphosphohydrolases) and ecto-5'-nucleotidase. Thus, we have investigated if hippocampal ecto-nucleotidase activities are altered at different time periods after one episode of seizure induced by kainic acid (KA) in 7 days old rats. We also have evaluated if 90 day-old rats previously submitted to seizure induced by KA at 7 days of age presented cognitive impairment in Y-maze behavior task. Our results have shown memory impairment of adult rats (Postnatal day 90) previously submitted to one single seizure episode in neonatal period (Postnatal day 7), which is accompanied by an increased ATP hydrolysis in hippocampal synaptosomes. The metabolism of ATP evaluated by HPLC confirmed that ATP hydrolysis was faster in adult rats treated with KA in neonatal period than in controls. Surprisingly, the mRNA and protein levels as seen by PCR and Western blot, respectively, were not altered by the KA administration in early age. Since we have found an augmented hydrolysis of ATP and this nucleotide seems to be important to LTP induction, we could assume that impairment of memory and learning observed in adult rats which have experienced a convulsive episode in postnatal period may be a consequence of the increased ATP hydrolysis. These findings correlate the purinergic signaling to the cognitive deficits induced by neonatal seizures and contribute to a better understanding about the mechanisms of seizure-induced memory dysfunction.

The hydrolysis of striatal adenine- and guanine-based purines in a 6-hydroxydopamine rat model of Parkinson's disease

Parkinson's disease (PD) is characterized by a progressive neurodegeneration in the substantia nigra and a striatal dopamine decrease. Striatal extracellular adenosine and ATP modulate the dopaminergic neurotransmission whereas guanosine has a protective role in the brain. Therefore, the regulation of their levels by enzymatic activity may be relevant to the clinical feature of PD. Here it was evaluated the extracellular nucleotide hydrolysis from striatal slices 4 weeks after a unilateral infusion with 6-OHDA into the medial forebrain bundle. This infusion increased ADP, AMP, and GTP hydrolysis by 15, 25, and 41%, respectively, and decreased GDP hydrolysis by 60%. There was no change in NTPDases1, 2, 3, 5, 6, and 5'-nucleotidase transcription. Dopamine depletion changes nucleotide hydrolysis and, therefore, alters the regulation of striatal nucleotide levels. These changes observed in 6-OHDA-lesioned animals may contribute to the symptoms observed in the model and provide evidence to indicate that extracellular purine hydrolysis is a key factor in understanding PD, giving hints for new therapies.

Peripheral nucleotide hydrolysis in rats submitted to a model of electroconvulsive therapy

Electroconvulsive therapy (ECT) is an efficacious and safe method for the treatment of mood disorders. Its utilization is accompanied by a myriad of biochemical and cellular changes, which are far from fully understood. The present work investigates in rat serum the effects of seizures induced by electroconvulsive shocks (ECS), an animal model of ECT, on enzymes that hydrolyze ATP, ADP and AMP to adenosine. Two different models of ECS were used, consisting in the application of one or eight ECS sessions, and respectively named acute or chronic. Serum samples were collected at several time points after the single shock in the acute and after the eighth and last shock in the chronic model. A single shock produced a sudden and short-lived inhibition of enzymatic activity (P<0.01 for ADP and AMP), whereas in the chronic model significant increases were noticed starting as early as 12 h after the last shock, remaining significantly elevated until the last measurement 7 days later for ATP and ADP. Analysis of hydrolysis was assessed at the selected time point of 7 days in cerebrospinal fluid samples, also demonstrating a significant activation in the chronic model (P<0.0001 for ATP and ADP). These results support the idea that adenosine nucleotides may be involved in the biochemical mechanisms underlying longer lasting therapeutic effects associated with ECT, and suggest that peripheral markers can possibly contribute to the evaluation of activity in the central nervous system.

The NMDA antagonist MK-801 induces hyperalgesia and increases CSF excitatory amino acids in rats: reversal by guanosine

Excitatory amino acids (EAAs) and their receptors play a central role in the mechanisms underlying pain transmission. NMDA-receptor antagonists such as MK-801 produce antinociceptive effects against experimental models of chronic pain, but results in acute pain models are conflicting, perhaps due to increased glutamate availability induced by the NMDA-receptor antagonists. Since guanosine and riluzole have recently been shown to stimulate glutamate uptake, the aim of this study was to examine the effects of guanosine or riluzole on changes in nociceptive signaling induced by MK-801 in an acute pain model. Rats received an i.p. injection of vehicle, morphine, guanosine, riluzole or MK-801 or a combined treatment (vehicle, morphine, guanosine or riluzole+MK-801) and were evaluated in the tail flick test, or had a CSF sample drawn after 30 min. Riluzole, guanosine, and MK-801 (0.01 or 0.1 mg/kg) did not affect basal nociceptive responses or CSF EAAs levels. However, MK-801 (0.5 mg/kg) induced hyperalgesia and increased the CSF EAAs levels; both effects were prevented by guanosine, riluzole or morphine. Hyperalgesia was correlated with CSF aspartate and glutamate levels. This study provides additional evidence for the mechanism of action of MK-801, showing that MK-801 induces hyperalgesia with parallel increase in CSF EAAs levels.

Adenine nucleotide hydrolysis in patients with aseptic and bacterial meningitis

The meningitis is a disease with high mortality rates capable to cause neurologic sequelae. The adenosine (the final product of ATP hydrolysis by ectonucleotidases), have a recognized neuroprotective actions in the central nervous system (CNS) in pathological conditions. The aim of the present study was evaluate the adenine nucleotides hydrolysis for to verify one possible role of ATP, ADP and AMP hydrolysis in inflammatory process such as meningitis. The hydrolysis was verified in cerebrospinal fluid (CSF) from human patients with aseptic and bacterial meningitis. Our results showed that the ATP hydrolysis was reduced 12.28% (P < 0.05) in bacterial meningitis and 22% (P < 0.05) in aseptic meningitis. ADP and AMP hydrolysis increased 79.13% (P < 0.05) and 26.37% (P < 0.05) in bacterial meningitis, respectively, and 57.39% (P < 0.05) and 42.64% (P < 0.05) in aseptic meningitis, respectively. This may be an important protective mechanism in order to increase adenosine production.

Proposal of a guanine-based purinergic system in the mammalian central nervous system

Guanine-based purines have been traditionally studied as modulators of intracellular processes, mainly G-protein activity. However, they also exert several extracellular effects not related to G proteins, including modulation of glutamatergic activity, trophic effects on neural cells, and behavioral effects. In this article, the putative roles of guanine-based purines on the nervous system are reviewed, and we propose a specific guanine-based purinergic system in addition to the well-characterized adenine-based purinergic system. Current evidence suggest that guanine-based purines modulate glutamatergic parameters, such as glutamate uptake by astrocytes and synaptic vesicles, seizures induced by glutamatergic agents, response to ischemia and excitotoxicity, and are able to affect learning, memory and anxiety. Additionally, guanine-based purines have important trophic functions affecting the development, structure, or maintenance of neural cells. Although studies addressing the mechanism of action (receptors and second messenger systems) of guanine-based purines are still insufficient, these findings point to the guanine-based purines (nucleotides and guanosine) as potential new targets for neuroprotection and neuromodulation.

Pentylenetetrazol kindling alters adenine and guanine nucleotide catabolism in rat hippocampal slices and cerebrospinal fluid

Pentylenetetrazol (PTZ) is commonly used as a convulsant drug. The enhanced seizure susceptibility induced by kindling is probably attributable to plastic changes in the synaptic efficacy. Adenosine and guanosine act both as important neuromodulators and neuroprotectors with mostly inhibitory effects on neuronal activity. Adenosine and guanosine can be released per se or generated from released nucleotides (ATP, ADP, AMP, GTP, GDP, and GMP) that are metabolized and rapidly converted to adenosine and guanosine. The aim of this study was to evaluate nucleotide hydrolysis by ecto- and soluble nucleotidases (hippocampal slices and CSF, respectively) after PTZ-kindling (stages 3, 4, or 5 seizures) or saline treatment in rats. Additionally, the levels of purines in rat cerebrospinal fluid (CSF), as well as ecto-NTPDases (1, 2, 3, 5, 6 and 8) and ecto- 5'-nucleotidase expression were determined. Ecto-enzyme assays demonstrated that ATP, AMP, GDP, and GMP hydrolysis enhanced when compared with controls. In addition, there was an increase of ADP, GDP, and GMP hydrolysis by soluble nucleotidases in PTZ-kindling rats compared to control group. The HPLC analysis showed a marked increase in PTZ-kindled CSF concentrations of GTP, ADP, and uric acid, but GDP, AMP, and hypoxanthine concentrations were decreased. Such alterations indicate that the modulatory role of purines in CNS could be affected by PTZ-kindling. However, the physiological significance of these findings remains to be elucidated.

Acute and chronic electroconvulsive shock in rats: Effects on peripheral markers of neuronal injury and glial activity

Electroconvulsive therapy is considered one of the most effective treatments of major depression, but controversy still exists on whether it may be brain damaging. The aim of this work was to evaluate the cerebrospinal fluid (CSF) levels of neuron specific enolase (NSE), protein S100B and lactate of rats submitted to acute and chronic models of ECS. Rats were submitted to either one shock (acute) or a series of eight shocks, applied one at every 48 h (chronic). CSF samples were collected at 0, 3, 6, 12, 24, 48 and 72 h after the shock in the acute model and at these same time intervals after the last shock in the chronic model. Both models did not produce significant alterations in the levels of NSE. S100B levels were significantly increased at 6 h in the chronic model (p<0.0001). There was a significant increase in the levels of lactate at 0 h in both models (p<0.001). These results support the proposition that ECS does not produce neural damage, and suggest that the alterations in the levels of S100B and lactate may reflect an astrocytic activity of a protective nature.

Biochemical brain markers and purinergic parameters in rat CSF after seizure induced by pentylenetetrazol

Cellular and molecular mechanisms involved in the generation of seizures and the magnitude of neural cells injury are not fully understood. We evaluated astrocyte and/or neuronal injury in rats in the pentylenetetrazol model of acute seizures by measuring S100B and NSE levels in cerebrospinal fluid. Additionally, we determined ADP and GDP hydrolysis by soluble nucleoside triphosphate diphosphohydrolase in the cerebrospinal fluid, and the concentration of nucleosides adenosine, inosine and guanosine as putative markers of brain injury. After pentylenetetrazol-induced seizures: (i) S100B values increased from 10 to 30 min, returning to control levels at 24 h; NSE levels presented a biphasic increase: an increase at 10 to 30 min returning to control levels, and again at 240 min followed by a decline at 24 h; (ii) nucleotidase activities increased from 10 min, returning to control levels at 240 min; (iii) guanosine and inosine levels increased exclusively after 30 min. In summary, this study showed biochemical changes in the cerebrospinal fluid occurring after seizures induced by pentylenetetrazol. Such events may have a modulating effect upon seizure expression, particularly nucleoside triphosphate diphosphohydrolase activities and nucleoside concentrations, but are nevertheless followed by neural death as evidenced by the increase in NSE and S100B levels.

Application of solid phase extraction and high-performance liquid chromatography to qualitative and quantitative analysis of nucleotides and nucleosides in human cerebrospinal fluid

New method of qualitative and quantitative analysis of nucleotides in human cerebrospinal fluid (CSF), based on the combination of extraction of purines and pyrimidines to the solid phase (SPE) and high-performance liquid chromatography (HPLC), was proposed. Use of SPE and lyophilization of samples allowed for the first time to detect the presence of di- and triphosphonucleotides in human CSF. Concentration of those compounds varied from 0.003 to 5.0 microM. Differences in the nucleotide mixture composition in human CSF detected with the new method are coupled with the neurological disorders and might be a basis for an efficient diagnostic tool.

Investigations into the electrooxidation of guanosine-5'-triphosphate at the pyrolytic graphite electrode

The electrochemical oxidation of guanosine-5'-triphosphate has been investigated in phosphate-containing electrolytes in the pH range 1.5-10.9 at a pyrolytic graphite electrode by cyclic sweep voltammetry, spectral studies, bulk electrolysis and related techniques. In this pH range, the oxidation occurred in a single well-defined peak (Ia). The peak potential of oxidation peaks (Ep) was found to be dependent on pH, concentration and sweep rate. The kinetics of the UV-absorbing intermediates was followed spectrophotometrically and the decay of the intermediate occurred in a pseudo-first-order reaction. The first-order rate constants for the disappearance of the UV-absorbing intermediate have also been calculated. The products of the electrode reaction were characterized by HPLC and GC/MS. A tentative mechanism for the formation of the products has also been suggested.

Effects of chronic administered guanosine on behavioral parameters and brain glutamate uptake in rats

Oral and intraperitoneal administration of the nucleoside guanosine have been shown to prevent quinolinic acid- (QA) and alpha-dendrotoxin-induced seizures, impair memory, and impair anxiety in rats and mice. We investigated the effect of 2-weeks ad lib orally administered guanosine (0.5 mg/ml) on seizures induced by QA, inhibitory avoidance memory, and locomotor performance in rats. We also studied the mechanism of action of guanosine through the measurement of its concentration in the cerebrospinal fluid (CSF) and its effect on glutamate uptake in cortical slices of rats. QA produced seizures in 85% of rats, an effect partially prevented by guanosine (53% of seizures; P = 0.0208). Guanosine also impaired retention on the inhibitory avoidance task (P = 0.0278) and decreased locomotor activity on the open field test (P = 0.0101). The CSF guanosine concentration increased twofold in the treated group compared to that in the vehicle group (P = 0.0178). Additionally, QA promoted a 30% decrease in glutamate uptake as compared to that with intracerebroventricular saline administration, an effect prevented by guanosine in animals protected against QA-induced seizures. Altogether, these findings suggest a potential role of guanosine for treating diseases involving glutamatergic excitotoxicity such as epilepsy. These effects seem to be related to modulation of glutamate uptake.

Increased cerebrospinal fluid levels of S100B protein in rat model of mania induced by ouabain

Bipolar disorder is a chronic and severe mental disorder. Recently, new animal models have emerged to further investigate underlying mechanisms of bipolar disorder such as ouabain-induced hyperactivity in rats. In this study, we investigated the cerebrospinal fluid levels of S100B protein as a putative marker of astrocytic activity in bipolar mania induced by intracerebroventricular administration of ouabain in rats. Ouabain induced a two-fold increase in crossing responses in the open field test and increased 30% the cerebrospinal fluid concentration of S100B, as compared to vehicle group. Our findings reinforce the role of astroglial cells in the pathogenesis of bipolar disorder and S100B protein as a marker of bipolar mania.

Anticonvulsant effect of GMP depends on its conversion to guanosine

Studies on the purinergic system normally deal with adenine-based purines, namely, adenine nucleotides and adenosine. However, a guanine-based purinergic system may also have important neuromodulatory roles. Guanine-based purines exert trophic effects on neural cells, protect brain slices in a model of hypoxia and stimulate glutamate uptake. In vivo, both guanosine 5'-monophosphate (GMP) and guanosine (GUO) protected against seizures. In this study, we investigated if the anticonvulsant effect of GMP is mediated by guanosine and if guanosine or GMP treatments were able to increase adenosine levels. Intraperitoneal (i.p.) treatments with 7.5 mg/kg GMP or guanosine prevented 50% of seizures by quinolinic acid (QA) and increased guanosine cerebrospinal fluid (CSF) levels around twofold and threefold, respectively; GMP and adenosine levels remained unchanged. Intracerebroventricular treatment with 960 nmol GMP prevented 80% of seizures and the 5'-nucleotidase inhibitor alpha-beta-methyleneadenosine 5'-diphosphate (AOPCP), when injected 3 min before, reduced this anticonvulsant effect to 30% protection as well as significantly decreased the conversion of GMP into guanosine measured in the CSF. This study shows that the previously reported effect of GMP as an anticonvulsant seems to be related to its ability to generate guanosine through the action of ecto-5'-nucleotidase.