André Prato Schmidt

Guanosine and GMP prevent seizures induced by quinolinic acid in mice

In the mammalian CNS, glutamate and GABA are the principal neurotransmitters mediating excitatory and inhibitory synaptic events, respectively, and have been implicated in the neurobiology of seizures. Guanine-based purines, including the nucleoside guanosine and the nucleotide GMP, have been shown to antagonize glutamatergic activity at the receptor level and the other purine nucleoside adenosine is a well-known modulator of seizure threshold. In the present study we investigated the anticonvulsant effect of i. p. guanosine and GMP against seizures induced by the glutamate agonist quinolinic acid (QA) or the GABA(A) antagonist picrotoxin in mice. Animals were pretreated with an i.p. injection of saline, guanosine or GMP 30 min before either an i.c.v. injection of 4 microliter QA (36.8 nmol) or a subcutaneous injection of picrotoxin (3.2 mg/kg). All animals pretreated with vehicle followed by QA or picrotoxin presented seizures, which were completely prevented by the NMDA antagonist MK-801 and the GABA agonist phenobarbital, respectively. Guanosine and GMP dose-dependently protected against QA-induced seizures, up to 70 and 80% at 7.5 mg/kg, with ED(50)=2. 6+/-0.4 and 1.7+/-0.6 mg/kg, respectively. Conversely, neither guanosine, GMP nor MK-801 affected picrotoxin-induced seizures, indicating some degree of specificity towards the glutamatergic system. This study suggests anticonvulsant properties of i.p. guanosine and GMP, which may be related with antagonism of glutamate receptors.

Effect of orally administered guanosine on seizures and death induced by glutamatergic agents.

Intraperitoneal guanosine has been shown to prevent quinolinic acid-induced seizures in mice. In this study, we investigated the effect of orally administered guanosine on seizures induced by the glutamate agonists quinolinic acid and kainate, and the endogenous glutamate releaser alpha-dendrotoxin. Guanosine (7.5 mg/kg, per os), administered 75 min in advance, prevented 70% of seizures induced by i.c.v. quinolinic acid, being as efficient as the NMDA channel blocker MK-801 administered intraperitoneally. Guanosine was ineffective against kainate-induced seizures, but significantly reversed the potentiation of seizures and death caused by the concomitant injection of MK-801. Guanosine also significantly prevented seizures and death induced by i.c.v. alpha-dendrotoxin, whereas MK-801 and phenobarbital only prevented death. Altogether, our findings underscore the therapeutic potential of oral administration of guanosine for treating diseases involving glutamatergic excitotoxicity, including epilepsy.

Chronically administered guanosine is anticonvulsant, amnesic and anxiolytic in mice

Acute administration of intraperitoneal and oral guanosine has been shown to prevent quinolinic acid and alpha-dendrotoxin-induced seizures in rats and mice. In this study, we investigated the effects of 2 weeks ad libitum consumption of guanosine (0.5 mg/ml) added to mice water supply on seizures and lethality induced by the alpha-dendrotoxin, hole-board behavior, inhibitory avoidance task, locomotor activity, motor coordination, rectal temperature, body weight, and water and food consumption. Guanosine prevented seizures in 40% and death in 50% on mice treated with i.c.v. alpha-dendrotoxin; it also impaired inhibitory avoidance memory and increased head-dipping behavior and locomotor activity on the hole-board test. Guanosine consumption did not alter any of the other parameters evaluated. The anticonvulsant, amnesic, and anxyolytic-like effects may be associated with the ability of guanosine in modulating the glutamatergic excitatory system. Adding to previously reported data, these findings suggest a potential role for chronic guanosine in the management of diseases associated with glutamatergic excitotoxicity, including epilepsy and anxiety.

Neuron-Specific Enolase, S100B, and Glial Fibrillary Acidic Protein Levels as Outcome Predictors in Patients With Severe Traumatic Brain Injury

BACKGROUND:The availability of markers able to provide an early insight related to prognostic and functional outcome of patients with traumatic brain injury (TBI) are limited. OBJECTIVE:The relationship of clinical outcome with CSF neuron-specific enolase (NSE), S100B and glial fibrillary acidic protein (GFAP) levels in patients with severe TBI was investigated. METHODS:Twenty patients with severe TBI (7 days at unit care) and controls were studied. Patients were grouped according to the outcome: (1) nonsurvival (n = 5): patients who died; (2) survival A (n = 15): CSF sampled between 1st and 3rd day from patients who survived after hospital admission; and (3) survival B (n = 7): CSF sampled between 4th and 7th day from patients who survived after hospital admission and were maintained with intraventricular catheter up to 7 days. RESULTS:Up to 3 days, S100B and NSE levels (ng/mL) were significantly elevated in the nonsurvival compared with survival A group (S100: 12.45 ± 5.46 vs 5.64 ± 3.36; NSE: 313.20 ± 45.51 vs 107.80 ± 112.10). GFAP levels did not differ between groups. In the survival B group S100B, GFAP, and NSE levels were still elevated compared with control (4.59 ± 2.19, 2.48 ± 2.55, and 89.80 ± 131.10, respectively). To compare S100B and NSE for the prediction of nonsurvival and survival patients we performed receiver operating characteristic curves. At admission, CSF NSE level predicts brain death more accurately than S100B. CONCLUSION:Early elevations (up to 3 days) of S100B and NSE secondary to severe TBI predict deterioration to brain death. However, this feature was more prominently associated with NSE than S100B.

Risk factors for postoperative anxiety in adults

We identified risk factors for postoperative anxiety and quantified their effect on 712 adults between 18 and 60u2003years of age (ASA I–III physical status) undergoing elective surgery under general anaesthesia, neural blockade or both. The measuring instruments were a structured questionnaire, a pain visual analogue scale, the McGill Pain Questionnaire, the State‐Trait Anxiety Inventory, the Montgomery–Äsberg Depression Rating Scale, a Self‐Reporting Questionnaire‐20, and a Self‐Perception of Future Questionnaire. Multivariate conditional regression modelling taking into account the hierarchical relationship between risk factors revealed that postoperative anxiety was associated with ASA status III (ORu2003=u20031.48), history of smoking (1.62), moderate to intense postoperative pain (ORu2003=u20032.62) and high pain rating index (ORu2003=u20032.35), minor psychiatric disorders (ORu2003=u20031.87), pre‐operative state‐anxiety (ORu2003=u20032.65), and negative future perception (ORu2003=u20032.20). Neural block anaesthesia (ORu2003=u20030.72), systemic multimodal analgesia (ORu2003=u20030.62) and neuroaxial opioids with or without local anaesthesia (ORu2003=u20030.63) were found to be protective factors against postoperative anxiety.

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.

Intracerebroventricular Guanine-Based Purines Protect Against Seizures Induced by Quinolinic Acid in Mice

Acute and chronic administration of the nucleoside guanosine have been shown to prevent quinolinic acid (QA) and α-dendrotoxin-induced seizures, as well as to impair memory and anxiety in rats and mice. In this study, we investigated the effect of i.c.v. administration of guanine-based purines (GTP, GDP, GMP, and guanosine) against seizures induced by the NMDA agonist and glutamate releaser quinolinic acid in mice. We also aimed to study the effects of the poorly hydrolysable analogs of GTP (GppNHp and GTPγS) and GDP (GDPβS) in this seizure model. QA produced seizures in 100% of mice, an effect partially prevented by guanine-based purines. In contrast to GTP (480 nmol), GDP (320–640 nmol), GMP (320–480 nmol) and guanosine (300–400 nmol), the poorly hydrolysable analogs of GTP and GDP did not affect QA-induced seizures. Thus, the protective effects of guanine nucleotides seem to be due to their conversion to guanosine. Altogether, these findings suggest a potential role of guanine-based purines for treating diseases involving glutamatergic excitotoxicity.

Anti-nociceptive properties of the xanthine oxidase inhibitor allopurinol in mice: role of A1 adenosine receptors

Background and purpose:u2002 Allopurinol is a potent inhibitor of the enzyme xanthine oxidase, used primarily in the treatment of hyperuricemia and gout. It is well known that purines exert multiple effects on pain transmission. We hypothesized that the inhibition of xanthine oxidase by allopurinol, thereby reducing purine degradation, could be a valid strategy to enhance purinergic activity. The aim of this study was to investigate the anti‐nociceptive profile of allopurinol on chemical and thermal pain models in mice.

In vivo quinolinic acid increases synaptosomal glutamate release in rats: reversal by guanosine.

Glutamate, the main excitatory neurotransmitter in the mammalian central nervous system (CNS), plays important role in brain physiological and pathological events. Quinolinic acid (QA) is a glutamatergic agent that induces seizures and is involved in the etiology of epilepsy. Guanine-based purines (GBPs) (guanosine and GMP) have been shown to exert neuroprotective effects against glutamatergic excitotoxic events. In this study, the influence of QA and GBPs on synaptosomal glutamate release and uptake in rats was investigated. We had previously demonstrated that QA “in vitro” stimulates synaptosomal L-[3H]glutamate release. In this work, we show that i.c.v. QA administration induced seizures in rats and was able to stimulatesynaptosomal L-[3H]glutamate release. This in vivo neurochemical effect was prevented by i.p. guanosine only when this nucleoside prevented QA-induced seizures. I.c.v. QA did not affect synaptosomal L-[3H]glutamate uptake. These data provided new evidence on the role of QA and GBPs on glutamatergic system in rat brain.

Effects of Undernutrition on Glutamatergic Parameters in Rat Brain

Early restriction of nutrients during the perinatal period has marked repercussions on CNS ontogeny, Leading to impaired functions. This study investigated the effects of pre- and postnatal (up to 75 days) undernutrition (diet: 8% protein; normonourished group: 25% protein) on some glutamatergic and behavioral parameters of rats. Undernutrition reduced: (i) seizures caused by ICV quinolinic acid (QA) administration; (ii) Na-independent [3H]glutamate binding in cell plasma membranes of cerebral cortex, and (ii) basal [3H]glutamate release from synaptosomal preparation. Behavioral parameters related to locomotion, anxiety, or memory were not affected. These results indicate that our model of undernutrition decreased the sensitivity to QA as convulsing agent and point to some putative glutamatergic parameters involved in this effect.