Diogo O. Souza

Caffeine and adenosine A2a receptor antagonists prevent β-amyloid (25–35)-induced cognitive deficits in mice

Consumption of caffeine, an adenosine receptor antagonist, was found to be inversely associated with the incidence of Alzheimers disease. Moreover, caffeine protects cultured neurons against beta-amyloid-induced toxicity, an effect mimicked by adenosine A(2A) but not A(1) receptor antagonists. We now tested if caffeine administration would prevent beta-amyloid-induced cognitive impairment in mice and if this was mimicked by A(2A) receptor blockade. One week after icv administration of the 25-35 fragment of beta-amyloid (Abeta, 3 nmol), mice displayed impaired performance in both inhibitory avoidance and spontaneous alternation tests. Prolonged treatment with caffeine (1 mg/ml) had no effect alone but prevented the Abeta-induced cognitive impairment in both tasks when associated with acute caffeine (30 mg/kg) 30 min treatment before Abeta administration. The same protective effect was observed after subchronic (4 days) treatment with daily injections of either caffeine (30 mg/kg) or the selective adenosine A(2A) receptor antagonist SCH58261 (0.5 mg/kg). This provides the first direct in vivo evidence that caffeine and A(2A) receptor antagonists afford a protection against Abeta-induced amnesia, which prompts their interest for managing Alzheimers disease.

Oxidative stress parameters in unmedicated and treated bipolar subjects during initial manic episode: a possible role for lithium antioxidant effects.

Studies have proposed the involvement of oxidative stress and neuronal energy dysfunctions in the pathophysiology of bipolar disorder (BD). This study evaluates plasma levels of the oxidative/energy metabolism markers, thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), catalase (CAT), and neuron-specific enolase (NSE) during initial episodes of mania compared to controls in 75 subjects. Two groups of manic subjects (unmedicated n=30, and lithium-treated n=15) were age/gender matched with healthy controls (n=30). TBARS and antioxidant enzymes activity (SOD and CAT) were increased in unmedicated manic patients compared to controls. Conversely, plasma NSE levels were lower during mania than in the controls. In contrast, acute treatment with lithium showed a significant reduction in both SOD/CAT ratio and TBARS levels. These results suggest that initial manic episodes are associated with both increased oxidative stress parameters and activated antioxidant defenses, which may be related to dysfunctions on energy metabolism and neuroplasticity pathways. Antioxidant effects using lithium in mania were shown, and further studies are necessary to evaluate the potential role of these effects in the pathophysiology and therapeutics of BD.

Neuroprotection by caffeine and adenosine A2A receptor blockade of β‐amyloid neurotoxicity

Adenosine is a neuromodulator in the nervous system and it has recently been observed that pharmacological blockade or gene disruption of adenosine A2A receptors confers neuroprotection under different neurotoxic situations in the brain. We now observed that coapplication of either caffeine (1–25 μM) or the selective A2A receptor antagonist, 4‐(2‐[7‐amino‐2(2‐furyl)(1,2,4)triazolo (2,3‐a)(1,3,5)triazin‐5‐ylamino]ethyl)phenol (ZM 241385, 50 nM), but not the A receptor antagonist, 8‐cyclopentyltheophylline (200 nM), prevented the neuronal cell death caused by exposure of rat cultured cerebellar granule neurons to fragment 25–35 of β‐amyloid protein (25 μM for 48 h), that by itself caused a near three‐fold increase of propidium iodide‐labeled cells. This constitutes the first in vitro evidence to suggest that adenosine A2A receptors may be the molecular target responsible for the observed beneficial effects of caffeine consumption in the development of Alzheimers disease.

Decreased Plasma Brain Derived Neurotrophic Factor Levels in Unmedicated Bipolar Patients During Manic Episode

BACKGROUND Bipolar disorder (BD) has been increasingly associated with abnormalities in neuroplasticity and cellular resilience. Brain Derived Neurotrophic Factor (BDNF) gene has been considered an important candidate marker for the development of bipolar disorder and this neurotrophin seems involved in intracellular pathways modulated by mood stabilizers. Also, previous studies demonstrated a role for BDNF in the pathophysiology and clinical presentation of mood disorders. METHODS We investigated whether BDNF levels are altered during mania. Sixty subjects (14 M and 46 F) were selected and included in the study. Thirty patients meeting SCID-I criteria for manic episode were age and gender matched with thirty healthy controls. Young Mania Rating Scale (YMRS) evaluated the severity of manic episode and its possible association with the neurotrophin levels. RESULTS Mean BDNF levels were significantly decreased in drug free/naive (224.8 +/- 76.5 pg/ml) compared to healthy controls (318.5 +/- 114.2), p < .001]. Severity of the manic episode presented a significant negatively correlation to plasma BDNF levels (r= .78; p < .001; Pearson test). CONCLUSIONS Overall, these results suggest that the decreased plasma BDNF levels may be directly associated with the pathophysiology and severity of manic symptoms in BD. Further studies are necessary to clarify the role of BDNF as a putative biological marker in BD.

Quinolinic acid stimulates synaptosomal glutamate release and inhibits glutamate uptake into astrocytes

Quinolinic acid (QA) is an endogenous neurotoxin involved in various neurological diseases, whose action seems to be exerted via glutamatergic receptors. However, the exact mechanism responsible for the neurotoxicity of QA is far from being understood. We have previously reported that QA inhibits vesicular glutamate uptake. In this work, investigating the effects of QA on the glutamatergic system from rat brain, we have demonstrated that QA (from 0.1 to 10mM) had no effect on synaptosomal L-[3H]glutamate uptake. The effect of QA on glutamate release in basal (physiological K+ concentration) or depolarized (40 mM KCl) conditions was evaluated. QA did not alter K+-stimulated glutamate release, but 5 and 10mM QA significantly increased basal glutamate release. The effect of dizolcipine (MK-801), a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptor on glutamate release was investigated. MK-801 (5 microM) did not alter glutamate release per se, but completely abolished the QA-induced glutamate release. NMDA (50 microM) also stimulated glutamate release, without altering QA-induced glutamate release, suggesting that QA effects were exerted via NMDA receptors. QA (5 and 10mM) decreased glutamate uptake into astrocyte cell cultures. Enhanced synaptosomal glutamate release, associated with inhibition of glutamate uptake into astrocytes induced by QA could contribute to increase extracellular glutamate concentrations which ultimately lead to overstimulation of the glutamatergic system. These data provide additional evidence that neurotoxicity of QA may be also related to disturbances on the glutamatergic transport system, which could result in the neurological manifestations observed when this organic acid accumulates in the brain.

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.

Riluzole enhances glutamate uptake in rat astrocyte cultures

Abstract1. Riluzole is used for the treatment of amyotrophic lateral sclerosis and reported to have neuroprotective effects in animal models of Parkinsons disease, Huntingtons disease, and brain ischemia. The neuroprotective action of riluzole has been attributed to its ability to inhibit glutamate release (A. Doble, Neurology47(4):233S–241S, 1996).2. The effect of riluzole on L-[2,3-3H] glutamate uptake was investigated in rat cortical astrocyte cultures.3. Riluzole showed a biphasic concentration-dependent effect on basal glutamate uptake. At low concentrations (1 and 10 μM) riluzole significantly increased glutamate uptake, whereas from 100 μM promoted a slight reduction.4. Considering the large range of glutamate levels in the synaptic cleft, we studied the 1 μM riluzole effect on uptake of glutamate at different concentrations (1–1000 μM). Riluzole was more effective at low glutamate concentrations (10 μM), enhancing the basal glutamate uptake up to 42%.5. The action of riluzole on astrocytic glutamate uptake could be an additional mechanism to its neuroprotective role, perhaps suggesting a modulatory action on glutamatergic system involving glutamate clearance from synaptic cleft.

Effects of Linalool on Glutamatergic System in the Rat Cerebral Cortex

Linalool is a monoterpene compound reported to be a major component of essential oils in, various aromatic species. Several Linalool-producing species are used in traditional medical systems, includingAeolanthus suaveolens G. Dom (Labiatae) used as anticonvulsant in the Brazilian Amazon. Psychopharmacological in vivo evaluation of Linalool showed that this compound have dose-dependent marked sedative effects at the Central Nervous System, including hypnotic, anticonvulsant and hypothermic properties. The present study reports an inhibitory effect of Linalool on Glutamate binding in rat cortex. It is suggested that this neurochemical effect might be underlining Linalool psychopharmacological effects. These findings provide a rational basis for many of the traditional medical use of Linalool producing plant species.

Agrp Neurons Mediate Sirt1's Action on the Melanocortin System and Energy Balance: Roles for Sirt1 in Neuronal Firing and Synaptic Plasticity

Sirt1 has been associated with various effects of calorie restriction, including an increase in lifespan. Here we show in mice that a central regulatory component in energy metabolism, the hypothalamic melanocortin system, is affected by Sirt1, which promotes the activity and connectivity of this system resulting in negative energy balance. In adult mice, the pharmacological inhibition of brain Sirt1 activity decreased Agrp neuronal activity and the inhibitory tone on the anorexigenic POMC neurons, as measured by the number of synaptic inputs to these neurons. When a Sirt1 inhibitor (EX-527) was injected either peripherally (i.p., 10 mg/kg) or directly into the brain (i.c.v., 1.5 nmol/mouse), it decreased both food intake during the dark cycle and ghrelin-induced food intake. This effect on feeding is mediated by upstream melanocortin receptors, because the MC4R antagonist, SHU9119, reversed Sirt1s effect on food intake. This action of Sirt1 required an appropriate shift in the mitochondrial redox state: in the absence of such an adaptation enabled by the mitochondrial protein, UCP2, Sirt1-induced cellular and behavioral responses were impaired. In accordance with the pharmacological results, the selective knock-out of Sirt1 in hypothalamic Agrp neurons through the use of Cre-Lox technology decreased electric responses of Agrp neurons to ghrelin and decreased food intake, leading to decreased lean mass, fat mass, and body weight. The present data indicate that Sirt1 has a central mode of action by acting on the NPY/Agrp neurons to affect body metabolism.

Methylmercury induces oxidative injury, alterations in permeability and glutamine transport in cultured astrocytes

The neurotoxicity of high levels of methylmercury (MeHg) is well established both in humans and experimental animals. Astrocytes accumulate MeHg and play a prominent role in mediating MeHg toxicity in the central nervous system (CNS). Although the precise mechanisms of MeHg neurotoxicity are ill-defined, oxidative stress and altered mitochondrial and cell membrane permeability appear to be critical factors in its pathogenesis. The present study examined the effects of MeHg treatment on oxidative injury, mitochondrial inner membrane potential, glutamine uptake and expression of glutamine transporters in primary astrocyte cultures. MeHg caused a significant increase in F(2)-isoprostanes (F(2)-IsoPs), lipid peroxidation biomarkers of oxidative damage, in astrocyte cultures treated with 5 or 10 microM MeHg for 1 or 6 h. Consistent with this observation, MeHg induced a concentration-dependant reduction in the inner mitochondrial membrane potential (DeltaPsi(m)), as assessed by the potentiometric dye, tetramethylrhodamine ethyl ester (TMRE). Our results demonstrate that DeltaPsi(m) is a very sensitive endpoint for MeHg toxicity, since significant reductions were observed after only 1 h exposure to concentrations of MeHg as low as 1 microM. MeHg pretreatment (1, 5 and 10 microM) for 30 min also inhibited the net uptake of glutamine ((3)H-glutamine) measured at 1 min and 5 min. Expression of the mRNA coding the glutamine transporters, SNAT3/SN1 and ASCT2, was inhibited only at the highest (10 microM) MeHg concentration, suggesting that the reduction in glutamine uptake observed after 30 min treatment with lower concentrations of MeHg (1 and 5 microM) was not due to inhibition of transcription. Taken together, these studies demonstrate that MeHg exposure is associated with increased mitochondrial membrane permeability, alterations in glutamine/glutamate cycling, increased ROS formation and consequent oxidative injury. Ultimately, MeHg initiates multiple additive or synergistic disruptive mechanisms that lead to cellular dysfunction and cell death.