Krista Minéia Wartchow

Oxidative stress mediated by NMDA, AMPA/KA channels in acute hippocampal slices: neuroprotective effect of resveratrol.

Glutamate is the major excitatory neurotransmitter in the brain and over-stimulation of the glutamate receptors, NMDA, AMPA and kainate (KA), may cause neuronal death in epilepsy, seizures and neurodegenerative diseases. Mitochondria have critical cellular functions that influence neuronal excitability, such as regulation of Ca(2+) homeostasis and ATP production to maintain Na(+)K(+)-ATPase in the central nervous system (CNS). However, mitochondria are also the primary site of reactive oxygen species (ROS) production, and oxidative stress can induce cellular damage. Resveratrol, a polyphenol found in grapes and wines, presents antioxidant and neuroprotective effects on brain pathologies. This study sought to determine the neuroprotective effect of resveratrol against glutamate toxicity in acute hippocampal slices, using specific inhibitors of glutamate channels, and to investigate the targets of glutamate excitotoxicity, such as mitochondrial membrane potential (ΔΨ(m)), Na(+)K(+)-ATPase and glutamine synthetase (GS) activity. Resveratrol decreases intracellular ROS production, most likely by mechanisms involving NMDA, AMPA/KA, intracellular Ca(2+) and the heme oxygenase 1 (HO1) pathway, and prevents mitochondrial dysfunction and impairments in Na(+)K(+)-ATPase and GS activity after glutamate activation. Taken together, these results show that resveratrol may exhibit an important neuroprotective mechanism against neuropsychiatric disorders, focusing on mitochondrial bioenergetics and oxidative stress, as well as inhibitory effects on ionic channels.

Neuroglial alterations in rats submitted to the okadaic acid-induced model of dementia.

Several types of animal models have been developed to investigate Alzheimers disease (AD). Okadaic acid (OA), a potent inhibitor of phosphatases 1 and 2A, induces characteristics that resemble AD-like pathology. Memory impairment induced by intra-hippocampal injection of OA has been reported, accompanied by remarkable neuropathological changes including hippocampal neurodegeneration, a paired helical filament-like phosphorylation of tau protein, and formation of β-amyloid containing plaque-like structures. Rats were submitted to bilateral intrahippocampal okadaic acid-injection (100 ng) and, 12 days after the surgery, behavioral and biochemical tests were performed. Using this model, we evaluated spatial cognitive deficit and neuroglial alterations, particularly astroglial protein markers such as glial fibrillary acidic protein (GFAP) and S100B, metabolism of glutamate, oxidative parameters and alterations in MAPKs. Our results indicate significant hippocampal changes, including increased GFAP, protein oxidation, and phosphorylation of p38(MAPK); and decreases in glutathione content, transporter EAAT2/GLT-1, and glutamine synthetase activity as well as a decrease in cerebrospinal fluid S100B. No alterations were observed in glutamate uptake activity and S100B content. In conclusion, the OA-induced model of dementia caused spatial cognitive deficit and oxidative stress in this model and, for the first time to our knowledge, specific astroglial alterations. Findings contribute to understanding diseases accompanied by cognitive deficits and the neural damage induced by AO administration.

The neuroprotective effect of two statins: simvastatin and pravastatin on a streptozotocin-induced model of Alzheimer’s disease in rats

Astrocytes play a fundamental role in glutamate metabolism by regulating the extracellular levels of glutamate and intracellular levels of glutamine. They also participate in antioxidant defenses, due to the synthesis of glutathione, coupled to glutamate metabolism. Although the cause of Alzheimer’s disease (AD) remains elusive, some changes in neurochemical parameters, such as glutamate uptake, glutamine synthetase activity and glutathione have been investigated in this disease. A possible neuroprotective effect of two statins, simvastatin and pravastatin (administered p.o.), was evaluated using a model of dementia, based on the intracerebroventricular (ICV) administration of streptozotocin (STZ), and astrocyte parameters were determined. We confirmed a cognitive deficit in rats submitted to ICV-STZ, and a prevention of this deficit by statin administration. Moreover, both statins were able to prevent the decrease in glutathione content and glutamine synthetase activity in this model of AD. Interestingly, simvastatin increased per se glutamate uptake activity, while both statins increased glutamine synthetase activity per se. These results support the idea that these drugs could be effective for the prevention of alterations observed in the STZ dementia model and may contribute to reduce the cognitive impairment and brain damage observed in AD patients.

Treadmill Exercise Induces Hippocampal Astroglial Alterations in Rats

Physical exercise effects on brain health and cognitive performance have been described. Synaptic remodeling in hippocampus induced by physical exercise has been described in animal models, but the underlying mechanisms remain poorly understood. Changes in astrocytes, the glial cells involved in synaptic remodeling, need more characterization. We investigated the effect of moderate treadmill exercise (20 min/day) for 4 weeks on some parameters of astrocytic activity in rat hippocampal slices, namely, glial fibrillary acidic protein (GFAP), glutamate uptake and glutamine synthetase (GS) activities, glutathione content, and S100B protein content and secretion, as well as brain-derived neurotrophic factor (BDNF) levels and glucose uptake activity in this tissue. Results show that moderate treadmill exercise was able to induce a decrease in GFAP content (evaluated by ELISA and immunohistochemistry) and an increase in GS activity. These changes could be mediated by corticosterone, whose levels were elevated in serum. BDNF, another putative mediator, was not altered in hippocampal tissue. Moreover, treadmill exercise caused a decrease in NO content. Our data indicate specific changes in astrocyte markers induced by physical exercise, the importance of studying astrocytes for understanding brain plasticity, as well as reinforce the relevance of physical exercise as a neuroprotective strategy.

Interleukin-6-induced S100B secretion is inhibited by haloperidol and risperidone

Although inflammation may be a physiological defense process, imbalanced neuroinflammation has been associated with the pathophysiology of brain disorders, including major depression and schizophrenia. Activated glia releases a variety of pro-inflammatory cytokines that contribute to neuronal dysfunction. Elevated levels of S100B, a glia derived protein, have been observed in the serum and CSF of schizophrenic patients suggesting a glial role in the disease. We evaluated whether S100B secretion (in C6 glioma cells and hippocampal slices in Wistar rats) could be directly modulated by the main inflammatory cytokines (IL-1β, TNF-α, IL-6 and IL-8) altered in schizophrenia, as well as the possible involvement of mitogen-activated protein kinase (MAPK) pathways in these responses. We also investigated the effects of typical and atypical antipsychotic drugs on glial cytokine-induced S100B release. Our results suggest that S100B secretion is increased by pro-inflammatory cytokines via MAPK and that oxidative stress may be a component of this modulation. These results reinforce the idea that the S100B protein is involved in the inflammatory response observed in many brain diseases, including schizophrenia. Moreover the antipsychotics, haloperidol and risperidone, were able to inhibit the secretion of S100B following IL-6 stimulation in C6 glioma cells.

Ammonia-induced oxidative damage in neurons is prevented by resveratrol and lipoic acid with participation of heme oxygenase 1.

Ammonia is a metabolite that, at high concentrations, is implicated in neurological disorders, such as hepatic encephalopathy (HE), which is associated with acute or chronic liver failure. Astrocytes are considered the primary target of ammonia toxicity in the central nervous system (CNS) because glutamine synthetase (GS), responsible for ammonia metabolism in CNS, is an astrocytic enzyme. Thus, neuronal dysfunction has been associated as secondary to astrocytic impairment. However, we demonstrated that ammonia can induce direct effects on neuronal cells. The cell viability was decreased by ammonia in SH-SY5Y cells and cerebellar granule neurons. In addition, ammonia induced increased reactive oxygen species (ROS) production and decreased GSH intracellular content, the main antioxidant in CNS. As ammonia neurotoxicity is strongly associated with oxidative stress, we also investigated the potential neuroprotective roles of the antioxidants, resveratrol (RSV) and lipoic acid (LA), against ammonia toxicity in cerebellar granule neurons. RSV and LA were able to prevent the oxidative damage induced by ammonia, maintaining the levels of ROS production and GSH close to basal values. Both antioxidants also decreased ROS production and increased GSH content under basal conditions (in the absence of ammonia). Moreover, we showed that heme oxygenase 1 (HO1), a protein associated with protection against stress conditions, is involved in the beneficial effects of RSV and LA in cerebellar granule neurons. Thus, this study reinforces the neuroprotective effects of RSV and LA. Although more studies in vivo are required, RSV and LA could represent interesting therapeutic strategies for the management of HE.

In vitro S100B secretion is reduced by apomorphine: Effects of antipsychotics and antioxidants

Astrocytes express dopamine receptors and respond to dopamine stimulation. However, the role of astrocytes in psychiatric disorders and the effects of antipsychotics on astroglial cells have only been investigated recently. S100B is a glial-derived protein, commonly used as a marker of astroglial activation in psychiatric disorders, particularly schizophrenia. We investigated S100B secretion in three different rat brain preparations (fresh hippocampal slices, C6 glioma cells and primary astrocyte cultures) exposed to apomorphine and antipsychotics (haloperidol and risperidone), aiming to evaluate, ex vivo and in vitro, whether dopamine activation and dopaminergic antagonists modulate astroglial activation, as measured by changes in the extracellular levels of S100B. The serum S100B elevation observed in schizophrenic patients is not reflected by the in vitro decrease of S100B secretion that we observed in hippocampal slices, cortical astrocytes and C6 glioma cells treated with apomorphine, which mimics dopaminergic hyperactivation. This decrease in S100B secretion can be explained by a stimulation of D2 receptors negatively coupled to adenyl cyclase. Antipsychotic medications and antioxidant supplementation were able to prevent the decline in S100B secretion. Findings reinforce the benefits of antioxidant therapy in psychiatric disorders. Based on our results, in hippocampal slices exposed to apomorphine, it may be suggested that antipsychotics could help to normalize S100B secretion by astrocytes.

Changes in Astroglial Markers in a Maternal Immune Activation Model of Schizophrenia in Wistar Rats are Dependent on Sex.

Data from epidemiological studies suggest that prenatal exposure to bacterial and viral infection is an important environmental risk factor for schizophrenia. The maternal immune activation (MIA) animal model is used to study how an insult directed at the maternal host can have adverse effects on the fetus, leading to behavioral and neurochemical changes later in life. We evaluated whether the administration of LPS to rat dams during late pregnancy affects astroglial markers (S100B and GFAP) of the offspring in later life. The frontal cortex and hippocampus were compared in male and female offspring on postnatal days (PND) 30 and 60. The S100B protein exhibited an age-dependent pattern of expression, being increased in the frontal cortex and hippocampus of the MIA group at PND 60, while at PND 30, male rats presented increased S100B levels only in the frontal cortex. Considering that S100B secretion is reduced by elevation of glutamate levels, we may hypothesize that this early increment in frontal cortex tissue of males is associated with elevated extracellular levels of glutamate and glutamatergic hypofunction, an alteration commonly associated with SCZ pathology. Moreover, we also found augmented GFAP in the frontal cortex of the LPS group at PND 30, but not in the hippocampus. Taken together data indicate that astroglial changes induced by MIA are dependent on sex and brain region and that these changes could reflect astroglial dysfunction. Such alterations may contribute to our understanding of the abnormal neuronal connectivity and developmental aspects of SCZ and other psychiatric disorders.

Insulin Stimulates S100B Secretion and These Proteins Antagonistically Modulate Brain Glucose Metabolism

Brain metabolism is highly dependent on glucose, which is derived from the blood circulation and metabolized by the astrocytes and other neural cells via several pathways. Glucose uptake in the brain does not involve insulin-dependent glucose transporters; however, this hormone affects the glucose influx to the brain. Changes in cerebrospinal fluid levels of S100B (an astrocyte-derived protein) have been associated with alterations in glucose metabolism; however, there is no evidence whether insulin modulates glucose metabolism and S100B secretion. Herein, we investigated the effect of S100B on glucose metabolism, measuring D-3H-glucose incorporation in two preparations, C6 glioma cells and acute hippocampal slices, and we also investigated the effect of insulin on S100B secretion. Our results showed that: (a) S100B at physiological levels decreases glucose uptake, through the multiligand receptor RAGE and mitogen-activated protein kinase/ERK signaling, and (b) insulin stimulated S100B secretion via PI3K signaling. Our findings indicate the existence of insulin-S100B modulation of glucose utilization in the brain tissue, and may improve our understanding of glucose metabolism in several conditions such as ketosis, streptozotocin-induced dementia and pharmacological exposure to antipsychotics, situations that lead to changes in insulin signaling and extracellular levels of S100B.

Hippocampal changes in STZ-model of Alzheimer's disease are dependent on sex.

HighlightsAlzheimer’s disease (AD) has prevalence dependent on gender.We investigated alterations dependent on sex in a streptozotocin model of AD in rats.Hippocampal parameters were investigated 2, 4 and 8 weeks after streptozotocin.Cholinergic neurons and glucose uptake decrease were dependent on sex.S100B alteration in the hippocampus were also dependent on sex, but not GFAP. ABSTRACT The majority of Alzheimer’s disease (AD) cases are sporadic and aging is the major risk factor for developing the disease, affecting more women than men. In spite of different gender prevalence, most experimental studies in animal models have been performed in male. This study investigates the streptozotocin (STZ)‐induced AD model at three different times (2, 4 and 8 weeks afterwards) and in male and female rats, evaluating cognitive deficit, cholinergic neurotransmission, glucose uptake, glutathione content and specific glial markers (GFAP and S100B protein) in the hippocampus of the rat. Our data reinforce the relevance of alterations in STZ model of dementia, reported in the genesis and/or progression of AD such as cholinergic deficit and glucose uptake decrease. All alterations in these parameters (except GFAP) were dependent on sex. It is unclear, at this moment, which alterations are due to sex steroid modulation. In spite of limitations of this experimental model, these data may contribute to understand AD susceptibility and progression dependent on sex.