Avaliação da neuroinflamação e da atividade astrocitária em modelo de epilepsia por Li-pilocarpina: S100B possível marcador e alvo farmacológico

A epilepsia do lobo temporal (ELT) é a um dos casos mais frequente epilepsia em humanos e de maior refratariedade nos pacientes. A maioria dos fármacos antiepilépticos são moduladores da atividade neuronal e atuam sobre canais iônicos do receptor GABAA. Estudos vêm demonstrando o papel das células gliais e da neuroinflamação na epileptogênese e a modulação desta resposta pode ser um alvo potencial para drogas adjuvantes aos fármacos anti-epilépticos. Astrócitos são células gliais participantes da sinapse tripartite, moduladores da atividade neuronal. Os astrócitos são capazes de promover a homeostase de íons e de neurotransmissores, são responsáveis pelo metabolismo energético e da produção de fatores neurotróficos, glutationa, glutamina, S100B e citocinas. Neste trabalho, induzimos status epilepticus (SE) em ratos jovens (PN28) através do modelo lítio-pilocarpina que mimetiza alterações neuronais, bioquímicas e morfológicas similares à ELT em humanos. Os animais foram divididos nos tempos 1, 14 e 56 dias após a indução de status epilepticus (SE). Estes períodos são caracterizados respectivamente como a fase aguda, latente e crônica da epilepsia. Inicialmente, analisamos as mudanças neuroquímicas e astrocitárias ao longo do tempo. Foi observada neuroinflamação inicial e transitória que promove morte neuronal e mudanças ao longo do tempo de astrogliose e disfunção astrocitária. Também foi observado que a proteína S100B, proteína ligante de cálcio, predominantemente astrocitária, pode ser considerado um marcador da disfunção neuronal e astrocitária promovida neste modelo de epilepsia. Em seguida, demonstramos que a modulação da secreção de S100B pelo anti-inflamatório dexametasona um dia após indução de SE reverte a neuroinflamação, astrogliose e disfunção astrocitária à curto e à longo prazo. Por conseguinte, observamos que a modulação do receptor GABAA através de agonistas e antagonistas GABAérgicos altera a secreção de S100B em fatias hipocampais agudas e em cultura de astrócitos. Portanto, pode-se sugerir que as alterações astrogliais e a neuroinflamação dependentes do tempo podem estar ligadas à excitabilidade neuronal e/ou à morte neuronal em ratos jovens em modelo de epilepsia; que a proteína S100B pode ser considerada um marcador deste modelo de epilepsia e que a modulação da sua secreção pode ser um possível alvo farmacológico no tratamento da epilepsia.Temporal lobe epilepsy (TLE) is the most frequent type of epilepsy in humans and is more associated to refractory to anti-epileptic drugs (AED) in patients. The most AEDs are modulators of neuronal activity and act on ion channels, such as GABAA receptor. Studies have been demonstrating the role of glial cells and neuroinflammation in epileptogenesis. The modulation of this response may be a potential target for adjunctive drugs to anti-epileptic drugs. Astrocytes are glial cells that participated in the tripartite synapse and modulated neuronal activity. Astrocytes are able to promote homeostasis of ions and neurotransmitters, are responsible for energy metabolism and the production of neurotrophic factors, glutathione, glutamine, S100B and cytokines. In this work, we induced status epilepticus (SE) in young rats (PN28) through the lithiumpilocarpine model that mimics neuronal, biochemical and morphological alterations similar to ELT in humans. The animals were divided at times 1, 14 and 56 days after the induction of SE. These periods are characterized respectively as the acute, latent and chronic phase of epilepsy. Initially, we analyzed neurochemical and astrocytic changes over time. Initial and transient neuroinflammation was observed and promoted over time neuronal death, astrogliosis and astrocytic dysfunction. It has also been observed that the protein S100B, a calcium-binding protein, predominantly astrocytic, can be considered a marker of neuronal and astrocytic dysfunction promoted by this model of epilepsy. Next, we demonstrate that the modulation of S100B secretion by the antiinflammatory dexamethasone one day after SE induction reverses neuroinflammation, astrogliosis and astrocytic dysfunction in the acute and chronic time. Therefore, we analyzed that modulation of the GABAA receptor through GABAergics agonists and antagonists alters the secretion of S100B in acute hippocampal slices and in astrocyte culture. Therefore, it may be suggested that astroglial changes and time dependent neuroinflammation may be related to neuronal excitability and/or neuronal death in young rats in this epilepsy model; that S100B protein can be considered a marker of this epilepsy model and that the modulation of its secretion may be a possible pharmacological target in the treatment of epilepsy

Effects of dexamethasone on the Li-pilocarpine model of epilepsy : protection against hippocampal inflammation and astrogliosis

Background: Temporal lobe epilepsy (TLE) is the most common form of partial epilepsy and is accompanied, in one third of cases, by resistance to antiepileptic drugs (AED). Most AED target neuronal activity modulated by ionic channels, and the steroid sensitivity of these channels has supported the use of corticosteroids as adjunctives to AED. Assuming the importance of astrocytes in neuronal activity, we investigated inflammatory and astroglial markers in the hippocampus, a key structure affected in TLE and in the Li-pilocarpine model of epilepsy. Methods: Initially, hippocampal slices were obtained from sham rats and rats subjected to the Li-pilocarpine model of epilepsy, at 1, 14, and 56 days after status epilepticus (SE), which correspond to the acute, silent, and chronic phases. Dexamethasone was added to the incubation medium to evaluate the secretion of S100B, an astrocyte-derived protein widely used as a marker of brain injury. In the second set of experiments, we evaluated the in vivo effect of dexamethasone, administrated at 2 days after SE, on hippocampal inflammatory (COX-1/2, PGE2, and cytokines) and astroglial parameters: GFAP, S100B, glutamine synthetase (GS) and water (AQP-4), and K+ (Kir 4.1) channels. Results: Basal S100B secretion and S100B secretion in high-K+ medium did not differ at 1, 14, and 56 days for the hippocampal slices from epileptic rats, in contrast to sham animal slices, where high-K+ medium decreased S100B secretion. Dexamethasone addition to the incubation medium per se induced a decrease in S100B secretion in sham and epileptic rats (1 and 56 days after SE induction). Following in vivo dexamethasone administration, inflammatory improvements were observed, astrogliosis was prevented (based on GFAP and S100B content), and astroglial dysfunction was partially abrogated (based on Kir 4.1 protein and GSH content). The GS decrease was not prevented by dexamethasone, and AQP-4 was not altered in this epileptic model. Conclusions: Changes in astroglial parameters emphasize the importance of these cells for understanding alterations and mechanisms of epileptic disorders in this model. In vivo dexamethasone administration prevented most of the parameters analyzed, reinforcing the importance of anti-inflammatory steroid therapy in the Li-pilocarpine model and possibly in other epileptic conditions in which neuroinflammation is present

Early effects of LPS-induced neuroinflammation on the rat hippocampal glycolytic pathway

Neuroinflammation is a common feature during the development of neurological disorders and neurodegenerative diseases, where glial cells, such as microglia and astrocytes, play key roles in the activation and maintenance of inflammatory responses in the central nervous system. Neuroinflammation is now known to involve a neurometabolic shift, in addition to an increase in energy consumption. We used two approaches (in vivo and ex vivo) to evaluate the effects of lipopolysaccharide (LPS)-induced neuroinflammation on neurometabolic reprogramming, and on the modulation of the glycolytic pathway during the neuroinflammatory response. For this, we investigated inflammatory cytokines and receptors in the rat hippocampus, as well as markers of glial reactivity. Mitochondrial respirometry and the glycolytic pathway were evaluated by multiple parameters, including enzymatic activity, gene expression and regulation by protein kinases. Metabolic (e.g., metformin, 3PO, oxamic acid, fluorocitrate) and inflammatory (e.g., minocycline, MCC950, arundic acid) inhibitors were used in ex vivo hippocampal slices. The induction of early inflammatory changes by LPS (both in vivo and ex vivo) enhanced glycolytic parameters, such as glucose uptake, PFK1 activity and lactate release. This increased glucose consumption was independent of the energy expenditure for glutamate uptake, which was in fact diverted for the maintenance of the immune response. Accordingly, inhibitors of the glycolytic pathway and Krebs cycle reverted neuroinflammation (reducing IL-1β and S100B) and the changes in glycolytic parameters induced by LPS in acute hippocampal slices. Moreover, the inhibition of S100B, a protein predominantly synthesized and secreted by astrocytes, inhibition of microglia activation and abrogation of NLRP3 inflammasome assembly confirmed the role of neuroinflammation in the upregulation of glycolysis in the hippocampus. Our data indicate a neurometabolic glycolytic shift, induced by inflammatory activation, as well as a central and integrative role of astrocytes, and suggest that interference in the control of neurometabolism may be a promising strategy for downregulating neuroinflammation and consequently for diminishing negative neurological outcomes