3-Nitropropionic acid neurotoxicity in hippocampal slice cultures: developmental and regional vulnerability and dependency on glucose

Ginsenoside Re blocks Bay k-8644-induced neurotoxicity via attenuating mitochondrial dysfunction and PKCδ activation in the hippocampus of mice: Involvement of antioxidant potential

Although the anticonvulsant effects of ginsenosides are recognized, little is known about their effects on the convulsive behaviors induced by the activation of L-type Ca²⁺ channels. Here, we investigated whether ginsenoside Re (GRe) modulates excitotoxicity induced by the L-type Ca²⁺ channel activator Bay k-8644. GRe significantly attenuated Bay k-8644-induced convulsive behaviors and hippocampal oxidative stress in mice. GRe-mediated antioxidant potential was more pronounced in the mitochondrial fraction than cytosolic fraction. As L-type Ca²⁺ channels are thought to be targets of protein kinase C (PKC), we investigated the role of PKC under excitotoxic conditions. GRe attenuated Bay k-8644-induced mitochondrial dysfunction, PKCδ activation, and neuronal loss. The PKCδ inhibition and neuroprotection mediated by GRe were comparable to those by the ROS inhibitor N-acetylcysteine, the mitochondrial protectant cyclosporin A, the microglial inhibitor minocycline, or the PKCδ inhibitor rottlerin. Consistently, the GRe-mediated PKCδ inhibition and neuroprotection were counteracted by the mitochondrial toxin 3-nitropropionic acid or the PKC activator bryostatin-1. GRe treatment did not have additional effects on PKCδ gene knockout-mediated neuroprotection, suggesting that PKCδ is a molecular target of GRe. Collectively, our results suggest that GRe-mediated anticonvulsive/neuroprotective effects require the attenuation of mitochondrial dysfunction and altered redox status and inactivation of PKCδ.

Noradrenaline-induced l-lactate production requires d-glucose entry and transit through the glycogen shunt in single-cultured rat astrocytes

During cognitive efforts mediated by local neuronal networks, approximately 20% of additional energy is required; this is mediated by chemical messengers such as noradrenaline (NA). NA targets astroglial aerobic glycolysis, the hallmark of which is the end product l-lactate, a fuel for neurons. Biochemical studies have revealed that astrocytes exhibit a prominent glycogen shunt, in which a portion of d-glucose molecules entering the cytoplasm is transiently incorporated into glycogen, a buffer and source of d-glucose during increased energy demand. Here, we studied single astrocytes by measuring cytosolic L-lactate ([lac]_i ) with the FRET nanosensor Laconic. We examined whether NA-induced increase in [lac]_i is influenced by: (a) 2-deoxy-d-glucose (2-DG, 3 mM), a molecule that enters the cytosol and inhibits the glycolytic pathway; (b) 1,4-dideoxy-1,4-imino-d-arabinitol (DAB, 300 µM), a potent inhibitor of glycogen phosphorylase and glycogen degradation; and (c) 3-nitropropionic acid (3-NPA, 1 mM), an inhibitor of the Krebs cycle. The results of these pharmacological experiments revealed that d-glucose uptake is essential for the NA-induced increase in [lac]_i , and that this exclusively arises from glycogen degradation, indicating that most, if not all, d-glucose molecules in NA-stimulated cells transit the glycogen shunt during glycolysis. Moreover, under the defined transmembrane d-glucose gradient, the glycolytic intermediates were not only used to produce l-lactate, but also to significantly support oxidative phosphorylation, as demonstrated by an elevation in [lac]_i when Krebs cycle was inhibited. We conclude that l-lactate production via aerobic glycolysis is an essential energy pathway in NA-stimulated astrocytes; however, oxidative metabolism is important at rest.

Fluidic system for long-term in vitro culturing and monitoring of organotypic brain slices

Brain slice preparations cultured in vitro have long been used as a simplified model for studying brain development, electrophysiology, neurodegeneration and neuroprotection. In this paper an open fluidic system developed for improved long term culturing of organotypic brain slices is presented. The positive effect of continuous flow of growth medium, and thus stability of the glucose concentration and waste removal, is simulated and compared to the effect of stagnant medium that is most often used in tissue culturing. Furthermore, placement of the tissue slices in the developed device was studied by numerical simulations in order to optimize the nutrient distribution. The device was tested by culturing transverse hippocampal slices from 7 days old NMRI mice for a duration of 14 days. The slices were inspected visually and the slices cultured in the fluidic system appeared to have preserved their structure better than the control slices cultured using the standard interface method.

Neuroprotective efficacy of naringin on 3-nitropropionic acid-induced mitochondrial dysfunction through the modulation of Nrf2 signaling pathway in PC12 cells

Oxidative stress and mitochondrial dysfunction are implicated in neuronal apoptosis associated with Huntington's disease. Naringin is the flavanone present in grapefruit and related citrus species possess diverse pharmacological and therapeutic properties including antioxidant, anti-apoptotic, and neuroprotective properties. The aim of this study was to investigate the protective effect of naringin on 3-nitropropionic acid (3-NP)-induced neurotoxicity in pheochromocytoma cells (PC12) cells and to explore its mechanism of action. Naringin protects PC12 cells from 3-NP neurotoxicity, as evaluated the by cell viability assays. The lactate dehydrogenase release was decreased upon naringin treatment in 3-NP-induced PC12 cells. Naringin treatment enhances the antioxidant defense by increasing the activities of enzymatic antioxidants and the level of reduced glutathione. The increase in levels of reactive oxygen species and lipid peroxidation induced by 3-NP were significantly decreased by naringin. PC12 cells induced with 3-NP showed decrease in the mitochondrial membrane potential and mitochondrial respiratory complex enzymes, succinate dehydrogenase and cytochrome c oxidase activities, and it was significantly altered to near normal upon naringin treatment. Naringin reduced the 3-NP-induced apoptosis through the modulation in expressions of B-cell lymphoma 2 and Bcl-2-associated X protein. Further, naringin enhances the nuclear translocation of Nrf2 and induces the

NAD(P)H

quinone oxidoreductase-1 and Heme oxygenase-1 expressions through the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway. Taken together, the above findings suggest that naringin augments cellular antioxidant defense capacity and reduces the 3-NP-induced neurotoxicity in PC12 cells through the PI-3K/Akt-dependent Nrf2 activation in PC12 cells.

Excitotoxic motoneuron degeneration induced by glutamate receptor agonists and mitochondrial toxins in organotypic cultures of chick embryo spinal cord

Glutamate receptor-mediated excitotoxicity and mitochondrial dysfunction appear to play an important role in motoneuron (MN) degeneration in amyotrophic lateral sclerosis (ALS). In the present study we used an organotypic slice culture of chick embryo spinal cord to explore the responsiveness of mature MNs to different excitotoxic stimuli and mitrochondrial inhibition. We found that, in this system, MNs are highly vulnerable to excitotoxins such as glutamate, N-methyl-D-aspartate (NMDA), and kainate (KA), and that the neuroprotective drug riluzole rescues MNs from KA-mediated excitotoxic death. MNs are also sensitive to chronic mitochondrial inhibition induced by malonate and 3-nitropropionic acid (3-NP) in a dose-dependent manner. MN degeneration induced by treatment with mitochondrial toxins displays structural changes similar to those seen following excitotoxicity and can be prevented by applying either the antiexcitotoxic drug 6-cyano-7-nitroquinoxaline-2,3-dione disodium (CNQX) or riluzole. Excitotoxicity results in an increased frequency of normal spontaneous Ca2+ oscillations in MNs, which is followed by a sustained deregulation of intracellular Ca2+. Tolerance to excitotoxic MN death resulting from chronic exposure to excitotoxins correlates with a reduced excitotoxin-induced increase in intracellular Ca2+ and increased thapsigargin-sensitive Ca2+ stores.

3-Nitropropionic acid toxicity in hippocampus: protection through N-methyl-D-aspartate receptor antagonism

The over-activation of glutamate receptors can lead to excitotoxic cell death and is believed to be involved in the progression of neurodegenerative events in the vulnerable hippocampus. Here, we used an in vitro slice model to study toxicity produced in the hippocampus by the mitochondrial toxin 3-nitropropionic acid (3-NP). The organotypic slice cultures exhibit native cellular organization as well as dense arborization of neuronal processes and synaptic contacts. The hippocampal slices were exposed to 3-NP for 2-20 days, causing calpain-mediated breakdown of the spectrin cytoskeleton, a loss of pre- and postsynaptic markers, and neuronal atrophy. The N-methyl-D-aspartate (NMDA) receptor antagonist memantine reduced both the cytoskeletal damage and synaptic decline in a dose-dependent manner. 3-NP-induced cytotoxicity, as determined by the release of lactate dehydrogenase, was also reduced by memantine with EC50 values from 1.7 to 2.3 microM. Propidium iodide fluorescence and phase contrast microscopy confirmed memantine neuroprotection against the chronic toxin exposure. In addition, the protected tissue exhibited normal neuronal morphology in the major hippocampal subfields. These results indicate that antagonists of NMDA-type glutamate receptors are protective during the toxic outcome associated with mitochondrial dysfunction. They also provide further evidence of memantine's therapeutic potential against neurodegenerative diseases.

Widespread Neonatal Brain Damage following Calcium Channel Blockade

An abundance of evidence exists that shows calcium channel blockade promotes injury in cultured neurons. However, few studies have addressed the in vivo toxicity of such agents. We now show that the L-type calcium channel antagonist nimodipine promotes widespread and robust injury throughout the neonatal rat brain, in an age-dependent manner. Using both isolated neuronal as well as brain slice approaches, we address mechanisms behind such injury. These expanded studies show a consistent pattern of injury using a variety of agents that lower intracellular calcium. Collectively, these observations indicate that postnatal brain development represents a transitional period for still developing neurons, from being highly sensitive to reductions in intracellular calcium to being less vulnerable to such changes. These observations directly relate to current therapeutic strategies targeting neonatal brain injury.

Creatine protects against 3-nitropropionic acid-induced cell death in murine corticostriatal slice cultures

In murine corticostriatal slice cultures, we studied the protective effects of the bioenergetic compound creatine on neuronal cell death induced by the mitochondrial toxin 3-nitropropionic acid (3-NP). 3-NP caused a dose-dependent neuronal degeneration accompanied by an increased lactate dehydrogenase (LDH) activity in the cell culture medium. An increased ratio of lactate to pyruvate concentration in the medium suggested that metabolic activity shifted to anaerobic energy metabolism. These effects were predominantly observed in the 24-h recovery period after 3-NP exposure. Creatine protected against 3-NP neurotoxicity: LDH activity was reduced and aerobic respiration of pyruvate was stimulated, which resulted in lower lactate levels and less cell death. In both striatum and cortex, apoptosis in 3-NP-exposed slices was demonstrated by increased activation of the pro-apoptotic protein caspase-3 and by numerous cells exhibiting DNA fragmentation detected by the terminal transferase-mediated biotinylated-UTP nick end-labeling (TUNEL) technique. Creatine administration to the 3-NP-exposed corticostriatal slices resulted in a reduced number of TUNEL-positive cells in the recovery period. However, in the striatum, an unexpected increase of both TUNEL-positive cells and caspase-3-immunostained cells was observed in the exposure phase in the presence of creatine. In the recovery phase, caspase-3-immunostaining decreased to basal levels in both striatum and cortex. These findings suggest that 3-NP-induced neuronal degeneration in corticostriatal slices results from apoptosis that in the cortex can be prevented by creatine, while in the more vulnerable striatal cells it may lead to an accelerated and increased execution of apoptotic cell death, preventing further necrosis-related damage in this region.

Lactate induced excitotoxicity in hippocampal slice cultures

During the initial minutes of cerebral ischemia, lactic acid accumulates and acidifies brain pH to 6.0-6.7. Glutamate is also released during ischemia that activates glutamate receptors and induces excitotoxicity. While glutamate excitotoxicity is well established to induce ischemic injury, a role of lactic acidosis in ischemic brain damage is poorly understood. This study analyzes acidosis neurotoxicity in hippocampal slice cultures in the presence or absence of lactate. At pH 6.7, neuronal loss was similar whether or not lactate was present. At pH 6.4, neuronal loss was significantly greater in the presence of lactate suggesting that lactate potentiates the acidosis toxicity. At pH 6.4 in the presence of lactate, NMDA or non-NMDA receptor antagonists reduced neuronal loss, while in the absence of lactate, NMDA or non-NMDA receptor antagonists had little effect. [3H]-Glutamate uptake was inhibited by acidic pH, and the amount of inhibition was significantly greater in the presence of lactate. These findings suggest that lactate plays a role in acidosis neurotoxicity by inducing excitotoxicity. Lactic acidosis and excitotoxicity have been previously thought to be independent events during ischemia. This study suggests that during ischemia, lactic acidosis contributes to excitotoxic neuronal loss.

17 Beta-oestradiol attenuates dexamethasone-induced lethal and sublethal neuronal damage in the striatum and hippocampus

Abnormal corticosteroid release is extensively associated with mood disorders. This association may result from the toxic actions of endogenous corticosteroids which can induce apoptosis of hippocampal neurons. Similarly, dexamethasone, a synthetic corticosteroid, can induce lethal and sublethal damage to rat hippocampal and striatal neurons and can result in steroid-induced psychoses in humans. The experiments reported here tested the hypothesis that pre-treatment with oestrogen would also attenuate dexamethasone-induced neuronal damage as oestrogens have neuroprotective actions against a variety of insults and falling levels of oestrogen are associated with increased vulnerability to mood disorders. Male Sprague-Dawley rats received three systemic injections which were a combination of vehicle, 17-beta-oestradiol (0.2 mg/kg, s.c.), the oestrogen receptor antagonist tamoxifen (10 mg/kg, s.c.) and dexamethasone (0.7 mg/kg, i.p.) and were killed 24 h after the final injection. Injections of dexamethasone (when preceded by vehicle injections) resulted in elevated levels of apoptosis and sub-lethal damage, as demonstrated by reduced levels of microtubule-associated protein-2-immunopositive neurons, in the striatum and hippocampus. This damage was regional with the dorsomedial caudate putamen and the dentate gyrus and CA1 and CA3 hippocampal sub-fields being particularly affected. Pretreatment with oestrogen substantially attenuated the dexamethasone-induced neuronal damage. This oestrogen-induced neuronal protection was in turn virtually eliminated by giving an initial injection of tamoxifen. These results suggest, therefore, that oestrogens can protect from corticosteroid-induced neuronal damage via an oestrogen receptor-mediated process.

Brain slice culture for analysis of developmental brain disorders with special reference to congenital cytomegalovirus infection

Cytomegalovirus (CMV) is the most significant infectious cause of congenital abnormalities of the central nervous system (CNS) with variation from the fatal cytomegalic inclusion disease to functional brain disorder. The phenotype and degree of the brain disorder depends on infection time during the developing stage, virulence, route of infection and the viral susceptibility of the cells. The pathogenesis of the CMV infection to the CNS seems to be strongly related to neural migration, neural death, cellular compositions and the immune system of the brain. To understand the complex mechanism of this disorder, we used organotypic brain slice cultures. In the brain slice culture system, migration of CMV-infected neuronal cells was observed, which reflects infectious dynamics in vivo. Neural progenitor cells or glial immature cells in the subventricular zone and marginal area are most susceptible to murine cytomegalovirus (MCMV) infection in this system. The susceptibility declined as the number of immature glial cells decreased with age. The immature glial cells proliferated in brain slice cultures during prolonged incubation, and the susceptibility to MCMV infection also increased in association with the proliferation of these cells. The brain slice from an immunocompromised mouse (Beige-SCID mouse) unexpectedly showed lower susceptibility than that of an immunocompetent mouse during any prolonged incubation. These results suggest that the number of immature glial cells might determine the susceptibility of CMV infection to the brain, independent of the immune system. We reviewed recent findings of CMV infection to the brain from the perspective of brain slice cultures and the possibility that this system could be a useful method to investigate mechanisms of congenital anomaly of the brain.

Quantitative on-line monitoring of hippocampus glucose and lactate metabolism in organotypic cultures using biosensor technology

Quantitative glucose and lactate metabolism was assessed in continuously perfused organotypic hippocampal slices under control conditions and during exposure to glutamate and drugs that interfere with aerobic and anaerobic metabolism. On-line detection was possible with a system based on slow perfusion rates, a half-open (medium/air interface) tissue chamber and a flow injection analytic system equipped with biosensors for glucose and lactate. Under basal conditions about 50% of consumed glucose was converted to lactate in hippocampal slice cultures. Using medium containing lactate (5 mm) instead of glucose (5 mm) significant lactate uptake was observed, but this uptake was less than the net uptake of lactate equivalents in glucose-containing medium. Glucose deprivation experiments suggested lactate efflux from glycogen stores. The effects of drugs compromising or stimulating energy metabolism, i.e. 2-deoxyglucose, 3-nitropropionic acid, alpha-cyano-4-hydroxycinnamate, l-glutamate, d-asparate, ouabain and monensin, were tested in this flow system. The data show that maintaining Na+ and K+ gradients consumed much of the energy but do not support the hypothesis that l-glutamate stimulates glycolysis in hippocampal slice cultures.