Effects of edaravone on N-methyl-D-aspartate (NMDA)-mediated cytochrome c release and apoptosis in neonatal rat cerebrocortical slices

Targeting NMDA Receptors at the Neurovascular Unit: Past and Future Treatments for Central Nervous System Diseases

The excitatory neurotransmission of the central nervous system (CNS) mainly involves glutamate and its receptors, especially N-methyl-D-Aspartate receptors (NMDARs). These receptors have been extensively described on neurons and, more recently, also on other cell types. Nowadays, the study of their differential expression and function is taking a growing place in preclinical and clinical research. The diversity of NMDAR subtypes and their signaling pathways give rise to pleiotropic functions such as brain development, neuronal plasticity, maturation along with excitotoxicity, blood-brain barrier integrity, and inflammation. NMDARs have thus emerged as key targets for the treatment of neurological disorders. By their large extracellular regions and complex intracellular structures, NMDARs are modulated by a variety of endogenous and pharmacological compounds. Here, we will present an overview of NMDAR functions on neurons and other important cell types involved in the pathophysiology of neurodegenerative, neurovascular, mental, autoimmune, and neurodevelopmental diseases. We will then discuss past and future development of NMDAR targeting drugs, including innovative and promising new approaches.

Simvastatin, edaravone and dexamethasone protect against kainate-induced brain endothelial cell damage

BACKGROUND

Excitotoxicity is a central pathological pathway in many neurological diseases with blood-brain barrier (BBB) dysfunction. Kainate, an exogenous excitotoxin, induces epilepsy and BBB damage in animal models, but the direct effect of kainate on brain endothelial cells has not been studied in detail. Our aim was to examine the direct effects of kainate on cultured cells of the BBB and to test three anti-inflammatory and antioxidant drugs used in clinical practice, simvastatin, edaravone and dexamethasone, to protect against kainate-induced changes.

METHODS

Primary rat brain endothelial cell, pericyte and astroglia cultures were used to study cell viability by impedance measurement. BBB permeability was measured on a model made from the co-culture of the three cell types. The production of nitrogen monoxide and reactive oxygen species was followed by fluorescent probes. The mRNA expression of kainate receptors and nitric oxide synthases were studied by PCR.

RESULTS

Kainate damaged brain endothelial cells and made the immunostaining of junctional proteins claudin-5 and zonula occludens-1 discontinuous at the cell border indicating the opening of the barrier. The permeability of the BBB model for marker molecules fluorescein and albumin and the production of nitric oxide in brain endothelial cells were increased by kainate. Simvastatin, edaravone and dexamethasone protected against the reduced cell viability, increased permeability and the morphological changes in cellular junctions caused by kainate. Dexamethasone attenuated the elevated nitric oxide production and decreased the inducible nitric oxide synthase (NOS2/iNOS) mRNA expression increased by kainate treatment.

CONCLUSION

Kainate directly damaged cultured brain endothelial cells. Simvastatin, edaravone and dexamethasone protected the BBB model against kainate-induced changes. Our results confirmed the potential clinical usefulness of these drugs to attenuate BBB damage.

Punicalagin ameliorates the elevation of plasma homocysteine, amyloid-β, TNF-α and apoptosis by advocating antioxidants and modulating apoptotic mediator proteins in brain

The present study investigated the neuroprotective role of punicalagin, a major polyphenolic compound of pomegranate on methionine-induced brain injury. Hyperhomocysteinemia (HHcy) was induced in two months old male BALB c mice by methionine supplementation in drinking water (1 g/kg body weight) for 30 days. Punicalagin (1 mg/kg) was injected i.p every other day concurrently with methionine. Punicalagin significantly prevented the rise in the levels of homocysteine, amyloid-β and TNF-α. HHcy is associated with a decrease in the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (PGx) and glutathione reductase (GR) and glutathione (GSH) levels in the brains of methionine-treated mice while these antioxidants are increased by punicalagin supplementation. The treatment with punicalagin significantly decreased oxidative stress as indicated by decreased malondialdehyde and protein carbonyl formation in the brain. Compared with methionine-treated animals, mice that treated with methionine and punicalagin remarkably displayed less apoptosis, indicated by the lower level of proapoptotic protein (Bax, caspases- 3, 9 and p53) and higher levels of antiapoptotic Bcl-2 protein than those in hyperhomocysteinemic mice. The potent bioactivity of punicalagin extends to protect neuronal DNA as evidenced by the inhibition of the increase of comet parameters compared to the methionine-treated mice. In conclusion, punicalagin protected from methionine-induced HHcy and brain damage with an ability to repress apoptosis by modulating apoptotic mediators and maintaining DNA integrity in the brain of mice.

Role of oxidative stress in retinal photoreceptor cell death in N-methyl-N-nitrosourea-treated mice

This study aimed to investigate whether oxidative stress contributes to retinal cell death in a mouse model of photoreceptor degeneration induced by N-methyl-N-nitrosourea (MNU). We measured in vitro MNU-induced radical production in retinal cell cultures of murine 661W photoreceptor-derived cells; RGC-5, a mouse ganglion cell line; and primary retinal cells. The addition of MNU induced oxidative radical generation in 661W and primary retinal cells, but not in RGC-5 cells. Edaravone, a free radical scavenger, at 1 µM reduced MNU-induced radical production in 661W and primary retinal cells. To induce in vivo retinal photoreceptor degeneration in mice, we administered 60 mg/kg MNU by intraperitoneal injection. We intravenously administered 1 mg/kg edaravone immediately and at 6 h after the MNU injection. Retinal photoreceptor degeneration was evaluated by measuring the thickness of the outer nuclear layer (ONL) by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining and by oxidative stress markers. MNU caused photoreceptor cell loss at 7 days after administration. Edaravone inhibited ONL thinning and reduced TUNEL-positive cells and the oxidative stress markers. These findings indicate that MNU leads to selective photoreceptor degradation via oxidative stress in vitro and in vivo and may help to understand the pathogenic mechanism of retinitis pigmentosa.

Edaravone, a free radical scavenger, protects against retinal damage in vitro and in vivo

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger, is used for the treatment of acute cerebral infarction. In this study, we investigated whether edaravone is neuroprotective against retinal damage. In vitro, we used a radical-scavenging capacity assay using reactive oxygen species-sensitive probes to investigate the effects of edaravone on H(2)O(2), superoxide anion (O(2)*), and hydroxyl radical (*OH) production in a rat retinal ganglion cell line (RGC-5). The effect of edaravone on oxygen-glucose deprivation (OGD)-induced RGC-5 damage was evaluated using a 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt assay of cell viability. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) significantly decreased radical generation and reduced the cell death induced by OGD stress. In vivo, retinal damage was induced by intravitreous injection of N-methyl-D-aspartate (NMDA; 5 nmol) and was evaluated by examining ganglion cell layer cell loss, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, and the expressions of two oxidant-stress markers [4-hydroxy-2-nonenal (4-HNE) and 8-hydroxy-2-deoxyguanosine (8-OHdG)]. In addition, activations of mitogen-activated protein kinases (MAPKs) [extracellular signal-regulated protein kinases (ERK), c-Jun NH(2)-terminal kinases (JNK), and p38 MAPK], as downstream signal pathways after NMDA receptor activation, were measured using immunoblotting and immunostaining. Edaravone at 5 and 50 nmol intravitreous injection or at 1 and 3 mg/kg i.v. significantly protected against NMDA-induced retinal cell death. At 50 nmol intravitreous injection, it 1) decreased the retinal expressions of TUNEL-positive cells, 4-HNE, and 8-OHdG and 2) reduced the retinal expressions of NMDA-induced phosphorylated JNK and phosphorylated p38 but not that of phosphorylated ERK. These findings suggest that oxidative stress plays a pivotal role in retinal damage and that edaravone may be a candidate for the effective treatment of retinal diseases.

Fructose-1,6-bisphosphate does not preserve ATP in hypoxic-ischemic neonatal cerebrocortical slices

Fructose-1,6-bisphosphate (FBP), an endogenous intracellular metabolite in glycolysis, was found in many preclinical studies to be neuroprotective during hypoxia-ischemia (HI) when administered exogenously. We looked for HI neuroprotection from FBP in a neonatal rat brain slice model, using 14.1 T (1)H/(31)P/(13)C NMR spectroscopy of perchloric acid slice extracts to ask: 1) if FBP preserves high energy phosphates during HI; and 2) if exogenous [1-(13)C]FBP enters cells and is glycolytically metabolized to [3-(13)C]lactate. We also asked: 3) if substantial superoxide production occurs during and after HI, thinking such might be treatable by exogenous FBP's antioxidant effects. Superfused P7 rat cerebrocortical slices (350 mum) were treated with 2 mM FBP before and during 30 min of HI, and then given 4 h of recovery with an FBP-free oxygenated superfusate. Slices were removed before HI, at the end of HI, and at 1 and 4 h after HI. FBP did not improve high energy phosphate levels or change (1)H metabolite profiles. Large increases in [3-(13)C]lactate were seen with (13)C NMR, but the lactate fractional enrichment was always (1.1+/-0.5)%, implying that all of lactate's (13)C was natural abundance (13)C, that none was from metabolism of (13)C-FBP. FBP had no effect on the fluorescence of ethidium produced from superoxide oxidation of hydroethidine. Compared to control slices, ethidium fluorescence was 25% higher during HI and 50% higher at the end of recovery. Exogenous FBP did not provide protection or enter glycolysis. Its use as an antioxidant might be worth studying at higher FBP concentrations.