Evidence that brain-derived neurotrophic factor neuroprotection is linked to its ability to reverse the NMDA-induced inactivation of protein kinase C in cortical neurons

A review of chitosan polysaccharides: Neuropharmacological implications and tissue regeneration

One of the current challenges in targeting neurological disorders is that many therapeutic molecules cannot cross the blood-brain barrier (BBB), which limits the use of natural molecules in nervous tissue regeneration. Thus, the development of new drugs to effectively treat neurological disorders would be a challenge. Natural resources are well known as a source of several therapeutic agents for the treatment of neurologic disorders. Recently, chitosan (CTS) and its derivatives from arthropod exoskeletons, have attracted much attention as a drug delivery system to transport therapeutic substances across the BBB and thanks to other neuroprotective effects including the participation to the CNS regenerations scaffolds to replicate the extracellular matrix and microenvironment of the body. This review will discuss the place of natural resource therapy in targeting neurological disorders. In particular, it will highlight recent understanding and progress in the applications of CTS as drug delivery systems and their therapeutic effects on these disorders through tissue regeneration, as well as the molecular mechanisms by which they exert these effects.

Nanowired Delivery of Cerebrolysin Together with Antibodies to Amyloid Beta Peptide, Phosphorylated Tau, and Tumor Necrosis Factor Alpha Induces Superior Neuroprotection in Alzheimer's Disease Brain Pathology Exacerbated by Sleep Deprivation

Sleep deprivation induces amyloid beta peptide and phosphorylated tau deposits in the brain and cerebrospinal fluid together with altered serotonin metabolism. Thus, it is likely that sleep deprivation is one of the predisposing factors in precipitating Alzheimer's disease (AD) brain pathology. Our previous studies indicate significant brain pathology following sleep deprivation or AD. Keeping these views in consideration in this review, nanodelivery of monoclonal antibodies to amyloid beta peptide (AβP), phosphorylated tau (p-tau), and tumor necrosis factor alpha (TNF-α) in sleep deprivation-induced AD is discussed based on our own investigations. Our results suggest that nanowired delivery of monoclonal antibodies to AβP with p-tau and TNF-α induces superior neuroprotection in AD caused by sleep deprivation, not reported earlier.

Selected Factors of Vascular Changes: The Potential Pathological Processes Underlying Primary Headaches in Children

Background: The prevalence, social consequences and complicated pathogenesis make headaches in children a significant clinical issue. Studies in adults suggest that primary headaches could be the first sign of atherosclerosis and platelet aggregation. Aim: To analyze the blood levels of selected biomarkers of vascular changes potentially associated with a higher risk of atherosclerosis in children with primary headaches. Methods: The medical family history, brain-derived neurotrophic factor (BDNF), soluble CD40 ligands (sCD40L), endothelial plasminogen activator inhibitor (PAI I), vascular endothelial growth factor (VEGF) and intima-media thickness (IMT) measurements were performed in the 83 children (52 with primary headaches, 31 controls). Selected factors were compared with basic laboratory parameters that are potentially related to atherosclerosis: C-reactive protein (CRP) and lipid concentration. Results: There were no significant differences in biomarkers of vascular changes in the study group and controls in general. In the study group, boys had a higher BDNF level than girls (p = 0.046). Normal-weight migraine patients had significantly higher PAI-I levels than controls (p = 0.034). A positive correlation between PAI-1 and triglycerides (TG) was observed. IMT did not differ between children with primary headaches and controls; however, IMT showed a positive correlation with BMI z-score and TG. Children with headaches had, more often, a positive family history of cardiovascular disease (p = 0.049). Conclusions: There were no clear clinical changes indicative of atherosclerosis in the study population. However, some trends are visible. Primary headaches are more often related to a family history of cardiovascular diseases. IMT is associated with TG levels and BMI z-score. The measured biomarkers of vascular changes show mutual relations.

Protective role of lidocaine against cerebral ischemia-reperfusion injury: An in vitro study

Lidocaine, a local anesthetic, is a valuable agent for the treatment of neuronal ischemia/reperfusion (I/R) injury. The aim of the present study was to investigate the role of lidocaine in oxygen-glucose deprivation/reperfusion (OGD/R)-induced cortical neurons and explore the related molecular mechanisms. Cerebral cortical neurons were isolated from Sprague-Dawley rat embryos and stimulated with OGD/R to establish an in vitro I/R injury model. Subsequently, neuronal cell viability, cytotoxicity and apoptosis were evaluated by performing the MTT assay, lactate dehydrogenase (LDH) assay and flow cytometry, respectively. The results suggested that OGD/R exposure significantly decreased cerebral cortical neuron cell viability, accelerated LDH release and induced cell apoptosis compared with control neurons, indicating that cerebral I/R injury was stimulated by OGD/R treatment. Further investigation indicated that 10 µM lidocaine significantly enhanced neuronal cell viability, and reduced LDH release and neuronal cell apoptosis in OGD/R-exposed cells compared with the OGD/R + saline group, which indicated that lidocaine displayed neuroprotective effects against I/R damage. In addition, the findings of the present study suggested that OGD/R exposure significantly decreased Bcl-2 and Bcl-xl protein expression levels, but increased Bax protein expression levels, the Bax/Bcl-2 ratio and caspase-3 activity compared with control neurons. However, lidocaine reversed OGD/R-mediated alterations to apoptosis-related protein expression. Furthermore, the results of the present study indicated that lidocaine increased Wnt3a, β-catenin and cyclin D1 expression levels in OGD/R-exposed cells compared with the OGD/R + saline group, thus activating the Wnt/β-catenin signaling pathway. The findings of the present study suggested that lidocaine served a protective role in OGD/R-triggered neuronal damage by activating the Wnt/β-catenin signaling pathway; therefore, lidocaine may serve as a potential candidate for the treatment of cerebral I/R injury.

Headache in Children: Selected Factors of Vascular Changes Involved in Underlying Processes of Idiopathic Headaches

Headaches are common complaints in children. The International Classification of Headache Disorders, 3^rd edition (beta version), defines more than 280 types of headaches. Primary headaches refer to independent conditions that cause pain and include migraine, tension-type headaches (TTH), and trigeminal autonomic cephalalgias (TACs). Several agents are involved in the pathogenesis of headaches. The factors associated with predisposition to atherosclerosis seem to be particularly important from the clinical point of view. The influence of obesity on the incidence of headaches has been well established. Moreover, idiopathic headaches, especially migraine, are thought to be one of the first signs of disorders in lipid metabolism and atherosclerosis. The risk of migraine increases with increasing obesity in children. Another factor that seems to be involved in both obesity and headaches is the adiponectin level. Recent data also suggest new potential risk factors for atherosclerosis and platelet aggregation such as brain-derived neurotrophic factor (BDNF), sCD40L (soluble CD40 ligand), serpin E1/PAI I (endothelial plasminogen activator inhibitor), and vascular endothelial growth factor (VEGF). However, their role is controversial because the results of clinical studies are often inconsistent. This review presents the current knowledge on the potential markers of atherosclerosis and platelet aggregation, which may be associated with primary headaches.

Epileptic seizures and oxidative stress in a mouse model over-expressing spermine oxidase

Several studies have demonstrated high polyamine levels in brain diseases such as epilepsy. Epilepsy is the fourth most common neurological disorder and affects people of all ages. Excitotoxic stress has been associated with epilepsy and it is considered one of the main causes of neuronal degeneration and death. The transgenic mouse line Dach-SMOX, with CD1 background, specifically overexpressing spermine oxidase in brain cortex, has been proven to be highly susceptible to epileptic seizures and excitotoxic stress induced by kainic acid. In this study, we analysed the effect of spermine oxidase over-expression in a different epileptic model, pentylenetetrazole. Behavioural evaluations of transgenic mice compared to controls showed a higher susceptibility towards pentylentetrazole. High-performance liquid chromatography analysis of transgenic brain from treated mice revealed altered polyamine content. Immunoistochemical analysis indicated a rise of 8-oxo-7,8-dihydro-2'-deoxyguanosine, demonstrating an increase in oxidative damage, and an augmentation of system xc- as a defence mechanism. This cascade of events can be initially linked to an increase in protein kinase C alpha, as shown by Western blot. This research points out the role of spermine oxidase, as a hydrogen peroxide producer, in the oxidative stress during epilepsy. Moreover, Dach-SMOX susceptibility demonstrated by two different epileptic models strongly indicates this transgenic mouse line as a potential animal model to study epilepsy.

Effects of Therapeutic Hypothermia Combined with Other Neuroprotective Strategies on Ischemic Stroke: Review of Evidence

Ischemic stroke is a major cause of death and disability globally, and its incidence is increasing. The only treatment approved by the US Food and Drug Administration for acute ischemic stroke is thrombolytic treatment with recombinant tissue plasminogen activator. As an alternative, therapeutic hypothermia has shown excellent potential in preclinical and small clinical studies, but it has largely failed in large clinical studies. This has led clinicians to explore the combination of therapeutic hypothermia with other neuroprotective strategies. This review examines preclinical and clinical progress towards developing highly effective combination therapy involving hypothermia for stroke patients.

An Overview of the Protective Effects of Chitosan and Acetylated Chitosan Oligosaccharides against Neuronal Disorders

Chitin is the second most abundant biopolymer on Earth and is mainly comprised of a marine invertebrate, consisting of repeating β-1,4 linked N-acetylated glucosamine units, whereas its N-deacetylated product, chitosan, has broad medical applications. Interestingly, chitosan oligosaccharides have therapeutic effects on different types of neuronal disorders, including, but not limited to, Alzheimer’s disease, Parkinson’s disease, and nerve crush injury. A common link among neuronal disorders is observed at a sub-cellular level, such as atypical protein assemblies and induced neuronal death. Chronic activation of innate immune responses that lead to neuronal injury is also common in these diseases. Thus, the common mechanisms of neuronal disorders might explain the general therapeutic effects of chitosan oligosaccharides and their derivatives in these diseases. This review provides an update on the pathogenesis and therapy for neuronal disorders and will be mainly focused on the recent progress made towards the neuroprotective properties of chitosan and acetylated chitosan oligosaccharides. Their structural features and the underlying molecular mechanisms will also be discussed.

Serum brain-derived neurotrophic factor levels associate with cognitive improvement in patients with schizophrenia treated with electroacupuncture

Accumulating evidence supports that acupuncture has been successfully used for the treatment of neurological disorders to improve cognitive function. This study was set to evaluate the efficacy of electroacupuncture (EA, using two acupoints: Baihui and Shenting) on clinical symptoms, cognitive function and brain-derived neurotrophic factor (BDNF) levels in patients with schizophrenia. Sixty-one inpatients diagnosed schizophrenia with DSM-IV criteria were recruited. The participants were randomly divided into an experimental group (n=30) and a control group (n=31). The patients were evaluated using the Positive and Negative Symptom Scale (PANSS), the Wisconsin Card Sorting Test (WCST) and Wechsler Memory Scale (WMS) at baseline and after EA treatment. There were no significant differences in the PANSS scores and serum BDNF levels between the experimental group and the control group, either at baseline or at the end of the 4-week study period. However, the EA treatment appeared to have significant benefits on memory and moderate benefits on executive functions and problem solving. Significant positive correlation was observed between the increase of BDNF levels and memory improvement after EA treatment. Our results indicated that EA treatment could improve cognitive function, and the cognitive benefits positively associate with serum BDNF levels in patients with schizophrenia.

From Drug-Induced Developmental Neuroapoptosis to Pediatric Anesthetic Neurotoxicity-Where Are We Now?

The fetal and neonatal periods are critical and sensitive periods for neurodevelopment, and involve rapid brain growth in addition to natural programmed cell death (i.e., apoptosis) and synaptic pruning. Apoptosis is an important process for neurodevelopment, preventing redundant, faulty, or unused neurons from cluttering the developing brain. However, animal studies have shown massive neuronal cell death by apoptosis can also be caused by exposure to several classes of drugs, namely gamma-aminobutyric acid (GABA) agonists and N-methyl-d-aspartate (NMDA) antagonists that are commonly used in pediatric anesthesia. This form of neurotoxic insult could cause a major disruption in brain development with the potential to permanently shape behavior and cognitive ability. Evidence does suggest that psychoactive drugs alter neurodevelopment and synaptic plasticity in the animal brain, which, in the human brain, may translate to permanent neurodevelopmental changes associated with long-term intellectual disability. This paper reviews the seminal animal research on drug-induced developmental apoptosis and the subsequent clinical studies that have been conducted thus far. In humans, there is growing evidence that suggests anesthetics have the potential to harm the developing brain, but the long-term outcome is not definitive and causality has not been determined. The consensus is that there is more work to be done using both animal models and human clinical studies.

Electroacupuncture analgesia is associated with increased serum brain-derived neurotrophic factor in chronic tension-type headache: a randomized, sham controlled, crossover trial

Background

Chronic tension-type headache (CTTH) is characterized by almost daily headaches and central sensitization, for which electroacupuncture (EA) might be effective. The central nervous system (CNS) plasticity can be tracked in serum using the brain-derived neurotrophic factor (BDNF), a neuroplasticity mediator. Thus, we tested the hypothesis that EA analgesia in CTTH is related to neuroplasticity indexed by serum BDNF.

Methods

We enrolled females aged 18–60 years with CTTH in a randomized, blinded, placebo-controlled crossover trial, comparing ten EA sessions applied for 30 minutes (2–10 Hz, intensity by tolerance) in cervical areas twice per week vs. a sham intervention. Treatment periods were separated by two washout weeks. Pain on the 10-cm visual analog scale (VAS) and serum BDNF were assessed as primary outcomes.

Results

Thirty-four subjects underwent randomization, and twenty-nine completed the protocol. EA was superior to sham to alleviate pain (VAS scores 2.38 ± 1.77 and 3.02 ± 2.49, respectively, P = 0.005). The VAS scores differed according to the intervention sequence, demonstrating a carryover effect (P < 0.05). Using multiple regression, serum BDNF was adjusted for the Hamilton depression rating scale (HDRS) and the VAS scores (r-squared = 0.07, standard β coefficients = −0.2 and −0.14, respectively, P < 0.001). At the end of the first intervention period, the adjusted BDNF was higher in the EA phase (29.31 ± 3.24, 27.53 ± 2.94 ng/mL, Cohen’s d = 0.55).

Conclusion

EA analgesia is related to neuroplasticity indexed by the adjusted BDNF. EA modulation of pain and BDNF occurs according to the CNS situation at the moment of its administration, as it was related to depression and the timing of its administration.

An Immunological Approach to Increase the Brain's Resilience to Insults

We have previously demonstrated the therapeutic potential of inducing a humoral response with autoantibodies to the N-methyl D-aspartate (NMDA) receptor using a genetic approach. In this study, we generated three recombinant proteins to different functional domains of the NMDA receptor, which is implicated in mediating brain tolerance, specifically NR1[21-375], NR1[313-619], NR1[654-800], and an intracellular scaffolding protein, Homer1a, with a similar anatomical expression pattern. All peptides showed similar antigenicity and antibody titers following systemic vaccination, and all animals thrived. Two months following vaccination, rats were administered the potent neurotoxin, kainic acid. NR1[21-375] animals showed an antiepileptic phenotype but no neuroprotection. Remarkably, despite ineffective antiepileptic activity, 6 of 7 seizing NR1[654-800] rats showed absolutely no injury with only minimal changes in the remaining animal, whereas the majority of persistently seizing rats in the other groups showed moderate to severe hippocampal injury. CREB, BDNF, and HSP70, proteins associated with preconditioning, were selectively upregulated in the hippocampus of NR1[654-800] animals, consistent with the observed neuroprotective phenotype. These results identify NR1 epitopes important in conferring anticonvulsive and neuroprotective effects and support the concept of an immunological strategy to induce a chronic state of tolerance in the brain.

Cell biology in neuroscience: Death of developing neurons: new insights and implications for connectivity

The concept that target tissues determine the survival of neurons has inspired much of the thinking on neuronal development in vertebrates, not least because it is supported by decades of research on nerve growth factor (NGF) in the peripheral nervous system (PNS). Recent discoveries now help to understand why only some developing neurons selectively depend on NGF. They also indicate that the survival of most neurons in the central nervous system (CNS) is not simply regulated by single growth factors like in the PNS. Additionally, components of the cell death machinery have begun to be recognized as regulators of selective axonal degeneration and synaptic function, thus playing a critical role in wiring up the nervous system.

Effect of electroacupuncture on brain-derived neurotrophic factor mRNA expression in mouse hippocampus following cerebral ischemia-reperfusion injury

OBJECTIVE

This work aims to observe the effects of electroacupuncture on brain-derived neurotrophic factor (BDNF) mRNA expression in mouse hippocampus following cerebral ischemia-reperfusion injury.

METHODS

The models of mouse cerebral ischemia-reperfusion injury were established. A total of 96 healthy mice were randomly assigned into 4 groups, namely, the sham surgery, model, model + electroacupuncture, and mode + hydergine groups. Mice in the model + electroacupuncture group were treated through electroacupuncture at the Shenshu (BL 23), Geshu (BL 17), and Baihui (GV 20) acupoints. Mice in the model+hydergine group were intragastrically administered with hydergine (0.77 mg/kg(-1) x day(-1)). The levels of BDNF mRNA expressions in the hippocampus were ana lyzed through a semi-quantitative reverse transcription-polymerase chain reaction assay on days 1 and 7 after the surgeries.

RESULTS

BDNF mRNA expressions in the mouse hippocampus of the model group on days 1 and 7 after the surgery were higher than those of the sham surgery group (both P < 0.01). On days 1 and 7 of the electroacupuncture treatment, BDNF mRNA expression in the mouse hippocampus of the model + electroacupuncture group was significantly elevated compared with the model group (both P < 0.01) or the model + hydergine group (both P < 0.01). On days 1 and 7 of the hydergine treatment, BDNF mRNA expression in the mouse hippocampus of the model + hydergine group tended to increase compared with the model group; however, statistical significance was not achieved (both P > 0.05).

CONCLUSION

Electroacupuncture treatment enhances endogenous BDNF expression, which may improve the survival environment for intracerebral neurons and inhibit the apoptosis of hippocampal cells.

Fingolimod, a sphingosine-1 phosphate receptor modulator, increases BDNF levels and improves symptoms of a mouse model of Rett syndrome

The functional relevance of brain-derived neurotrophic factor (BDNF) is beginning to be well appreciated not only in mice, but also in humans. Because reduced levels typically correlate with impaired neuronal function, increasing BDNF levels with well-tolerated drugs diffusing into the central nervous system may help in ameliorating functional deficits. With this objective in mind, we used the sphingosine-1 phosphate receptor agonist fingolimod, a drug that crosses the blood-brain barrier. In addition, fingolimod has recently been introduced as the first oral treatment for multiple sclerosis. In cultured neurons, fingolimod increases BDNF levels and counteracts NMDA-induced neuronal death in a BDNF-dependent manner. Ongoing synaptic activity and MAPK signaling is required for fingolimod-induced BDNF increase, a pathway that can also be activated in vivo by systemic fingolimod administration. Mice lacking Mecp2, a gene frequently mutated in Rett syndrome, show decreased levels of BDNF, and fingolimod administration was found to partially rescue these levels as well as the size of the striatum, a volumetric sensor of BDNF signaling in rodents. These changes correlate with increased locomotor activity of the Mecp2-deficient animals, suggesting that fingolimod may improve the functional output of the nervous system, in addition to its well-documented effects on lymphocyte egress from lymph nodes.

Functional recovery after transplantation of neural stem cells modified by brain-derived neurotrophic factor in rats with cerebral ischaemia

Functional recovery after transplantation of brain-derived neurotrophic factor (BDNF)-modified neural stem cells (NSCs) was evaluated in a rat model of cerebral ischaemia damage induced by temporary middle cerebral artery occlusion (tMCAO). Western blotting and enzyme-linked immunosorbent assay demonstrated upregulated BDNF protein expression by rat embryonic NSCs transfected with the human BDNF gene (BDNF-NSCs). BDNF-NSCs stimulated neurite outgrowth in cocultured dorsal root ganglion neurons, suggesting that BDNF increased neurogenesis in vitro. In vivo, BDNF promoted recovery of tMCAO. Phosphate-buffered saline, untransformed NSCs or BDNF-NSCs were introduced into the penumbra zone of the right striatum of tMCAO rats and neurological function deficit was assessed for up to 12 weeks using the neurological severity score (NSS). The NSS was significantly lower in the BDNF-NSC transfected transplant group than in all the other groups from week 10. BDNF-NSCs recovered 1 week after transplantation expressed BDNF protein. Transplanted NSCs had differentiated into mature neurons 12 weeks after transplantation. Transgenic NSCs have potential as a therapeutic agent for brain ischaemia.

Neuroprotective properties of chitosan and its derivatives

Neuronal cells are extremely vulnerable and have a limited capacity for self-repair in response to injury. For those reasons, there is obvious interest in limiting neuronal damage. Mechanisms and strategies used in order to protect against neuronal injury, apoptosis, dysfunction, and degeneration in the central nervous system are recognized as neuroprotection. Neuroprotection could be achieved through several classes of natural and synthetic neuroprotective agents. However, considering the side effects of synthetic neuroprotective agents, the search for natural neuroprotective agents has received great attention. Recently, an increasing number of studies have identified neuroprotective properties of chitosan and its derivatives; however, there are some significant challenges that must be overcome for the success of this approach. Hence, the objective of this review is to discuss neuroprotective properties of chitosan and its derivatives.

Different mechanisms of NMDA-mediated protection against neuronal apoptosis: a stimuli-dependent effect

The mechanisms of protective effect of N-methyl-D-aspartate (NMDA) receptor stimulation on apoptosis of neurons at their early stage of development are poorly understood. In the present study, we investigated the effects of NMDA on staurosporine (St)- and low-potassium (LP)-evoked apoptotic cell death in primary cerebellar granule cell (CGC) cultures at 7 days in vitro (DIV). We found that NMDA (200 microM) attenuated the St (0.5 microM)- and LP (5 mM KCl)-induced neuronal cell death in 7 but not 12 DIV CGC as confirmed by LDH release and MTT reduction assays. Moreover, NMDA attenuated St-and LP-evoked DNA fragmentation and cytosolic apoptosis inducing factor (AIF) protein level but not caspase-3 activation induced by both pro-apoptotic factors. Neuroprotective effects of NMDA on St-induced apoptosis in CGC were attenuated by inhibitors of ERK/MAPK-signaling, PD 98059 and U0126 but not by NMDA receptor antagonists, AP-5 (100 microM) and MK-801 (1 microM) or by inhibitors of PI3-K/Akt pathway (LY 294002 and wortmannin). In contrast to staurosporine model of apoptosis, AP-5 and MK-801 but not inhibitors of PI3-K/Akt and MAPK/ERK1/2 prevented the NMDA-mediated neuroprotection in LP-induced apoptosis of CGC. In separate experiments, we observed also the anti-apoptotic action of NMDA on St (0.5 microM)- and salsolinol (250 microM)-evoked cell death in human neuroblastoma SH-SY5Y cells without its influence on caspase-3 activity, induced by these pro-apoptotic factors. These data indicate that neuroprotection evoked by NMDA in CGC strongly depends on used pro-apoptotic agent and could engage NMDA channel function or be connected with the activation of pro-survival MAPK/ERK1/2 pathway. It is also suggested that anti-apoptotic effects of NMDA is connected with inhibition of fragmentation of DNA via caspase-3-independent mechanism.

Protective effects of brain-derived neurotrophic factor against neurotoxicity of 3-nitropropionic acid in rat cortical neurons

Brain-derived neurotrophic factor (BDNF) deficiency has been implicated in pathogenesis of Huntington's disease (HD). 3-Nitropropionic acid (3-NP), an irreversible mitochondrial complex II inhibitor, has been commonly used as a pharmacological model recapitulating HD phenotypes in rodents and nonhuman primates. Herein we test whether BDNF may exert neuroprotective effects against mitochondrial dysfunction caused by 3-NP in primary culture of fetal rat cortical neurons. Preconditioning of neuronal cells with BDNF (100 ng/ml for 8h) attenuated 3-NP toxicity (2.5 mM for additional 24h) based on Hoechst and propidium iodide (PI) staining. BDNF effects can be inhibited by the nitric oxide synthase (NOS) inhibitor L-nitroarginine methylester (L-NAME, 100 microM), the cGMP-dependent protein kinase (PKG) inhibitor KT5823 (2 microM), the thioredoxin reductase inhibitor 1-chloro-2,4-dinitrobenzene (DNCB, 5 microM), and a membrane-permeable Bcl-2 inhibitor (12.5 microM). 8-Br-cGMP is a cGMP analogue capable of activating PKG independent of NO. Exogenous application of 8-Br-cGMP (3-30 microM) and purified thioredoxin (3-5 microM) partially mimicked BDNF effects in conferring 3-NP resistance to cortical cells. These results, together with our previous report showing NO donor S-nitrosoglutathione (GSNO)-mediated neuroprotective effects against 3-NP toxicity, suggest that BDNF may protect neurons from mitochondrial dysfunction at least partly via activation of the signaling cascades involving NOS/NO, PKG, thioredoxin and Bcl-2.

The phosphatase inhibitor, okadaic acid, strongly protects primary rat cortical neurons from lethal oxygen-glucose deprivation

The protein kinase-mediated actions of peptide growth factors such as IGF-1 and bFGF protect cultured neurons from being killed by the oxygen and glucose deprivations (OGD) that prevail in the 'stroked brain'. Here, we show that neuroprotection by IGF-1 is mediated by PI-3K/Akt, whereas that of bFGF is mediated by MAPK. IGF-1 and bFGF together did not further increase protection suggesting a downstream convergence of their pathways. Since protein kinases mediated the protection, a phosphatase inhibitor such as okadaic acid (OA) might be as protective as the growth factors against OGD. Here, we show that OA is actually a much more effective protector. It increased the phosphorylation of both PI-3K/Akt and MAPK, and stimulated new protein synthesis. OA also acted independently of the CREB activation and FKHRL1 and GSK-3 inactivation which have been implicated in IGF-1 actions.

PLC-dependent intracellular Ca2+ release was associated with C6-ceramide-induced inhibition of Na+ current in rat granule cells

In this report, the effects of C(6)-ceramide on the voltage-gated inward Na(+) currents (I(Na)), two types of main K(+) current [outward rectifier delayed K(+) current (I(K)) and outward transient K(+) current (I(A))], and cell death in cultured rat cerebellar granule cells were investigated. At concentrations of 0.01-100 microM, ceramide produced a dose-dependent and reversible inhibition of I(Na) without alteration of the steady-state activation and inactivation properties. Treatment with C(2)-ceramide caused a similar inhibitory effect on I(Na). However, dihydro-C(6)-ceramide failed to modulate I(Na). The effect of C(6)-ceramide on I(Na) was abolished by intracellular infusion of the Ca(2+)-chelating agent, 1,2-bis (2-aminophenoxy) ethane-N, N, N9, N9-tetraacetic acid, but was mimicked by application of caffeine. Blocking the release of Ca(2+) from the sarcoplasmic reticulum with ryanodine receptor blocker induced a gradual increase in I(Na) amplitude and eliminated the effect of ceramide on I(Na). In contrast, the blocker of the inositol 1,4,5-trisphosphate-sensitive Ca(2+) receptor did not affect the action of C(6)-ceramide. Intracellular application of GTPgammaS also induced a gradual decrease in I(Na) amplitude, while GDPbetaS eliminated the effect of C(6)-ceramide on I(Na). Furthermore, the C(6)-ceramide effect on I(Na) was abolished after application of the phospholipase C (PLC) blockers and was greatly reduced by the calmodulin inhibitors. Fluorescence staining showed that C(6)-ceramide decreased cell viability and blocking I(Na) by tetrodotoxin did not mimic the effect of C(6)-ceramide, and inhibiting intracellular Ca(2+) release by dantrolene could not decrease the C(6)-ceramide-induced cell death. We therefore suggest that increased PLC-dependent Ca(2+) release through the ryanodine-sensitive Ca(2+) receptor may be responsible for the C(6)-ceramide-induced inhibition of I(Na), which does not seem to be associated with C(6)-ceramide-induced granule neuron death.

T cell independent mechanism for copolymer-1-induced neuroprotection

Despite active investigation of copolymer-1 (Cop-1) for nearly 40 years the mechanisms underlying its neuroprotective properties remain contentious. Nonetheless, current dogma for Cop-1 neuroprotective activities in autoimmune and neurodegenerative diseases include bystander suppression of autoimmune T cells and attenuation of microglial responses. In this report, we demonstrate that Cop-1 interacts directly with primary human neurons and decreases neuronal cell death induced by staurosporine or oxidative stress. This neuroprotection is mediated through protein kinase Calpha and brain-derived neurotrophic factor. Dendritic cells (DC) uptake Cop-1, deliver it to the injury site, and release it in an active form. Interactions between Cop-1 and DC enhance DC blood brain barrier migration. In a rat model with optic nerve crush injury, Cop-1-primed DC induce T cell independent neuroprotection. These findings may facilitate the development of neuroprotective approaches using DC-mediated Cop-1 delivery to diseased nervous tissue.

Neuroprotective effects of short peptides derived from the Insulin-like growth factor 1

Insulin-like growth factor I (IGF-1) is a peptide synthesized in response to growth hormone stimulation. While most of the circulating IGF-1 comes from the liver, it can also be produced in other tissues and both its expression and processing undergo tissue-specific regulation. The predominant form, IGF-1Ea is a circulating factor while two others, IGF-1Eb and IGF-1Ec (MGF), are mostly expressed in different tissues or in response to various stimuli and show some preferences with respect to the signal transduction pathways they activate. In skeletal muscle specific forms of IGF-1 play a role in development and growth and in addition to these physiological roles IGF-1 functions in the damaged muscle. IGF-1 is also important for the developing and adult brain and can reduce neuronal death caused by different types of injuries. Like many other peptide hormones IGF-1 originates from a precursor pro-hormone that undergoes extensive post-translational modifications. Processing liberates the mature peptide, which acts via the specific IGF-1 receptor but additional short peptides can arise from both N- and C-termini of various IGF-1 isoforms. These derivatives function as autonomous biologically active peptides and extremely potent neuroprotective agents. Their biological effects are independent of the activation of the IGF-1 receptor. Unfortunately, little is known about their mechanism(s) of action. Likewise, the existence of the endogenous production and wider biological effects of these short peptides are uncertain. However, considering the difference in the modes of action it might be possible to dissociate the unwanted and potentially dangerous mitogenic activity of the full-length IGF-1 exerted via its receptor from the neuroprotective effects of short derivatives mediated through different pathways. Such small molecules show good penetration through the blood brain barrier, can be inexpensively manufactured and modified to increase their stability. Therefore, they are good candidates for development into a neuroprotective therapeutic modality.

The attenuating effect of memantine on staurosporine-, salsolinol- and doxorubicin-induced apoptosis in human neuroblastoma SH-SY5Y cells

Memantine, a clinically used N-methyl-D-aspartate (NMDA)-receptor antagonist, has been shown to prevent apoptotic neuronal damage connected with the over-activity of NMDA receptors. In the present study, we examined the effect of memantine on staurosporine-, salsolinol- and doxorubicin-induced apoptosis in the SH-SY5Y cell line which does not possess functional NMDA receptors. Electrophysiological recordings and toxicity studies showed no response to NMDA-evoked currents in this cell line, irrespective of the stage of its neuronal differentiation. Memantine (0.1-2 microM) attenuated staurosporine-induced apoptosis as evidenced by reversal of the changes in mitochondrial membrane potential (DeltaPsi(m)) and decreased caspase-3 activity, lactate dehydrogenase (LDH) release and DNA fragmentation. Wortmannin (10 nM) and LY 294002 (10 microM) (inhibitors of phosphatidylinositol-3-kinase, PI3-K) reversed the inhibitory effect of memantine on the staurosporine-induced LDH release, suggesting that the PI3-K/Akt prosurvival pathway is a possible target for antiapoptotic action of memantine. Memantine at low micromolar concentrations also attenuated salsolinol- and doxorubicin-induced LDH release and DNA fragmentation, but only in the case of salsolinol was this effect accompanied by a decrease in caspase-3 activity. The present data indicate that memantine attenuates the toxic effects of various proapoptotic agents and the cytoprotective effect of memantine does not seem to be connected with its action on NMDA receptor but rather with its influence on intracellular pathways engaged in cellular survival/apoptotic processes.

Insulin-like growth factor-I enhances the biological activity of brain-derived neurotrophic factor on cerebrocortical neurons

Insulin-like growth factor (IGF)-I and brain-derived neurotrophic factor (BDNF) act within the brain to enhance neuronal survival and plasticity. We extend these findings by showing that the presence of both neurotrophins is required to depress the rise in intracellular Ca2+ caused by glutamate in primary cultures of cerebrocortical neurons. IGF-I enhanced expression of BDNF receptors (Trk-B) and increased the ability of BDNF to induce ERK1/2 phosphorylation. This IGF-I-induced increase in BDNF responsiveness describes a new interaction between these peptides in the brain.

Pb2+ reduces PKCs and NF-κB in vitro

The mechanism of lead (Pb(2+))-induced neurotoxicity has not yet been fully elucidated. The purpose of this study was to examine the effects of Pb(2+) on several protein kinase C (PKC) isoforms and the nuclear factor-kappaB (NF-kappaB)-I-kappaB kinase-alpha (IKK-alpha) axis in cultured neuronal cells. Neurons were isolated from rat fetal brain at the 18th day of gestation of pregnant Sprague Dawley rats and cultured for 10 days before use. Neurons were exposed to Pb(2+) at concentrations of 10(-10), 10(-9), 10(-8), and 10(-7) mol/L for 14 h and antigens of typical PKC-alpha,beta,gamma; novel PKC (epsilon, delta), atypical PKC (lambda), NF-kappaB (p50), and IKK-alpha were enriched by immunoprecipitation and determined by western blotting. Total, calcium-dependent and independent PKC activities were also determined by counting the transferred gamma-(32) P in the substrate-histone. The results indicated that inorganic Pb(2+) significantly reduced all PKC isoforms (alpha,beta,gamma, epsilon, lambda) except delta, inhibiting the total, calcium-dependent and calcium-independent PKC activities in a dose-dependent manner. Additionally, Pb(2+) gradually reduced NF-kappaB (p50) and IKK-alpha protein levels. This suggests that Pb(2+) exhibits varying preference for individual PKC isoforms but reduces the NF-kappaB-IKK-alpha axis to a similar extent.

Glutamic acid reverses Pb2+-induced reductions of NMDA receptor subunits in vitro

The objective of this study is to determine the effects of Pb2+ on N-methyl-d-aspartate receptor (NMDAR) subunits--NR1C1, NR2A and NR2B in primary cultured neuronal cells. We hypothesize that L-glutamic acid (GA) reverses Pb2+-induced NMDAR damage. Neuronal cells were isolated from the fetus brain at 18-20th day of gestation of pregnant Sprague Dawley (SD) rats. All experiments were included three independent cell preparations (N=3). The neuronal cells were exposed to Pb2+ (10(-10), 10(-9), 10(-8) and 10(-7)M) for 24 h. Neurons were pretreated with NMDAR agonist--L-glutamic acid (GA) (200 microM) and antagonists dizocipine (MK-801, 50 nM) for 1h and then exposed to 10(-7)M of Pb2+ for 24 h. Finally, GA at 2, 0.2 and 0.02 mM was incubated with neurons prior to Pb2+ exposure. Aliquots of NR1, NR2A and NR2B proteins from cell homogenate were immunoprecipitated with protein A agarose and detected by Western blotting. The addition of GA unconventionally reversed the reductions of NMDAR by Pb at protein levels, whereas MK-801 exacerbated Pb2+-induced damage. The protection by GA against Pb2+-induced reduction of NMDAR was dose-dependent. These findings suggest that the administration of GA may be a potential approach to intervene the Pb2+-induced NMDAR alterations.

Memantine attenuates staurosporine-induced activation of caspase-3 and LDH release in mouse primary neuronal cultures

Developmental aspects of pro- and antiapoptotic action of some NMDA receptor antagonists in the central nervous system have been postulated. In order to further elucidate this problem, we investigated effect of memantine, an uncompetitive NMDA receptor antagonist and staurosporine alone and in combination on caspase-3 activity and lactate dehydrogenase (LDH) release in primary hippocampal, neocortical and striatal cell cultures on 7 and 12 days in vitro. The data showed that the vulnerability of neuronal cells to induction of caspase-3 activity by staurosporine was higher on 7 DIV than on 12 DIV, whereas staurosporine-mediated LDH release increased with days in vitro in striatal culture only. A specific inhibitor of caspase-3, AcDEVDCHO (60 microM), completely abolished the effect of staurosporine on this enzyme's activity, but only partially attenuated staurosporine-induced LDH release in hippocampal cells. Memantine alone (0.05-2.0 microM) did not induce any cytotoxic effect but attenuated the staurosporine-induced caspase-3 activity and LDH release in hippocampal cultured neurons on each investigated day in vitro. In striatal culture, memantine had a moderate inhibitory effect on staurosporine-evoked LDH release only on 7 DIV with no significant influence on caspase-3 activity. As for neocortical cultures, memantine partially inhibited staurosporine-induced neuronal injury only on 7 DIV. These data showed that the induction of caspase-3 activity by staurosporine was more profound in immature cells, however, the staurosporine neurotoxicity, as reflected by LDH release, only partially depended on caspase-3 activation and stage of cell development. Furthermore, memantine attenuated staurosporine-induced apoptosis more efficiently in hippocampal cultures than in neocortical and striatal ones, which points to tissue specificity of effects of this neuroprotectant.

Conventional protein kinase C isoforms mediate neuroprotection induced by phorbol ester and estrogen

Rapid signal transduction pathways play a prominent role in mediating neuroprotective actions of estrogen in the CNS. We have previously shown that estrogen-induced neuroprotection of primary cerebrocortical neurons from beta-amyloid peptide (Abeta) toxicity depends on activation of protein kinase C (PKC). PKC activation with phorbol-12-myristate-13-acetate (PMA) also provides neuroprotection in this paradigm. Because the PKC family includes several isoforms that have opposing roles in regulating cell survival, we sought to identify which PKC isoforms contribute to neuroprotection induced by PMA and estrogen. We detected protein expression of multiple PKC isoforms in primary neuron cultures, including conventional (alpha, betaI, betaII), novel (delta, epsilon, theta) and atypical (zeta, iota/lambda) PKC. Using a panel of isoform-specific peptide inhibitors and activators, we find that novel and atypical PKC isoforms do not participate in the mechanism of either PMA or estrogen neuroprotection. In contrast, a selective peptide activator of conventional PKC isoforms provides dose-dependent neuroprotection against Abeta toxicity. In addition, peptide inhibitors of conventional, betaI, or betaII PKC isoforms significantly reduce protection afforded by PMA or 17beta-estradiol. Taken together, these data provide evidence that conventional PKC isoforms mediate phorbol ester and estrogen neuroprotection of cultured neurons challenged by Abeta toxicity.

Effect of NMDA on staurosporine-induced activation of caspase-3 and LDH release in mouse neocortical and hippocampal cells

To achieve a better understanding of developmentally regulated NMDA- and staurosporine-induced apoptotic processes, we investigated the concerted action of these agents on caspase-3 activity and LDH release in neocortical and hippocampal cell cultures at different stages in vitro (DIV). Hoechst 33342 and MAP-2 stainings were additionally employed to visualize apoptotic changes and cell damage. The vulnerability of neocortical cells to NMDA was more prominent at later culture stages, whereas hippocampal neurons were more susceptible to NMDA treatment at earlier stages. A persistent activation of caspase-3 by staurosporine was found at all experimental stages. Despite of certain differences in susceptibility to NMDA and staurosporine, both tissues responded to regulatory action of NMDA towards staurosporine-activated caspase-3 in a similar way. Combined treatment with NMDA and staurosporine resulted in a substantial increase in caspase-3 activity in neocortical and hippocampal neurons on 2 DIV. Additive effects were also observed in neocortical cultures on 12 DIV. In contrast, NMDA substantially inhibited staurosporine-induced caspase-3 activity on 7 DIV in neocortical and hippocampal cultures. Additionally, pro-apoptotic effects of 17beta-estradiol were attenuated by NMDA on 7 DIV. Changes in vulnerability to NMDA- and staurosporine-mediated activation of caspase-3 were not strictly related to LDH release. Our data revealed that NMDA can both enhance and inhibit the staurosporine-induced neuronal cell apoptosis. The pro-apoptotic effect of NMDA was exhibited at early and late culture stages, whereas the anti-apoptotic effect was transient occurring on 7 DIV only.

A strong neuroprotective effect of the autonomous C‐terminal peptide of IGF‐1 Ec (MGF) in brain ischemia

The ischemic stroke is the third leading cause of death in developed countries. The C-terminal peptide of mechano-growth factor (MGF), an alternatively spliced variant of insulin-like growth factor 1 (IGF-1), was found to function independently from the rest of the molecule and showed a neuroprotective effect in vivo and in vitro. In vivo, in a gerbil model of transient brain ischemia, treatment with the synthetic MGF C-terminal peptide provided very significant protection to the vulnerable neurons. In the same model, ischemia evoked increased expression of endogenous MGF in the ischemia-resistant hippocampal neurons, suggesting that the endogenous MGF might have an important neuroprotective function. In an in vitro organotypic hippocampal culture model of neurodegeneration, the synthetic peptide was as potent as the full-length IGF-1 while its effect lasted significantly longer than that of recombinant IGF-1. While two peptides showed an additive effect, the neuroprotective action of the C-terminal MGF was independent from the IGF-1 receptor, indicating a new mode of action for this molecule. Although MGF is known for its regenerative capability in skeletal muscle, our findings demonstrate for the first time a neuroprotective role against ischemia for this specific IGF-1 isoform. Therefore, the C-terminal MGF peptide has a potential to be developed into a therapeutic modality for the prevention of neuronal damage.

Magnesium blocks the loss of protein kinase C, leads to a transient translocation of PKCα and PKCε, and improves recovery after anoxia in rat hippocampal slices

Magnesium is a potent neuroprotective agent against damage to synaptic transmission during cerebral anoxia and reoxygenation. We investigated the mechanisms of anoxic transmission damage and magnesium neuroprotection by examining the response of PKC isoforms to an anoxic insult in the rat hippocampal slice model. A 2-min anoxic period, which resulted in almost complete recovery of synaptic function, did not result in PKC downregulation. In contrast, inducing long-term damage with 10-min anoxia resulted in the downregulation of the conventional PKCs betaI, betaII and gamma immediately after the insult and after 1-h reoxygenation. There was additional loss of PKC(alpha) and PKC(epsilon) after 1-h reoxygenation. Magnesium treatment improved the recovery of synaptic transmission, blocked the loss of PKC and resulted in a transient translocation of PKC(alpha) and PKC(epsilon) to the membrane fraction. Selective downregulation of cPKCs and PKC(epsilon) correlated with permanent damage to synaptic transmission while translocation of PKC(alpha) and PKC(epsilon) correlated with preservation of synaptic function. The mechanisms of magnesium neuroprotection may include altering the PKC response to an anoxic insult.

2-iodomelatonin prevents apoptosis of cerebellar granule neurons via inhibition of A-type transient outward K+ currents

Compelling evidence indicates that excessive K+ efflux and intracellular K+ depletion are key early steps in apoptosis. Previously, we reported that apoptosis of cerebellar granular neurons induced by incubation under low K+ (5 mM) conditions was associated with an increase in delayed rectifier outward K+ current (IK) amplitude and caspase-3 activity. Moreover, the melatonin receptor antagonist 4P-PDOT abrogated the effects of 2-iodomelatonin on IK augmentation, caspase-3 activity and apoptosis. Here, we show that incubation under low K+/serum-free conditions for 6 hr led to a dramatic increase in the A-type transient outward K+ current (IA) (a 27% increase; n=31); in addition, fluorescence staining showed that under these conditions, cell viability decreased by 30% compared with the control. Treatment with 2-iodomelatonin inhibited the IA amplitude recorded from control and apoptotic cells in a concentration-dependent manner and modified the IA channel activation kinetics of cells under control conditions. Moreover, 2-iodomelatonin increased the viability of cell undergoing apoptosis. Interestingly, 4P-PDOT did not abrogate the effect of 2-iodomelatonin on IA augmentation under these conditions; in the presence of 4P-PDOT (100 microm), 2-iodomelatonin reduced the average IA by 41+/-4%, which was similar to the effect of 2-iodomelatonin alone. These results suggest that the neuroprotective effects of 2-idomelatonin are not only because of its antioxidant or receptor-activating properties, but rather that 2-iodomelatonin may inhibit IA channels by acting as a channel blocker.

Neuroprotection via pro‐survival protein kinase C isoforms associated with Bcl‐2 family members

This study provides new insights into neuroprotection involving interaction of protein kinase C (PKC) pathway with Bcl-2 family proteins. Using a model of serum deprivation, we investigated the mechanism by which the anti-Parkinson/monoamine oxidase (MAO)-B inhibitor drug, rasagiline, exerts its neuroprotective effect in rat pheochromocytoma PC12 cells. Here, we report that rasagiline (0.1-10 microM) decreased apoptosis via multiple protection mechanisms, including the stimulation of PKC phosphorylation; up-regulation of PKCalpha and PKC mRNAs, induction of Bcl-xL, Bcl-w, and brain-derived neurotrophic factor (BDNF) mRNAs; and down-regulation of Bad and Bax mRNAs. Moreover, rasagiline inhibited the cleavage and activation of procaspase-3 and poly (ADP-ribose) polymerase (PARP), whereas the PKC inhibitor, GF109203X, reversed these actions. Similarly, rasagiline decreased serum-free-induced levels of the important regulator of cell death, Bad, which was also blocked by GF109203X, indicating the involvement of PKC in rasagiline-induced cell survival. Furthermore, these studies have established that PKC- and Bcl-2-dependent neuroprotective activity of rasagiline is dependent on its propargyl moiety, because propargylamine had similar effects with the same potency.

Hypothermia and brain-derived neurotrophic factor reduce glutamate synergistically in acute stroke

Moderate hypothermia and application of brain-derived neurotrophic factor (BDNF) have separately been identified as neuroprotective strategies in experimental cerebral ischemia. To assess their separate and combined effects on striatal glutamate release in the hyperacute phase of stroke, we inserted microdialysis probes into the striatum of rats 2 h before permanent middle cerebral artery occlusion (MCAO). The animals (N = 28) were randomly assigned to one of four treatment strategies commencing 30 min after MCAO: (1) hypothermia at 33 degrees C (n = 7); (2) intravenous BDNF infusion [300 microg/(kg/h) for 2 h, n = 7]; (3) combination of hypothermia and BDNF (n = 7); (4) control group (saline, n = 7). Infarct size at 5 h after MCAO was assessed with the silver-staining method. Total infarct volume was significantly reduced in the hypothermia (202.7 +/- 3.5 mm(3), P = 0.0002) and BDNF group (206.5 +/- 6.9 mm(3), P = 0.0006) as compared to control group (254.4 +/- 9.3 mm(3)). In the combination group, infarct size was further reduced with overall significance in post hoc tests (157.3 +/- 6.2 mm(3), P < 0.0001). Postischemic glutamate concentrations in the control group constantly remained significantly higher than in all other treatment groups. At 255 and 270 min after MCAO, striatal glutamate in the combination group decreased significantly more than in animals treated with hypothermia or BDNF alone.Combining hypothermia and BDNF therapy in the acute stage of ischemia has a synergistic effect in attenuating striatal glutamate release and reducing early infarct size.

Rasagiline: Neurodegeneration, neuroprotection, and mitochondrial permeability transition

Mitochondria are involved directly in cell survival and death. The assumption has been made that drugs that protect mitochondrial viability and prevent apoptotic cascade-induced mitochondrial permeability transition pore (MPTp) opening will be cytoprotective. Rasagiline (N-propargyl-1R-aminoindan) is a novel, highly potent irreversible monoamine oxidase (MAO) B inhibitor anti-Parkinson drug. Unlike selegiline, it is not derived from amphetamine, and is not metabolized to neurotoxic L-methamphetamine derivative. In addition, it does not have sympathomimetic activity. Rasagiline is effective as monotherapy or adjunct to levodopa for patients with early and late Parkinson's disease (PD) and adverse events do not occur with greater frequency in subjects receiving rasagiline than in those on placebo. Phase III controlled studies indicate that it might have a disease-modifying effect in PD that may be related to its neuroprotective activity. Its S isomer, TVP1022, is more than 1,000 times less potent as an MAO inhibitor. Both drugs, however, have neuroprotective activity in neuronal cell cultures in response to various neurotoxins, and in vivo in response to global ischemia, neurotrauma, head injury, anoxia, etc., indicating that MAO inhibition is not a prerequisite for neuroprotection. Their neuroprotective effect has been demonstrated to be associated directly with the propargylamine moiety, which protects mitochondrial viability and MTPp by activating Bcl-2 and protein kinase C (PKC) and by downregulating the proapoptotic FAS and Bax protein families. Rasagiline and its derivatives also process amyloid precursor protein (APP) to the neuroprotective, neurotrophic, soluble APP alpha (sAPPalpha) by PKC- and MAP kinase-dependent activation of alpha-secretase. The identification of the propargylamine moiety as the neuroprotective component of rasagiline has led us to development of novel bifunctional anti-Alzheimer drugs (ladostigil) possessing cholinesterase and brain-selective MAO inhibitory activity and a similar neuroprotective mechanism of action.

Prevention of NMDA-induced death of cortical neurons by inhibition of protein kinase Czeta

Excitotoxicity through stimulation of N-methyl-d-aspartate (NMDA) receptors contributes to neuronal death in brain injuries, including stroke. Several lines of evidence suggest a role for protein kinase C (PKC) isoforms in NMDA excitotoxicity. We have used specific peptide inhibitors of classical PKCs (alpha, beta, and gamma), novel PKCs delta and epsilon, and an atypical PKCzeta in order to delineate which subspecies are involved in NMDA-induced cell death. Neuronal cell cultures were prepared from 15-day-old mouse embryos and plated onto the astrocytic monolayer. After 2 weeks in vitro the neurons were exposed to 100 micro m NMDA for 5 min, and 24 h later the cell viability was examined by measuring the lactate dehydrogenase release and bis-benzimide staining. While inhibitors directed to classical (alpha, beta, and gamma) or novel PKCs (delta or epsilon) had no effect, the PKCzeta inhibitor completely prevented the NMDA-induced necrotic neuronal death. Confocal microscopy confirmed that NMDA induced PKCzeta translocation, which was blocked by the PKCzeta inhibitor. The NMDA-induced changes in intracellular free Ca2+ were not affected by the peptides. In situ hybridization experiments demonstrated that PKCzeta mRNA is induced in the cortex after focal brain ischemia. Altogether, the results indicate that PKCzeta activation is a downstream signal in NMDA-induced death of cortical neurons.

Anti-epileptic drugs as possible neuroprotectants in cerebral ischemia

Many similarities exist between cerebral ischemia and epilepsy regarding brain-damaging and auto-protective mechanisms that are activated following the injurious insult. Therefore, drugs that are effective in minimizing seizure-induced brain damage may also be useful in minimizing ischemic injury. Use of such drugs in stroke victims may have important clinical and financial advantages. Therefore, the authors conducted a Medline search of studies involving the use of anti-epileptic drugs (AEDs) as possible neuroprotectants and summarize the data. Most AEDs have been tested in animal models of focal or global ischemia and some were already tested in humans, for a possible neuroprotective effect. The existing data is rather scant and insufficient but it appears that only drugs that have multiple mechanisms of action seem to have some potential in conferring a degree of neuroprotection that could be clinically applicable to stroke patients. In conclusion, some of the newer AEDs show promise as possible neuroprotectants in the setup of acute ischemic stroke but more studies are needed before clinical trials in humans could be undertaken.

Brain-derived neurotrophic factor regulates surface expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid receptors by enhancing the N-ethylmaleimide-sensitive factor/GluR2 interaction in developing neocortical neurons

In hippocampal neurons, the exocytotic process of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)-type glutamate receptors is known to depend on activation of N-methyl-d-aspartate channels and its resultant Ca(2+) influx from extracellular spaces. Here we found that brain-derived neurotrophic factor (BDNF) induced a rapid surface translocation of AMPA receptors in an activity-independent manner in developing neocortical neurons. The receptor translocation became evident within hours as monitored by [(3)H]AMPA binding and was resistant against ionotropic glutamate receptor antagonists as evidenced with surface biotinylation assay. This process required intracellular Ca(2+) and was inhibited by the blockers of conventional exocytosis, brefeldin A, botulinum toxin B, and N-ethylmaleimide. To explore the translocation mechanism of individual AMPA receptor subunits, we utilized the human embryonic kidney (HEK) 293 cells carrying the BDNF receptor TrkB. After the single transfection of GluR2 cDNA or GluR1 cDNA into HEK/TrkB cells, BDNF triggered the translocation of GluR2 but not that of GluR1. Subsequent mutation analysis of GluR2 carboxyl-terminal region indicated that the translocation of GluR2 subunit in HEK293 cells involved its N-ethylmaleimide-sensitive factor-binding domain but not its PDZ-interacting site. Following co-transfection of GluR1 and GluR2 cDNAs, solid phase cell sorting revealed that GluR1 subunits were also able to translocate to the cell surface in response to BDNF. An immunoprecipitation assay confirmed that BDNF stimulation can enhance the interaction of GluR2 with N-ethylmaleimide-sensitive factor. These results reveal a novel role of BDNF in regulating the surface expression of AMPA receptors through a GluR2-NSF interaction.

Involvement of protein kinase C activation and cell survival/ cell cycle genes in green tea polyphenol (-)-epigallocatechin 3-gallate neuroprotective action

Studies from our laboratory have demonstrated that the major green tea polyphenol, (-)-epigallocatechin 3-gallate (EGCG), exerts potent neuroprotective actions in the mice model of Parkinson's disease. These studies were extended to neuronal cell culture employing the parkinsonism-inducing neurotoxin, 6-hydroxydopamine (6-OHDA). Pretreatment with EGCG (0.1-10 microm) attenuated human neuroblastoma (NB) SH-SY5Y cell death, induced by a 24-h exposure to 6-OHDA (50 microm). Potential cell signaling candidates involved in this neuroprotective effect were further examined. EGCG restored the reduced protein kinase C (PKC) and extracellular signal-regulated kinases (ERK1/2) activities caused by 6-OHDA toxicity. However, the neuroprotective effect of EGCG on cell survival was abolished by pretreatment with PKC inhibitor GF 109203X (1 microm). Because EGCG increased phosphorylated PKC, we suggest that PKC isoenzymes are involved in the neuroprotective action of EGCG against 6-OHDA. In addition, gene expression analysis revealed that EGCG prevented both the 6-OHDA-induced expression of several mRNAs, such as Bax, Bad, and Mdm2, and the decrease in Bcl-2, Bcl-w, and Bcl-x(L). These results suggest that the neuroprotective mechanism of EGCG against oxidative stress-induced cell death includes stimulation of PKC and modulation of cell survival/cell cycle genes.

Cerebral ischemia and trauma-different etiologies yet similar mechanisms: neuroprotective opportunities

Cerebral ischemia leads to brain damage caused by pathogenetic mechanisms that are also activated by neurotrauma. These mechanisms include among others excitotoxicity, over production of free radicals, inflammation and apoptosis. Furthermore, cerebral ischemia and trauma both trigger similar auto-protective mechanisms including the production of heat shock proteins, anti-inflammatory cytokines and endogenous antioxidants. Neuroprotective therapy aims at minimizing the activation of toxic pathways and at enhancing the activity of endogenous neuroprotective mechanisms. The similarities in the damage-producing and endogenous auto-protective mechanisms may imply that neuroprotective compounds found to be active against one of these conditions may indeed be also protective in the other. This review summarizes the pathogenetic events of ischemic and traumatic brain injury and reviews the neuroprotective strategies employed thus far in each of these conditions with a special emphasize on their clinical relevance and on future directions in the field of neuronal protection.

Gangliosides prevent excitotoxicity through activation of TrkB receptor

Gangliosides protect cerebellar granule cells from excitotoxicity; however, their mechanism of action remains to be fully characterized. GM1 ganglioside has been shown to activate Trk, the tyrosine kinase receptor implicated in the neuroprotective properties of the neurotrophins. In these studies, we used primary cultures of cerebellar granule cells to determine whether gangliosides exert neuroprotective effect via the activation of Trk receptors. We first examined the relative potency of the neurotrophins, brain derived neurotrophic factor (BDNF), neurotrophin-3 and nerve growth factor to prevent glutamate-mediated apoptosis. BDNF was the only neurotrophin that elicited a complete neuronal protection against glutamate. GM1 and its semisynthetic compound LIGA20 also prevented glutamate toxicity, however, LIGA20 was more potent than GM1. Both LIGA20 and BDNF blocked glutamate-mediated activation of caspase-3 and consequently apoptosis; however, the anticaspase-3 activity was seen only when these compounds were added to the cultures several hours before glutamate, suggesting that LIGA20 and BDNF share an identical molecular mechanism. To test this hypothesis, we compared the ability of LIGA20 and BDNF to activate TrkB. Both compounds elicited a similar time-dependent increase in Trk tyrosine phosphorylation. Moreover, the neuroprotective effect of BDNF and LIGA20 was abolished in neurons exposed to the Trk tyrosine kinase inhibitor k252a, demonstrating a relationship between neuroprotection and activation of Trk receptors. Our data suggest that by activating the Trk neurotrophin receptors, gangliosides may be used as neuroprotective agents.

Brain-derived neurotrophic factor superinduction parallels anti-epileptic--neuroprotective treatment in the pilocarpine epilepsy model

Antiepileptic drugs provide neuroprotection in several animal models of brain damage, including those induced by status epilepticus (SE). The mechanisms involved in this action are unknown, but neurotrophic factors such as brain-derived neurotrophic factor (BDNF) may play a role. In this study we investigated the changes in BDNF levels in rats in which SE had been induced by pilocarpine injection (400 mg/kg i.p.) and continued for several hours (unprotected group). In other animals (protected groups), SE was suppressed after 30 min by intraperitoneal injection of either diazepam (10 mg/kg) + pentobarbital (30 mg/kg) or paraldehyde (0.3 mg/kg). In diazepam + pentobarbital-treated rats the hippocampal damage caused by SE was significantly lower (p < 0.05) than in unprotected animals. In addition, 2 and 24 h after pilocarpine injection, the levels of BDNF mRNA were moderately increased in the unprotected group, but 'superinduced' in protected animals, especially in the neocortex and hippocampus. A time-dependent increase in BDNF immunoreactivity was also found by western blot analysis in rats treated with diazepam + pentobarbital. In contrast, a decrease of BDNF immunoreactivity occurred in the unprotected group. In conclusion, these results show that neuroprotection induced by anti-epileptic drugs in pilocarpine-treated rats is accompanied by strong potentiation of BDNF synthesis in brain regions involved in SE.