A beacon of hope in stroke therapy-Blockade of pathologically activated cellular events in excitotoxic neuronal death as potential neuroprotective strategies

Extrasynaptic NMDA receptors in acute and chronic excitotoxicity: implications for preventive treatments of ischemic stroke and late-onset Alzheimer's disease

Stroke and late-onset Alzheimer's disease (AD) are risk factors for each other; the comorbidity of these brain disorders in aging individuals represents a significant challenge in basic research and clinical practice. The similarities and differences between stroke and AD in terms of pathogenesis and pathophysiology, however, have rarely been comparably reviewed. Here, we discuss the research background and recent progresses that are important and informative for the comorbidity of stroke and late-onset AD and related dementia (ADRD). Glutamatergic NMDA receptor (NMDAR) activity and NMDAR-mediated Ca²⁺ influx are essential for neuronal function and cell survival. An ischemic insult, however, can cause rapid increases in glutamate concentration and excessive activation of NMDARs, leading to swift Ca²⁺ overload in neuronal cells and acute excitotoxicity within hours and days. On the other hand, mild upregulation of NMDAR activity, commonly seen in AD animal models and patients, is not immediately cytotoxic. Sustained NMDAR hyperactivity and Ca²⁺ dysregulation lasting from months to years, nevertheless, can be pathogenic for slowly evolving events, i.e. degenerative excitotoxicity, in the development of AD/ADRD. Specifically, Ca²⁺ influx mediated by extrasynaptic NMDARs (eNMDARs) and a downstream pathway mediated by transient receptor potential cation channel subfamily M member (TRPM) are primarily responsible for excitotoxicity. On the other hand, the NMDAR subunit GluN3A plays a "gatekeeper" role in NMDAR activity and a neuroprotective role against both acute and chronic excitotoxicity. Thus, ischemic stroke and AD share an NMDAR- and Ca²⁺-mediated pathogenic mechanism that provides a common receptor target for preventive and possibly disease-modifying therapies. Memantine (MEM) preferentially blocks eNMDARs and was approved by the Federal Drug Administration (FDA) for symptomatic treatment of moderate-to-severe AD with variable efficacy. According to the pathogenic role of eNMDARs, it is conceivable that MEM and other eNMDAR antagonists should be administered much earlier, preferably during the presymptomatic phases of AD/ADRD. This anti-AD treatment could simultaneously serve as a preconditioning strategy against stroke that attacks ≥ 50% of AD patients. Future research on the regulation of NMDARs, enduring control of eNMDARs, Ca²⁺ homeostasis, and downstream events will provide a promising opportunity to understand and treat the comorbidity of AD/ADRD and stroke.

Comparative Investigation of Expression of Glutamatergic and GABAergic Genes in the Rat Hippocampus after Focal Brain Ischemia and Central LPS Administration

Among the responses in the early stages of stroke, activation of neurodegenerative and proinflammatory processes in the hippocampus is of key importance for the development of negative post-ischemic functional consequences. However, it remains unclear, what genes are involved in these processes. The aim of this work was a comparative study of the expression of genes encoding glutamate and GABA transporters and receptors, as well as inflammation markers in the hippocampus one day after two types of middle cerebral artery occlusion (according to Koizumi et al. method, MCAO-MK, and Longa et al. method, MCAO-ML), and direct pro-inflammatory activation by central administration of bacterial lipopolysaccharide (LPS). Differences and similarities in the effects of these challenges on gene expression were observed. Expression of a larger number of genes associated with activation of apoptosis and neuroinflammation, glutamate reception, and markers of the GABAergic system changed after the MCAO-ML and LPS administration than after the MCAO-MK. Compared with the MCAO-ML, the MCAO-MK and LPS challenges caused changes in the expression of more genes involved in glutamate transport. The most pronounced difference between the responses to different challenges was the changes in expression of calmodulin and calmodulin-dependent kinases genes observed after MCAO, especially MCAO-ML, but not after LPS. The revealed specific features of the hippocampal gene responses to the two types of ischemia and a pro-inflammatory stimulus could contribute to further understanding of the molecular mechanisms underlying diversity of the post-stroke consequences both in the model studies and in the clinic.

Necroptosis and Alzheimer's Disease: Pathogenic Mechanisms and Therapeutic Opportunities

Alzheimer's disease (AD) is considered to be the most common neurodegenerative disease, with clinical symptoms encompassing progressive memory loss and cognitive impairment. Necroptosis is a form of programmed necrosis that promotes cell death and neuroinflammation, which further mediates the pathogenesis of several neurodegenerative diseases, especially AD. Current evidence has strongly suggested that necroptosis is activated in AD brains, resulting in neuronal death and cognitive impairment. We searched the PubMed database, screening all articles published before September 28, 2022 related to necroptosis in the context of AD pathology. The keywords in the search included: "necroptosis", "Alzheimer's disease", "signaling pathways", "Aβ", Aβo", "Tau", "p-Tau", "neuronal death", "BBB damage", "neuroinflammation", "microglia", "mitochondrial dysfunction", "granulovacuolar degeneration", "synaptic loss", "axonal degeneration", "Nec-1", "Nec-1s", "GSK872", "NSA", "OGA", "RIPK1", "RIPK3", and "MLKL". Results show that necroptosis has been involved in multiple pathological processes of AD, including amyloid-β aggregation, Tau accumulation, neuronal death, and blood-brain barrier damage, etc. More importantly, existing research on AD necroptosis interventions, including drug intervention and potential gene targets, as well as its current clinical development status, was discussed. Finally, the issues pertaining to necroptosis in AD were presented. Accordingly, this review may provide further insight into clinical perspectives and challenges for the future treatment of AD by targeting the necroptosis pathway.

Tongmai granules improve rat hippocampal injury by regulating TLR4/MyD88/AP-1 signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Tongmai granules (TMG) is composed of Salvia miltiorrhiza Bge., Radix puerariae Lobata., and Ligusticum chuanxiong hort. TMG is mainly used for ischemic cardiovascular, cerebrovascular diseases, atherosclerosis, coronary heart disease, cerebral infarction and cerebral ischemia. TMG is a kind of traditional compound granule, which has a protective effect on brain injury. However, the potential protective mechanism of the TMG has not been elucidated.

AIM OF THE STUDY

TMG has a good effect on brain injury, but its brain protective mechanism is still unclear. The purpose of this study was to confirm the neuroprotective mechanism of TMG, reveal its target genes and identify the active components of TMG.

MATERIALS AND METHODS

High-performance liquid chromatography (HPLC) was used to identify the fingerprint of TMG. UPLC-Q-TOF-MSE was used to analyze the base peak intensity (BPI) chromatograms of TMG. TMG was pre-administered for one week, brain injury and edema were induced by injection of glutamate (Glu) into the lateral ventricles of rats. HE staining was used to investigate the pathological damage caused by Glu in the hippocampus of rats, and the RNA-seq was used to analyze the changes of different genes before and after TMG treatment. Finally, changes of related proteins were analyzed by qRT-PCR, Western blot, and other molecular biological methods. Dosage of TMG were set to 0.6 g/kg, 1.2 g/kg and 2.4 g/kg.

RESULTS

We found that TMG contained many active components, including salvianolic acid, puerarin, ferulic acid, etc. TMG could improve cerebral edema and brain injury induced by Glu. After TMG treatment, differential gene analysis showed that differential genes were significantly enriched in toll-like receptor signaling pathway. qRT-PCR validation results were consistent with RNA-Seq analysis results. Combined with Western blot analysis, we found that TMG ultimately regulated the expression of inflammatory cytokines by affecting the TLR4/MyD88/AP-1 pathway.

CONCLUSIONS

In this study, we combined TMG with RNA-seq analysis to demonstrate that TMG may play a neuroprotective role by regulating Toll-like receptor signaling pathway and down-regulating the expression of inflammatory cytokine. TMG may become a kind of traditional Chinese medicine with neuroprotective potential.

Roles of N-Methyl-D-Aspartate Receptors (NMDARs) in Epilepsy

Epilepsy is one of the most common neurological disorders characterized by recurrent seizures. The mechanism of epilepsy remains unclear and previous studies suggest that N-methyl-D-aspartate receptors (NMDARs) play an important role in abnormal discharges, nerve conduction, neuron injury and inflammation, thereby they may participate in epileptogenesis. NMDARs belong to a family of ionotropic glutamate receptors that play essential roles in excitatory neurotransmission and synaptic plasticity in the mammalian CNS. Despite numerous studies focusing on the role of NMDAR in epilepsy, the relationship appeared to be elusive. In this article, we reviewed the regulation of NMDAR and possible mechanisms of NMDAR in epilepsy and in respect of onset, development, and treatment, trying to provide more evidence for future studies.

Novel insights into RIPK1 as a promising target for future Alzheimer's disease treatment

Alzheimer's disease (AD) is an intractable neurodegenerative disease showing a clinical manifestation with memory loss, cognitive impairment and behavioral dysfunction. The predominant pathological characteristics of AD include neuronal loss, β-amyloid (Aβ) deposition and hyperphosphorylated Tau induced neurofibrillary tangles (NFTs), while considerable studies proved these could be triggered by neuronal death and neuroinflammation. Receptor-interacting protein kinase 1 (RIPK1) is a serine/threonine kinase existed at the cross-point of cell death and inflammatory signaling pathways. Emerging investigations have shed light on RIPK1 for its potential role in AD progression. The present review makes a bird's eye view on the functions of RIPK1 and mainly focus on the underlying linkages between RIPK1 and AD from comprehensive aspects including neuronal death, Aβ and Tau, inflammasome activation, BBB rupture, AMPK/mTOR, mitochondrial dysfunction and O-glcNAcylation. Moreover, the discovery of RIPK1 inhibitors, ongoing clinical trials along with future RIPK1-targeted therapeutics are also reviewed.

Regulation of post-ischemic inflammatory response: A novel function of the neuronal tyrosine phosphatase STEP

The neuron-specific tyrosine phosphatase STEP is emerging as a key neuroprotectant against acute ischemic stroke. However, it remains unclear how STEP impacts the outcome of stroke. We find that the exacerbation of ischemic brain injury in STEP deficient mice involves an early onset and sustained activation of neuronal p38 mitogen activated protein kinase, a substrate of STEP. This leads to rapid increase in the expression of neuronal cyclooxygenase-2 and synthesis of prostaglandin E₂, causing change in microglial morphology to an amoeboid activated state, activation of matrix metalloproteinase-9, cleavage of tight junction proteins and extravasation of IgG into the ischemic brain. Restoration of STEP signaling with intravenous administration of a STEP-derived peptide mimetic reduces the post-ischemic inflammatory response and attenuates brain injury. The findings identify a unique role of STEP in regulating post-ischemic neuroinflammation and further emphasizes the therapeutic potential of the STEP-mimetic in neurological disorders where inflammation contributes to brain damage.

Xenon Exerts Neuroprotective Effects on Kainic Acid-Induced Acute Generalized Seizures in Rats via Increased Autophagy

Xenon has been shown to have neuroprotective effects and is clinically used as a favorable safe inhalation anesthetic. We previously confirmed the neuroprotective effects of xenon treatment in epileptic animals. However, the mechanism underlying these protective effects remains unclear. We aimed to assess the effects of xenon inhalation on autophagy in neuronal injury induced by acute generalized seizures. Kainic acid (KA) was injected into the lateral ventricle of male Sprague–Dawley rats to induce acute generalized seizures. Next, the rats were treated via inhalation of a 70% xenon/21% oxygen/9% nitrogen mixture for 60 min immediately after KA administration. The control group was treated via inhalation of a 79% nitrogen/21% oxygen mixture. Subsequently, two inhibitors (3-methyladenine or bafilomycin A₁) or an autophagy inducer (rapamycin) were administered, respectively, before KA and xenon administration to determine the role of autophagy in the protective effects of xenon. The levels of apoptosis, neuronal injury, and autophagy were determined in all the rats. Xenon inhalation significantly attenuated the severity of the seizure-induced neuronal injury. Increased autophagy accompanied this inhibitive effect. Autophagy inhibition eliminated these xenon neuroprotective effects. A simulation of autophagy using rapamycin recapitulated xenon’s protective effects on KA-induced acute generalized seizures in the rats. These findings confirmed that xenon exerts strong neuroprotective effects in KA-induced acute generalized seizures. Further, they indicate that increased autophagy may underlie the protective effects of xenon. Therefore, xenon and autophagy inducers may be useful clinical options for their neuroprotective effects in epileptic seizures.

Role of neuronal nitric oxide synthase on cardiovascular functions in physiological and pathophysiological states

This review describes and summarizes the role of neuronal nitric oxide synthase (nNOS) on the central nervous system, particularly on brain regions such as the ventrolateral medulla (VLM) and the periaqueductal gray matter (PAG), and on blood vessels and the heart that are involved in the regulation and control of the cardiovascular system (CVS). Furthermore, we shall also review the functional aspects of nNOS during several physiological, pathophysiological, and clinical conditions such as exercise, pain, cerebral vascular accidents or stroke and hypertension. For example, during stroke, a cascade of molecular, neurochemical, and cellular changes occur that affect the nervous system as elicited by generation of free radicals and nitric oxide (NO) from vulnerable neurons, peroxide formation, superoxides, apoptosis, and the differential activation of three isoforms of nitric oxide synthases (NOSs), and can exert profound effects on the CVS. Neuronal NOS is one of the three isoforms of NOSs, the others being endothelial (eNOS) and inducible (iNOS) enzymes. Neuronal NOS is a critical homeostatic component of the CVS and plays an important role in regulation of different systems and disease process including nociception. The functional and physiological roles of NO and nNOS are described at the beginning of this review. We also elaborate the structure, gene, domain, and regulation of the nNOS protein. Both inhibitory and excitatory role of nNOS on the sympathetic autonomic nervous system (SANS) and parasympathetic autonomic nervous system (PANS) as mediated via different neurotransmitters/signal transduction processes will be explored, particularly its effects on the CVS. Because the VLM plays a crucial function in cardiovascular homeostatic mechanisms, the neuroanatomy and cardiovascular regulation of the VLM will be discussed in conjunction with the actions of nNOS. Thereafter, we shall discuss the up-to-date developments that are related to the interaction between nNOS and cardiovascular diseases such as hypertension and stroke. Finally, we shall focus on the role of nNOS, particularly within the PAG in cardiovascular regulation and neurotransmission during different types of pain stimulus. Overall, this review focuses on our current understanding of the nNOS protein, and provides further insights on how nNOS modulates, regulates, and controls cardiovascular function during both physiological activity such as exercise, and pathophysiological conditions such as stroke and hypertension.

Mode-Dependent Effect of Xenon Inhalation on Kainic Acid-Induced Status Epilepticus in Rats

Previous studies have reported the possible neuroprotective effects of xenon treatment. The purpose of this study was to define the range of effective xenon ratio, most effective xenon ratio, and time-window for intervention in the kainic acid (KA) – induced status epilepticus (SE) rat model. Different ratios of xenon (35% xenon, 21% oxygen, 44% nitrogen, 50% xenon, 21% oxygen, 29% nitrogen, 70% xenon, 21% oxygen, and 9% nitrogen) were used to treat the KA-induced SE. Our results confirmed the anti-seizure role of 50 and 70% xenon mixture, with a stronger effect from the latter. Further, 70% xenon mixture was dispensed at three time points (0 min, 15 min delayed, and 30 min delayed) after KA administration, and the results indicated the anti-seizure effect at all treated time points. The results also established that the neuronal injury in the hippocampus and entorhinal cortex (EC), assessed using Fluoro-Jade B (FJB) staining, were reversed by the xenon inhalation, and within 30 min after KA administration. Our study, therefore, indicates the appropriate effective xenon ratio and time-window for intervention that can depress seizures. The prevention of neuronal injury and further reversal of the loss of effective control of depress network in the hippocampus and EC may be the mechanisms underlying the anti-seizure effect of xenon.

Quantitative proteomic analyses of dynamic signalling events in cortical neurons undergoing excitotoxic cell death

Excitotoxicity, caused by overstimulation or dysregulation of ionotropic glutamate receptors (iGluRs), is a pathological process directing neuronal death in many neurological disorders. The aberrantly stimulated iGluRs direct massive influx of calcium ions into the affected neurons, leading to changes in expression and phosphorylation of specific proteins to modulate their functions and direct their participation in the signalling pathways that induce excitotoxic neuronal death. To define these pathways, we used quantitative proteomic approaches to identify these neuronal proteins (referred to as the changed proteins) and determine how their expression and/or phosphorylation dynamically changed in association with excitotoxic cell death. Our data, available in ProteomeXchange with identifier PXD008353, identified over 100 changed proteins exhibiting significant alterations in abundance and/or phosphorylation levels at different time points (5–240 min) in neurons after glutamate overstimulation. Bioinformatic analyses predicted that many of them are components of signalling networks directing defective neuronal morphology and functions. Among them, the well-known neuronal survival regulators including mitogen-activated protein kinases Erk1/2, glycogen synthase kinase 3 (GSK3) and microtubule-associated protein (Tau), were selected for validation by biochemical approaches, which confirmed the findings of the proteomic analysis. Bioinformatic analysis predicted Protein Kinase B (Akt), c-Jun kinase (JNK), cyclin-dependent protein kinase 5 (Cdk5), MAP kinase kinase (MEK), Casein kinase 2 (CK2), Rho-activated protein kinase (Rock) and Serum/glucocorticoid-regulated kinase 1 (SGK1) as the potential upstream kinases phosphorylating some of the changed proteins. Further biochemical investigation confirmed the predictions of sustained changes of the activation states of neuronal Akt and CK2 in excitotoxicity. Thus, future investigation to define the signalling pathways directing the dynamic alterations in abundance and phosphorylation of the identified changed neuronal proteins will help elucidate the molecular mechanism of neuronal death in excitotoxicity.

Kallmes D. Memantine for the treatment of ischemic stroke: experimental benefits and clinical lack of studies

Stroke is an important cause of mortality and disability worldwide. Immediately after stroke onset, the ischemic cascade initiates and deleteriously affects neural cells. Time to reperfusion therapy is a critical determinant of functional recovery in stroke patients. Although recent trials have shown the significant efficacy of endovascular thrombectomy, either alone or with intravenous tissue plasminogen activator, in improving the functional outcomes of stroke patients with large vessel occlusion, hours can pass before patients receive reperfusion therapy. Moreover, many patients do not meet the eligibility criteria to receive reperfusion treatments. Therefore, an adjunct and alternative agent that can protect ischemic neuronal tissue during the hyperacute phase until reperfusion therapy can be administered may prevent further brain damage and enhance functional recovery. Memantine is a US Food and Drug Administration approved drug for the treatment of Alzheimer’s disease. Memantine blocks overstimulated N-methyl-d-aspartate receptors and prevents neurotoxicity caused by massive glutamate release. Preclinical studies show that memantine decreases infarction volume and improves neurologic outcomes. However, few clinical studies have evaluated the safety and efficacy of memantine in stroke patients. This review article summarizes the current evidence for the role of memantine in the treatment of ischemic stroke and highlights areas for future research.

Z-Guggulsterone attenuates astrocytes-mediated neuroinflammation after ischemia by inhibiting toll-like receptor 4 pathway

Inflammatory damage plays a pivotal role in ischemic stroke pathogenesis and may represent one of the therapeutic targets. Z-Guggulsterone (Z-GS), an active component derived from myrrh, has been used to treat various diseases. The traditional uses suggest that myrrh is a good candidate for anti-inflammatory damage. This study was to investigate the anti-inflammatory and neuroprotective effects of Z-GS following cerebral ischemic injury, as well as the exact mechanisms behind them. Rat middle cerebral artery occlusion (MCAO) model and in vitro astrocytes oxygen-glucose deprivation (OGD) model were adopted to simulate ischemic stroke. Z-GS (30 or 60 mg/kg) was administered intraperitoneally immediately after reperfusion, while astrocytes were maintained in 30 or 60 μM Z-GS before OGD treatment. The results indicated that Z-GS significantly alleviated neurological deficits, infarct volume and histopathological damage in vivo, and increased the astrocytes viability in vitro. Moreover, the treatment of Z-GS inhibited the astrocytes activation and down-regulated the mRNA levels of pro-inflammatory cytokines. Furthermore, the activated TLR4-NF-κB signaling pathways induced by MCAO or OGD were significantly suppressed by Z-GS treatment, which was achieved via inhibiting the phosphorylation of JNK. Our results demonstrated that Z-GS exerted neuroprotective and anti-inflammatory properties through preventing activation of TLR4-mediated pathway in the activated astrocytes after ischemia injury. Therefore, Z-GS could be considered as a promising candidate for the treatment of ischemic stroke.

The biomedical challenge of neurodegenerative disorders: an opportunity for cannabinoid-based therapies to improve on the poor current therapeutic outcomes

At the beginning of the 21st century, the therapeutic management of neurodegenerative disorders remains a major biomedical challenge, particularly given the worldwide ageing of the population over the past 50 years that is expected to continue in the forthcoming years. This review will focus on the promise of cannabinoid-based therapies to address this challenge. This promise is based on the broad neuroprotective profile of cannabinoids, which may cooperate to combat excitotoxicity, oxidative stress, glia-driven inflammation and protein aggregation. Such effects may be produced by the activity of cannabinoids through their canonical targets (e.g. cannabinoid receptors and endocannabinoid enzymes) and also via non-canonical elements and activities in distinct cell types critical for cell survival or neuronal replacement (e.g. neurons, glia and neural precursor cells). Ultimately, the therapeutic events driven by endocannabinoid signalling reflect the activity of an endogenous system that regulates the preservation, rescue, repair and replacement of neurons and glia. LINKED ARTICLES: This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Differential gene expression profiles between two subtypes of ischemic stroke with blood stasis syndromes

Ischemic stroke is a cerebrovascular thrombotic disease with high morbidity and mortality. Qi deficiency blood stasis (QDBS) and Yin deficiency blood stasis (YDBS) are the two major subtypes of ischemic stroke according to the theories of traditional Chinese medicine. This study was conducted to distinguish these two syndromes at transcriptomics level and explore the underlying mechanisms. Male rats were randomly divided into three groups: sham group, QDBS/MCAO group and YDBS/MCAO group. Morphological changes were assessed after 24 h of reperfusion. Microarray analysis with circulating mRNA was then performed to identify differential gene expression profile, gene ontology and pathway enrichment analyses were carried out to predict the gene function, gene co-expression and pathway networks were constructed to identify the hub biomarkers, which were further validated by western blotting and Tunel staining analysis. Three subsets of dysregulated genes were acquired, including 445 QDBS-specific genes, 490 YDBS-specific genes and 1676 blood stasis common genes. Our work reveals for the first time that T cell receptor, MAPK and apoptosis pathway were identified as the hub pathways based on the pathway networks, while Nfκb1, Egfr and Casp3 were recognized as the hub genes by co-expression networks. This research helps contribute to a clearer understanding of the pathological characteristics of ischemic stroke with QDBS and YDBS syndrome, the proposed biomarkers might provide insight into the accurate diagnose and proper treatment for ischemic stroke with blood stasis syndrome.

Improvement of 2-Vessel Occlusion Cerebral Ischaemia/Reperfusion-Induced Corticostriatal Electrolyte and Redox Imbalance, Lactic Acidosis and Modified Acetylcholinesterase Activity by Kolaviron Correlates with Reduction in Neurobehavioural Deficits

Background

Disruption of electrolyte, redox and neurochemical homeostasis alongside cellular energy crisis is a hallmark of cerebral ischaemia and reperfusion injury.

Purpose

This study investigated the effect of kolaviron (KV) on cortical and striatal cation imbalance, oxidative stress and neurochemical disturbances as well as neurobehavioural deficits in animals subjected to bilateral common carotid artery occlusion (BCCAO)-induced ischaemia/reperfusion injury.

Methods

KV was administered at a dose of 100 or 200 mg/kg to male Wistar rats 1 h before a 30 min BCCAO/4 h reperfusion (I/R). This was followed by neurobehavioral assessment and biochemical evaluations of cation levels, oxidative stress indicators, lactate dehydrogenase activity and acetylcholinesterase (AChE) activity in the brain of animals.

Conclusion

KV significantly restored altered cortical and striatal Ca²⁺, Na⁺, K⁺ and Mg²⁺ levels, ameliorated redox imbalance, lactic acidosis and modified AChE activity caused by I/R injury. The favourable neurobehavioural effects of KV correlated with biochemical outcomes. The pharmacological potential of KV in the treatment and management of ischemic stroke and allied pathological conditions via multiple targets (neurotransmitter metabolism, bioenergetic failure and ionic homeostasis) is highlighted by the study.

Effects of Dimeric PSD-95 Inhibition on Excitotoxic Cell Death and Outcome After Controlled Cortical Impact in Rats

Therapeutic effects of PSD-95 inhibition have been demonstrated in numerous studies of stroke; however only few studies have assessed the effects of PSD-95 inhibitors in traumatic brain injury (TBI). As the pathophysiology of TBI partially overlaps with that of stroke, PSD-95 inhibition may also be an effective therapeutic strategy in TBI. The objectives of the present study were to assess the effects of a dimeric inhibitor of PSD-95, UCCB01-144, on excitotoxic cell death in vitro and outcome after experimental TBI in rats in vivo. In addition, the pharmacokinetic parameters of UCCB01-144 were investigated in order to assess uptake of the drug into the central nervous system of rats. After a controlled cortical impact rats were randomized to receive a single injection of either saline or two different doses of UCCB01-144 (10 or 20 mg/kg IV) immediately after injury. Spatial learning and memory were assessed in a water maze at 2 weeks post-trauma, and at 4 weeks lesion volumes were estimated. Overall, UCCB01-144 did not protect against NMDA-toxicity in neuronal cultures or experimental TBI in rats. Important factors that should be investigated further in future studies assessing the effects of PSD-95 inhibitors in TBI are discussed.

Modeling Neurodegenerative Disorders for Developing Cannabinoid-Based Neuroprotective Therapies

The increase in lifespan during the last 50 years, mainly in developed countries, has originated a progressive elevation in the incidence of chronic neurodegenerative disorders, for which aging is the key risk factor. This fact will definitively become the major biomedical challenge during the present century, in part because the expectation of a persisting elevation in the population older than 65 years over the whole population and, on the other hand, because the current lack of efficacious therapies to control these disorders despite years of intense research. This chapter will address this question and will stress the urgency of developing better neuroprotective and neurorepair strategies that may delay/arrest the progression of these disorders, reviewing the major needs to solve the causes proposed for the permanent failures experienced in recent years, e.g., to develop multitarget strategies, to use more predictive experimental models, and to identify early disease biomarkers. This chapter will propose the cannabinoids and their classic (e.g., endocannabinoid receptors and enzymes) and nonclassic (e.g., peroxisome proliferator-activated receptors, transcription factors) targets as a useful strategy for developing novel therapies for these disorders, based on their broad-spectrum neuroprotective profile, their activity as an endogenous protective system, the location of the endocannabinoid targets in cell substrates critical for neuronal survival, and their ability to serve for preservation and rescue, but also for repair and/or replacement, of neurons and glial cells against cytotoxic insults.

Mitochondrial form, function and signalling in aging

Aging is often accompanied by a decline in mitochondrial mass and function in different tissues. Additionally, cell resistance to stress is frequently found to be prevented by higher mitochondrial respiratory capacity. These correlations strongly suggest mitochondria are key players in aging and senescence, acting by regulating energy homeostasis, redox balance and signalling pathways central in these processes. However, mitochondria display a wide array of functions and signalling properties, and the roles of these different characteristics are still widely unexplored. Furthermore, differences in mitochondrial properties and responses between tissues and cell types, and how these affect whole body metabolism are also still poorly understood. This review uncovers aspects of mitochondrial biology that have an impact upon aging in model organisms and selected mammalian cells and tissues.

Assessment of the Neuroprotective Effects of Arginine-Rich Protamine Peptides, Poly-Arginine Peptides (R12-Cyclic, R22) and Arginine-Tryptophan-Containing Peptides Following In Vitro Excitotoxicity and/or Permanent Middle Cerebral Artery Occlusion in Rats

We have demonstrated that arginine-rich and poly-arginine peptides possess potent neuroprotective properties with arginine content and peptide positive charge being particularly critical for neuroprotective efficacy. In addition, the presence of other amino acids within arginine-rich peptides, as well as chemical modifications, peptide length and cell-penetrating properties also influence the level of neuroprotection. Against this background, we have examined the neuroprotective efficacy of arginine-rich protamine peptides, a cyclic (R12-c) poly-arginine peptide and a R22 poly-arginine peptide, as well as arginine peptides containing tryptophan or other amino acids (phenylalanine, tyrosine, glycine or leucine) in in vitro glutamic acid excitotoxicity and in vivo rat permanent middle cerebral artery occlusion models of stroke. In vitro studies demonstrated that protamine and poly-arginine peptides (R12-c, R22) were neuroprotective. Arginine-tryptophan-containing peptides were highly neuroprotective, with R12W8a being the most potent arginine-rich peptide identified in our laboratory. Peptides containing phenylalanine or tyrosine substituted in place of tryptophan in R12W8a were also highly neuroprotective, whereas leucine, and in particular glycine substitutions, decreased peptide efficacy. In vivo studies with protamine administered intravenously at 1000 nmol/kg 30 min after MCAO significantly reduced infarct volume and cerebral oedema by 22.5 and 38.6%, respectively. The R12W8a peptide was highly toxic when administered intravenously at 300 or 100 nmol/kg and ineffective at reducing infarct volume when administered at 30 nmol/kg 30 min after MCAO, unlike R18 (30 nmol/kg), which significantly reduced infarct volume by 20.4%. However, both R12W8a and R18 significantly reduced cerebral oedema by 19.8 and 42.2%, respectively. Protamine, R12W8a and R18 also reduced neuronal glutamic acid-induced calcium influx. These findings further highlight the neuroprotective properties of arginine-rich peptides and support the view that they represent a new class of neuroprotective agent.

iTRAQ-based proteomics analysis of hippocampus in spatial memory deficiency rats induced by simulated microgravity

It has been demonstrated that simulated microgravity (SM) may lead to cognitive dysfunction. However, the underlying mechanism remains unclear. In present study, tail-suspension (30°) rat was employed to explore the effects of 28 days of SM on hippocampus-dependent learning and memory capability and the underlying mechanisms. We found that 28-day tail-suspension rats displayed decline of learning and memory ability in Morris water maze (MWM) test. Using iTRAQ-based proteomics analysis, a total of 4774 proteins were quantified in hippocampus. Of these identified proteins, 147 proteins were differentially expressed between tail-suspension and control group. Further analysis showed these differentially expressed proteins (DEPs) involved in different molecular function categories, and participated in many biological processes. Based on the results of PANTHER pathway analysis and further western blot verification, we observed the expression of glutamate receptor 1 (GluR1) and glutamate receptor 4 (GluR4) which involved in metabotropic glutamate receptor group III pathway and ionotropic glutamate receptor pathway were significantly induced by SM. Moreover, an increased concentration of glutamic acid (Glu) was also found in hippocampus while the concentrations of 5-hydroxytryptamine (5-HT), dopamine (DA), γ-amino acid butyric acid (GABA) and epinephrine (E) were decreased. Our finding confirms that 28-day SM exposure can cause degrading of the spatial learning and memory capability and the possible mechanisms might be related with glutamate excitotoxicity and imbalances in specific neurotransmitters.

BIOLOGICAL SIGNIFICANCE

The goal of sending astronauts farther into space and extending the duration of spaceflight missions from months to years will challenge the current capabilities of bioastronautics. The investigation of the physiological and pathological changes induced by spaceflight will be critical in developing countermeasures to ensure astronauts to complete spaceflight mission accurately and effectively and return to earth safely. It has been demonstrated that spaceflight may lead to impairments in cognitive function which is crucial for mission success. Here we show that long-term simulated microgravity, the most potent environment risk factor during spaceflight, impairs the spatial learning and memory of rats and the underlying mechanism may be involved in glutamate excitotoxicity and imbalances in specific neurotransmitters release in hippocampus, which may provide new insight for the countermeasures of cognitive impairment during spaceflight.

Genistein inhibits hypoxia, ischemic-induced death, and apoptosis in PC12 cells

A hypoxia/ischemia neuronal model was established in PC12 cells using oxygen-glucose deprivation (OGD). OGD-induced neuronal death, apoptosis, glutamate receptor subunit GluR2 expression, and potassium channel currents were evaluated in the present study to determine the effects of genistein in mediating the neuronal death and apoptosis induced by hypoxia and ischemia, as well as its underlying mechanism. OGD exposure reduced the cell viability, increased apoptosis, decreased the GluR2 expression, and decreased the voltage-activated potassium currents. Genistein partially reversed the effects induced by OGD. Therefore, genistein may prevent hypoxia/ischemic-induced neuronal apoptosis that is mediated by alterations in GluR2 expression and voltage-activated potassium currents.

Memantine attenuates cell apoptosis by suppressing the calpain-caspase-3 pathway in an experimental model of ischemic stroke

Ischemic stroke, the second leading cause of death worldwide, leads to excessive glutamate release, over-activation of N-methyl-D-aspartate receptor (NMDAR), and massive influx of calcium (Ca²⁺), which may activate calpain and caspase-3, resulting in cellular damage and death. Memantine is an uncompetitive NMDAR antagonist with low-affinity/fast off-rate. We investigated the potential mechanisms through which memantine protects against ischemic stroke in vitro and in vivo. Middle cerebral artery occlusion-reperfusion (MCAO) was performed to establish an experimental model of ischemic stroke. The neuroprotective effects of memantine on ischemic rats were evaluated by neurological deficit scores and infarct volumes. The activities of calpain and caspase-3, and expression levels of microtubule-associated protein-2 (MAP2) and postsynaptic density-95 (PSD95) were determined by Western blotting. Additionally, Nissl staining and immunostaining were performed to examine brain damage, cell apoptosis, and neuronal loss induced by ischemia. Our results show that memantine could significantly prevent ischemic stroke-induced neurological deficits and brain infarct, and reduce ATP depletion-induced neuronal death. Moreover, memantine markedly suppressed the activation of the calpain-caspase-3 pathway and cell apoptosis, and consequently, attenuated brain damage and neuronal loss in MCAO rats. These results provide a molecular basis for the role of memantine in reducing neuronal apoptosis and preventing neuronal damage, suggesting that memantine may be a promising therapy for stroke patients.

The Neuroprotective Peptide Poly-Arginine-12 (R12) Reduces Cell Surface Levels of NMDA NR2B Receptor Subunit in Cortical Neurons; Investigation into the Involvement of Endocytic Mechanisms

We have previously reported that cationic poly-arginine and arginine-rich cell-penetrating peptides display high-level neuroprotection and reduce calcium influx following in vitro excitotoxicity, as well as reduce brain injury in animal stroke models. Using the neuroprotective peptides poly-arginine R12 (R12) and the NR2B9c peptide fused to the arginine-rich carrier peptide TAT (TAT-NR2B9c; also known as NA-1), we investigated the mechanisms whereby poly-arginine and arginine-rich peptides reduce glutamate-induced excitotoxic calcium influx. Using cell surface biotin protein labeling and western blot analysis, we demonstrated that R12 and TAT-NR2B9c significantly reduced cortical neuronal cell surface expression of the NMDA receptor subunit NR2B. Chemical endocytic inhibitors used individually or in combination prior to glutamate excitotoxicity did not significantly affect R12 peptide neuroprotective efficacy. Similarly, pretreatment of neurons with enzymes to degrade anionic cell surface proteoglycans, heparan sulfate proteoglycan (HSPG), and chondroitin sulfate proteoglycan (CSPG), as well as sialic acid residues, did not significantly affect peptide neuroprotective efficacy. While the exact mechanisms responsible for R12 peptide-mediated NMDA receptor NR2B subunit cell surface downregulation were not identified, an endocytic process could not be ruled out. The study supports our hypothesis that arginine-rich peptides reduce excitotoxic calcium influx by reducing the levels of cell surface ion channels.

Characterisation of neuroprotective efficacy of modified poly-arginine-9 (R9) peptides using a neuronal glutamic acid excitotoxicity model

In a recent study, we highlighted the importance of cationic charge and arginine residues for the neuroprotective properties of poly-arginine and arginine-rich peptides. In this study, using cortical neuronal cultures and an in vitro glutamic acid excitotoxicity model, we examined the neuroprotective efficacy of different modifications to the poly-arginine-9 peptide (R9). We compared an unmodified R9 peptide with R9 peptides containing the following modifications: (i) C-terminal amidation (R9-NH2); (ii) N-terminal acetylation (Ac-R9); (iii) C-terminal amidation with N-terminal acetylation (Ac-R9-NH2); and (iv) C-terminal amidation with D-amino acids (R9D-NH2). The three C-terminal amidated peptides (R9-NH2, Ac-R9-NH2, and R9D-NH2) displayed neuroprotective effects greater than the unmodified R9 peptide, while the N-terminal acetylated peptide (Ac-R9) had reduced efficacy. Using the R9-NH2 peptide, neuroprotection could be induced with a 10 min peptide pre-treatment, 1-6 h before glutamic acid insult, or when added to neuronal cultures up to 45 min post-insult. In addition, all peptides were capable of reducing glutamic acid-mediated neuronal intracellular calcium influx, in a manner that reflected their neuroprotective efficacy. This study further highlights the neuroprotective properties of poly-arginine peptides and provides insight into peptide modifications that affect efficacy.

Roles of PTEN with DNA Repair in Parkinson's Disease

Oxidative stress is considered to play key roles in aging and pathogenesis of many neurodegenerative diseases such as Parkinson’s disease, which could bring DNA damage by cells. The DNA damage may lead to the cell apoptosis, which could contribute to the degeneration of neuronal tissues. Recent evidence suggests that PTEN (phosphatase and tensin homolog on chromosome 10) may be involved in the pathophysiology of the neurodegenerative disorders. Since PTEN expression appears to be one dominant determinant of the neuronal cell death, PTEN should be a potential molecular target of novel therapeutic strategies against Parkinson’s disease. In addition, defects in DNA damage response and DNA repair are often associated with modulation of hormone signaling pathways. Especially, many observations imply a role for estrogen in a regulation of the DNA repair action. In the present review, we have attempted to summarize the function of DNA repair molecules at a viewpoint of the PTEN signaling pathway and the hormone related functional modulation of cells, providing a broad interpretation on the molecular mechanisms for treatment of Parkinson’s disease. Particular attention will be paid to the mechanisms proposed to explain the health effects of food ingredients against Parkinson’s disease related to reduce oxidative stress for an efficient therapeutic intervention.

Central Role of Glutamate Metabolism in the Maintenance of Nitrogen Homeostasis in Normal and Hyperammonemic Brain

Glutamate is present in the brain at an average concentration—typically 10–12 mM—far in excess of those of other amino acids. In glutamate-containing vesicles in the brain, the concentration of glutamate may even exceed 100 mM. Yet because glutamate is a major excitatory neurotransmitter, the concentration of this amino acid in the cerebral extracellular fluid must be kept low—typically µM. The remarkable gradient of glutamate in the different cerebral compartments: vesicles > cytosol/mitochondria > extracellular fluid attests to the extraordinary effectiveness of glutamate transporters and the strict control of enzymes of glutamate catabolism and synthesis in well-defined cellular and subcellular compartments in the brain. A major route for glutamate and ammonia removal is via the glutamine synthetase (glutamate ammonia ligase) reaction. Glutamate is also removed by conversion to the inhibitory neurotransmitter γ-aminobutyrate (GABA) via the action of glutamate decarboxylase. On the other hand, cerebral glutamate levels are maintained by the action of glutaminase and by various α-ketoglutarate-linked aminotransferases (especially aspartate aminotransferase and the mitochondrial and cytosolic forms of the branched-chain aminotransferases). Although the glutamate dehydrogenase reaction is freely reversible, owing to rapid removal of ammonia as glutamine amide, the direction of the glutamate dehydrogenase reaction in the brain in vivo is mainly toward glutamate catabolism rather than toward the net synthesis of glutamate, even under hyperammonemia conditions. During hyperammonemia, there is a large increase in cerebral glutamine content, but only small changes in the levels of glutamate and α-ketoglutarate. Thus, the channeling of glutamate toward glutamine during hyperammonemia results in the net synthesis of 5-carbon units. This increase in 5-carbon units is accomplished in part by the ammonia-induced stimulation of the anaplerotic enzyme pyruvate carboxylase. Here, we suggest that glutamate may constitute a buffer or bulwark against changes in cerebral amine and ammonia nitrogen. Although the glutamate transporters are briefly discussed, the major emphasis of the present review is on the enzymology contributing to the maintenance of glutamate levels under normal and hyperammonemic conditions. Emphasis will also be placed on the central role of glutamate in the glutamine-glutamate and glutamine-GABA neurotransmitter cycles between neurons and astrocytes. Finally, we provide a brief and selective discussion of neuropathology associated with altered cerebral glutamate levels.