Acute and long-term NCX activation reduces brain injury and restores behavioral functions in mice subjected to neonatal brain ischemia

Amiodarone Administration during Cardiopulmonary Resuscitation Is Not Associated with Changes in Short-Term Mortality or Neurological Outcomes in Cardiac Arrest Patients with Shockable Rhythms

Background: The search for the best therapeutic approach in cardiopulmonary resuscitations (CPR) remains open to question. In this study, we evaluated if Amiodarone administration during CPR was associated with short-term mortality or neurological development. Methods: A total of 232 patients with sudden cardiac arrest (CA) with shockable rhythms were included in our analysis. Propensity score matching based on age, gender, type of CA, and CPR duration was used to stratify between patients with and without Amiodarone during CPR. Primary endpoints were short-term mortality (30-day) and neurological outcomes assessed by the cerebral performance category. Secondary endpoints were plasma lactate, phosphate levels at hospital admission, and the peak Neuron-specific enolase. Results: Propensity score matching was successful with a caliper size used for matching of 0.089 and a sample size of n = 82 per group. The 30-day mortality rates were similar between both groups (p = 0.24). There were no significant differences in lactate levels at hospital admission and during the following five days between the groups. Patients receiving Amiodarone showed slightly higher phosphate levels at hospital admission, while the levels decreased to a similar value during the following days. Among CA survivors to hospital discharge, no differences between the proportion of good neurological outcomes were detected between the two groups (p = 0.58), despite slightly higher peak neuron-specific enolase levels in CA patients receiving Amiodarone (p = 0.03). Conclusions: Amiodarone administration is not associated with short-term mortality or neurological outcomes in CA patients with shockable rhythms receiving CPR.

Expression of Na+/Ca2+ exchangers was enhanced following pre-treatment of olive leaf extract and olive oil in animal model of ischemic stroke

BACKGROUND

Neuroprotective role of olive and its natural products can introduce them as alternative candidates for the management of neurodegenerative diseases including stroke. The present study was designed to evaluate whether pretreatment of olive oil and leaf extract can attenuate the most important destructive processes in cerebral ischemia called excitotoxicity.

MATERIAL AND METHODS

The male rats were categorized into control, virgin olive oil (OVV), MCAO, MCAO + OVV (with doses of 0.25, 0.50 and 0.75 ml/kg as treatment groups), olive leaf extract, MCAO + olive leaf extract (with doses 50, 75 and 100 mg/kg as treatment groups) groups. Rats of treatment groups received gastric gavage with olive oil or leaf extract for 30 consecutive days. After pretreatment, the intraluminal filament technique was used to block middle cerebral artery (MCA) transiently. Neurological deficits, infarct volume and expression of Na+/Ca2+ exchangers (NCX1, NCX2 and NCX3) proteins were measured.

RESULTS

The results revealed that olive oil at doses of 0.50 and 0.75 ml/kg reduced the infarction and neurological score and upregulated NCXs expression in rat brain. In addition, olive leaf extract at doses of 75 and 100 mg/kg attenuated the infarction and neurological score and enhanced NCXs expression in rat brain.

CONCLUSION

These findings support the view that olive oil and leaf extract play the neuroprotective role in cerebral ischemia due to the upregulation of NCXs protein expression.

Structural insight into the allosteric inhibition of human sodium-calcium exchanger NCX1 by XIP and SEA0400

Sodium-calcium exchanger proteins influence calcium homeostasis in many cell types and participate in a wide range of physiological and pathological processes. Here, we elucidate the cryo-EM structure of the human Na+/Ca2+ exchanger NCX1.3 in the presence of a specific inhibitor, SEA0400. Conserved ion-coordinating residues are exposed on the cytoplasmic face of NCX1.3, indicating that the observed structure is stabilized in an inward-facing conformation. We show how regulatory calcium-binding domains (CBDs) assemble with the ion-translocation transmembrane domain (TMD). The exchanger-inhibitory peptide (XIP) is trapped within a groove between the TMD and CBD2 and predicted to clash with gating helices TMs1/6 at the outward-facing state, thus hindering conformational transition and promoting inactivation of the transporter. A bound SEA0400 molecule stiffens helix TM2ab and affects conformational rearrangements of TM2ab that are associated with the ion-exchange reaction, thus allosterically attenuating Ca2+-uptake activity of NCX1.3.

Chronic exposure to l-BMAA cyanotoxin induces cytoplasmic TDP-43 accumulation and glial activation, reproducing an amyotrophic lateral sclerosis-like phenotype in mice

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a progressive and often fatal neurodegenerative disease characterized by the loss of Motor Neurons (MNs) in spinal cord, motor cortex and brainstem. Despite significant efforts in the field, the exact pathogenetic mechanisms underlying both familial and sporadic forms of ALS have not been fully elucidated, and the therapeutic possibilities are still very limited. Here we investigate the molecular mechanisms of neurodegeneration induced by chronic exposure to the environmental cyanotoxin L-BMAA, which causes a form of ALS/Parkinson's disease (PD) in several populations consuming food and/or water containing high amounts of this compound.

METHODS

In this effort, mice were chronically exposed to L-BMAA and analyzed at different time points to evaluate cellular and molecular alterations and behavioral deficits, performing MTT assay, immunoblot, immunofluorescence and immunohistochemistry analysis, and behavioral tests.

RESULTS

We found that cyanotoxin L-BMAA determines apoptotic cell death and a marked astrogliosis in spinal cord and motor cortex, and induces neurotoxicity by favoring TDP-43 cytoplasmic accumulation.

CONCLUSIONS

Overall, our results characterize a new versatile neurotoxic animal model of ALS that may be useful for the identification of new druggable targets to develop innovative therapeutic strategies for this disease.

Ischemia Reperfusion Injury Induced Blood Brain Barrier Dysfunction and the Involved Molecular Mechanism

Stroke is characterized by the abrupt failure of blood flow to a specific brain region, resulting in insufficient supply of oxygen and glucose to the ischemic tissues. Timely reperfusion of blood flow can rescue dying tissue but can also lead to secondary damage to both the infarcted tissues and the blood-brain barrier, known as ischemia/reperfusion injury. Both primary and secondary damage result in biphasic opening of the blood-brain barrier, leading to blood-brain barrier dysfunction and vasogenic edema. Importantly, blood-brain barrier dysfunction, inflammation, and microglial activation are critical factors that worsen stroke outcomes. Activated microglia secrete numerous cytokines, chemokines, and inflammatory factors during neuroinflammation, contributing to the second opening of the blood-brain barrier and worsening the outcome of ischemic stroke. TNF-α, IL-1β, IL-6, and other microglia-derived molecules have been shown to be involved in the breakdown of blood-brain barrier. Additionally, other non-microglia-derived molecules such as RNA, HSPs, and transporter proteins also participate in the blood-brain barrier breakdown process after ischemic stroke, either in the primary damage stage directly influencing tight junction proteins and endothelial cells, or in the secondary damage stage participating in the following neuroinflammation. This review summarizes the cellular and molecular components of the blood-brain barrier and concludes the association of microglia-derived and non-microglia-derived molecules with blood-brain barrier dysfunction and its underlying mechanisms.

Neonatal Arterial Ischaemic Stroke: Advances in Pathologic Neural Death, Diagnosis, Treatment, and Prognosis

Neonatal arterial ischaemic stroke (NAIS) is caused by focal arterial occlusion and often leads to severe neurological sequelae. Neural deaths after NAIS mainly include necrosis, apoptosis, necroptosis, autophagy, ferroptosis, and pyroptosis. These neural deaths are mainly caused by upstream stimulations, including excitotoxicity, oxidative stress, inflammation, and death receptor pathways. The current clinical approaches to managing NAIS mainly focus on supportive treatments, including seizure control and anticoagulation. In recent years, research on the pathology, early diagnosis, and potential therapeutic targets of NAIS has progressed. In this review, we summarise the latest progress of research on the pathology, diagnosis, treatment, and prognosis of NAIS and highlight newly potential diagnostic and treatment approaches.

Ruta graveolens water extract (RGWE) ameliorates ischemic damage and improves neurological deficits in a rat model of transient focal brain ischemia

INTRODUCTION AND AIMS

The limited therapeutic options for ischemic stroke treatment render necessary the identification of new strategies. In recent years, it has been shown that natural compounds may represent a valid therapeutic opportunity. Therefore, the present study aimed to evaluate the protective effect of Ruta graveolens water extract (RGWE) in an in vivo experimental model of brain ischemia.

METHODS

RGWE effects on ischemic damage and neurological function were evaluated in adult rats subjected to transient occlusion of the Middle Cerebral Artery (tMCAO), receiving two intraperitoneal injections of RGWE, 100 and 300 min after the induction of ischemia. In addition, astroglial and microglial activation was measured as GFAP and IBA-1 expression by immunofluorescence and confocal microscopy analysis.

RESULTS

Treatment with RGWE containing 10 mg/kg of Rutin, the major component, ameliorates the ischemic damage and improves neurological performances. Interestingly, the pro-inflammatory states of astrocytes and microglia, respectively detected by using C3 and iNOS markers, were significantly reduced in ipsilateral cortical and striatal areas in ischemic RGWE-treated rats.

CONCLUSIONS

RGWE shows a neuroprotective effect on brain infarct volume extent in a transient focal cerebral ischemia model and this effect was paralleled by the prevention of pro-inflammatory astroglial and microglial activation. Collectively, our findings support the idea that natural compounds may represent potential therapeutic opportunities against ischemic stroke.

Excitatory Synaptic Transmission in Ischemic Stroke: A New Outlet for Classical Neuroprotective Strategies

Stroke is one of the leading causes of death and disability in the world, of which ischemia accounts for the majority. There is growing evidence of changes in synaptic connections and neural network functions in the brain of stroke patients. Currently, the studies on these neurobiological alterations mainly focus on the principle of glutamate excitotoxicity, and the corresponding neuroprotective strategies are limited to blocking the overactivation of ionic glutamate receptors. Nevertheless, it is disappointing that these treatments often fail because of the unspecificity and serious side effects of the tested drugs in clinical trials. Thus, in the prevention and treatment of stroke, finding and developing new targets of neuroprotective intervention is still the focus and goal of research in this field. In this review, we focus on the whole processes of glutamatergic synaptic transmission and highlight the pathological changes underlying each link to help develop potential therapeutic strategies for ischemic brain damage. These strategies include: (1) controlling the synaptic or extra-synaptic release of glutamate, (2) selectively blocking the action of the glutamate receptor NMDAR subunit, (3) increasing glutamate metabolism, and reuptake in the brain and blood, and (4) regulating the glutamate system by GABA receptors and the microbiota–gut–brain axis. Based on these latest findings, it is expected to promote a substantial understanding of the complex glutamate signal transduction mechanism, thereby providing excellent neuroprotection research direction for human ischemic stroke (IS).

Preconditioning in hypoxic-ischemic neonate mice triggers Na+-Ca2+ exchanger-dependent neurogenesis

To identify alternative interventions in neonatal hypoxic-ischemic encephalopathy, researchers’ attention has been focused to the study of endogenous neuroprotective strategies. Based on the preconditioning concept that a subthreshold insult may protect from a subsequent harmful event, we aimed at identifying a new preconditioning protocol able to enhance Ca²⁺-dependent neurogenesis in a mouse model of neonatal hypoxia ischemia (HI). To this purpose, we also investigated the role of the preconditioning-linked protein controlling ionic homeostasis, Na⁺/Ca²⁺ exchanger (NCX). Hypoxic Preconditioning (HPC) was reproduced by exposing P7 mice to 20’ hypoxia. HI was induced by isolating and cutting the right common carotid artery. A significant reduction in ischemic damage was observed in mice subjected to 20’ hypoxia followed,3 days later, by 60’ HI, thus suggesting that 20’ hypoxia functions as preconditioning stimulus. HPC promoted neuroblasts proliferation in the dentate gyrus mirrored by an increase of NCX1 and NCX3-positive cells and an improvement of behavioral motor performances in HI mice. An attenuation of HPC neuroprotection as well as a reduction in the expression of neurogenesis markers, including p57 and NeuroD1, was observed in preconditioned mice lacking NCX1 or NCX3. In summary, PC in neonatal mice triggers a neurogenic process linked to ionic homeostasis maintenance, regulated by NCX1 and NCX3.

Experimental Models for Testing the Efficacy of Pharmacological Treatments for Neonatal Hypoxic-Ischemic Encephalopathy

Representing an important cause of long-term disability, term neonatal hypoxic-ischemic encephalopathy (HIE) urgently needs further research aimed at repurposing existing drug as well as developing new therapeutics. Since various experimental in vitro and in vivo models of HIE have been developed with distinct characteristics, it becomes important to select the appropriate preclinical screening cascade for testing the efficacy of novel pharmacological treatments. As therapeutic hypothermia is already a routine therapy for neonatal encephalopathy, it is essential that hypothermia be administered to the experimental model selected to allow translational testing of novel or repurposed drugs on top of the standard of care. Moreover, a translational approach requires that therapeutic interventions must be initiated after the induction of the insult, and the time window for intervention should be evaluated to translate to real world clinical practice. Hippocampal organotypic slice cultures, in particular, are an invaluable intermediate between simpler cell lines and in vivo models, as they largely maintain structural complexity of the original tissue and can be subjected to transient oxygen-glucose deprivation (OGD) and subsequent reoxygenation to simulate ischemic neuronal injury and reperfusion. Progressing to in vivo models, generally, rodent (mouse and rat) models could offer more flexibility and be more cost-effective for testing the efficacy of pharmacological agents with a dose-response approach. Large animal models, including piglets, sheep, and non-human primates, may be utilized as a third step for more focused and accurate translational studies, including also pharmacokinetic and safety pharmacology assessments. Thus, a preclinical proof of concept of efficacy of an emerging pharmacological treatment should be obtained firstly in vitro, including organotypic models, and, subsequently, in at least two different animal models, also in combination with hypothermia, before initiating clinical trials.

Prolonged NCX activation prevents SOD1 accumulation, reduces neuroinflammation, ameliorates motor behavior and prolongs survival in a ALS mouse model

Imbalance in cellular ionic homeostasis is a hallmark of several neurodegenerative diseases including Amyotrophic Lateral Sclerosis (ALS). Sodium-calcium exchanger (NCX) is a membrane antiporter that, operating in a bidirectional way, couples the exchange of Ca²⁺ and Na ⁺ ions in neurons and glial cells, thus controlling the intracellular homeostasis of these ions. Among the three NCX genes, NCX1 and NCX2 are widely expressed within the CNS, while NCX3 is present only in skeletal muscles and at lower levels of expression in selected brain regions. ALS mice showed a reduction in the expression and activity of NCX1 and NCX2 consistent with disease progression, therefore we aimed to investigate their role in ALS pathophysiology. Notably, we demonstrated that the pharmacological activation of NCX1 and NCX2 by the prolonged treatment of SOD1^G93A mice with the newly synthesized compound neurounina: (1) prevented the reduction in NCX activity observed in spinal cord; (2) preserved motor neurons survival in the ventral spinal horn of SOD1^G93A mice; (3) prevented the spinal cord accumulation of misfolded SOD1; (4) reduced astroglia and microglia activation and spared the resident microglia cells in the spinal cord; (5) improved the lifespan and mitigated motor symptoms of ALS mice. The present study highlights the significant role of NCX1 and NCX2 in the pathophysiology of this neurodegenerative disorder and paves the way for the design of a new pharmacological approach for ALS.

The hypoxia sensitive metal transcription factor MTF-1 activates NCX1 brain promoter and participates in remote postconditioning neuroprotection in stroke

Remote limb ischemic postconditioning (RLIP) is an experimental strategy in which short femoral artery ischemia reduces brain damage induced by a previous harmful ischemic insult. Ionic homeostasis maintenance in the CNS seems to play a relevant role in mediating RLIP neuroprotection and among the effectors, the sodium-calcium exchanger 1 (NCX1) may give an important contribution, being expressed in all CNS cells involved in brain ischemic pathophysiology. The aim of this work was to investigate whether the metal responsive transcription factor 1 (MTF-1), an important hypoxia sensitive transcription factor, may (i) interact and regulate NCX1, and (ii) play a role in the neuroprotective effect mediated by RLIP through NCX1 activation. Here we demonstrated that in brain ischemia induced by transient middle cerebral occlusion (tMCAO), MTF-1 is triggered by a subsequent temporary femoral artery occlusion (FAO) and represents a mediator of endogenous neuroprotection. More importantly, we showed that MTF-1 translocates to the nucleus where it binds the metal responsive element (MRE) located at -23/-17 bp of Ncx1 brain promoter thus activating its transcription and inducing an upregulation of NCX1 that has been demonstrated to be neuroprotective. Furthermore, RLIP restored MTF-1 and NCX1 protein levels in the ischemic rat brain cortex and the silencing of MTF-1 prevented the increase of NCX1 observed in RLIP protected rats, thus demonstrating a direct regulation of NCX1 by MTF-1 in the ischemic cortex of rat exposed to tMCAO followed by FAO. Moreover, silencing of MTF-1 significantly reduced the neuroprotective effect elicited by RLIP as demonstrated by the enlargement of brain infarct volume observed in rats subjected to RLIP and treated with MTF-1 silencing. Overall, MTF-dependent activation of NCX1 and their upregulation elicited by RLIP, besides unraveling a new molecular pathway of neuroprotection during brain ischemia, might represent an additional mechanism to intervene in stroke pathophysiology.

Neuroprotective effect of heparin Trisulfated disaccharide on ischemic stroke

Cells undergoing hypoxia experience intense cytoplasmic calcium (Ca2+) overload. High concentrations of intracellular calcium ([Ca2+]i) can trigger cell death in the neural tissue, a hallmark of stroke. Neural Ca2+ homeostasis involves regulation by the Na+/Ca2+ exchanger (NCX). Previous data published by our group showed that a product of the enzymatic depolymerization of heparin by heparinase, the unsaturated trisulfated disaccharide (TD; ΔU, 2S-GlcNS, 6S), can accelerate Na+/Ca2+ exchange via NCX, in hepatocytes and aorta vascular smooth muscle cells. Thus, the objective of this work was to verify whether TD could act as a neuroprotective agent able to prevent neuronal cell death by reducing [Ca2+]i. Pretreatment of N2a cells with TD reduced [Ca2+]i rise induced by thapsigargin and increased cell viability under [Ca2+]I overload conditions and in hypoxia. Using a murine model of stroke, we observed that pretreatment with TD decreased cerebral infarct volume and cell death. However, when mice received KB-R7943, an NCX blocker, the neuroprotective effect of TD was abolished, strongly suggesting that this neuroprotection requires a functional NCX to happen. Thus, we propose TD-NCX as a new therapeutic axis for the prevention of neuronal death induced by [Ca2+]i overload.

miR-16-5p, miR-103-3p, and miR-27b-3p as Early Peripheral Biomarkers of Fetal Growth Restriction

Current tests available to diagnose fetal hypoxia in-utero lack sensitivity thus failing to identify many fetuses at risk. Emerging evidence suggests that microRNAs derived from the placenta circulate in the maternal blood during pregnancy and may be used as non-invasive biomarkers for pregnancy complications. With the intent to identify putative markers of fetal growth restriction (FGR) and new therapeutic druggable targets, we examined, in maternal blood samples, the expression of a group of microRNAs, known to be regulated by hypoxia. The expression of microRNAs was evaluated in maternal plasma samples collected from (1) women carrying a preterm FGR fetus (FGR group) or (2) women with an appropriately grown fetus matched at the same gestational age (Control group). To discriminate between early- and late-onset FGR, the study population was divided into two subgroups according to the gestational age at delivery. Four microRNAs were identified as possible candidates for the diagnosis of FGR: miR-16-5p, miR-103-3p, miR-107-3p, and miR-27b-3p. All four selected miRNAs, measured by RT-PCR, resulted upregulated in FGR blood samples before the 32nd week of gestation. By contrast, miRNA103-3p and miRNA107-3p, analyzed between the 32nd and 37th week of gestation, showed lower expression in the FGR group compared to aged matched controls. Our results showed that measurement of miRNAs in maternal blood may form the basis for a future diagnostic test to determine the degree of fetal hypoxia in FGR, thus allowing the start of appropriate therapeutic interventions to alleviate the burden of this disease.

Sodium/calcium exchanger as main effector of endogenous neuroprotection elicited by ischemic tolerance

The ischemic tolerance (IT) paradigm represents a fundamental cell response to certain types or injury able to render an organ more "tolerant" to a subsequent, stronger, insult. During the 16th century, the toxicologist Paracelsus described for the first time the possibility that a noxious event might determine a state of tolerance. This finding was summarized in one of his most important mentions: "The dose makes the poison". In more recent years, ischemic tolerance in the brain was first described in 1991, when it was demonstrated by Kirino and collaborators that two minutes of subthreshold brain ischemia in gerbils produced tolerance against global brain ischemia. Based on the time in which the conditioning stimulus is applied, it is possible to define preconditioning, perconditioning and postconditioning, when the subthreshold insult is applied before, during or after the ischemic event, respectively. Furthermore, depending on the temporal delay from the ischemic event, two different modalities are distinguished: rapid or delayed preconditioning and postconditioning. Finally, the circumstance in which the conditioning stimulus is applied on an organ distant from the brain is referred as remote conditioning. Over the years the "conditioning" paradigm has been applied to several brain disorders and a number of molecular mechanisms taking part to these protective processes have been described. The mechanisms are usually classified in three distinct categories identified as triggers, mediators and effectors. As concerns the putative effectors, it has been hypothesized that brain cells appear to have the ability to adapt to hypoxia by reducing their energy demand through modulation of ion channels and transporters, which delays anoxic depolarization. The purpose of the present review is to summarize the role played by plasmamembrane proteins able to control ionic homeostasis in mediating protection elicited by brain conditioning, particular attention will be deserved to the role played by Na⁺/Ca²⁺ exchanger.

New perspectives for selective NCX activators in neurodegenerative diseases

The Na⁺/Ca²⁺ exchanger plays a relevant role in several neurological disorders, thus the pharmacological modulation of its isoforms might represent a promising strategy to ameliorate the course of some neurological pathologies including stroke, neonatal hypoxia, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Alzheimer Disease (AD), and spinal muscular atrophy (SMA). This review will summarize heterocyclic, peptidergic, genetic and epigenetic compounds activating or inhibiting the expression/activity of each NCX isoform. In addition, we will focus our attention on the development of new strategies aimed to ameliorate the pathophysiological conditions in which NCX isoform changes are found.

Amiodarone exacerbates brain injuries after hypoxic-ischemic insult in mice

Background

Sodium ion transportation plays a crucial role in the pathogenesis of hypoxic–ischemic brain injury. Amiodarone, a Vaughan-Williams class III antiarrhythmic drug, has been widely used to treat life-threatening arrhythmia and cardiac arrest worldwide. In addition to its inhibitory effects on the potassium channel, amiodarone also blocks various sodium ion transporters, including the voltage-gated sodium channel, sodium pump, and Na⁺/Ca⁺ exchanger. Considering these pharmacological profile, amiodarone may affect the influx–efflux balance of sodium ion in the hypoxic–ischemic brain. Previous studies suggest that the blockade of the voltage-gated sodium channel during hypoxic–ischemic brain injury exerts neuroprotection. On the contrary, the blockade of sodium pump or Na⁺/Ca⁺ exchanger during hypoxia–ischemia may cause further intracellular sodium accumulation and consequent osmotic cell death. From these perspectives, the effects of amiodarone on sodium ion balance on the hypoxic–ischemic brain can be both protective and detrimental depending on the clinical and pathophysiological conditions. In this study, we therefore investigated the effect of amiodarone on hypoxic–ischemic brain injury using a murine experimental model.

Results

Compared with the control group mice, mice that received amiodarone after induction of 40-min hypoxic–ischemic brain injury exhibited lower survival rates over 7 days and worse neurological function. After 25-min hypoxic–ischemic brain injury, amiodarone treated mice exhibited larger infarct volumes (16.0 ± 6.9 vs. 24.2 ± 6.8 mm³, P < 0.05) and worse neurological function. In addition, the brains harvested from the amiodarone-treated mice contained larger amounts of sodium (194.7 ± 45.1 vs. 253.5 ± 50.9 mEq/kg dry weight, P < 0.01) and water (259.3 ± 8.9 vs. 277.2 ± 12.5 mg, P < 0.01). There were no significant differences in hemodynamic parameters between groups.

Conclusions

Amiodarone exacerbated brain injuries and neurological outcomes after hypoxic–ischemic insults. Severe brain sodium accumulation and brain edema were associated with the detrimental effects of amiodarone. Amiodarone at the clinical dose can exacerbate brain injury after hypoxic–ischemic insult by affecting sodium ion transportation and facilitate intracellular sodium accumulation in the brain.

Roles Played by the Na+/Ca2+ Exchanger and Hypothermia in the Prevention of Ischemia-Induced Carrier-Mediated Efflux of Catecholamines into the Extracellular Space: Implications for Stroke Therapy

The release of [³H]dopamine ([³H]DA) and [³H]noradrenaline ([³H]NA) in acutely perfused rat striatal and cortical slice preparations was measured at 37 °C and 17 °C under ischemic conditions. The ischemia was simulated by the removal of oxygen and glucose from the Krebs solution. At 37 °C, resting release rates in response to ischemia were increased; in contrast, at 17 °C, resting release rates were significantly reduced, or resting release was completely prevented. The removal of extracellular Ca²⁺ further increased the release rates of [³H]DA and [³H]NA induced by ischemic conditions. This finding indicated that the Na⁺/Ca²⁺ exchanger (NCX), working in reverse in the absence of extracellular Ca²⁺, fails to trigger the influx of Ca²⁺ in exchange for Na⁺ and fails to counteract ischemia by further increasing the intracellular Na⁺ concentration ([Na⁺]_i). KB-R7943, an inhibitor of NCX, significantly reduced the cytoplasmic resting release rate of catecholamines under ischemic conditions and under conditions where Ca²⁺ was removed. Hypothermia inhibited the excessive release of [³H]DA in response to ischemia, even in the absence of Ca²⁺. These findings further indicate that the NCX plays an important role in maintaining a high [Na⁺]_i, a condition that may lead to the reversal of monoamine transporter functions; this effect consequently leads to the excessive cytoplasmic tonic release of monoamines and the reversal of the NCX. Using HPLC combined with scintillation spectrometry, hypothermia, which enhances the stimulation-evoked release of DA, was found to inhibit the efflux of toxic DA metabolites, such as 3,4-dihydroxyphenylacetaldehyde (DOPAL). In slices prepared from human cortical brain tissue removed during elective neurosurgery, the uptake and release values for [³H]NA did not differ from those measured at 37 °C in slices that were previously maintained under hypoxic conditions at 8 °C for 20 h. This result indicates that hypothermia preserves the functions of the transport and release mechanisms, even under hypoxic conditions. Oxidative stress (H₂O₂), a mediator of ischemic brain injury enhanced the striatal resting release of [³H]DA and its toxic metabolites (DOPAL, quinone). The study supports our earlier findings that during ischemia transmitters are released from the cytoplasm. In addition, the major findings of this study that hypothermia of brain slice preparations prevents the extracellular calcium concentration ([Ca²⁺]_o)-independent non-vesicular transmitter release induced by ischemic insults, inhibiting Na⁺/Cl⁻-dependent membrane transport of monoamines and their toxic metabolites into the extracellular space, where they can exert toxic effects.

Development, Validation of LC-MS/MS Method and Determination of Pharmacokinetic Parameters of the Stroke Neuroprotectant Neurounina-1 in Beagle Dog Plasma After Intravenous Administration

Neurounina-1 [chemical name: 7-nitro-5-phenyl-1-(pyrrolidin-1-ylmethyl)-1H-benzo[e][1,4]diazepin-2(3H)-one] is a new compound provided with relevant neuroprotective effect during stroke and in neonatal hypoxia by increasing the Na⁺/Ca²⁺ exchanger (NCX) isoforms NCX1 and NCX2 activity. This study shows for the first time, the development and validation of a sensitive and selective method for analysis of neurounina-1 in beagle dog plasma by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The sample preparation consisted of extraction of the analyte and the internal standard (IS) (ropivacaine) from plasma (50 μL) by liquid-liquid extraction using acetonitrile (100 μL). The selected reaction monitoring mode of the positive ion was performed and the precursor to the product ion transitions of m/z 365 > 83 and m/z 275 > 126 were used to measure the derivative of neurounina-1 and ropivacaine. The chromatographic separation was achieved using a Phenomenex C18 Luna (150 mm × 4.6 mm × 5 μm) analytical column with an isocratic mobile phase composed of methanol/acetonitrile/water (50/40/10, v/v/v) + 0.1% formic acid + 1 M ammonium formate. The method was linear over a concentration range of 1-500 ng/mL. The method was applied to evaluate the pharmacokinetics of neurounina-1 after a single intravenous administration of three different doses (0.1 mg/kg, 0.3 mg/kg, and 1 mg/kg) to beagle dogs (n = 5). The mean AUC_0-tlast values were 26.10, 115.81, and 257.28 ng^∗h/mL following intravenous administration of 0.1, 0.3, and 1 mg/kg, respectively. Linear pharmacokinetics was observed up to 1.0 mg/kg. The neurounina-1 was rapidly eliminated, with mean CL values of 46.24, 47.57, and 69.15 L/h, Vd of 130.31, 154.15, and 210.79 L and t_1/2 of 2.14, 2.54, and 2.04 h after intravenous administration of 0.1, 0.3, and 1 mg/kg, respectively. This new analytical method allows the rapid determination of the neurounina-1, a new developed compound, able to exert a remarkable neuroprotective effect in the low nanomolar range.

Models and methods for conditioning the ischemic brain

BACKGROUND

In the last decades the need to find new neuroprotective targets has addressed the researchers to investigate the endogenous molecular mechanisms that brain activates when exposed to a conditioning stimulus. Indeed, conditioning is an adaptive biological process activated by those interventions able to confer resistance to a deleterious brain event through the exposure to a sub-threshold insult. Specifically, preconditioning and postconditioning are realized when the conditioning stimulus is applied before or after, respectively, the harmul ischemia.

AIMS AND RESULTS

The present review will describe the most common methods to induce brain conditioning, with particular regards to surgical, physical exercise, temperature-induced and pharmacological approaches. It has been well recognized that when the subliminal stimulus is delivered after the ischemic insult, the achieved neuroprotection is comparable to that observed in models of ischemic preconditioning. In addition, subjecting the brain to both preconditioning as well as postconditioning did not cause greater protection than each treatment alone.

CONCLUSIONS

The last decades have provided fascinating insights into the mechanisms and potential application of strategies to induce brain conditioning. Since the identification of intrinsic cell-survival pathways should provide more direct opportunities for translational neuroprotection trials, an accurate examination of the different models of preconditioning and postconditioning is mandatory before starting any new project.