Isoflurane posttreatment reduces neonatal hypoxic-ischemic brain injury in rats by the sphingosine-1-phosphate/phosphatidylinositol-3-kinase/Akt pathway

Preconditioning and Posttreatment Strategies in Neonatal Hypoxic-Ischemic Encephalopathy: Recent Advances and Clinical Challenges

Neonatal hypoxic-ischemic encephalopathy (HIE) is a severe neurological disorder caused by impaired cerebral blood flow and brain hypoxia, resulting in high morbidity and mortality rates. While therapeutic hypothermia remains the standard treatment and has been shown to reduce mortality to some extent, its therapeutic efficacy is limited, and it applies only to a select group of neonates who meet stringent inclusion criteria. Advances in our understanding of the pathophysiology of HIE have led to the identification of several promising neuroprotective strategies designed to mitigate or prevent the neurological damage induced by hypoxia-ischemia. Among these, preconditioning has emerged as a potent neuroprotective approach, enhancing cellular resilience to subsequent injury and potentially reducing treatment complexity and healthcare costs. Preconditioning/pretreatment and posttreatment offer significant promise in attenuating the neurological damage associated with HIE. Thus, exploring early intervention strategies for neonatal HIE, focusing on the comparative mechanisms and therapeutic targets of preconditioning and postconditioning, is critical to developing more effective treatment modalities. This review summarizes the current understanding of the pathophysiological mechanisms underlying neonatal HIE and its prevention and treatment strategies, providing new perspectives and a theoretical foundation for future neuroprotective interventions.

Isoflurane lowers the cerebral metabolic rate of oxygen and prevents hypoxia during cortical spreading depolarization in vitro: An integrative experimental and modeling study

Cortical spreading depolarization (SD) imposes a massive increase in energy demand and therefore evolves as a target for treatment following acute brain injuries. Anesthetics are empirically used to reduce energy metabolism in critical brain conditions, yet their effect on metabolism during SD remains largely unknown. We investigated oxidative metabolism during SD in brain slices from Wistar rats. Extracellular potassium ([K+]o), local field potential and partial tissue oxygen pressure (ptiO2) were measured simultaneously. The cerebral metabolic rate of oxygen (CMRO2) was calculated using a reaction-diffusion model. By that, we tested the effect of clinically relevant concentrations of isoflurane on CMRO2 during SD and modeled tissue oxygenation for different capillary pO2 values. During SD, CMRO2 increased 2.7-fold, resulting in transient hypoxia in the slice core. Isoflurane decreased CMRO2, reduced peak [K+]o, and prolonged [K+]o clearance, which indicates reduced synaptic transmission and sodium-potassium ATPase inhibition. Modeling tissue oxygenation during SD illustrates the need for increased capillary pO2 levels to prevent hypoxia. In the absence thereof, isoflurane could improve tissue oxygenation by lowering CMRO2. Therefore, isoflurane is a promising candidate for pre-clinical studies on neuronal survival in conditions involving SD.

Desflurane improves electrical activity of neurons and alleviates oxygen-glucose deprivation-induced neuronal injury by activating the Kcna1-dependent Kv1.1 channel

Several volatile anesthetics have presented neuroprotective functions in ischemic injury. This study investigates the effect of desflurane (Des) on neurons following oxygen-glucose deprivation (OGD) challenge and explores the underpinning mechanism. Mouse neurons HT22 were subjected to OGD, which significantly reduced cell viability, increased lactate dehydrogenase release, and promoted cell apoptosis. In addition, the OGD condition increased oxidative stress in HT22 cells, as manifested by increased ROS and MDA contents, decreased SOD activity and GSH/GSSG ratio, and reduced nuclear protein level of Nrf2. Notably, the oxidative stress and neuronal apoptosis were substantially blocked by Des treatment. Bioinformatics suggested potassium voltage-gated channel subfamily A member 1 (Kcna1) as a target of Des. Indeed, the Kcna1 expression in HT22 cells was decreased by OGD but restored by Des treatment. Artificial knockdown of Kcna1 negated the neuroprotective effects of Des. By upregulating Kcna1, Des activated the Kv1.1 channel, therefore enhancing K+ currents and inducing neuronal repolarization. Pharmacological inhibition of the Kv1.1 channel reversed the protective effects of Des against OGD-induced injury. Collectively, this study demonstrates that Des improves electrical activity of neurons and alleviates OGD-induced neuronal injury by activating the Kcna1-dependent Kv1.1 channel.

The Current Landscape in the Development of Small-molecule Modulators Targeting Sphingosine-1-phosphate Receptors to Treat Neurodegenerative Diseases

Sphingosine 1-phosphate (S1P) is extensively researched as a lysophospholipid and is crucial in various physiological and pathological processes. It achieves this via signalling through five different subtypes of G protein-coupled receptors (GPCRs), namely S1PR1 to S1PR5. S1PR modulators possess the ability to traverse the blood-brain barrier, potentially leading to direct actions within the Central Nervous System (CNS). S1PR modulators specifically bind to receptors located on the surface of naive and central memory lymphocytes, causing these cells to be trapped or confined within the lymph node. The investigation of the S1P pathway has resulted in the approval of three S1PR modulators, namely fingolimod, siponimod, and ozanimod, as medications for the treatment of patients suffering from Multiple Sclerosis (MS). Additionally, new S1PR modulators, such as ponesimod and etrasimod, are currently being developed and tested in clinical trials. Research on the creation of S1P modulators in neurodegenerative illnesses is ongoing as scientists continue to explore novel possibilities for selective S1P modulators. This study provides a concise overview of sphingolipid metabolism, the mechanism by which S1P receptors are affected, and the structural characteristics of several small molecule S1P modulators, with a particular focus on their structure-activity connections.

Brain Tissue Oxygen Dynamics Under Localised Hypoxia in the Awake State and the Physical Neuroprotective Effects of General Anaesthesia

Brain health directly depends on maintaining a level of tissue oxygen that is high enough to avoid global hypoxia and local brain ischaemia. It is well documented that general anaesthesia has an anti-hypoxic neuroprotective effect. Previous studies of this effect primarily assessed the biochemical actions of anaesthetics. Physical actions were not well studied because the quantification of oxygen dynamics has only recently been described. Based on known oxygen, blood, and neuronal measurements, under various anaesthesia protocols and in the awake state, we mathematically analysed physical anaesthesia effects on oxygen distribution for localised hypoxia. From this, we built a universal equation of oxygen dynamics which can be applied to both animal and human subjects in awake and anaesthetised states, under normoxia, hyperoxia, and hypoxia. Using this equation, we determined that a proper anaesthesia protocol can protect up to 167 mm3 of local hypoxic cortical brain tissue via oxygen diffusion from healthy neighbouring areas.

HIF-1, an important regulator in potential new therapeutic approaches to ischemic stroke

Ischemic stroke is a leading cause of disability and mortality worldwide due to the narrow therapeutic window of the only approved therapies like intravenous thrombolysis and thrombectomy. Hypoxia inducible factor-1α (HIF-1α) is a sensitive regulator of oxygen homeostasis, and its expression is rapidly induced after hypoxia/ischemia. It plays an extensive role in the pathophysiology of stroke by regulating multiple pathways including glucose metabolism, angiogenesis, neuronal survival, neuroinflammation and blood brain barrier regulation. Here, we give a brief overview of the HIF-1α-targeting strategies currently under investigation and summarise recent research on how HIF-1α is regulated in various brain cells, including neurons and microglia, at various stages in ischemic stroke. The roles of HIF-1 in stroke varies with ischemic time and degree of ischemia, are still up for debate. More focus has been placed on prospective HIF-1α targeting drugs, such as HIF-1α activator, HIF-1α stabilizers, and natural compounds. In this review, we have highlighted the regulation of HIF-1α in the novel therapeutic approaches for treatment of stroke.

Neuroprotection Is in the Air-Inhaled Gases on Their Way to the Neurons

Cerebral injury is a leading cause of long-term disability and mortality. Common causes include major cardiovascular events, such as cardiac arrest, ischemic stroke, and subarachnoid hemorrhage, traumatic brain injury, and neurodegenerative as well as neuroinflammatory disorders. Despite improvements in pharmacological and interventional treatment options, due to the brain's limited regeneration potential, survival is often associated with the impairment of crucial functions that lead to occupational inability and enormous economic burden. For decades, researchers have therefore been investigating adjuvant therapeutic options to alleviate neuronal cell death. Although promising in preclinical studies, a huge variety of drugs thought to provide neuroprotective effects failed in clinical trials. However, utilizing medical gases, noble gases, and gaseous molecules as supportive treatment options may offer new perspectives for patients suffering neuronal damage. This review provides an overview of current research, potentials and mechanisms of these substances as a promising therapeutic alternative for the treatment of cerebral injury.

Optimizing intraluminal monofilament model of ischemic stroke in middle-aged Sprague-Dawley rats

Intraluminal monofilament model of middle cerebral artery occlusion (MCAO) is widely adopted for ischemic stroke; and Sprague-Dawley (SD) rats are commonly used rodents for preclinical research. Due to the paucity of information on the appropriate monofilament size for inducing MCAO in SD rats and the importance of including middle-aged models in ischemic stroke studies, we aimed to: (i). determine an appropriate Doccol^® monofilament size for middle-aged male SD rats which weighed > 500 g following 24-h transient MCAO survival as well as (ii). demonstrate the optimal Doccol^® filament size for middle-aged males (≤ 500 g) and females (273-300 g) while using young adult male SD rats (372-472 g) as control for severity of infarct volume following 7-days post-MCAO. All rats were subjected to 90-min transient MCAO. We show that 0.43 mm Doccol^® monofilament size is more appropriate to induce large infarct lesion and optimal functional deficit when compared to 0.45 mm and 0.47 mm at 24 h post-MCAO. Our data on infarct volumes at 7 days post-MCAO as well as the observed weight loss and functional deficits at post-MCAO days 1, 3 and 7 demonstrate that 0.41 mm, 0.37 mm and 0.39 mm are optimal Doccol^® filament sizes for middle-aged male (477.3 ± 39.61 g) and female (302.6 ± 26.28 g) as well as young-adult male (362.2 ± 28.38 g) SD rats, respectively.

Somatosensory Cortical Electrical Stimulation After Reperfusion Attenuates Ischemia/Reperfusion Injury of Rat Brain

Objective: Ischemic stroke is an important cause of death and disability worldwide. Early reperfusion by thrombolysis or thrombectomy has improved the outcome of acute ischemic stroke. However, the therapeutic window for reperfusion therapy is narrow, and adjuvant therapy for neuroprotection is demanded. Electrical stimulation (ES) has been reported to be neuroprotective in many neurological diseases. In this study, the neuroprotective effect of early somatosensory cortical ES in the acute stage of ischemia/reperfusion injury was evaluated.

Methods: In this study, the rat model of transient middle cerebral artery occlusion was used to explore the neuroprotective effect and underlying mechanisms of direct primary somatosensory (S1) cortex ES with an electric current of 20 Hz, 2 ms biphasic pulse, 100 μA for 30 min, starting at 30 min after reperfusion.

Results: These results showed that S1 cortical ES after reperfusion decreased infarction volume and improved functional outcome. The number of activated microglia, astrocytes, and cleaved caspase-3 positive neurons after ischemia/reperfusion injury were reduced, demonstrating that S1 cortical ES alleviates inflammation and apoptosis. Brain-derived neurotrophic factor (BDNF) and phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway were upregulated in the penumbra area, suggesting that BDNF/TrkB signals and their downstream PI3K/Akt signaling pathway play roles in ES-related neuroprotection.

Conclusion: This study demonstrates that somatosensory cortical ES soon after reperfusion can attenuate ischemia/reperfusion injury and is a promising adjuvant therapy for thrombolytic treatment after acute ischemic stroke. Advanced techniques and devices for high-definition transcranial direct current stimulation still deserve further development in this regard.

NLRP3 Inflammasome: A Potential Target in Isoflurane Pretreatment Alleviates Stroke-Induced Retinal Injury in Diabetes

Ischemic stroke remains a devastating disease which is the leading cause of death worldwide. Visual impairment after stroke is a common complication which may lead to vision loss, greatly impacting life quality of patients. While ischemic stroke is traditionally characterized by a blockage of blood flow to the brain, this may coincide with reduced blood flow to the eye, resulting in retinal ischemia and leading to visual impairment. Diabetes increases the risk of ischemic stroke and induces diabetic retinopathy; the latter may be more sensitive to the ischemic retinal injury. In diabetic status, the underlying mechanism in stroke-induced retinal injury has not been fully clarified. The NLR pyrin domain containing 3 (NLRP3) inflammasome is an important activator of inflammation, which may play a critical role in catalyzing and forming certain pro-inflammatory cytokines in both cerebral and retinal ischemia. Isoflurane has been demonstrated to inhibit the activation of the NLRP3 inflammasome and show neuroprotective effects. In this study, we established a diabetic mouse model and performed the middle cerebral artery occlusion procedure to induce ischemic stroke. Our results revealed that cerebral ischemia-induced retinal injury in the diabetic model. Isoflurane pretreatment alleviated the cerebral and retinal injury after ischemic stroke. Of note, isoflurane pretreatment inhibited the NLRP3 inflammasome activation in the retina, indicating that isoflurane pretreatment may provide substantial retinal protection in stroke-induced retinal injury in diabetes.

Molecular Aspects of Volatile Anesthetic-Induced Organ Protection and Its Potential in Kidney Transplantation

Ischemia reperfusion injury (IRI) is inevitable in kidney transplantation and negatively impacts graft and patient outcome. Reperfusion takes place in the recipient and most of the injury following ischemia and reperfusion occurs during this reperfusion phase; therefore, the intra-operative period seems an attractive window of opportunity to modulate IRI and improve short- and potentially long-term graft outcome. Commonly used volatile anesthetics such as sevoflurane and isoflurane have been shown to interfere with many of the pathophysiological processes involved in the injurious cascade of IRI. Therefore, volatile anesthetic (VA) agents might be the preferred anesthetics used during the transplantation procedure. This review highlights the molecular and cellular protective points of engagement of VA shown in in vitro studies and in vivo animal experiments, and the potential translation of these results to the clinical setting of kidney transplantation.

Plasma ceramides are associated with outcomes in acute ischemic stroke patients

BACKGROUND/PURPOSE

Sphingolipids are major constituents of eukaryotic cell membranes and play key roles in cellular regulatory processes. Our recent results in an experimental stroke animal model demonstrated changes in sphingolipids in response to acute ischemic brain injury. This study aimed to investigate the plasma levels of sphingosine-1-phosphate (S1P) and ceramides in acute ischemic stroke (AIS) patients and their associations with functional outcomes.

METHODS

Plasma samples were collected from patients with AIS at <48 and 48-72 h post stroke and from nonstroke controls. The levels of S1P and ceramides with different fatty acyl chain lengths were measured by the ultra-high-pressure liquid chromatography-electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS). A poor functional outcome was defined as a modified Rankin Scale (mRS) score ≥2 at 3 months after AIS.

RESULTS

The results showed that S1P and very-long-chain ceramides were significantly decreased in AIS patients (n = 87; poor outcome, 56.3%) compared to nonstroke controls (n = 30). In contrast, long-chain ceramides were significantly increased in AIS patients. More importantly, higher levels of Cer(d18:1/18:0), Cer(d18:1/20:0), and Cer(d18:1/22:0) at 48-72 h were significantly associated with poor functional outcomes after adjusting for potential clinical confounders, including age, sex, hypertension, and National Institutes of Health Stroke Scale score at admission.

CONCLUSION

Our study supported the dynamic metabolism of sphingolipids after the occurrence of AIS. Ceramides could be potential prognostic markers for patients with AIS.

Subanesthetic isoflurane abates ROS-activated MAPK/NF-κB signaling to repress ischemia-induced microglia inflammation and brain injury

Isoflurane (ISO) elicits protective effects on ischemia-induced brain injury. We investigated whether sub-anesthetic (0.7%) ISO post-conditioning attenuates the inflammation and apoptosis in oxygen-glucose deprivation (OGD)-insulted co-cultures (microglia and neurons) in vitro and the brain injury of the middle cerebral arterial occlusion (MCAO) rat. We demonstrated that ISO augmented the viability of OGD-treated microglia and neurons. ISO reduced the expression and activation of COX2 and iNOS in OGD-challenged microglia. ISO repressed the production of tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-8, and monocyte chemoattractant protein-1 in OGD-exposed microglia. ISO also decreased nucleosomal fragmentation and caspase-3 activity but increased mitochondrial membrane potential in OGD-stimulated microglia and neurons. Mechanistically, ISO suppressed OGD-induced microglial inflammation by blocking ROS-regulated p38 MAPK/NF-κB signaling pathway and hampered OGD-triggered microglial apoptosis in a ROS- or NO-dependent fashion. In vivo results with MCAO rats were partly consistent with the in vitro observation. These findings indicate that sub-anesthetic ISO post-conditioning abates the inflammation and apoptosis in OGD-stimulated rat microglia and the apoptosis of OGD-exposed neurons and the brain injuries of MCAO rats, suggesting it as a potentially effective therapeutic approach for ischemic brain damages.

Sphingosine 1-phosphate signaling in ischemia and reperfusion injury

Ischemia and reperfusion injury is a complex hemodynamic pathological phenomenon that engages the metabolic to inflammatory machinery in development of disease conditions like heart failure, stroke and acute kidney failure. Target specific therapeutic approaches for ischemia reperfusion injury remains critical despite the extensive studies contributing to the understanding of its pathogenesis. Ischemic or pharmacological conditionings have been long established manipulations to harness the endogenous protective mechanisms against ischemia reperfusion injury that fostered the development of potential therapeutic targets such as sphingolipids signaling. Sphingosine 1-phosphate has been emerged as a crucial metabolite of sphingolipids to regulate the cell survival, vascular integrity and inflammatory cascades in ischemia reperfusion injury. Sphingosine 1-phosphate signaling process has been implicated to downgrade the mitochondrial dysfunction, apoptotic assembly along with upregulation of RISK and SAFE pro-survival pathways. It also regulates the endothelial dysfunction and immune cells behavior to control the vascular permeability and immune cells infiltration at ischemia reperfusion injury site. Targeting the signaling of this single moiety holds the vast potential to extensively influence the detrimental signaling of ischemia reperfusion injury. This review highlights the role and significance of S1P signaling that can be therapeutically exploit to treat ischemia reperfusion injury mediated pathological conditions in different organs.

Non-Mitogenic Fibroblast Growth Factor 1 Enhanced Angiogenesis Following Ischemic Stroke by Regulating the Sphingosine-1-Phosphate 1 Pathway

Ischemic strokes account for about 80% of all strokes and are associated with a high risk of mortality. Angiogenesis of brain microvascular endothelial cells may contribute to functional restoration following ischemia. Fibroblast growth factor 1 (FGF1), a member of FGF superfamily, involved in embryonic development, angiogenesis, wound healing, and neuron survival. However, the mitogenic activity of FGF1 is known to contribute to several human pathologies, thereby questioning the safety of its clinical applications. Here, we explored the effects and mechanism of action of non-mitogenic FGF1 (nmFGF1) on angiogenesis in mice after ischemia stroke and an oxygen-glucose deprivation (OGD)-induced human brain microvascular endothelial cells (HBMECs) injury model. We found that intranasal administration nmFGF1 significantly promoted angiogenesis in mice after stroke, and significantly increased the formation of matrigel tube and promoted scratch migration in a dose-dependent manner in OGD-induced HBMECs in vitro. However, the co-administration of an FGF receptor 1 (FGFR1)-specific inhibitor PD173074 significantly reversed the effects of nmFGF1 in vitro, suggesting that nmFGF1 functions via FGFR1 activation. Moreover, nmFGF1 activated sphingosine-1-phosphate receptor 1 (S1PR1, S1P1) in mice after stroke in vivo. S1P1 protein antagonist VPC23019 and agonist FTY720 were used to confirm that nmFGF1 promotes angiogenesis in vitro partially through the S1P1 pathway. OGD induced downregulation of S1P1 expression. The S1P1 antagonist VPC23019 blocked the stimulatory effects of nmFGF1, whereas the S1P1 agonist FTY720 exerted effects comparable with those of nmFGF1. Furthermore, PD173074 reversed the effect of nmFGF1 on upregulating S1P1 signaling. In conclusion, nmFGF1 enhanced angiogenesis in mice following stroke and OGD-induced HBMECs through S1P1 pathway regulation mediated via FGFR1 activation. This new discovery suggests the potential therapeutic role of nmFGF1 for the treatment of ischemic strokes.

Homer1a protects against neuronal injury via PI3K/AKT/mTOR signaling pathway

Purpose: Homer1a is a member of the post-synaptic density protein family that plays an important role in neuronal synaptic activity and is extensively involved in neurological disorders. The aim of this study is to investigate the role of Homer1a in modulating neuronal survival using an in vitro traumatic neuronal injury model.Materials and methods: Neurons were extracted from rats and identifited. Then, the cells were treated with Homerla overexpression or interference vectors. Western blot was performed to evaluate the expression of Homerla, apoptosis-related proteins(caspase3, caspase8, caspase9, Fasl, Bax, and p53), autophagy-related proteins (LC3ll and Beclin1), and the activiation of PI3K/AKT/mTOM pathway. In addition, the cell viability and apoptosis rate were measured. Results: After transfection with overexpression or interference vectors, the mRNA and protein expression of Homer1a increased or decreased significantly, respectively. Upregulation of Homer1a significantly alleviated apoptosis and enhanced cell viability and autophagy after traumatic neuronal injury. Homer1a overexpression also significantly decreased the expression of the pro-apoptosis proteins caspase 3, caspase 8, caspase 9, Fasl, Bax, and p53 in neurons. Furthermore, neuron autophagy was increased after traumatic neuronal injury as demonstrated by the greater accumulation of autophagosomes and higher expression of LC3II and Beclin1 induced by Homer1a overexpression. In addition, Homer1a overexpression inhibited the activation of PI3K/AKT/mTOR signaling. Conclusion: These findings indicated that Homer1a potentially protects neurons from traumatic injury by regulating apoptosis and autophagy via the caspase and PI3K/AKT/mTOR signaling pathways and may be an effective intervention target in traumatic brain injury.

Geniposide attenuates neonatal mouse brain injury after hypoxic-ischemia involving the activation of PI3K/Akt signaling pathway

Perinatal hypoxic-ischemia (HI) is a leading cause of acute mortality and neurologic complications in newborns. Geniposide, a natural product extracted from the herb Gardenia jasminoides, has been shown to possess neuroprotective effects in neurologic deficits. This study aims to investigate whether Geniposide has therapeutic potential to HI brain injury and the underlying mechanisms. C57/bl6 mice were subjected to HI insult on postnatal day 10. Geniposide (20 mg/kg b.w.) was administered intragastrically every day after HI insult for 7 successional days. Then mice at P18 were sacrificed and brain tissues were collected for further analysis. Geniposide treatment significantly inhibited cell apoptosis, reduced serum IgG leakage into brain tissue, attenuated astrogliosis and microgliosis, prevented loss of pericytes, loss of tight junction and adherens junction proteins. The PI3K/Akt signaling pathway, which related proteins were downregulated after HI insult, was activated by Geniposide treatment. Geniposide treatment after neonatal HI insult attenuated HI-induced cell apoptosis, IgG leakage, microgliosis, astrogliosis, pericytes loss and junction protein degradation. Geniposide could protect against HI-induced brain injury, which might be through the activation of PI3K/Akt signaling pathway.

Sphingosine 1-Phosphate Receptors and Metabolic Enzymes as Druggable Targets for Brain Diseases

The central nervous system is characterized by a high content of sphingolipids and by a high diversity in terms of different structures. Stage- and cell-specific sphingolipid metabolism and expression are crucial for brain development and maintenance toward adult age. On the other hand, deep dysregulation of sphingolipid metabolism, leading to altered sphingolipid pattern, is associated with the majority of neurological and neurodegenerative diseases, even those totally lacking a common etiological background. Thus, sphingolipid metabolism has always been regarded as a promising pharmacological target for the treatment of brain disorders. However, any therapeutic hypothesis applied to complex amphipathic sphingolipids, components of cellular membranes, has so far failed probably because of the high regional complexity and specificity of the different biological roles of these structures. Simpler sphingosine-based lipids, including ceramide and sphingosine 1-phosphate, are important regulators of brain homeostasis, and, thanks to the relative simplicity of their metabolic network, they seem a feasible druggable target for the treatment of brain diseases. The enzymes involved in the control of the levels of bioactive sphingoids, as well as the receptors engaged by these molecules, have increasingly allured pharmacologists and clinicians, and eventually fingolimod, a functional antagonist of sphingosine 1-phosphate receptors with immunomodulatory properties, was approved for the therapy of relapsing-remitting multiple sclerosis. Considering the importance of neuroinflammation in many other brain diseases, we would expect an extension of the use of such analogs for the treatment of other ailments in the future. Nevertheless, many aspects other than neuroinflammation are regulated by bioactive sphingoids in healthy brain and dysregulated in brain disease. In this review, we are addressing the multifaceted possibility to address the metabolism and biology of bioactive sphingosine 1-phosphate as novel targets for the development of therapeutic paradigms and the discovery of new drugs.

Callistephin enhances the protective effects of isoflurane on microglial injury through downregulation of inflammation and apoptosis

Microglia are the major immune cells in the central nervous system. Microglial activation can be beneficial or detrimental depending on the stimuli and the physiopathological environment. Microglial activation is involved in a variety of neurodegenerative disorders. Different anesthetic agents have exhibited diverse effects on microglial activation and the engulfment process. The anthocyanin callistephin has been demonstrated to have antioxidant and anti‑inflammatory properties, and these were assessed in the present study, with a focus on its effect on microglial activation. Mouse microglial cells C8‑4B were treated with 100 ng/µl lipopolysaccharide (LPS) and 1 ng/µl interferon‑γ. Cells were subsequently treated with 2% isoflurane, 100 µM callistephin or both. LPS promoted apoptosis in C8‑B4 cells, and this was reduced following treatment with isoflurane and callistephin. LPS‑treated C8‑B4 cells also exhibited enhanced production of reactive oxygen species and nitric oxide, excessive engulfment and increased caspase 3/7 activity. These detrimental alterations were suppressed following co‑treatment with isoflurane and callistephin. LPS‑induced apoptosis was facilitated via the expression of B‑cell lymphoma‑2 like 1 and poly (ADP‑ribose) polymerase, which were subsequently restored following treatment with isoflurane and callistephin. Callistephin was demonstrated to be involved in the modulation of inducible nitric oxide synthase, cytochrome c oxidase subunit 2, tumor necrosis factor‑α and nuclear factor‑κ B. Callistephin enhanced the protective effects of isoflurane by modulating engulfment and apoptosis in C8‑B4 cells. The potential underlying mechanism was identified to be the suppression of p38 phosphorylation. The present study thus suggested that the negative effects on microglial activity induced by LPS were ameliorated following treatment with callistephin, which also enhanced the effects of isoflurane. Callistephin may therefore constitute a candidate drug agent that may target inflammatory and growth regulatory signaling pathways, thus ameliorating certain aspects of neurodegenerative diseases.

Silencing MicroRNA-134 Alleviates Hippocampal Damage and Occurrence of Spontaneous Seizures After Intraventricular Kainic Acid-Induced Status Epilepticus in Rats

Epilepsy is a disorder of abnormal brain activity typified by spontaneous and recurrent seizures. MicroRNAs (miRNAs) are short non-coding RNAs, critical for the post-transcriptional regulation of gene expression. MiRNA dysregulation has previously been implicated in the induction of epilepsy. In this study, we examined the effect of silencing miR-134 against status epilepticus (SE). Our results showed that level of miR-134 was significantly up-regulated in rat brain after Kainic acid (KA)-induced SE. TUNEL staining showed that silencing miR-134 alleviated seizure-induced neuronal apoptosis in the CA3 subfield of the hippocampus. Western blot showed that a miR-134 antagonist suppressed lesion-induced endoplasmic reticulum (ER) stress and apoptosis related expression of CHOP, Bim and Cytochrome C, while facilitated the expression of CREB at 24 h post KA-induced lesion in the hippocampus. Consistently, silencing miR-134 significantly diminished loss of CA3 pyramidal neurons using Nissl staining as well as reducing aberrant mossy fiber sprouting (MFS) in a rat epileptic model. In addition, the results of EEG and behavior analyses showed seizures were alleviated by miR-134 antagonist in our experimental models. These results suggest that silencing miR-134 modulates the epileptic phenotype by upregulating its target gene, CREB. This in turn attenuates oxidative and ER stress, inhibits apoptosis, and decreases MFS long term. This indicates that silencing miR-134 might be a promising intervention for the treatment of epilepsy.

Inhibition of the PI3K/Akt signaling pathway impedes the restoration of neurological function following hypoxic-ischemic brain damage in a neonatal rabbit model

OBJECTIVE

Hypoxic-ischemic brain damage (HIBD), frequently occurring in infancy and childhood, is a major cause of mortality and severe neurologic impairment. This study was performed to examine the effect of the PI3K/Akt signaling pathway on HIBD in a neonatal rabbit model.

MATERIALS AND METHODS

Uterine artery occlusion was used to establish HIBD models in neonatal rabbits, which were then subjected to sham operation, dimethyl sulfoxide (2 mL) or LY294002 (inhibitor of PI3K/Akt signaling pathway, 6.4 μg/kg). Behavioral neurological assessment was performed in neonatal rabbits delivered by cesarean section, after which serum neuron-specific enolase (NSE) level and cerebral water content were determined. The level of cleaved caspase-3 level and apoptosis of neurons were observed by immunohistochemistry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining. Furthermore, the expression of PI3K/Akt signaling pathway- and apoptosis-related factors was examined.

RESULTS

In neonatal rabbits, HIBD increased the fetal death rate; reduced neurological scores of posture, righting reflex, and deglutition reflex; elevated serum NSE levels, cerebral water content, cleaved caspase-3-positive expression in hippocampal CA1 region and apoptotic neurons; inactivated PI3K/Akt signaling pathway as well as reduced Bcl-2 expression and increased BAD and Bax expression. Notably, the treatment of LY294002 further aggravated neurological impairment in neonatal rabbits in response to HIBD.

CONCLUSION

Following the HIBD caused by intrauterine asphyxia, the LY294002 administered through auricular vein infusion into pregnant rabbits exacerbates neurological impairment of neonatal rabbits, suggesting that inhibition of PI3K/Akt signaling pathway may serve as a candidate therapeutic target for neurological recovery.

Developing a standardized system of exposure and intervention endpoints for isoflurane in preclinical stroke models

Isoflurane is a regularly used anesthetic in translational research. Isoflurane facilitates invasive surgery and a rapid recovery. Specifically, in the pathology of stroke, controversy has surrounded isoflurane's intrinsic neuroprotective abilities, affecting apoptosis, excitotoxicity, and blood brain barrier disruption. Due to the intrinsic neuroprotective nature and lack of standardized guidelines for the use of isoflurane, research has shifted away from this gas in most animal models. Antagonistically, studies have also reported that no neuroprotective effects are observed when a surgery is accompanied with isoflurane exposure under 20 minutes. Isoflurane affects the pathophysiology in stroke patients by altering critical pathways in endothelial, neuronal, and microglial cells. Current studies have elucidated isoflurane neuroprotection to be time dependent and may be minimized in experimental designs if the exposure time is limited to a specific window. Therefore, with detailed and extensive literature on anesthetics, we can hypothesize that isoflurane exposure under the 20-minute benchmark, behavior and molecular pathways can be evaluated at any time-point following ischemic insult without confounding artifacts from isoflurane; however, If the exposure to isoflurane exceeds 20 minutes, the acute neuroprotective effects are evident for 2 weeks in the model, which should be accounted for in molecular and behavioral assessments, with either isoflurane inhibitors or a control group at 2 weeks post middle cerebral artery occlusion. The purpose of this review is to suggest a detailed and standardized outline for interventions and behavioral assessments after the use of isoflurane in experimental designs.

Effects of ADAM2 silencing on isoflurane-induced cognitive dysfunction via the P13K/Akt signaling pathway in immature rats

Volatile anesthetics, including isoflurane, have been reported to have negative effects on cognitive dysfunction characterized by cognitive deficits following anesthesia. The aim of the current study was to investigate the effects involved with disintegrin and metallopeptidase domain 2 (ADAM2) silencing on isoflurane-induced cognitive dysfunction via the P13 K/Akt signaling pathway in immature rats. One week old healthy Sprague-Dawley (SD) rats were recruited and administered isoflurane anesthesia. The rats were then subjected to shADAM2 or wortmannin (PI3K/Akt signaling pathway inhibitor) to identify the effects of ADAM2 and the PI3K/Akt signaling pathway on the cognitive function of rats. Morris water maze and passive-avoidance tests were performed to examine the cognitive function of the rats. TUNEL staining was conducted to detect neuronal apoptosis in the hippocampal CA1 region. The obtained experimental results demonstrated that isoflurane anesthesia led to increased escape latency, reaction time, number of errors and TUNEL-positive neurons, along with a decreased latency time. In response to treatment with shADAM2, escape latency, reaction time, number of errors and TUNEL-positive cells were all noted to have decreased, in addition to elevated latency time, while contrasting trends were observed in regard to treatment with wortmannin. Taken together, the key findings of the present study revealed that shADAM2 activated the PI3K/Akt signaling pathway, resulting in elevated expressions of PI3K and Akt. Our study ultimately identified that ADAM2 silencing alleviates isoflurane-induced cognitive dysfunction by activating the P13 K/Akt signaling pathway in immature rats.

A companion to the preclinical common data elements on neurobehavioral comorbidities of epilepsy: a report of the TASK3 behavior working group of the ILAE/AES Joint Translational Task Force

The provided companion has been developed by the Behavioral Working Group of the Joint Translational Task Force of the International League Against Epilepsy (ILAE) and the American Epilepsy Society (AES) with the purpose of assisting the implementation of Preclinical Common Data Elements (CDE) for studying and for reporting neurobehavioral comorbidities in rodent models of epilepsy. Case Report Forms (CRFs) are provided, which should be completed on a per animal/per test basis, whereas the CDEs are a compiled list of the elements that should be reported. This companion is not designed as a list of recommendations, or guidelines for how the tests should be run-rather, it describes the different types of assessments, and highlights the importance of rigorous data collection and transparency in this regard. The tests are divided into 7 categories for examining behavioral dysfunction on the syndrome level: deficits in learning and memory; depression; anxiety; autism; attention deficit/hyperactivity disorder; psychosis; and aggression. Correspondence and integration of these categories into the National Institute of Mental Health (NIMH) Research Domain Criteria (RDoC) is introduced. Developmental aspects are addressed through the introduction of developmental milestones. Discussion includes complexities, limitations, and biases associated with neurobehavioral testing, especially when performed in animals with epilepsy, as well as the importance of rigorous data collection and of transparent reporting. This represents, to our knowledge, the first such resource dedicated to preclinical CDEs for behavioral testing of rodents.

A Mild Traumatic Brain Injury in Mice Produces Lasting Deficits in Brain Metabolism

Metabolic uncoupling has been well-characterized during the first minutes-to-days after a traumatic brain injury (TBI), yet mitochondrial bioenergetics during the weeks-to-months after a brain injury is poorly defined, particularly after a mild TBI. We hypothesized that a closed head injury (CHI) would be associated with deficits in mitochondrial bioenergetics at one month after the injury. A significant decrease in state-III (adenosine triphosphate production) and state-V (complex-I) driven mitochondrial respiration was found at one month post-injury in adult C57Bl/6J mice. Isolation of synaptic mitochondria demonstrated that the deficit in state-III and state-V was primarily neuronal. Injured mice had a temporally consistent deficit in memory recall at one month post-injury. Using proton magnetic resonance spectroscopy (¹H MRS) at 7-Tesla, we found significant decreases in phosphocreatine, N-Acetylaspartic acid, and total choline. We also found regional variations in cerebral blood flow, including both hypo- and hyperperfusion, as measured by a pseudocontinuous arterial spin labeling MR sequence. Our results highlight a chronic deficit in mitochondrial bioenergetics associated with a CHI that may lead toward a novel approach for neurorestoration after a mild TBI. MRS provides a potential biomarker for assessing the efficacy of candidate treatments targeted at improving mitochondrial bioenergetics.

PR-957 mediates neuroprotection by inhibiting Th17 differentiation and modulating cytokine production in a mouse model of ischaemic stroke

Acute ischaemic stroke can induce secondary brain injury by activating an inflammatory response that contributes to clinical impairment. As a specific inhibitor of the immunoproteasome subunit low molecular weight polypeptide 7 (LMP7), PR-957 may participate in regulating pathophysiological and inflammatory responses in multiple diseases of the central nervous system (CNS). We investigated the neuroprotective properties of PR-957 in a mouse model of stroke, induced by middle cerebral artery occlusion (MCAO). After MCAO and injections of PR-957 or vehicle, we evaluated mice behaviourally using modified Neurological Severity Scores (mNSS) and sensorimotor tests, including the adhesive-removal test, a foot-fault test and an inclined plane test. Infarct volume was measured 24 and 72 h after MCAO. Infiltration by different lymphocyte subpopulations was evaluated by flow cytometry and immunofluorescent staining of brain tissue from the penumbral area. Quantitative real-time polymerase chain reaction analysis and enzyme-linked immunosorbent assay were used to measure the expression of proinflammatory cytokines: interkeukin (IL)-1α, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12, IL-17A, interferon (IFN)-γ, tumour necrosis factor (TNF)-α, granulocyte colony-stimulating factor (GCSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Expression of phosphorylated signal transducer and activator of transcription 3 (pSTAT-3) protein levels in brain was measured by immunoblot. MCAO mice treated with PR-957 showed a significant decrease in infarct volume and had mild neurological deficits compared to vehicle-treated mice. PR-957 administration also significantly decreased IL-1β, IL-6, IL-12, IL-17A and TNF-α. PR-957 provides neuroprotection via inhibiting T lymphocyte infiltration and decreasing T helper type 17 (Th17) cell differentiation in MCAO mice, which may result from the reduced expression of pSTAT-3. The neuroprotective effect of PR-957 indicates its potential utility as anti-inflammatory therapy for ischaemic stroke.

S100β in newborns after C-section with general vs. epidural anesthesia: a prospective observational study

BACKGROUND

Preclinical evidence suggests that general anesthetics can dose dependently induce neurodegeneration in the developing brains of animals which can be reliably determined by measurement of blood S100β, but this correlation remains unclear in humans. We hypothesized that S100β would not be increased in cord arterial blood of fetuses exposed briefly to general anesthetics during a C-section, compared with epidural anesthesia.

METHODS

A prospective observational clinical study comparatively measured changes of brain damage biomarker S100β ratio of umbilical artery over vein (changes after fetus circulation) immediately after delivery under C-section with either epidural or general anesthesia. Newborn blood gas measurements, APGAR scores, and maternal well-being were also compared.

RESULTS

Compared with epidural anesthesia, general anesthesia resulted in the lower S100β ratio of umbilical artery over the vein (medium 2.64 [quartiles 1.39, 3.45] vs. medium 1.59 [quartiles 0.88, 2.01], P = 0.031), without changing the S100β level in the vein of the mother. There was no significant difference between general and epidural anesthesia when comparing other maternal and newborn parameters.

CONCLUSION

S100β levels in newborn after C-section is lower with general anesthesia than epidural anesthesia, with unclear mechanisms.

Resveratrol post-treatment protects against neonatal brain injury after hypoxia-ischemia

Neonatal hypoxic-ischemic brain injury is a devastating disease with limited treatment options. Preventive treatment with resveratrol has indicated to be well tolerated and has lower toxicity in both experimental models and human patients. However, whether resveratrol administration post-hypoxic-ischemic protects against neonatal hypoxic-ischemic injury is not known. Here we reported that post-treatment with resveratrol significantly reduced brain damage at 7-day after the injury. We found that resveratrol reduced the expression levels of key inflammatory factors at the mRNA and protein levels, and at least partially via inhibiting microglia activation. Moreover, resveratrol exerted an anti-apoptotic effect, as assessed by TUNEL staining, and altered the expression of the apoptosis-related genes Bax, Bcl-2 and caspase3. Our data indicate that post-treatment with resveratrol protects against neonatal hypoxic-ischemic brain injury and suggest a promising therapeutic strategy to this disease.

IRE1α inhibition decreased TXNIP/NLRP3 inflammasome activation through miR-17-5p after neonatal hypoxic-ischemic brain injury in rats

Background

The endoplasmic reticulum (ER) is responsible for the control of correct protein folding and protein function which is crucial for cell survival. However, under pathological conditions, such as hypoxia–ischemia (HI), there is an accumulation of unfolded proteins thereby triggering the unfolded protein response (UPR) and causing ER stress which is associated with activation of several stress sensor signaling pathways, one of them being the inositol requiring enzyme-1 alpha (IRE1α) signaling pathway. The UPR is regarded as a potential contributor to neuronal cell death and inflammation after HI. In the present study, we sought to investigate whether microRNA-17 (miR-17), a potential IRE1α ribonuclease (RNase) substrate, arbitrates downregulation of thioredoxin-interacting protein (TXNIP) and consequent NLRP3 inflammasome activation in the immature brain after HI injury and whether inhibition of IRE1α may attenuate inflammation via miR-17/TXNIP regulation.

Methods

Postnatal day 10 rat pups (n = 287) were subjected to unilateral carotid artery ligation followed by 2.5 h of hypoxia (8% O₂). STF-083010, an IRE1α RNase inhibitor, was intranasally delivered at 1 h post-HI or followed by an additional one administration per day for 2 days. MiR-17-5p mimic or anti-miR-17-5p inhibitor was injected intracerebroventricularly at 48 h before HI. Infarct volume and body weight were used to evaluate the short-term effects while brain weight, gross and microscopic brain tissue morphologies, and neurobehavioral tests were conducted for the long-term evaluation. Western blots, immunofluorescence staining, reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR), and co-immunoprecipitation (Co-IP) were used for mechanism studies.

Results

Endogenous phosphorylated IRE1α expression was significantly increased after HI. Intranasal administration of STF-083010 alleviated brain injury and improved neurological behavior. MiR-17-5p expression was reduced after HI, and this decrease was attenuated by STF-083010 treatment. MiR-17-5p mimic administration ameliorated TXNIP expression, NLRP3 inflammasome activation, caspase-1 cleavage, and IL-1β production, as well as brain infarct volume. Conversely, anti-miR-17-5p inhibitor reversed IRE1α inhibition-induced decrease in TXNIP expression and inflammasome activation, as well as exacerbated brain injury after HI.

Conclusions

IRE1a-induced UPR pathway may contribute to inflammatory activation and brain injury following neonatal HI. IRE1a activation, through decay of miR-17-5p, elevated TXNIP expression to activate NLRP3 inflammasome and aggravated brain damage.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1077-9) contains supplementary material, which is available to authorized users.

Remote ischemic postconditioning confers neuroprotective effects via inhibition of the BID-mediated mitochondrial apoptotic pathway

Ischemic postconditioning has been demonstrated to alleviate brain ischemia/reperfusion-induced neuronal apoptosis; however, the protective mechanisms underlying the improved and more convenient method of remote ischemic postconditioning (RIPostC) are only recently beginning to be elucidated. Mitochondria are important in the regulation of cell apoptosis, and the B-cell lymphoma 2 (Bcl-2) homology 3 interacting-domain death agonist (BID) promotes the insertion/oligomerization of Bcl-2-associated X protein into the mitochondrial outer membrane, leading to the release of proapoptotic proteins from the mitochondria. The present study hypothesized that RIPostC targets the BID-mediated mitochondrial apoptotic pathway to exert neuroprotective effects, and the optimal time window for RIPostC application was investigated. RIPostC was conducted as follows: Three 10-min cycles of bilateral femoral artery occlusion with intervals of 10 min reperfusion after 0, 10 or 30 min of brain reperfusion. The results revealed that reperfusion induced significant activation of BID, via proteolytic cleavage and translocation to the mitochondria, as determined using western blot analysis and immunofluorescence staining. Mitochondrial release of cytochrome c was additionally detected during BID activation, all of which were inhibited by the application of RIPostC. When RIPostC was applied during reperfusion, it demonstrated a significant protective effect. Furthermore, the infarct volume, neurological function and the degree of neuronal apoptosis were improved with application of RIPostC. These results suggested that the protective mechanisms of RIPostC may be associated with inhibition of the BID-mediated mitochondrial apoptotic pathway, which may act as a potential molecular target for therapeutic intervention in the future.

Emulsified isoflurane postconditioning improves survival and neurological outcomes in a rat model of cardiac arrest

Emulsified isoflurane (EIso) has a protective effect against ischemia/reperfusion (I/R) injury in animal models. However, the protective effects of EIso on global cerebral I/R injury remain unclear. The present study aimed to investigate whether EIso postconditioning was able to improve survival and neurological outcomes in a rat model of cardiac arrest (CA). Rats were randomly divided into five groups, namely the control, EIso-2ml, EIso-4ml, isoflurane (Iso) and emulsion (E) groups. All rats were resuscitated by a standardized method following 6 min of asphyxia. Furthermore, all interventions were administered immediately following the return of spontaneous circulation (ROSC). The animal survival was recorded daily, and evaluations of behavioral and brain morphology were assessed at 1 and 7 days after ROSC. The results showed that EIso treatment increased the survival rate 7 days after ROSC, with a 41.7% 7-day survival in the EIso-2ml group, 66.7% in the EIso-4ml group and 50% in the Iso group compared with 33.3% survival in the control and E groups. Moreover, the neural deficit score and memory function were improved in the EIso-4ml group, and this treatment also ameliorated brain hippocampal cell injury and apoptosis. In addition, a better brain protective effect was observed in the EIso-4ml group compared with the EIso-2ml, Iso and E groups. In summary, the data of the present study suggest that EIso postconditioning improved the survival and neurological outcomes following CA in a dose-dependent manner.

Neuroprotection provided by isoflurane pre-conditioning and post-conditioning

Isoflurane, a volatile and inhalational anesthetic, has been extensively used in perioperative period for several decades. A large amount of experimental studies have indicated that isoflurane exhibits neuroprotective properties when it is administrated before or after (pre-conditioning and post-conditioning) neurodegenerative diseases (e.g., hypoxic ischemia, stroke and trauma). Multiple mechanisms are involved in isoflurane induced neuroprotection, including activation of glycine and γ-aminobutyric acid receptors, antagonism of ionic channels and alteration of the function and activity of other cellular proteins. Although neuroprotection provided by isoflurane is observed in many animal studies, convincing evidence is lacking in human trials. Therefore, there is still a long way to go before translating its neuroprotective properties into clinical practice.

Isoflurane Postconditioning Inhibits tPA-Induced Matrix Metalloproteinases Activation After Hypoxic Injury via Low-Density Lipoprotein Receptor-Related Protein and Extracellular Signal-Regulated Kinase Pathway

Tissue plasminogen activator (tPA) is the only recommended pharmacological treatment for acute ischemic stroke. However, tPA can induce intracerebral hemorrhage by blood-brain barrier breakdown through an increase in matrix metalloproteinases (MMPs). Previously, we showed that isoflurane postconditioning reduced intracranial hemorrhage following tPA treatment after cerebral ischemia. Here, we investigated the mechanism by which isoflurane postconditioning reduces tPA-induced MMP-2 and MMP-9 activation following hypoxia/reoxygenation (H/R) in brain endothelial cells. Mouse brain endothelial cells (bEnd.3) were exposed to 6 h of oxygen-glucose deprivation and 3 h of reoxygenation with tPA. Cells were treated with isoflurane for 1 h of the reoxygenation condition and the effect of isoflurane postconditioning on MMP-2 and MMP-9 activation was assessed. Involvement of low-density lipoprotein receptor-related protein (LRP), which is a receptor for tPA, and the extracellular signal-regulated kinase (ERK) and NF-κB pathway in isoflurane postconditioning was assessed using LRP inhibitor (receptor-associated protein, RAP) and ERK-1/2 inhibitor (PD98059). Isoflurane postconditioning decreased tPA-induced MMP-2 and MMP-9 activation under H/R. tPA treatment under H/R increased expression of LRP and the active form of NF-κB. Isoflurane postconditioning suppressed LRP expression, increased ERK-1/2 activation, and suppressed MMP-2 and MMP-9 activation, comparable to the effect of RAP. Activation of ERK-1/2, inhibition of NF-κB activation, and suppression of MMP-2 and MMP-9 activation by isoflurane postconditioning were abolished with PD98059 treatment. These finding indicate that isoflurane postconditioning inhibits tPA-induced MMP-2 and MMP-9 activation following H/R via the LRP/ERK/NF-κB pathway in bEnd.3.

Blood -brain barrier disruption was less under isoflurane than pentobarbital anesthesia via a PI3K/Akt pathway in early cerebral ischemia

One of the important factors altering the degree of blood-brain barrier (BBB) disruption in cerebral ischemia is the anesthetic used. The phosphoinositide 3-kinase (PI3K)/Akt signaling pathway has been reported to be involved in modulating BBB permeability and in isoflurane induced neuroprotection. This study was performed to compare the degree of BBB disruption in focal cerebral ischemia under isoflurane vs pentobarbital anesthesia and to determine whether inhibition of PI3K/Akt would affect the disruption in the early stage of focal cerebral ischemia. Permanent middle cerebral artery (MCA) occlusion was performed in rats under 1.4% isoflurane or pentobarbital (50mg/kg i.p.) anesthesia with controlled ventilation. In half of each group LY294002, which is a PI3K/Akt inhibitor, was applied on the ischemic cortex immediately after MCA occlusion. After one hour of MCA occlusion, the transfer coefficient (K_i) of ¹⁴C-α-aminoisobutyric acid (¹⁴C-AIB) was determined to quantify the degree of BBB disruption. MCA occlusion increased the K_i both in the isoflurane and pentobarbital anesthetized rats. However, the value of K_i was lower under isoflurane (11.5±6.0μL/g/min) than under pentobarbital (18.3±7.1μL/g/min) anesthesia. The K_i of the contralateral cortex of the pentobarbital group was higher (+74%) than that of the isoflurane group. Application of LY294002 on the ischemic cortex increased the K_i (+99%) only in the isoflurane group. The degree of BBB disruption by MCA occlusion was significantly lower under isoflurane than pentobarbital anesthesia in the early stage of cerebral ischemia. Our data demonstrated the importance of choice of anesthetics and suggest that PI3K/Akt signaling pathway plays a significant role in altering BBB disruption in cerebral ischemia during isoflurane but not during pentobarbital anesthesia.

[Isoflurane provides neuroprotection in neonatal hypoxic ischemic brain injury by suppressing apoptosis]

BACKGROUND AND OBJECTIVES

Isoflurane is halogenated volatile ether used for inhalational anesthesia. It is widely used in clinics as an inhalational anesthetic. Neonatal hypoxic ischemia injury ensues in the immature brain that results in delayed cell death via excitotoxicity and oxidative stress. Isoflurane has shown neuroprotective properties that make a beneficial basis of using isoflurane in both cell culture and animal models, including various models of brain injury. We aimed to determine the neuroprotective effect of isoflurane on hypoxic brain injury and elucidated the underlying mechanism.

METHODS

A hippocampal slice, in artificial cerebrospinal fluid with glucose and oxygen deprivation, was used as an in vitro model for brain hypoxia. The orthodromic population spike and hypoxic injury potential were recorded in the CA1 and CA3 regions. Amino acid neurotransmitters concentration in perfusion solution of hippocampal slices was measured.

RESULTS

Isoflurane treatment caused delayed elimination of population spike and improved the recovery of population spike; decreased frequency of hypoxic injury potential, postponed the onset of hypoxic injury potential and increased the duration of hypoxic injury potential. Isoflurane treatment also decreased the hypoxia-induced release of amino acid neurotransmitters such as aspartate, glutamate and glycine induced by hypoxia, but the levels of γ-aminobutyric acid were elevated. Morphological studies showed that isoflurane treatment attenuated edema of pyramid neurons in the CA1 region. It also reduced apoptosis as evident by lowered expression of caspase-3 and PARP genes.

CONCLUSIONS

Isoflurane showed a neuro-protective effect on hippocampal neuron injury induced by hypoxia through suppression of apoptosis.

Class I PI3K inhibitor ZSTK474 mediates a shift in microglial/macrophage phenotype and inhibits inflammatory response in mice with cerebral ischemia/reperfusion injury

Background

Microglia/macrophages play a critical role in the inflammatory and immune processes of cerebral ischemia/reperfusion injury. Since microglia/macrophages can reversibly shift their phenotype toward either a “detrimental” or a “restorative” state in the injured central nervous system (CNS), compounds mediate that shift which could inhibit inflammation and restore the ability to alleviate cerebral ischemia/reperfusion injury would have therapeutic potential.

Methods

Transient middle cerebral artery occlusion was induced in male C57BL/6 mice. Mice were randomly separated into a sham-operated group, a control group, and a ZSTK474-treated group. We investigated the effect of ZSTK474 by assessing neurological deficits, infarct volume, and histopathological changes. We then determined the potential mechanism by immunofluorescent staining, quantitative real-time polymerase chain reaction (PCR), and Western blot analysis. The Tukey’s test or Mann–Whitney U test was used to compare differences among the groups.

Results

ZSTK474 alleviated neurological deficits and reduced infarct volume in the cerebral ischemia/reperfusion injury model. Presumably, ZSTK474 shifted the phenotype of microglia/macrophages to a restorative state, since this treatment decreased the secretion of pro-inflammatory factors and advanced the secretion of anti-inflammatory factors. These neuroprotective properties of ZSTK474 may be mediated by the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin complex 1 (mTORC1) pathway.

Conclusions

ZSTK474 can mediate a shift in microglia/macrophage phenotype and inhibit the inflammatory response in cerebral ischemia reperfusion injury of mice. These effects appeared to ensue via the PI3K/AKT/mTORC1 pathway. Therefore, ZSTK474 may represent a therapeutic intervention with potential for circumventing the catastrophic aftermath of ischemic stroke.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0660-1) contains supplementary material, which is available to authorized users.

Critical Role of the Sphingolipid Pathway in Stroke: a Review of Current Utility and Potential Therapeutic Targets

Sphingolipids are a series of cell membrane-derived lipids which act as signaling molecules and play a critical role in cell death and survival, proliferation, recognition, and migration. Sphingosine-1-phosphate acts as a key signaling molecule and regulates lymphocyte trafficking, glial cell activation, vasoconstriction, endothelial barrier function, and neuronal death pathways which plays a critical role in numerous neurological conditions. Stroke is a second leading cause of death all over the world and effective therapies are still in great demand, including ischemic stroke and hemorrhagic stroke as well as poststroke repair. Significantly, sphingolipid activities change after stroke and correlate with stroke outcome, which has promoted efforts to testify whether the sphingolipid pathway could be a novel therapeutic target in stroke. The sphingolipid metabolic pathway, the connection between the pathway and stroke, as well as therapeutic interventions to manipulate the pathway to reduce stroke-induced brain injury are discussed in this review.

Isoflurane reduces oxygen-glucose deprivation-induced oxidative, inflammatory, and apoptotic responses in H9c2 cardiomyocytes

Isoflurane (ISO) protects the heart from hypoxia-reperfusion injury. However, the molecular mechanisms of ISO in oxygen-glucose deprivation (OGD)-induced H9c2 cardiomyocyte injury is yet to be understood. Using H9c2 cells cultured in vitro, we examined the cytotoxicity of different doses of ISO (0.7%, 1.4%, and 2.1%) to H9c2 cells and found that 2.1% ISO had significant toxicity to the cell. Thus, 1.4% ISO was selected for the subsequent experiments. ISO notably ameliorated cell viability loss, lactate dehydrogenase release, and creatine kinase activity of H9c2 cells that were treated with OGD. ISO suppressed OGD-induced pro-inflammatory tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-8 production, and nuclear factor (NF)-κB activation in H9c2 cells. ISO reduced the reactive oxygen species and malondialdehyde generation, but it enhanced the superoxide dismutase activity in OGD-stimulated H9c2 cells. In addition, diminished OGD-induced cell apoptosis and preserved mitochondrial membrane potential were observed in ISO-treated H9c2 cells. ISO markedly up-regulated the anti-apoptotic Bcl-2 expression but inhibited the pro-apoptotic expressions of Bax, procaspase-3, cleaved caspase-3, and caspase-3 activity. Mechanistically, the cardioprotective effects of ISO on OGD-induced H9c2 cell injury were mediated by the Akt signaling pathway. These findings suggest that ISO alleviates OGD-induced H9c2 cell injury and may therefore be used to prevent and treat ischemic heart diseases.

Isoflurane provides neuroprotection in neonatal hypoxic ischemic brain injury by suppressing apoptosis

BACKGROUND AND OBJECTIVES

Isoflurane is halogenated volatile ether used for inhalational anesthesia. It is widely used in clinics as an inhalational anesthetic. Neonatal hypoxic ischemia injury ensues in the immature brain that results in delayed cell death via excitotoxicity and oxidative stress. Isoflurane has shown neuroprotective properties that make a beneficial basis of using isoflurane in both cell culture and animal models, including various models of brain injury. We aimed to determine the neuroprotective effect of isoflurane on hypoxic brain injury and elucidated the underlying mechanism.

METHODS

A hippocampal slice, in artificial cerebrospinal fluid with glucose and oxygen deprivation, was used as an in vitro model for brain hypoxia. The orthodromic population spike and hypoxic injury potential were recorded in the CA1 and CA3 regions. Amino acid neurotransmitters concentration in perfusion solution of hippocampal slices was measured.

RESULTS

Isoflurane treatment caused delayed elimination of population spike and improved the recovery of population spike; decreased frequency of hypoxic injury potential, postponed the onset of hypoxic injury potential and increased the duration of hypoxic injury potential. Isoflurane treatment also decreased the hypoxia-induced release of amino acid neurotransmitters such as aspartate, glutamate and glycine induced by hypoxia, but the levels of γ-aminobutyric acid were elevated. Morphological studies showed that isoflurane treatment attenuated edema of pyramid neurons in the CA1 region. It also reduced apoptosis as evident by lowered expression of caspase-3 and PARP genes.

CONCLUSIONS

Isoflurane showed a neuro-protective effect on hippocampal neuron injury induced by hypoxia through suppression of apoptosis.

Artesunate Protected Blood-Brain Barrier via Sphingosine 1 Phosphate Receptor 1/Phosphatidylinositol 3 Kinase Pathway After Subarachnoid Hemorrhage in Rats

Blood-brain barrier preservation plays an important role in attenuating vasogenic brain edema after subarachnoid hemorrhage (SAH). This study was designed to investigate the protective effect and mechanism of artesunate, a traditional anti-malaria drug, on blood-brain barrier after SAH. Three hundred and seventy-seven (377) male Sprague-Dawley rats were subjected to endovascular perforation model for SAH. The rats received artesunate alone or in combination with Sphingosine-1-phosphate receptor-1 (S1P1) small interfering RNA (siRNA), antagonist VPC23019, or phosphatidylinositol 3-kinase inhibitor wortmannin after SAH. Modified Garcia score, SAH grades, brain water content, Evans blue leakage, transmission electron microscope, immunohistochemistry staining, Western blot, and cultured endothelial cells were used to investigate the optimum concentration and the therapeutic mechanism of artesunate. We found that artesunate (200 mg/kg) could do better in raising modified Garcia score, reducing brain water content and Evans blue leakage than other groups after SAH. Moreover, artesunate elevated S1P1 expression, enhanced phosphatidylinositol 3-kinase activation, lowered GSK-3β activation, stabilized β-catenin, and improved the expression of Claudin-3 and Claudin-5 after SAH in rats. These effects were eliminated by S1P1 siRNA, VPC23019, and wortmannin. This study revealed that artesunate could preserve blood-brain barrier integrity and improve neurological outcome after SAH, possibly through activating S1P₁, enhancing phosphatidylinositol 3-kinase activation, stabilizing β-catenin via GSK-3β inhibition, and then effectively raising the expression of Claudin-3 and Claudin-5. Therefore, artesunate may be favorable for the blood-brain barrier (BBB) protection after SAH and become a potential candidate for the treatment of SAH patients.

Isoflurane postconditioning induces concentration- and timing-dependent neuroprotection partly mediated by the GluR2 AMPA receptor in neonatal rats after brain hypoxia-ischemia

BACKGROUND

It has been demonstrated that preconditioning with 1.5 % isoflurane reduces hypoxia/ischemia (HI)-induced brain loss/injury in neonatal rats. Ca(2+) influx mediated by α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) is involved in HI-induced neuronal death. Here, we investigated the effective concentrations and time windows for neuroprotection by isoflurane postconditioning in neonatal rats after brain HI and determined whether GluR2-containing AMPARs mediate this neuroprotection.

METHODS

Seven-day-old Sprague-Dawley (SD) rats were randomly divided into eight groups (n = 40 in each). The rats underwent left common carotid arterial ligation (brain HI) or sham surgery, followed by exposure to 8 % oxygen for 2 h at 37 °C in a thermoregulated environment. Post-conditioning with 1, 1.5, or 2 % isoflurane for 30 min was performed immediately after brain HI. Others were post-treated with 1.5 % isoflurane for 30 min at 3, 6, and 12 h after brain HI. The weight ratio, neuronal density ratio in the ventral posteromedial thalamic nucleus, and retrosplenial granular cortex of left to right cerebral hemispheres at 7 days after brain HI were evaluated in all groups. Cerebral hemispheres were harvested for Western-blot analysis of GluR2 on the cellular membranes 24 h after HI or sham surgery in neonatal rats from the sham group, the HI group, and the HI + immediate exposure to the 1.5 % isoflurane group. In another experiment, the function of learning and memory were assessed in adolescence (4 weeks) using Morris water maze.

RESULTS

Compared with the control (sham) group, brain HI decreased the weight ratio and the neuronal density ratio in the ventral posteromedial thalamic nucleus and the retrosplenial granular cortex of the left to right cerebral hemispheres (p < 0.05). These effects of brain HI were reduced by postconditioning with 1.5 or 2 % isoflurane for 30 min within 6 h of HI, which coincided with the results of Morris water maze. GluR2 protein expression on cellular membranes was reduced after HI compared with sham surgery group (p < 0.05); this down-regulation was attenuated by isoflurane postconditioning.

CONCLUSIONS

Postconditioning with 1.5 and 2 % isoflurane affords neuroprotection in neonatal rats. The time window for isoflurane postconditioning to be effective against neonatal HI-induced brain injury was 0-6 h after HI. This protection may be mediated by GluR2-containing AMPARs.

Osteopontin-Rac1 on Blood-Brain Barrier Stability Following Rodent Neonatal Hypoxia-Ischemia

Osteopontin (OPN) is a neuroprotective molecule that is upregulated following rodent neonatal hypoxic-ischemic (nHI) brain injury. Because Rac1 is a regulator of blood-brain barrier (BBB) stability, we hypothesized a role for this in OPN signaling. nHI was induced by unilateral ligation of the right carotid artery followed by hypoxia (8 % oxygen for 2 h) in P10 Sprague-Dawley rat pups. Intranasal (iN) OPN was administered at 1 h post-nHI. Groups consisted of: (1) Sham, (2) Vehicle, (3) OPN, and (4) OPN + Rac1 inhibitor (NSC23766). Evans blue dye extravasation (BBB permeability) was quantified 24 h post-nHI, and brain edema at 48 h. Increased BBB permeability and brain edema following nHI was ameliorated in the OPN treatment group. However, those rat pups receiving OPN co-treatment with the Rac1 inhibitor experienced no improvement compared with vehicle. OPN protects the BBB following nHI, and this was reversed by Rac1 inhibitor (NSC23766).

Toxic and protective effects of inhaled anaesthetics on the developing animal brain: systematic review and update of recent experimental work

BACKGROUND

Accumulating preclinical data indicate that neonatal exposure to general anaesthetics is detrimental to the central nervous system. Some studies, however, display potential protective effects of exactly the same anaesthetic agents on the immature brain. The effects of inhaled anaesthetics on the developing brain have received close attention from researchers, clinicians and the public in recent decades.

OBJECTIVES

To summarise the preclinical evidence reported in the last 5 years on both the deleterious effects and the neuroprotective potential in special indications, of inhaled anaesthetics on the developing brain.

DESIGN

A systematic review.

DATA SOURCES

PubMed search performed in June 2013.

ELIGIBILITY CRITERIA

Search terms included brain, development, inhaled anaesthetic, toxicity and protection within the scope of the last 5 years with animals. The reference lists of relevant articles and recent reviews were also hand-searched for additional studies. The type, dose and exposure duration of anaesthetics, species and age of animals, histopathologic indicators, outcomes and affected brain areas, neuro developmental test modules and outcomes, as well as other outcomes and comments were summarised.

RESULTS

Two hundred and nineteen relevant titles were initially revealed. In total, 81 articles were identified, with 68 articles assessing the detrimental effects induced by inhaled anaesthetics in the immature brain along with possible treatments. The remaining 13 articles focused on the protective profile of inhaled anaesthetics on perinatal hypoxic-ischaemic brain injury. Administration of inhaled anaesthetic agents to the immature brain was shown to be deleterious in several preclinical studies. In perinatal hypoxic-ischaemic brain injury models, pre- and postconditioning of inhalational anaesthetics exerted neuroprotective effects.

CONCLUSION

The majority of studies have linked inhaled anaesthetics to toxic effects in the neonatal brain of rodents, piglets and primates. Only a few studies, however, could demonstrate long-lasting cognitive impairment. The results of inhalational anaesthetic-induced neuroprotection in perinatal hypoxic-ischaemic brain injury are a promising basis for more research in this field. In general, prospective clinical trials are needed to further differentiate the effects of inhaled anaesthetics on the immature brain.