Isoflurane preconditioning neuroprotection in experimental focal stroke is androgen-dependent in male mice

Veterinary medical care in rodent models of stroke: Pitfalls and refinements to balance quality of science and animal welfare

Rodent models of cerebral ischemia provide a valuable contribution to a better understanding of stroke pathophysiology, to validate diagnostic methods, and to enable testing of new treatments for ischemia-reperfusion damage and comorbidities. However, ethical concerns have led to increased attention to the welfare aspects of such models. Supportive therapies are an essential part of the overall animal care and use program and should be tailored to the experimental model being studied, the regulatory requirements, and research objectives to achieve high-quality preclinical studies and ethical research practices. On the other hand, the use of veterinary medical treatments in preclinical models of stroke must balance the needs of animal care and potential sources of bias in experimental results. This report provides a systematic review of the scientific literature covering the relevant period from years 1988 to September 2024, with the aim to investigating veterinary medical interventions useful to minimize suffering in rodent models of stroke without producing experimental bias. The research findings, consolidated from 181 selected studies, published from 1991 to 2023, indicate the feasibility of implementing personalized protocols of anesthesia, analgesics, antibiotics, and other supportive therapies in rodent models of stroke, while avoiding scientific interferences. These data fill a gap in current knowledge and could be of interest for an interdisciplinary audience working with rodent models of stroke, stimulating further refinements to safeguard both animal welfare and the validity of experimental findings, and may promote the culture of ethical conduct in various research fields and disciplines.

Sex Difference in Capillary Reperfusion After Transient Middle Cerebral Artery Occlusion in Diabetic Mice

BACKGROUND

Type 2 diabetes (DM2) exacerbates stroke injury, reduces efficacy of endovascular therapy, and worsens long-term functional outcome. Sex differences exist in stroke incidence, response to therapy, poststroke microvascular dysfunction, and functional recovery. In this study, we tested the hypotheses that poor outcome after stroke in the setting of DM2 is linked to impaired microvascular tissue reperfusion and that male and female DM2 mice exhibit different microvascular reperfusion response after transient middle cerebral artery occlusion (MCAO).

METHODS

Transient MCAO was induced for 60 minutes using an intraluminal filament in young adult DM2 and nondiabetic control male and female mice. Capillary flux in deep cortical layers was assessed using optical coherence tomography-based optical microangiography (OMAG), and associated regional brain infarct size was evaluated by hematoxylin and eosin staining.

RESULTS

Compared to baseline, MCAO reduced absolute capillary red blood cell flux by 84% at 24 hours post-MCAO in male DM2 (P<0.001) but not male control mice. When normalized to pre-MCAO baseline, red blood cell flux 24 hours after stroke was 64% lower in male DM2 mice than male nondiabetic controls (P<0.01). In females, MCAO decreased capillary flux by 48% at 24 hours post-MCAO compared with baseline in DM2 (P<0.05) but not in control mice. Red blood cell flux of female DM2 mice did not differ from that of nondiabetic controls either before or 24 hours after MCAO. Furthermore, normalized capillary flux 24 hours after MCAO failed to differ between female DM2 mice and nondiabetic controls. Concomitantly, male but not female DM2 mice experienced 25% larger infarct in caudate-putamen versus respective nondiabetic controls (P<0.05).

CONCLUSIONS

DM2 impairs capillary perfusion and exacerbates ischemic deep brain injury in male but not female young adult mice. Premenopausal females appear to be protected against DM2-related capillary dysfunction and brain injury.

Functional Restoration following Global Cerebral Ischemia in Juvenile Mice following Inhibition of Transient Receptor Potential M2 (TRPM2) Ion Channels

Hippocampal cell death and cognitive dysfunction are common following global cerebral ischemia across all ages, including children. Most research has focused on preventing neuronal death. Restoration of neuronal function after cell death is an alternative approach (neurorestoration). We previously identified transient receptor potential M2 (TRPM2) ion channels as a potential target for acute neuroprotection and delayed neurorestoration in an adult CA/CPR mouse model. Cardiac arrest/cardiopulmonary resuscitation (CA/CPR) in juvenile (p20-25) mice was used to investigate the role of ion TRPM2 channels in neuroprotection and ischemia-induced synaptic dysfunction in the developing brain. Our novel TRPM2 inhibitor, tatM2NX, did not confer protection against CA1 pyramidal cell death but attenuated synaptic plasticity (long-term plasticity (LTP)) deficits in both sexes. Further, in vivo administration of tatM2NX two weeks after CA/CPR reduced LTP impairments and restored memory function. These data provide evidence that pharmacological synaptic restoration of the surviving hippocampal network can occur independent of neuroprotection via inhibition of TRPM2 channels, providing a novel strategy to improve cognitive recovery in children following cerebral ischemia. Importantly, these data underscore the importance of age-appropriate models in disease research.

Experimental pediatric stroke shows age-specific recovery of cognition and role of hippocampal Nogo-A receptor signaling

Ischemic stroke is a leading cause of death worldwide and clinical data suggest that children may recover from stroke better than adults; however, supporting experimental data are lacking. We used our novel mouse model of experimental juvenile ischemic stroke (MCAO) to characterize age-specific cognitive dysfunction following ischemia. Juvenile and adult mice subjected to 45-min MCAO, and extracellular field recordings of CA1 neurons were performed to assess hippocampal synaptic plasticity changes after MCAO, and contextual fear conditioning was performed to evaluate memory and biochemistry used to analyze Nogo-A expression. Juvenile mice showed impaired synaptic plasticity seven days after MCAO, followed by full recovery by 30 days. Memory behavior was consistent with synaptic impairments and recovery after juvenile MCAO. Nogo-A expression increased in ipsilateral hippocampus seven days after MCAO compared to contralateral and sham hippocampus. Further, inhibition of Nogo-A receptors reversed MCAO-induced synaptic impairment in slices obtained seven days after juvenile MCAO. Adult MCAO-induced impairment of LTP was not associated with increased Nogo-A. This study demonstrates that stroke causes functional impairment in the hippocampus and recovery of behavioral and synaptic function is more robust in the young brain. Nogo-A receptor activity may account for the impairments seen following juvenile ischemic injury.

An appropriate level of autophagy reduces emulsified isoflurane-induced apoptosis in fetal neural stem cells

Autophagy plays essential roles in cell survival. However, the functions and regulation of the autophagy-related proteins Atg5, LC3B, and Beclin 1 during anesthetic-induced developmental neurotoxicity remain unclear. This study aimed to understand the autophagy pathways and mechanisms that affect neurotoxicity, induced by the anesthetic emulsified isoflurane, in rat fetal neural stem cells. Fetal neural stem cells were cultured, in vitro, and neurotoxicity was induced by emulsified isoflurane treatment. The effects of pretreatment with the autophagy inhibitors 3-methyladenine and bafilomycin and the effects of transfection with small interfering RNA against ATG5 (siRNA-Atg5) were observed. Cell viability was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and apoptosis was assessed using flow cytometry. Ultrastructural changes were analyzed through transmission electron microscopy. The levels of the autophagy-related proteins LC3B, Beclin 1, Atg5, and P62 and the pro-apoptosis-related protein caspase-3 were analyzed using western blot assay. The inhibition of cell proliferation and that of apoptosis rate increased after treatment with emulsified isoflurane. Autophagolysosomes, monolayer membrane formation due to lysosomal degradation, were observed. The autophagy-related proteins LC3B, Beclin 1, Atg5, and P62 and caspase-3 were upregulated. These results confirm that emulsified isoflurane can induce toxicity and autophagy in fetal neural stem cells. Pre-treatment with 3-methyladenine and bafilomycin increased the apoptosis rate in emulsified isoflurane-treated fetal neural stem cells, which indicated that the complete inhibition of autophagy does not alleviate emulsified isoflurane-induced fetal neural stem cell toxicity. Atg5 expression was decreased significantly by siRNA-Atg5 transfection, and cell proliferation was inhibited. These results verify that the Atg5 autophagy pathway can be regulated to maintain appropriate levels of autophagy, which can inhibit the neurotoxicity induced by emulsified isoflurane anesthetic in fetal neural stem cells.

Sex differences in the therapeutic effects of anti-PDL2 neutralizing antibody on stroke

Inflammation involving migration of immune cells across the damaged blood-brain barrier (BBB), activation of resident innate microglia and production of inflammatory humoral mediators such as cytokines and chemokines play a critical role in the pathogenesis of ischemic stroke. Cell-cell signaling involved in the process also includes checkpoint interaction between programmed death receptor (PD1) and programmed death ligands, PDL1 and PDL2. Based on our previous studies showing reduced MCAO infarct volumes in PDL2 deficient mice, we evaluated the ability of anti-PDL2 mAb to treat MCAO in male and female C57BL/6 mice. We found that anti-PDL2 neutralizing antibody treatment of MCAO significantly reduced infarct volumes in male mice but had no protective effects in female mice even at a 5-fold increased dose of anti-PDL2 mAb. The protection in male mice was likely mediated by reduced percentages in the spleen of PDL2⁺CD19⁺ B cells, PDL1⁺CD4⁺ T cells and CD86⁺CD11b⁺ macrophages in concert with reduced expression of PDL1 and TNFα and continued expression of CD206, in the injured ipsilateral brain hemisphere. The lack of a therapeutic benefit of anti-PDL2 on stroke-induced infarct volumes in female mice was reflected by no detectable reduction in expressed PDL2 or PDL1 and an increased frequency of Th₁ and Th₁₇ pro-inflammatory T cell subsets in the spleen, an effect not seen in PDL2 mAb treated males. This result potentially limits the utility of anti-PDL2 mAb therapy in stroke to males but underscores the importance of meeting the STAIR requirements for development of new stroke therapies for both sexes.

Androgens augment pulmonary responses to ozone in mice

Ozone causes airway hyperresponsiveness, a defining feature of asthma, and is an asthma trigger. In mice, ozone-induced airway hyperresponsiveness is greater in males than in females, suggesting a role for sex hormones in the response to ozone. To examine the role of androgens in these sex differences, we castrated 4-week-old mice. Controls underwent sham surgery. At 8 weeks of age, mice were exposed to ozone (2ppm, 3 h) or room air. Twenty-four hours later, mice were anesthetized and measurements of airway responsiveness to inhaled aerosolized methacholine were made. Mice were then euthanized and bronchoalveolar lavage was performed. Castration attenuated ozone-induced airway hyperresponsiveness and reduced bronchoalveolar lavage cells. In intact males, flutamide, an androgen receptor inhibitor, had similar effects to castration. Bronchoalveolar lavage concentrations of several cytokines were reduced by either castration or flutamide treatment, but only IL-1α was reduced by both castration and flutamide. Furthermore, an anti-IL-1α antibody reduced bronchoalveolar lavage neutrophils in intact males, although it did not alter ozone-induced airway hyperresponsiveness. Our data indicate that androgens augment pulmonary responses to ozone and that IL-1α may contribute to the effects of androgens on ozone-induced cellular inflammation but not airway hyperresponsiveness.

Reversal of Global Ischemia-Induced Cognitive Dysfunction by Delayed Inhibition of TRPM2 Ion Channels

Hippocampal injury and cognitive impairments are common after cardiac arrest and stroke and do not have an effective intervention despite much effort. Therefore, we developed a new approach aimed at reversing synaptic dysfunction by targeting TRPM2 channels. Cardiac arrest/cardiopulmonary resuscitation (CA/CPR) in mice was used to investigate cognitive deficits and the role of the calcium-permeable ion channel transient receptor potential-M2 (TRPM2) in ischemia-induced synaptic dysfunction. Our data indicates that absence (TRPM2^-/-) or acute inhibition of TRPM2 channels with tatM2NX reduced hippocampal cell death in males only, but prevented synaptic plasticity deficits in both sexes. Remarkably, administration of tatM2NX weeks after injury reversed hippocampal plasticity and memory deficits. Finally, TRPM2-dependent activation of calcineurin-GSK3β pathway contributes to synaptic plasticity impairments. These data suggest persistent TRPM2 activity following ischemia contributes to impairments of the surviving hippocampal network and that inhibition of TRPM2 channels at chronic time points may represent a novel strategy to improve functional recovery following cerebral ischemia that is independent of neuroprotection.

Exposure to female estrous is beneficial for male mice against transient ischemic stroke

OBJECTIVE

Exposure to female estrous, a natural rewarding experience, alleviates anxiety and depression, and the contribution of this behavior to stroke outcome is unknown. The aim of this study was to evaluate whether exposure to female estrous is beneficial to recovery following transient ischemic stroke in male mice.

METHODS

Cerebral ischemia was induced in male ICR mice with thread occlusion of the middle cerebral artery (MCAO) for 30 min followed by reperfusion. MCAO mice were randomly divided into MCAO group and Estrous Female Exposure (EFE) group. The mice in the EFE group were subjected to estrous female mouse interaction from day 1 until the end of the experiment. Mortality was recorded during the investigation. Behavioral functions were assessed by a beam-walking test and corner test from day 1 to day 10 after MCAO. Serum testosterone levels were analyzed with ELISA, and the expression levels of growth-associated protein-43 (GAP-43) and synaptophysin in the cortex of the ischemic hemisphere were determined by western blot on day 7 after MCAO.

RESULTS

Exposure to female estrous reduced the mortality induced by cerebral ischemic lesions. The beam-walking test demonstrated that exposure to female estrous significantly improved motor function recovery. The serum testosterone levels and ischemic cortex GAP-43 expression were significantly higher in MCAO male mice exposed to female estrous.

CONCLUSION

Exposure to female estrous reduces mortality and improves functional recovery in MCAO male mice. The study provides the first evidence to support the importance of female interaction to male stroke rehabilitation.

ABBREVIATIONS

GAP-43: growth-associated protein-43; SYP: Synaptophysin; MCAO: middle cerebral artery occlusion; OVXs: ovariectomies; CCA: common carotid artery; ECA: external carotid artery; EFE: estrous female exposure; TTC: 2,3,5-triphenyltetrazolium chloride; PAGE: polyacrylamide gel electrophoresis; PVDF: polyvinylidene difluoride; ANOVA: analysis of variance; LSD: least significant difference.

Sex hormones modulate pathogenic processes in experimental traumatic brain injury

Clinical and animal studies have revealed sex-specific differences in histopathological and neurological outcome after traumatic brain injury (TBI). The impact of perioperative administration of sex steroid inhibitors on TBI is still elusive. Here, we subjected male and female C57Bl/6N mice to the controlled cortical impact (CCI) model of TBI and applied pharmacological inhibitors of steroid hormone synthesis, that is, letrozole (LET, inhibiting estradiol synthesis by aromatase) and finasteride (FIN, inhibiting dihydrotestosterone synthesis by 5α-reductase), respectively, starting 72 h prior CCI, and continuing for a further 48 h after CCI. Initial gene expression analyses showed that androgen (Ar) and estrogen receptors (Esr1) were sex-specifically altered 72 h after CCI. When examining brain lesion size, we found larger lesions in male than in female mice, but did not observe effects of FIN or LET treatment. However, LET treatment exacerbated neurological deficits 24 and 72 h after CCI. On the molecular level, FIN administration reduced calpain-dependent spectrin breakdown products, a proxy of excitotoxicity and disturbed Ca²⁺ homeostasis, specifically in males, whereas LET increased the reactive astrocyte marker glial fibrillary acid protein specifically in females. Examination of neurotrophins (brain-derived neurotrophic factor, neuronal growth factor, NT-3) and their receptors (p75^NTR , TrkA, TrkB, TrkC) revealed CCI-induced down-regulation of TrkB and TrkC protein expression, which was reduced by LET in both sexes. Interestingly, FIN decreased neuronal growth factor mRNA expression and protein levels of its receptor TrkA only in males. Taken together, our data suggest a sex-specific impact on pathogenic processes in the injured brain after TBI. Sex hormones may thus modulate pathogenic processes in experimental TBI.

Juvenile cerebral ischemia reveals age-dependent BDNF-TrkB signaling changes: Novel mechanism of recovery and therapeutic intervention

Global ischemia in childhood often leads to poor neurologic outcomes, including learning and memory deficits. Using our novel model of childhood cardiac arrest/cardiopulmonary resuscitation (CA/CPR), we investigate the mechanism of ischemia-induced cognitive deficits and recovery. Memory is impaired seven days after juvenile CA/CPR and completely recovers by 30 days. Consistent with this remarkable recovery not observed in adults, hippocampal long-term potentiation (LTP) is impaired 7-14 days after CA/CPR, recovering by 30 days. This recovery is not due to the replacement of dead neurons (neurogenesis), but rather correlates with brain-derived neurotrophic factor (BDNF) expression, implicating BDNF as the molecular mechanism underlying impairment and recovery. Importantly, delayed activation of TrkB receptor signaling reverses CA/CPR-induced LTP deficits and memory impairments. These data provide two new insights (1) endogenous recovery of memory and LTP through development may contribute to improved neurological outcome in children compared to adults and (2) BDNF-enhancing drugs speed recovery from pediatric cardiac arrest during the critical school ages.

Mangiferin Potentiates Neuroprotection by Isoflurane in Neonatal Hypoxic Brain Injury by Reducing Oxidative Stress and Activation of Phosphatidylinositol-3-Kinase/Akt/Mammalian Target of Rapamycin (PI3K/Akt/mTOR) Signaling

Background

Hypoxic-ischemic brain injury in the perinatal period is a main cause of perinatal mortality and neurologic complications in neonates and children. Recent studies have focused on the neuroprotective effect of anesthetic drugs. The volatile anesthetic isoflurane has been shown to exert neuroprotective effects in cerebral ischemia. Mangiferin is a natural polyphenol with various pharmacological properties, including antioxidant and ant-tumor effects. This study aimed to determine whether mangiferin potentiates the neuroprotective effects of isoflurane and also if mangiferin when administered alone exerts neuroprotective effects following hypoxic-ischemic brain injury.

Material/Methods

Sprague-Dawley rats were subjected to cerebral hypoxic ischemia on postnatal day 10 (P10). Mangiferin (50, 100, or 200 mg/kg b.w.) was intragastrically administered from P3 to P12 and 1 h prior to insult on the day of ischemic induction. At 3 h after hypoxia-ischemia (HI) insult, separate groups of rat pups were exposed to isoflurane (1.5%) for 6 h. Following 48 h of HI, the rats were sacrificed and brain tissues were used for analysis.

Results

Mangiferin treatment attenuated neuronal apoptosis and reduced cerebral infarct volume. The expression of cleaved caspase-3 and apoptotic cascade proteins were regulated. The levels of reactive oxygen species (ROS) and malondialdehyde were reduced by mangiferin and/or isoflurane exposure. The levels of antioxidant glutathione were considerably raised under HI injury, which was modulated by mangiferin and isoflurane exposure. The PI3K/Akt signaling pathway, which was downregulated following HI insult, was activated by mangiferin and/or isoflurane.

Conclusions

This study reveals the potent neuroprotective efficacy of mangiferin against HI-induced brain injury via effectively modulating apoptotic pathways, ROS levels, and PI3K/Akt cascades while potentiating protective effects of isoflurane.

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.

Does long-term androgen deficiency lead to metabolic syndrome in middle-aged rats?

Evidence from clinical observational studies and animal experiments suggests that hypogonadism is associated with the metabolic syndrome. In most of the experiments, androgen deficiency is induced by gonadectomy in the adulthood and relatively short-term effects of hypogonadism on metabolic parameters are usually observed. The purpose of this study was to evaluate the metabolic effects of long-term androgen deficiency starting before puberty in middle-aged male rats. The components of the metabolic syndrome were examined in male, female and gonadectomized male rats at the age of 18months. Sex differences were observed in plasma testosterone, cholesterol, high-density lipoproteins and also in body weight and in glycemia dynamics during oral glucose tolerance test. Gonadectomy and long-term hypogonadism did not affect most of the analyzed metabolic parameters such as blood pressure, glycemia, plasma insulin and uric acid. The only exception was the significantly higher liver enzymes in plasma and triacylglycerol in liver found in gonadectomized males. Except low-density lipoprotein, neither treatment of middle-aged males and females with letrozole, nor supplementation of estradiol as the metabolite of testosterone in gonadectomized male rats changed any of the observed metabolic parameters. Our results suggest that long-term hypogonadism started before puberty does not induce metabolic syndrome in middle-aged male rats, but may affect the liver. Sex differences in metabolic parameters in middle-aged rats are not mediated by testosterone. Whether hypogonadism predispose to metabolic syndrome in combination with other risk factors needs further clarification.

Hemodynamic effects of intraoperative anesthetics administration in photothrombotic stroke model: a study using laser speckle imaging

Background

Previous neuroimaging studies have shown the hemodynamic effect of either preconditioning or postconditioning anesthesia in ischemic stroke model. However, the anesthetic effect in hemodynamics during and immediately after the stroke modeling surgery remains unknown due to the lack of appropriate anesthesia-free stroke model and intraoperative imaging technology. In the present study, we utilized our recently developed photothrombotic model of focal cerebral ischemia in conscious and freely moving rats, and investigated transient hemodynamic changes with or without isoflurane administration. Laser speckle imaging was applied to acquire real-time two-dimensional full-field cerebral blood flow (CBF) information throughout the surgical operations and early after.

Results

Significantly larger CBF reduction area was observed in conscious rats from 8 min immediately after the onset of stroke modeling, compared with anesthetized rats. Stroke rats without isoflurane administration also showed larger lesion volume identified by magnetic resonance imaging 3 h post occlusion (58.9%), higher neurological severity score 24 h post occlusion (28.3%), and larger infarct volume from 2,3,5-triphenyltetrazolium chloride staining 24 h post occlusion (46.9%).

Conclusions

Our results demonstrated that the hemodynamic features were affected by anesthetics at as early as during the stroke induction. Also, our findings about the neuroprotection of intraoperative anesthetics administration bring additional insights into understanding the translational difficulty in stroke research.

Paradigms and mechanisms of inhalational anesthetics mediated neuroprotection against cerebral ischemic stroke

Cerebral ischemic stroke is a leading cause of serious long-term disability and cognitive dysfunction. The high mortality and disability of cerebral ischemic stroke is urging the health providers, including anesthesiologists and other perioperative professioners, to seek effective protective strategies, which are extremely limited, especially for those perioperative patients. Intriguingly, several commonly used inhalational anesthetics are recently suggested to possess neuroprotective effects against cerebral ischemia. This review introduces multiple paradigms of inhalational anesthetic treatments that have been investigated in the setting of cerebral ischemia, such as preconditioning, proconditioning and postconditioning with a variety of inhalational anesthetics. The pleiotropic mechanisms underlying these inhalational anesthetics-afforded neuroprotection against stroke are also discussed in detail, including the common pathways shared by most of the inhalational anesthetic paradigms, such as anti-excitotoxicity, anti-apoptosis and anti-inflammation. There are also distinct mechanisms involved in specific paradigms, such as preserving blood brain barrier integrity, regulating cerebral blood flow and catecholamine release. The ready availability of these inhalational anesthetics bedside and renders them a potentially translatable stroke therapy attracting great efforts for understanding of the underlying mechanisms.

Neuroprotection by combination of resveratrol and enriched environment against ischemic brain injury in rats

OBJECTIVES

Both resveratrol (RV) and enriched environment (EE) exert beneficial effects on neurological functional recovery after an ischemic brain injury.

METHODS

The neuroprotective effect of combined treatment of RV and EE was examined in a rat model of middle cerebral artery occlusion (MCAO), aiming to further promote neurological functional recovery.

RESULTS

The combined therapy of RV and EE clearly improved locomotor activity and behaviour examination, compared to the monotherapy of RV or EE alone. Stroke severity was also markedly ameliorated by the co-treatment. Mechanistic study revealed that the combined treatment reduced oxidative stress. Moreover, the detrimental ERK1/2 signalling upregulated by MCAO injury was markedly suppressed by the co-treatment, compared to RV or EE monotherapy.

DISCUSSION

Altogether, the combined therapy of RV and EE showed a clearly enhanced neuroprotective effect, compared to RV or EE monotherapy, which might be a new strategy for the treatment of ischemic brain injury.

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.

Protective effect of ginsenoside Rb1 on integrity of blood-brain barrier following cerebral ischemia

Ginsenosides, the major bioactive compounds in ginseng root, have been found to have antioxidant, immunomodulatory, and anti-inflammatory activities. In the present study, we sought to investigate whether and how ginsenoside Rb1 (GS-Rb1), the most abundant ginsenoside, can protect blood-brain barrier (BBB) integrity following cerebral ischemia in middle cerebral artery occlusion (MCAO) animal model. ICR mice underwent MCAO and received GS-Rb1 by intraperitoneal injection at 3 h after reperfusion. We evaluated infarction, neurological scores, brain edema, Evans blue (EB) extravasation, and tight junction protein expression at 48 h after MCAO. We further examined whether GS-Rb1 protected BBB integrity by suppressing post-ischemic inflammation-induced activity of matrix metalloproteinase-9 (MMP-9) and nicotinamide adenine dinucleotide phosphate oxidase (NOX). First, GS-Rb1 decreased infarction and improved neurological deficits in MCAO animals. In addition, GS-Rb1 reduced EB extravasation and brain edema and preserved expression of tight junction proteins in the ischemic brain. Moreover, GS-Rb1 inhibited expression of pro-inflammatory factors including nitric oxide synthase and IL-1β, but increased expression of anti-inflammatory markers arginase 1 and IL-10 in the ischemic brain. Consistently, GS-Rb1 attenuated ischemia-induced expression and activity of MMP9. Finally, GS-Rb1 reduced NOX-4 mRNA expression and NOX activity in ischemic brain. These results suggest that GS-Rb1 protects loss of BBB integrity in ischemic stroke by suppressing neuroinflammation induction of MMP-9 and NOX4-derived free radicals, and indicate its potential for treating brain injuries, such as ischemia and stroke.

Sphingosine kinase 1 mediates neuroinflammation following cerebral ischemia

Sphingosine kinases (Sphks) are the rate-limiting kinases in the generation of sphingosine-1-phosphate, which is a well-established intracellular pro-survival lipid mediator. Sphk2 has been reported to be protective following experimental stroke. We investigated the role of Sphk1 in cerebral ischemia using a mouse middle cerebral artery occlusion (MCAO) model and an in vitro glucose-oxygen deprivation (OGD) model. Sphk expression and activity were assessed in the ischemic brain with quantitative PCR (qPCR), Western blot, immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). Pharmacological and gene knockdown approaches were utilized to investigate the effects of Sphk1 on stroke outcomes. The expression of Sphk1 but not that of Sphk2 was rapidly induced in the cortical penumbra over 96h after MCAO, and the microglia were one of the major cellular sources of Sphk1 induction. Consistently, Sphk activity was enhanced in the cortical penumbra. In contrast to the protective role of Sphk2, pharmacological inhibition and cortical knockdown of Sphk1 reduced infarction at 24 and 96h after reperfusion. Additionally, the Sphk1 inhibitor improved the neurological deficits at 96h after reperfusion. Mechanistically, Sphk1 inhibition and knockdown significantly attenuated MCAO-induced expression of inflammatory mediators in the cortical penumbra. Moreover, using a conditioned medium transfer approach, we demonstrated that OGD-treated neurons induced the expression of Sphk1 and pro-inflammatory mediators in primary microglia, and the microglial induction of pro-inflammatory mediators by ischemic neurons was blunted by Sphk1 inhibition. Taken together, our results indicate that Sphk1 plays an essential role in mediating post-stroke neuroinflammation.

Recombinant T-cell receptor ligand RTL1000 limits inflammation and decreases infarct size after experimental ischemic stroke in middle-aged mice

We have previously demonstrated that recombinant T-cell receptor ligand 1000 (RTL1000) reduces infarct size and improves long-term functional recovery after experimental stroke in young transgenic mice expressing human leukocyte antigen DR2 (DR2-Tg). In this study, we determined the effect of RTL1000 on infarct size in 12-month-old middle-aged DR2-Tg mice, and investigated its mechanism of action. Twelve-month-old male DR2-Tg mice underwent 60min of intraluminal reversible middle cerebral artery occlusion (MCAO). Vehicle or RTL1000 was injected 4, 24, 48 and 72h after MCAO. Cortical, striatal and total hemispheric infarcts were measured 96h after stroke. Spleen and brain tissues were collected 96h after stroke for immunological analysis. Our data showed that RTL1000 significantly reduced infarct size 96h after MCAO in middle-aged male DR2-Tg mice. RTL1000 decreased the number of activated monocytes/microglia cells (CD11b(+)CD45(hi)) and CD3(+) T cells in the ischemic hemisphere. RTL1000 also reduced the percentage of total T cells and inflammatory neutrophils in the spleen. These findings suggest that RTL1000 protects against ischemic stroke in middle-aged male mice by limiting post-ischemic inflammation.

Anesthetic preconditioning inhibits isoflurane-mediated apoptosis in the developing rat brain

BACKGROUND

We hypothesized that preconditioning (PC) with a short exposure to isoflurane (ISO) would reduce neurodegeneration induced by prolonged exposure to ISO in neonatal rats, as previously shown in neuronal cell culture.

METHODS

We randomly divided 7-day-old Sprague-Dawley rats into 3 groups: control, 1.5% ISO, and PC + 1.5% ISO. The control group was exposed to carrier gas (30% oxygen balanced in nitrogen) for 30 minutes and then to carrier gas again for 6 hours the following day. The 1.5% ISO group was exposed to carrier gas for 30 minutes and then to 1.5% ISO for 6 hours the following day. The PC + 1.5% ISO group was preconditioned with a 30-minute 1.5% ISO exposure and then exposed to 1.5% ISO for 6 hours the following day. Blood and brain samples were collected 2 hours after the exposures for determination of neurodegenerative biomarkers, including caspase-3, S100β, caspase-12, and an autophagy biomarker Beclin-1.

RESULTS

Prolonged exposure to ISO significantly increased cleaved caspase-3 expression in the cerebral cortex of 7-day-old rats compared with the group preconditioned with ISO and the controls using Western blot assays. However, significant differences were not detected for other markers of neuronal injury.

CONCLUSIONS

The ISO-mediated increase in cleaved caspase-3 in the postnatal day 7 rat brain is ameliorated by PC with a brief anesthetic exposure, and differences were not detected in other markers of neuronal injury.

Preclinical evaluation of recombinant T cell receptor ligand RTL1000 as a therapeutic agent in ischemic stroke

Recombinant T cell Receptor Ligand 1000 (RTL1000), a partial human major histocompatibility complex (MHC) molecule coupled to a human myelin peptide, reduces infarct size after experimental stroke in HLA-DRB1*1502 transgenic (DR2-Tg) mice. In this study, we characterized the therapeutic time window of opportunity for RTL1000; we explored the efficacy of a single dose of RTL1000 administration and determined if RTL1000 affords long-term neurobehavioral functional improvement after ischemic stroke. Male DR2-Tg mice underwent 60 min of intraluminal reversible middle cerebral artery occlusion (MCAO). RTL1000 or vehicle was injected 4, 6, or 8 h after MCAO, followed by three daily injections. In the single-dose study, one-time injection of RTL1000 was applied 4 h after MCAO. Cortical, striatal, and hemispheric infarct sizes were measured 24 or 96 h after stroke. Behavioral testing, including neuroscore evaluation, open field, paw preference, and novel object recognition, was performed up to 28 days after stroke. Our data showed that RTL1000 significantly reduced the infarct size 96 h after MCAO when the first injection was given at 4 and 6 h, but not 8 h, after the onset of stroke. A single dose of 400 or 100 μg RTL1000 also significantly reduced the infarct size 24 h after MCAO. Behavioral testing showed that RTL1000 treatment used 4 h after MCAO improved long-term cognitive outcome 28 days after stroke. Taken together, RTL1000 protects against acute injury if applied within a 6-h time window and improves long-term functional recovery after experimental stroke in DR2-Tg mice.

Improvement of functional recovery by chronic metformin treatment is associated with enhanced alternative activation of microglia/macrophages and increased angiogenesis and neurogenesis following experimental stroke

Acute AMPK activation exacerbates ischemic brain damage experimentally. Paradoxically, the clinical use of an AMPK activator metformin reduces the incidence of stroke. We investigated whether post-stroke chronic metformin treatment promotes functional recovery and tissue repair via an M2-polarization mechanism following experimental stroke. Mice were randomly divided to receive metformin or vehicle daily beginning at 24h after middle cerebral artery occlusion (MCAO). Neurological deficits were monitored for 30days following MCAO. To characterize the polarization of the microglia and infiltrating macrophages, the expression of the M1 and M2 signature genes was analyzed with qPCR, ELISA and immunohistochemistry. Post-MCAO angiogenesis and neurogenesis were examined immunohistochemically. An in vitro angiogenesis model was employed to examine whether metformin promoted angiogenesis in a M2 polarization-dependent manner. Post-stroke chronic metformin treatment had no impact on acute infarction but enhanced cerebral AMPK activation, promoted functional recovery and skewed the microglia/macrophages toward an M2 phenotype following MCAO. Metformin also significantly increased angiogenesis and neurogenesis in the ischemic brain. Consistently, metformin-induced M2 polarization of BV2 microglial cells depended on AMPK activation in vitro. Furthermore, treatment of brain endothelial cells with conditioned media collected from metformin-polarized BV2 cells promoted angiogenesis in vitro. In conclusion, post-stroke chronic metformin treatment improved functional recovery following MCAO via AMPK-dependent M2 polarization. Modulation of microglia/macrophage polarization represents a novel therapeutic strategy for stroke.

Recombinant T cell receptor ligand treatment improves neurological outcome in the presence of tissue plasminogen activator in experimental ischemic stroke

RTL1000 is a partial human MHC molecule coupled to a human myelin peptide. We previously demonstrated that RTL1000 was protective against experimental ischemic stroke in HLA-DR2 transgenic (DR2-Tg) mice. Since thrombolysis with recombinant tissue plasminogen activator (t-PA) is a standard therapy for stroke, we determined if RTL1000 efficacy is altered when combined with t-PA in experimental stroke. Male DR2-Tg mice underwent 60 min of intraluminal middle cerebral artery occlusion (MCAO). t-PA or vehicle was infused intravenously followed by either a single or four daily subcutaneous injections of RTL1000 or vehicle. Infarct size was measured by 2, 3, 5-triphenyltetrazolium chloride staining at 24 or 96 h of reperfusion. Our data showed that t-PA alone reduced infarct size when measured at 24 h but not at 96 h after MCAO. RTL1000 alone reduced infarct size both at 24 and 96 h after MCAO. Combining RTL1000 with t-PA did not alter its ability to reduce infarct size at either 24 or 96 h after MCAO and provides additional protection in t-PA treated mice at 24 h after ischemic stroke. Taken together, RTL1000 treatment alone improves outcome and provides additional protection in t-PA-treated mice in experimental ischemic stroke.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

Recombinant T cell receptor ligands improve outcome after experimental cerebral ischemia

A key target for novel stroke therapy is the regulation of post-ischemic inflammatory mechanisms. Recent evidence emphasizes the role of T lymphocytes of differing subtypes in the evolution is ischemic brain damage. We have recently demonstrated the benefit of myelin antigen-specific immunodulatory agents known as recombinant T cell receptor ligands (RTLs) in a standard murine model of focal stroke. The aim of the current study was to extend this initial observation to RTL treatment in a therapeutically relevant timing after middle cerebral artery occlusion (MCAO) and verify functional benefit to complement histological outcome measures. We observed that the administration of mouse-specific RTL551 reduced infarct size and improved sensorimotor outcome when administered within a 3 h post-ischemic therapeutic window. RTL551 treatment reduced cortical, caudate putamen, and total infarct volume as compared to vehicle-treated mice. Using a standard behavioral testing repertoire, we observed that RTL551 reduced sensorimotor impairment 3 days after MCAO. Humanized RTL1000 (HLA-DR2 moiety linked to hMOG-35-55 peptide) also reduced infarct size in HLA-DR2 transgenic mice. These data indicate that this neuroantigen-specific immunomodulatory agent reduces damage when administered in a therapeutically relevant reperfusion timeframe.

Effects of androgens on early post-ischemic neurogenesis in mice

Although androgens are reported to affect stroke outcomes by altering ischemic tissue damage, their effect on post-injury repair is unknown. Since neurogenesis has recently been recognized as contributing to stroke outcomes, we investigated the role of androgens on stroke-induced neurogenesis. Adult male mice were subjected to transient middle cerebral artery occlusion (MCAO) and neurogenesis was examined 1 week later by quantifying BrdU/doublecortin-positive and BrdU/NeuN-positive neurons in brain germinal regions as well as the injured striatum. To elucidate the role of endogenous androgens, post-MCAO neurogenesis was examined in gonadally intact males, intact males implanted with the androgen receptor antagonist flutamide, and surgically castrated males. Surgical castration or pharmacologic androgen receptor blockade had no effects on post-ischemic neurogenesis, except that continuous androgen receptor blockade unexpectedly suppressed maturation of newborn neurons (BrdU/NeuN-positive cells) in the dentate gyrus. Post-MCAO neurogenesis was also examined in surgically castrated mice treated with continuous release implants containing testosterone or dihydrotestosterone (DHT). Testosterone and DHT robustly inhibited post-ischemic neurogenesis in the dentate gyrus, and the more potent androgen DHT virtually abolished the presence of immature newborn neurons (BrdU/doublecortin-positive cells) in the injured striatum. Our data suggest that endogenous androgens do not alter post-stroke neurogenesis quantitatively, but the presence of supra-physiological androgen stimulation profoundly suppresses early neurogenesis in germinal brain areas and reduces cellular repair in injured tissue after cerebral ischemia. These results advance the understanding of the role that androgens play in stroke outcomes.

Global cerebral ischemia: synaptic and cognitive dysfunction

Cardiopulmonary arrest is one of the leading causes of death and disability, primarily occurring in the aged population. Numerous global cerebral ischemia animal models induce neuronal damage similar to cardiac arrest. These global cerebral ischemia models range from vessel occlusion to total cessation of cardiac function, both of which have allowed for the investigation of this multifaceted disease and detection of numerous agents that are neuroprotective. Synapses endure a variety of alterations after global cerebral ischemia from the resulting excitotoxicity and have been a major target for neuroprotection; however, neuroprotective agents have proven unsuccessful in clinical trials, as neurological outcomes have not displayed significant improvements in patients. A majority of these neuroprotective agents have specific neuronal targets, where the success of future neuroprotective agents may depend on non-specific targets and numerous cognitive improvements. This review focuses on the different models of global cerebral ischemia, neuronal synaptic alterations, synaptic neuroprotection and behavioral tests that can be used to determine deficits in cognitive function after global cerebral ischemia.

Flutamide Enhances Neuroprotective Effects of Testosterone during Experimental Cerebral Ischemia in Male Rats

Testosterone has been shown to worsen histological and neurological impairment during cerebral ischemia in animal models. Cell culture studies revealed that testosterone is implicated in protecting neural and glial cells against insults, and they started to elucidate testosterone pathways that underlie these protective effects. These studies support the hypothesis that testosterone can be neuroprotective throughout an episode of cerebral ischemia. Therefore, we evaluated the mechanisms underlying the shift between testosterone protective and deleterious effects via block testosterone aromatization and androgen receptors in rats subjected to 60-minute middle cerebral artery occlusion. Fifty rats were divided into five equal groups: gonadally intact male; castrated male; intact male + flutamide; intact male + letrozole; intact male + combination flutamide and letrozole. Our results indicated that castration has the ability to reduce histological damage and to improve neurological score 24 hours after middle cerebral artery occlusion. Moreover, flutamide improved histologic and neurological impairment better than castration. Letrozole induced increases in striatal infarct volume and seizures in gonadally intact rats. Combination of flutamide and letrozole showed that letrozole can reverse beneficial effects of flutamide. In conclusion, it seems that the beneficial effects of flutamide are the prevention of the deleterious effects and enhancement of neuroprotective effects of testosterone during cerebral ischemia.

Intrastriatal B-cell administration limits infarct size after stroke in B-cell deficient mice

Recent evidence emphasizes B-cells as a major regulatory cell type that plays an important role in limiting the pathogenic effects of ischemic stroke. The aim of the current study was to extend this initial observation to specifically examine the infiltration of regulatory B-cells and to determine if the effect of B-cells to limit the inflammatory response to cerebral ischemia is mediated by their action centrally or peripherally. Our data demonstrate the increased presence of a regulatory B-cell subset in the affected hemisphere of wild-type mice after middle cerebral artery occlusion (MCAO). We further explored the use of a novel method of stereotaxic cell delivery to bypass the blood brain barrier (BBB) and introduce CD19(+) B-cells directly into the striatum as compared to peripheral administration of B-cells. Infarct volumes after 60 minutes of MCAO and 48 hours of reperfusion were determined in B-cell deficient μMT( -/- ) mice with and without replacement of either B-cells or medium. Infarct size was significantly decreased in cerebral cortex after intrastriatal transfer of 100,000 B-cells to μMT(-/-) mice vs. controls, with a comparable effect on infarct size as obtained by 50 million B-cells transferred intraperitoneally. These findings support the hypothesis that B-cells play a protective role against ischemic brain injury, and suggest that B-cells may serve as a novel therapeutic agent for modulating the immune response in central nervous system inflammation after stroke.

Inhalation versus endovenous sedation in subarachnoid hemorrhage patients: effects on regional cerebral blood flow

OBJECTIVE

Isoflurane is a volatile anesthetic that has a vasodilating effect on cerebral vessels producing a cerebral blood flow increase. Furthermore, it has been shown in animal studies that isoflurane, when used as a preconditioning agent, has neuroprotective properties, inducing tolerance to ischemia. However, it is not routinely used in neurointensive care because of the potential increase in intracranial pressure caused by the rise in cerebral blood flow. Nevertheless, subarachnoid hemorrhage patients who are at risk for vasospasm may benefit from an increase in cerebral blood flow. We measured regional cerebral blood flow during intravenous sedation with propofol and during sedation with isoflurane in patients with severe subarachnoid hemorrhage not having intracranial hypertension.

DESIGN

The study is a crossover, open clinical trial (NCT00830843).

SETTING

Neurointensive care unit of an academic hospital.

PATIENTS

Thirteen patients with severe subarachnoid hemorrhage, (median Fisher scale 4), monitored on clinical indication with intracranial pressure device and a thermal diffusion probe for the assessment of regional cerebral blood flow. An intracranial pressure>18 mm Hg was an exclusion criterion.

INTERVENTIONS

Cerebral and hemodynamic variables were assessed at three steps. Step 1: sedation with propofol 3-4 mg/kg/hr; step 2: after 1 hr of propofol discontinuation and isoflurane 0.8%; step 3: after 1 hr of propofol at the same previous infusion rate. Cerebral perfusion pressure and arterial PCO2 were maintained constant. Mean cerebral artery flow velocity and jugular vein oxygen saturation were measured at the end of each step.

MEASUREMENTS AND MAIN RESULTS

Regional cerebral blood flow increased significantly during step 2 (39.3±29 mL/100 hg/min) compared to step 1 (20.8±10.7) and step 3 (24.7±8). There was no difference in regional cerebral blood flow comparing step 1 vs. step 3. No significant difference in intracranial pressure, mean cerebral artery transcranial Doppler velocity, PaCO2, cerebral perfusion pressure between the different steps.

CONCLUSIONS

Isoflurane increases regional cerebral blood flow in comparison to propofol. Intracranial pressure did not change significantly in the population not affected by intracranial hypertension.

Preconditioning with volatile anaesthetic sevoflurane in ischemic retinal lesion in rats

Volatile anaesthetic agents have been recognized for their neuroprotective properties since the 1960s. However, little is known regarding the potential retinoprotective effects of preconditioning by anaesthetic drugs. Retinal ischemia can be modeled by permanent bilateral common carotid artery occlusion (BCCAO). Here we studied the degree of ischemic injury with preconditioning by sevoflurane in the rat retina. During the BCCAO operation and preconditioning Wistar rats were anaesthetized with 1 MAC of sevoflurane. The oxygen, carbon dioxide, and anaesthetic vapor concentration in the anaesthetizing box was monitored with a gas analyzer. We examined 4 groups: non- and preconditioning groups in control and BCCAO animals. The duration of preconditioning period was 1 h and it was performed 1 day before BCCAO. The retinas were processed for histological evaluation after 2 weeks survival to determine the cell number in the ganglion cell layer and the thickness of the whole retina and that of all retinal layers. BCCAO-induced retinal ischemic injury was ameliorated by sevoflurane preconditioning. Retinal thickness and the cell number in the ganglion cell layer were more retained in preconditioned animals after BCCAO compared to non-preconditioned group. These results suggest that preconditioning using sevoflurane could provide a new perspective in retinoprotective strategies.

Isoflurane preconditioning protects astrocytes from oxygen and glucose deprivation independent of innate cell sex

BACKGROUND

Isoflurane exposure can protect the mammalian brain from subsequent insults such as ischemic stroke. However, this protective preconditioning effect is sexually dimorphic, with isoflurane preconditioning decreasing male while exacerbating female brain damage in a mouse model of cerebral ischemia. Emerging evidence suggests that innate cell sex is an important factor in cell death, with brain cells having sex-specific sensitivities to different insults. We used an in vitro model of isoflurane preconditioning and ischemia to test the hypothesis that isoflurane preconditioning protects male astrocytes while having no effect or even a deleterious effect in female astrocytes after subsequent oxygen and glucose deprivation (OGD).

METHODS

Sex-segregated astrocyte cultures derived from postnatal day 0 to 1 mice were allowed to reach confluency before being exposed to either 0% (sham preconditioning) or 3% isoflurane preconditioning for 2 hours. Cultures were then returned to normal growth conditions for 22 hours before undergoing 10 hours of OGD. Twenty-four hours after OGD, cell viability was quantified using a lactate dehydrogenase assay.

RESULTS

Isoflurane preconditioning increased cell survival after OGD compared with sham preconditioning independent of innate cell sex.

CONCLUSION

More studies are needed to determine how cell type and cell sex may impact on anesthetic preconditioning and subsequent ischemic outcomes in the brain.

Isoflurane enhanced hemorrhagic transformation by impairing antioxidant enzymes in hyperglycemic rats with middle cerebral artery occlusion

BACKGROUND AND PURPOSE

Because the potential neuroprotective effect of isoflurane is controversial, we attempted to study whether isoflurane after treatment provides neuroprotection in a rat model of hyperglycemia-induced ischemic hemorrhagic transformation.

METHODS

Rats received an injection of 50% dextrose (6 mL/kg intraperitoneally) and had a middle cerebral artery occlusion 30 minutes later. Four groups were included: sham-operated, ischemia/reperfusion, isoflurane treatment, and vehicle groups. In the treatment group, after 2 hours of ischemia, 2% isoflurane was administered at the onset of reperfusion. We measured the level of blood glucose at 0, 2.5, 4.5, and 6.5 hours after dextrose injection. Infarct and hemorrhagic volumes, neurological scores, oxidative stress (malondialdehyde, 4-hydroxy-2-nonenal, and nitrotyrosine) and the activities of superoxide dismutase and catalase were measured at 24 hours after ischemia.

RESULTS

Isoflurane had no effects on blood glucose, it failed to reduce infarct, hemorrhage volume, and brain edema, and it enhanced neurobehavioral deficits when compared with the ischemia/reperfusion group at 24 hours after middle cerebral artery occlusion. On the contrary, isoflurane exacerbated these parameters compared with the vehicle group. In addition, it increased the expressions of malondialdehyde, 4-hydroxy-2-nonenal, and nitrotyrosine, and it decreased the activities of superoxide dismutase and catalase compared to the vehicle group.

CONCLUSIONS

Isoflurane after treatment worsened physiological and neurological outcomes in this ischemia hyperglycemia-induced hemorrhagic transformation possibly by impairing the antioxidant defense system.